Sciencemadness Discussion Board - Building a rotatory evaporator

Building a rotatory evaporator

xwonchem - 30-11-2006 at 20:22

Hi everybody!
If I want to make of a rotatory evaporator, and what I need to prepare it. And I just want to build up a simple system that anybody can manage it easily.

Edit by chemoleo: Title

[Edited on 2-12-2006 by chemoleo]

Drunkguy - 1-12-2006 at 09:57

It might be an idea to learn how to spell before you try and undertake this project.

Nerro - 1-12-2006 at 11:50

English is not everybodies first language Drunkguy.

You would need something that can make a decent vacuum, something you can hook flasks on to rotate them and a condenser that would catch the solvent that evaporates.

Much more crude and wasteful but simpler would be to just make an attachement for a flask directly hooked up to a waterjet pump. The solvents would be sucked into the waterjet and be lost but it would save you the trouble of making a rotator and a condenser.

The first Rotary Evaporator

leu - 1-12-2006 at 19:55

This may be helpful, the attached Deja Vu file describes the very first rotary evaporator ever constructed by Craig, Gregory and Hausmann of the Rockefeller Institute for Medical Research; published in Anal Chem 22 1462 (1950) :cool:

Attachment: rotovap.zip (24kB)
This file has been downloaded 2671 times

The_Davster - 1-12-2006 at 20:27

A simple flask heated and with powerfull magnetic stirring and provided with vaccuum pasing through a cold trap(LN2 or for less volatile solvents, salt ice bath) has worked for me on an occasion.

smaerd - 10-1-2012 at 11:12

Didn't want to start a new thread about this topic. So I ungraved this one, hopefully that is okay. Though the design in the above has historic value, and is probably functional. Modern materials may make this a bit easier. I have attached an a article from the 70's about building a simple roto-vap. Though the prices of things have certainly changed I believe the idea still stands.
Attachment: The Construction of an Inexpensive Rotary Evaporator.pdf (677kB)
This file has been downloaded 3349 times

This blog also has a low cost design - http://microblog.routed.net/2007/03/19/how-to-make-a-rotary-... - though I consider it uninteresting, and they aren't even recycling solvents with it.

I also have a really rough 'schematic' of what my of attack is. I'd like to receive some input or start a more serious discussion about this because I know NOTHING about engineering, and even less about electrical engineering(for the motor).

My drawings are not to scale and are very crude, no ruler used, and the teflon stirring assembly looks phallic and wonky at best

. So please try not to judge on artistry.

How it should work:
a gear-driven motor which can handle the load of the 'carved' teflon rod, bump trap, and a flask, spins a belt. The belt rotates a gear fixed onto the teflon rod which is seated in a 1" inner diameter bearing to keep it in place.

As the teflon rod spins it also moves everything attached to the 24/40 end, while the ball bearing end which makes a connection to the condenser takes advantage of PTFE's low coefficient of friction with a good dab of greese, keeping the condenser still.

The flask is heated by a hot-plate(something we should all have) water/oil bath depending on the application.

The construction of the support stand and ''bearing/rod holder'' is all done in wood. Ideally aluminum or machined steel would be used, though these are expensive and hard to work with at home(unless you fancy ruining every drill-bit in your set). For the 'angle adjusters'(real technical term there

) rather then using nuts and washers as my schematic suggests. Perhaps boss head clamps and wooden wedges would make it easier to raise and lower the spinning assembly.

Caveats/Potential Problems:
- Filing/Carving/Sanding PTFE may not be a walk in the park. Especially to get to the desired joint sizes. Having never worked with the stuff I can only speculate.

- Fixing the bearing and the gear to the PTFE tube may not be straight-forward. Hopefully JB weld or a similar product will work.

- Finding an affordable motor that can support the load and still spin at around 60RPM without hopefully hogging 120V. I did find a 6V 60RPM motor with a torque rating of 4kg cm(~55.55 in oz) for under 10 USD on ebay, though my calculations are likely way off here. The paper says 60RPM with at least 30 in oz torque. Could one of these cheap things really work?

- Securing the bump-trap. It would be nice to use keck-clips or maybe some sort of clamp because there will be lee-way to carve a notch or two into the rod. Though this is very important and I almost forgot to add it.

Benefits:
- Save 70$-500$ on buying a used or new rotary evaporator motor. Using this design if it works you could make two rotary evaporators for the fraction of the cost of buying one used one. What would you need two rotary evaporators for as an amateur? No idea.
- If it breaks you know how to fix it yourself and the components are cheap. Having recently read a thread about someone having to pay up nearly 100$ for a PART of their motor, this actually holds merit.
- Satisfaction of building your own functional(hopefully) apparatus

.
- Chemically resistant(it's PTFE), air tight(so long as the connections are good), extra teflon material to carve out that 10/30 stopper you can't find anywhere for a reasonable price. Okay fine, I admit, I'm rationalizing at this point.

Items necessary:
Motor, Appropriate power supply, Pinion gear, 2x 'Drive' gears, belt, 12" or 6" with 1" diameter Mechanical Grade PTFE rod, 1" ID bearing, Wood, 6 feet threaded metal rod(for support stand), Some nuts/washers, lots of TIME, and hopefully some support from sciencemadness

.

edit - last-edit I promise

[Edited on 10-1-2012 by smaerd]

watson.fawkes - 10-1-2012 at 12:50

Quote: Originally posted by smaerd

- Fixing the bearing and the gear to the PTFE tube may not be straight-forward. Hopefully JB weld or a similar product will work.

JB Weld doesn't stick really well to nylon, much less PTFE. (I have a recent joint I need to redesign as a result, although I did read that formic acid does wonders sensitizing nylon to epoxies.) There might be some chemical magic that works to make PTFE sensitive to adhesives, but I don't know of it.

More importantly, your design seems to want to use a PTFE taper joint to transfer torque to a glass vessel. PTFE has a fairly low coefficient of friction generally, and it's not clear to me that it's not going to slip. The second is that I'd be worried about torsion creep in the material itself.

As for making the taper and ball ends, I'd recommend cutting them on a lathe. Small lathes are just not that expensive for someone wanting to make their own gear. And if not owning, there are many ways of getting access to machine tools for project use.

smaerd - 10-1-2012 at 14:09

Torsional creep was something I was not aware of. I'm sure it would take some hundreds or thousands of hours of use(?), though machining and replacing these rotors would be a huge pain. An example of non-reinforced 'virgin' grade PTFE rod, torsional strength of 1600 kg per sq.cm. If you look here http://www.buchiglas.com/products/pressure-reactors-stirred-... they are using a PTFE stirring assembly with a maximum of 250N M, which 250 [N·m] newton meter ~ 35,403 [in oz] ounce-force inch under a maximum pressure of 10 bars. 35,400 in oz is quite massive compared to the 55 in oz or as paper suggests 30in oz. Sorry to use these disgusting unit's it's bad habit. I think it looks as though it will work and hold up fine?

Thanks for the word on JB weld. Go figure in the paper they posted they leave out all of the information concerning how they fixed the pulley and bearing to the teflon rod, hmmm. The gear could probably be screwed on so long as the screws are short. As for the bearing though... It would need some kind of adhesive. I'll do some research here, much appreciated again

.

I was also worried about the teflon being used to transfer torque, however in the article it appears as though they had no real issue with it. They don't even mention a keck clip. I wonder if this material can be 'roughed up' enough to make good contact with the ground glass? Another big thing to think about, perhaps I can devise a simple clip to hold the flasks in place for extra measure.

Lathe is a great concept some of these plastic sellers even say they will machine parts for you. Not sure what the cost would come out to be. I'll likely improvise a set-up with a drill or drill press to get the dimensions close, and then sand and file down to snug fits.

It seems my best bet would be to buy a foot of ptfe rod, and give it a shot. I figure with a 4 inch length I have 3 tries to get it right. See if I can assemble the rotor. It's under 15$ its worth the experimentation and the scrap itself would be useful.

[Edited on 10-1-2012 by smaerd]

watson.fawkes - 10-1-2012 at 18:58

Quote: Originally posted by smaerd

Torsional creep was something I was not aware of. [...]

The gear could probably be screwed on so long as the screws are short. As for the bearing though... It would need some kind of adhesive. [...]

I was also worried about the teflon being used to transfer torque, however in the article it appears as though they had no real issue with it. They don't even mention a keck clip. I wonder if this material can be 'roughed up' enough to make good contact with the ground glass? Another big thing to think about, perhaps I can devise a simple clip to hold the flasks in place for extra measure.

Lathe is a great concept some of these plastic sellers even say they will machine parts for you. Not sure what the cost would come out to be. I'll likely improvise a set-up with a drill or drill press to get the dimensions close, and then sand and file down to snug fits.

If other people are using PTFE in such a sustained torsional application, I guess it's fine. I was worried, I suppose, out of personal inexperience with that material.

For affixing the gear, use a gear with a keyway (a slot in the inner hole) and woodruff key (those little moon-shaped pieces). You'll need to machine a recess for the key with a slot cutter. To hold both the gear and the bearing in place, you can use a pair of E-clips on each side. This means 4 grooves in the shaft.

As for torque transfer, try just the friction fit first. It might be adequate.

If you've got a community college with a machine shop class, you can likely get access to a lathe yourself. Paying someone to do all this machining may become prohibitive for you. Alternately, you can get a fair way with a rigged up lathe, but it will be hard to get a close fitting taper. If you end up needing to hand-fit a lot, look up "machine scraping". You could likely scrape the taper to fit, particularly because you won't need the special carbide tool.

FYI: The taper on ST joints is 1:10. That's the tangent of the cone half-angle, the angle between the axis and a cone line.

Perhaps the easiest way to cut the ball at the end with improvised tools is with a round-over bit in a router. You'll need to spin the axle in a jig for this to have any hope of working.

smaerd - 10-1-2012 at 19:09

The input you've provided here as been incredibly valuable.

I did some zooming in on the schematic in the paper and it is fairly telling about how they went about fixing the pulley and gear in place. Looks like you can use the low coefficient of friction to your advantage in some regards.

I'm a community college student and I'm sure we've got a machine shop hanging around at one of the campuses.

I'm going to think about this over night and see if I can crystallize the concept a bit finer.

watson.fawkes - 10-1-2012 at 19:58

Quote: Originally posted by smaerd

I did some zooming in on the schematic in the paper and it is fairly telling about how they went about fixing the pulley and gear in place. Looks like you can use the low coefficient of friction to your advantage in some regards.

I'm a community college student and I'm sure we've got a machine shop hanging around at one of the campuses.

It looks they're using set screws to hold things in place. That will work, likely just fine. I recommended a woodruff key because it's got a larger bearing area, thus lower contact pressure, and overall less materials stress. With the relatively small loads here, though, I'm not sure how much it would matter in practice.

It looks like they're using an o-ring drive belt, from the shape of the sheaves ("pulley"). Is that right? It doesn't matter a huge amount, but do ensure that you pick an easy-to-obtain belt for when it needs replacing.

Don't hesitate to bring project drawings to your machine shop class. Having a concrete project makes skill learning all the faster, and your instructor will know it.

You're welcome for the input.

smaerd - 11-1-2012 at 16:32

Rotor:
I would say they are using an o-ring belt, they said the pulley was machined from aluminum. That's strange that they would use an O-ring belt on pretty high torque application.

So I ordered a 1" OD by 12" PTFE rod, and some really wonderful PTFE bearings
http://www.amazon.com/TriSteel-Sleeve-Bearing-TriStar-TSI16P...
I can score the outside of them(if the outside is impregnated with PTFE) and easily glue them into the wooden support. Also I can use one of them to punch two screws through into the rod to keep the rod from sliding outside of the bearing shaft while still providing a low friction connection. Which can be flipped and/or replace with ease.

edit -
Looks like they make sheaves with mounting spots in them, and they are pretty affordable even from a company known to jossle prices.
http://www.grainger.com/Grainger/CONGRESS-VBelt-Pulley-3LC07
Doesn't get much easier than that, .. Until I try to find a pulley with a key adjustment to fit the 4mm motor shaft that also uses a 3L,4L or A V belt... If anyone knows where to find a vast assortment of pulley's and pulley/motor assemblies please let me know.

Motor
Kind of worried about the wiring for the motor. I found a suitable 12V motor for 11$ on ebay it spins at 120RPM with 60N cm of torque(overkill but I can always choose a different motor), but I figure the RPM's will be reduced as I up size to the larger pulley to drive the rotor. Runs on 12v dc, not clear on the amperage or if it varies with load?

Does anyone have any resources to share that explain primitive wiring and power sources for DC electric motors? Or could I just slap a 12v 1amp cell-phone charger, bridge the posts with a proper uF capacitor, and rig to a switch and potentiometer?

Banter:
I sure hope this works out, if not suppose I'm only 15$ in the hole so far. I do need a motor, some gears, and pulley's anyways to build a kind of spinning rxn vessel for solid state reactions that require inert atmospheres, as well as a peristaltic pump. So if this flops at least the components will go to good use

. I think it'll work out just fine though.

edit again: Well I also realized that the ball joint is probably going to be the hardest to machine. However, who is to say I need a ball valve? Rotovap condensers are expensive, ball joints on them are not common, but perhaps I can rig something else that will rotate smooth, air-tight, and use glass-ware I already have available

.

[Edited on 12-1-2012 by smaerd]

smaerd - 14-1-2012 at 13:11

Not trying to bump this thread but I unfortunately cannot edit my last post to include this.

It appears an improvised lathe using a drill press is entirely possible. Here is a video of someone shaping PTFE rod using a drill press and a utility knife.
http://www.youtube.com/watch?v=foR6teWZZG8

Honestly this seems like a valuable skill for anyone trying to build DIY PTFE stoppers perhaps even stirrer bearings, etc. Considering a 24/40 ptfe stopper costs 20 dollars and 13 dollars of ptfe tubing could make maybe 10 of them to whatever specific design you would like/can fashion. I'm quite surprised I haven't heard of this on here before

.

Anyways I'm still waiting for my rod to come via post, then I will hopefully be able to select a proper motor now that the pulleys are figured out(zoro tools has cheap pulleys and belts U.S.) and assemble this thing

.

Total cost assuming this works and the motor I choose will work is looking like 45$ USD.

Also instead of using a ball-bearing joint I am considering simply using a tapered cone to fit onto some greased tygon tubing leading to a vertical vacuum adapter, round bottom recovery flask on the bottom, friedrich condenser on top. No need to buy any fancy bucci specific condenser/glass-ware adding to additional savings(hundreds of dollars) and modular design. We'll see

.

If I did a write-up describing the hole process where should I post it? Technochemistry?

edit - apparently the design in that paper was even pretty much a commercial design at one point or another.

Apparently this is called a Calab Rotary Evaporator. I like the mounting idea they have. a Nice solid bracket would be easy to cut with a jigsaw out of wood which could be screwed down with nuts and bolts.

Will teflon alone hold the flask? Yes.(sorry for wonky resizing)

[Edited on 15-1-2012 by smaerd]

leu - 17-1-2012 at 14:59

Quote:

Though the design in the above has historic value, and is probably functional.

The article that was posted above was a description of the very first rotary evaporator constructed, and worked quite well for many years

There have been many improvements since then, and modern materials such as polytetrafluoroethylene have made fabrication much easier

It's considered good practice to provide the citation and the doi of an article that's posted, in this case:

The construction of an inexpensive rotary evaporator
R. V. Hoffman
J. Chem. Educ. , 1976, 53 (7), p 459
doi: 10.1021/ed053p459

:cool:

smaerd - 5-2-2012 at 18:45

Thanks for finding that reference so I got the PTFE rod this week, finally had time between home-work and building a polarimeter to do a little DIY machining.

I made a 'jig' with an old door-hinge some scrap-wood and a screw with two nuts. To this I fixed two peices of cut wood with those 1 inch PTFE lined bearings inside to fit the rod snugly. I adjusted the angle by adjusting the nuts to 93* using a protractor. I then unbolted my dads drill press to give me more working space rotated it and bolted it back down. All on a level surface. I then rotated the rod with a sanding attachment in the press testing it FREQUENTLY with a 24/40 joint as well as measuring the top diameter(20mm) and the bottom diameter(24mm).

Wasn't too hard took an hour or so. And I took a picture to show that the rod will hold a flask pictured is a 250mL flask but I also did the same test with a 500mL recovery with NO problems even wiggling it. Sanding the joint ruffs it up pretty damn nice.

First try, the joint fits very snuggly. Hopefully this is encouraging other people to try this out. I've got to figure out the pulley thing still but I did manage to get a wicked motor from a broken appliance.

edit - not that I am trying to 'prove' something but I do hope people aren't avoiding responding in this thread because they think I'm a thinker/dreamer rather then someone putting ideas in motion. Either way I hope it's okay if I document my build, even though it is not chemistry related(directly at least)

It may be a little while before I update as I need to find pulley's or a way to make them and wait for another motor to arrive. So I can decide which is best for a peristaltic pump(which I might also document) and which is best for the rotary evaporator.

[Edited on 6-2-2012 by smaerd]

Dr.Bob - 5-2-2012 at 19:17

Quote: Originally posted by smaerd

Will teflon alone hold the flask? Yes.(sorry for wonky resizing)

Actually, if you can buy a simple rotator like that one, that is what I used during my undergrad research as a rotovap, hook that to a vacuum with a good trap or condenser, then use a water bath on a hotplate (or a steam bath like I used - for the really old people here who know what that is) to warm the flask. We still use those simple rotators with a high vacuum pump to remove DMF or other higher boiling solvents.

With the number of places closing, you might be able to pick up a simple vacuum rotator or even a whole rotovap cheap. A friend bought a good one, for the biotech he got a job with, for about $1000, complete and brand new, on Ebay. It is amazing how many of these are being put on the market lately.

But I am still interested to see what people can build at home as well. Teflon will hold a flask under vacuum and spin, but making moving parts from teflon is a bad idea, they wear out quickly and will break easily. Try a design like the one above, where there are few parts and most are glass or stainless. The rotating mechanism can be very simple.

smaerd - 5-2-2012 at 19:25

Hmmm, going 'low-tech' is not a bad idea. I would like to never have to machine teflon again, not that is was too hard but if my rotor broke I would be pretty upset. Stainless steel is a good idea, solvents won't really react with it, and it's not like there will be strong acids or base going into the thing.

What I was considering was carving out a cone in the tail end of the PTFE and using a greased piece of tubing, and connecting the tubing to a 24/40 take off with a condenser ontop and a collection flask on the bottom. So it is similar to that design except using the teflon as the rotor which is a bit of a no-no.

The main thing I am stuck on is the rotation. Which is why I liked the idea of just drilling a pulley onto a teflon rotor

. Or using a key-way of sorts. I'll have to check a schematic or two for one of these lower-tech devices to see if I can't figure out a way to get the 24/40 attachment I just built spinning but the vacuum take off stationary while maintaining a vacuum.

[Edited on 6-2-2012 by smaerd]

watson.fawkes - 6-2-2012 at 04:54

Quote: Originally posted by smaerd

would like to never have to machine teflon again, not that is was too hard but if my rotor broke I would be pretty upset. [...]
The main thing I am stuck on is the rotation. Which is why I liked the idea of just drilling a pulley onto a teflon rotor

In lots of machines the main rotor is the machine, which all the other parts supporting the action of the rotor. This seems one of those case. It's important to avoid undue wear on the shaft of such devices. Old-style was to use a steel shaft and a soft metal bearing surface, generically called babbitt metal, a soft alloy usually based on lead and/or tin. In such a case the wear surface was on the soft metal. Ball bearings assemblies also shift the wear off the shaft and onto the bearing race.

If you're not going to use bearings, as you could with pillow blocks, you'll want to use an even softer material than PTFE. You want to make the softer material be the one that wears out. That could mean rubber in the form of O-rings, as implicitly pointed out by Dr.Bob:

Quote: Originally posted by Dr.Bob

But I am still interested to see what people can build at home as well. Teflon will hold a flask under vacuum and spin, but making moving parts from teflon is a bad idea, they wear out quickly and will break easily. Try a design like the one above, where there are few parts and most are glass or stainless. The rotating mechanism can be very simple.

The take-off in the picture he showed is just a metal sleeve. It's sealed against the rotating shaft by a pair of O-rings (or their moral equivalent), one under each end of the sleeve. In that device, the shaft is center-drilled only part-way, making a blind hole. At the end of the blind hole, the shaft is cross drilled, meeting the end of the blind hold. The resulting channel allows egress of vapors.

In your case, you could combine these ideas. Make up a combination pillow-block and vapor take-off. Use O-rings as your bearings against the PTFE. You can rotate the shaft as you had planned to, with a sheave, belt, and outboard motor, which may be the best if you have a scavenged motor whose rotational speed doesn't already match your application. You'll have to replace the O-rings periodically, but that's definitely cheaper than remaking a main shaft. The vapor take-off manifold in the picture looks like it's stainless steel with a welded outlet tube. It may be cheaper to buy a PTFE block and drill it out if you're limited in metal-working gear and only want to make one of them.

smaerd - 6-2-2012 at 12:15

This has given me a lot to think about and the design may actually be a lot simpler then the article's design I posted.

I decided I will likely fashion the pulley myself out of wood. Cutting ruff with a jig-saw using a glued on outline and sanding it down fine, then tooling a groove.

Thanks a lot for the ideas for which I was completely unaware of Dr. Bob and Watson. I'll hit the drawing board do some research, see whats available(repeat until something works) and hopefully will be posting back soon

golfin_ernie - 7-2-2012 at 09:39

Rotovaps usually go pretty cheap from this auction house:

http://auctions.biosurplus.com/view-auctions/individual-lots...

smaerd - 7-2-2012 at 20:46

to the more engineering minds out there, is it a big no-no to put a rotating load directly on a motor shaft?

Here's a sketch of more what I'm considering now. Hopefully, my handwriting is legible enough.

The idea is real simplistic, the steel rotor/vapor tube will be filed down so a key-way can put put onto the teflon cone, and is directly attached to the motor. Where the outlet will be on the outer length of steel tubing there is a hole drilled into the rotor so vapors can escape(hopefully this isn't problematic with condensation). An o-ring from the cone to the outer pipe creates an vacuum tight seal and acts as a bearing. This isn't a final idea but one of the more interesting ones I came up with.

I found a rather interesting article:

Attachment: A simple, inexpensive rotary film evaporator.pdf (524kB)
This file has been downloaded 1381 times
A simple, inexpensive rotary film evaporator
Edward M. Arnett
J. Chem. Educ., 1960, 37 (5), p 247
DOI: 10.1021/ed037p247
Publication Date: May 1960

What they did was replaced the motor shaft with a hollow tube

, though this is interesting. I'm not sure it's all that practical, and I will not follow this design. Posting it for perhaps a future lurker strolling through the thread looking for 'inspirado'. Back to the drawing board, but it does appear mounting directly to a motor is okay.

Attachment: INEXPENSIVE APPARATUS FOR SPEEDY EVAPORATION.pdf (720kB)
This file has been downloaded 1294 times
Inexpensive apparatus for speedy evaporation
Frances Greef and Clifford T. Larsen
J. Chem. Educ., 1956, 33 (11), p 556
DOI: 10.1021/ed033p556
Publication Date: November 1956

Another pretty interesting idea. Not sure how exactly they managed rotation with this though?

[Edited on 8-2-2012 by smaerd]

watson.fawkes - 8-2-2012 at 07:50

Quote: Originally posted by smaerd

to the more engineering minds out there, is it a big no-no to put a rotating load directly on a motor shaft?

What kind of load? Every shaft has loads on it, at the very least torque loads around the axis of the shaft as one part turns another.

As to your drawing, you'll need two O-rings to seal any kind of fixed sleeve system, or else you've got an undeclared wear surface. Also, you need to make sure that the shaft doesn't slip downward in its slightly-tilted position of operation. That could be as simple as grooves in the sleeve and the shaft.

smaerd - 2-10-2012 at 13:50

I guess I'll post my 'final design' because someone else started another thread. Though the PTFE to tubing connection(left hand side) will probably be replaced with a ball-joint instead because tubing won't really hold up over time with that kind of wear.

So it's basically the same as in the paper with the teflon rotor. Only change I'll be making is using a stainless steel(pretty inert) rotor with teflon attachments. So if something goes bad due to wear and tear it can be easily replaced and uses less teflon. It can also be machined(set-screws, etc) whereas teflon isn't really good for that.

Yikes it's been about a year since I first started this.

[Edited on 2-10-2012 by smaerd]

microtron - 23-11-2012 at 23:46

I have an IKA motor and vapor duct (d=20mm), but no suitable condenser, any ideas? somebody know what condensers would suit it? I have even brand new seals. perhaps to use some adapters? I have not seen any cheap IKA condensers that I could buy so I need other options. People who have experiences with different rotary evaporator brands, or any advice, let me know. Thanks.

smaerd - 15-12-2012 at 11:01

@microton -
I plan on using a friedrich condenser but a dry-ice condenser/cold-finger would probably be preferred.

@everyone -
Alright so I've ordered everything I need to make this thing work except, I still cannot find a way to get a pulley onto the 4mm diameter DC motor I have.

Whats on the list is:
1)Some 1" outer diameter aluminum tubing - light weight in comparison to teflon and rigid enough to support the load and easier to work with via drill & file then Stainless steel. Light weight means less load on the motor then a solid teflon rod.
2)1" bore pillow bearing
3)1" shaft collar
4)3" O.D. 1" Bore sheave with a set-screw.

Ran me about 40 bucks but I gave up on cheaping out. I'd rather spend 100 dollars and make something that will last and function right and is my own design then machine some teflon hope I get it right and it holds up to time, which it likely wouldn't.

Hopefully I can finally finish this thing over winter-break. Got a bunch of extra aluminum tubing in-case I really mess up a couple times putting in key-ways for set screws and putting screws in to the PTFE attachments. Doubt I will but you never know.

I still need to 'machine' and find a way to polish the PTFE attachment for the ball-joint but I'll cross that road when it needs to be done.

One real problem still remains:
Finding a pulley or an attachment to a pulley that will fit my DC motor. I went to a hobby shop and asked questions, I've been googling and still can't find anything concrete. Might need to "machine" something out of scrap teflon rod? Seems a bit preposterous though, and teflon is slippery not ideal for a v-belt or an o-ring. I've also heard about this stuff called "Shape-Lock"(http://shapelock.com/page2.html), I just don't know if I really trust it. Claims to be a high strength polymer that can be molded and set at 150*F or 65*C?

edit- guess I found this but jeese it sure looks junky:
http://www.babelduck.biz/product/60mm-pulley-4mm-bore-brass-...

[Edited on 15-12-2012 by smaerd]

Vogelzang - 16-12-2012 at 05:42

http://www.google.com/patents?id=6f1jAAAAEBAJ&pg=PA1&...

smaerd - 16-12-2012 at 06:22

Interesting that they use a PTFE only rotor in their design as well. I also like the housing on the rotor and motor assembly, prevents sparks from being an issue with solvents.

Maybe the aluminum tubing was a bit over-kill then. Oh well, I still like the aluminum idea more because it gives me more teflon to work with, makes errors cheaper(don't own a lathe so its all by hand/file and drill-press). 2 feet of of aluminum costs about 5 bucks plus shipping versus two feet of PTFE rod costs 20 dollars plus shipping. I also have more confidence in machined aluminum over teflon for the reasons stated earlier in the thread such as torsional creep, and I'm not ultimately confident that its really an ideal material to handle heat and an axial load over time.

smaerd - 19-12-2012 at 10:33

Well I finally figured out how to attach the motor to a pulley. I have bought an aluminum 0.188inch or 4.77mm bore "set-screw shaft-collar" for basically 1 USD and some change. This could be easily and securely fastened directly to the motor pin using the set-screw. Most hard-ware stores also sell cheap white plastic pulleys, the one I had laying in my basement was measured and it will fit a 3L V-Belt. I will rip it from its casing and hacksaw off the rivit, drill/file down the plastic cylindrical part in the center so it lays flat. I will put two screws through the aluminum shaft collar and secure the shaft collar to the pulley with some nuts. FINALLY solved that problem, if everything goes as planned this will be done by the end of January and I will be updating this thread with more physical progress as it comes along. No more planning, just action, until I hit an inevitable road-block.

I hate to pollute the forum with my rantings and ravings, I'm sure its annoying for anyone following. Though, I figure once I build this thing it will really help others out to do the same and learn from my mistakes and successes to hopefully build their own functioning rotary evaporator.

smaerd - 22-12-2012 at 14:58

Making progress. I cut the aluminum rod by taking a piece of paper wrapped around the aluminum tube making sure it was straight. I taped the paper down firmly, and put the tube into a series of clamps and busted out the old hack-saw. Cut through it like butter, much easier then cutting through wood to be honest. I cut through a side, rotated the tube, cut through another, etc. Then handfiled the tubing smooth.

The pillowblock bearing was fit onto the rod the marks for the set screws were marked with permanant marker. Notches were filed into the tubing to match them and the bearing placed on and set screwed in firmly. This was repeated using the pulley. Both items are on firmly and even on man-handling attempts they do not move.

So glad I chose aluminum and not stainless steel. Was done in about an hour from tube to rotor.Tommarrow the teflon rod will be machined to fit firmly into the aluminum tubing. Screws will be put through and perhaps extra plumbers tape(PTFE) to keep the connection air-tight.

Organikum - 22-12-2012 at 16:51

Did some PTFE work myself lately and would like to share some findings:

- It is impossible to CUT threads into this material even if under/oversized IT WILL NOT GIVE A TIGHT FIT. No screw is going to hold.
A search revealed this is a known issue and Threads must be formed by the kind of tools which do not cut, with abrasion, but those kind which presses the thread into the material, rolling the threads would be the industrial equivalent.
- Holes bored to size will be oversized. Always. Possible is to bore a good way undersized and press a metal-rod of fitting diameter through the hole. Heating the PTFE helps a lot for the large expansion of the material.
- And whatever tricks are applied when PTFE undergoes the change in crystall-lattice (at about 16°C IIRC) it may come loose again anyways for then size mofe or less changes by some percent instantly.

For your balljoint: If still possible change it to a conical connection - this is used in industrial vessels as vacuum-seal since ages and is named to be THE final solution. A little pressure on the seal is needed but very little for start, gravity usually suffices, then vacuum does the job. This seal will not mind some shrinking, it just slides in a bit deeper and still fits over the conus. A balljoint when one partner shrinks or expands far more then the partner, the sealing area is factually diminished to a fraction.

Balljoint or conus, cutting and polishing is problematic. Try by any means to finish the part by compression, pressing it into a negativ-form by a good amount of pressure, mechanical is ok no need to whip out the hydraulics.
Time is the key. PTFE has the "cold flow" which makes it creep nicely and compress to smooth surfaces which are also compacted and more durable then. But it takes time. Some weeks would be best, some days a must.

Good luck for your interesting project!
PTFE is tricky, MODIFIED PTFE which just hits the market is superior and cheaper too. PEEK would be best probably, but thats streetrobbery not trade what they are doing.

/ORG

smaerd - 22-12-2012 at 18:00

I have no intentions of putting a thread in this stuff. Figured I could pop a screw in slowly. You sure a screw won't sink in? I have a hard time believing it. This stuff is solid enough to clock someone out with and took a long time to whipe it away with a sanding drill attachment.

On further research it appears you are right. DAMN! The solution appears to be a "Form Tap" I've never heard of this.
Ref: http://polyfluoroltd.blogspot.com/2012/02/normal.html

Orrr, what about two set screws? Tapping aluminum(6061) would be easier(tube is 1/8inch or 0.315cm thick) and cheaper. I've never tapped anything before in my life though and I'd have to get it right a few times in a row. The air-tight seal will be coming from the PTFE tape and a hopefully very close tight fit. Maybe an o-ring or two if it comes down too it(cheap fix).

Edit - I'm afraid the teflon might sheer under the load though.

Edit again - Actually I think it will be okay, because the vacuum will be holding some of the weight(shouldn't rely on that though), and I will be fastening the flask or bump-trap with some kind of clip to the aluminum which will also reduce the load. Will only be working with about 5mm in depth of teflon however. Not planning on using 1L flasks(don't even own one).

Information regarding teflon(tensile strength etc..):
http://www.boedeker.com/teflon_p.htm

I could also punch a hole through both sides, tighten it with a hex-nut, and cover it with some tubing and use tubing clamps so theres no air leak. Again though I'm afraid it might shear.

Then there's also this horrible idea. Use some 1 inch OD PTFE tubing, machine in a "Step" to the teflon attachment, then use two hose clamps to fix the tubing to the ptfe attachment as well as the aluminum tubing. Awful idea I know but I'm trying to think outside of the box.

About the other attachment:
I initially was going to use a conical connection but I'm not sure what I could use for the female part? It seems to polish up with gentle heat from a lighter - at least a little bit(just did a quick test don't want to breath teflon fumes).

Thanks for the heads up this could have been a real fiasco!

[Edited on 23-12-2012 by smaerd]

smaerd - 23-12-2012 at 08:30

So I bought a tap (6-32) and a set-screw(6-32). Having no idea what I was doing I punched two holes into the rotor. Put the tap into a set of pliers with some PEG oil. Gently went back and forth until the tap could be screwed by finger in both holes. Put the set screw into both with an alan wrench. No issues. Whew. This should work out

Machining the teflon 24/40 attachment now then I'll be back to post a picture or two(in this same post so I'm not post-whoring).

Edit/Update: Finished machining the teflon. Tried using PTFE tape to make an air-tight seal didn't quite cut it. No big deal that was pretty expected. Will scoop up o-rings soon, or something similar. Here's some more pictures I guess.

The set-screw seems to work as expected. 7$($6 tap+bit and 0.50$ set screw) fix whew. Feeling pretty good about this now.

edit - update again

Stuffed an o-ring onto the teflon rotor with a bit of PTFE tape, lined the set screw with a bit of PTFE tape. It holds a vacuum!

[Edited on 23-12-2012 by smaerd]

[Edited on 23-12-2012 by smaerd]

smaerd - 24-12-2012 at 07:50

What about using a glass stirrer bearing? for the end connection? They use them for air-tight stirring with teflon rotors right? Heating wouldn't be an issue because the application is low RPMs and ideally low friction.

Finding a spherical joint for this is looking to be very expensive and elusive. 35/25 is too big for 1" OD teflon rod, its either 18/9 or 18/7 and I can't find this size anywere other then for "glass-stock". I REALLY don't want to hand-carve two parts to a ball/socket joint to make this work but if that's what it comes down too I guess I'll have too(have plenty of left over teflon)...

I also figured out how to "polish" the PTFE smooth. I have been slowly grinding the material away with a sanding attachment on the drill-press(with a shop-vac to remove the fine dust clamped nearby and a dust mask + goggles). This makes the surface rough, good for the 24/40 attachment, bad for the ball-valve or other vacuum connection. All that needs to be done is take a small kitchen knife and gently peel away a layer of the stuff. Might take a bit of 'chipping away' but it creates a nice smooth surface. Figured this out by cleaning up some of my sanding work.

All that's basically left to do is carve the ball-joint(which I'll need a ball-joint for to make sure I do this right as I'm doing it all by hand), already have the air-tight end finished with the set-screw notch in place. Then hook up the motor assembly and mount.

and another picture just for kicks

[Edited on 24-12-2012 by smaerd]

smaerd - 28-12-2012 at 10:57

well the forums been down but I've still been at work. I built the motor assembly using washers, a motor shaft collar, a couple bolts, and like I said before a plastic pulley harvested from a cheap rope pulley.

Now I am working on the stand which will be adjustable so that it can be tilted. The motor is going at about ~80 RPM without a loaded flask. It originally was a 100RPM motor rated for high torque. This might be a little on the slow-side but buying another motor wouldn't be an issue, and I'm pretty sure this will work just fine. So I probably won't buy another motor until this one dies. Also my power supply is 12V and only 350mA so if I had a higher current I'm sure it could go 100 RPMs without an issue.

edit - please ignore the frankenstien set-screw on the motor hahaha.

update - built the stand with 4 bolts and 8 nuts and 4 washers to adjust the angle of the stand. Going to throw some paint on it and fine tune one thing and then all I need to do is machine one last part and it'll be ready for its first real test-run!

[Edited on 29-12-2012 by smaerd]

smaerd - 31-12-2012 at 14:36

Finished up the wiring today. It's a very simple circuit. Positive lead goes to a SPST switch, then to a potentiometer, then to a 1000uF(35VDC rated) capacitor and the motor. Negative lead goes straight to the 1000uF capacitor and the negative terminal on the motor. Runs great! Took a few seconds to charge up the capacitor but no big deal it does make the rotation smoother, or at least it seems too. The size is probably over-kill, but it works. Using a 12V DC wall brick that claims 1A but really its 350mA tested with a multimeter. Oh well what do you expect for 2 dollars shipped from china...

Now to order the glass-blank spherical adapter or socket adapter. It's outer diameter needs to be smaller then 1 inch so that basically leaves two sensible sizes. 18/9 and 18/7, sadly these are pretty rare. Figure a glass-blank with a tight-fit rubber stopper should do the trick... Not ideal but don't have much else to work with.

Sorry to be picture and post-whoring it's not my intentions. I guess this thread shouldn't be a blog but I figure it'll help other people out later(I hope). It actually looks pretty nice in my opinion at least.

smaerd - 3-1-2013 at 15:22

Capicitor was way too big. Blew my power-supply. Hopefully didn't fry my motor... Live and learn hahaha. I shoulda known better. On the bright side I finished machining the ball joint and it spins no problem on glass joint stock I bought from SafetyEmporium. Circuit blew up before I could do a vacuum test, so that'll have to wait. Murphy's law always likes to strike when the end of a project is in sight.

[Edited on 3-1-2013 by smaerd]

smaerd - 4-1-2013 at 15:17

Well my ball joint doesn't hold a vacuum. I can't get it to the right dimensions with the sanding attachment on a drill-press and by chipping away by hand. Spent a few hours on it today. Does anyone have access to a lathe and is capable of making an attachment like this? I am willing to send some unused teflon rod and pay for shipping both ways and throw some money towards the person doing it. Other-wise this project is at a stand-still.

watson.fawkes - 8-1-2013 at 07:51

Quote: Originally posted by smaerd

Well my ball joint doesn't hold a vacuum.

I doubt a ball joint is ever going to make a good seal, particularly because it won't wear well, since one or both parts of the joint will stop being spherical.

Look up "rotary seal" or "rotating seal". For example, the Rotary Seal Design Guide from Parker has lots and lots of pictures of rotary seals for different applications. These are COTS (commercial off-the-shelf) products and have a large range of distributors.

Ephesian - 8-1-2013 at 12:43

I have a buchi rotovap that is fully functional, U2U me its up for $200 USD

smaerd - 8-1-2013 at 14:15

Watson the problem isn't that I've made a good ball-joint and it doesn't hold vacuum. It's that my ball-joint is pretty bad. So I'm looking at local machine shops to help out. I'd love to make one of those rotary seals instead. I'll look into it but I'm still pretty trusting that this publication and the other models of rotary evaporators using the same premise work fine.

Ephesian I'd gladly buy it if I had the cash but I sadly don't, and I'm not about to give up on this project, it's so close.

Vogelzang - 10-1-2013 at 15:09

More interesting patents.

http://www.google.com/patents/US4790911?pg=PA1&dq=479091...

http://www.google.com/patents?id=gNxHAAAAEBAJ&pg=PA1&...

http://www.google.com/patents?id=mcJXAAAAEBAJ&pg=PA1&...

[Edited on 10-1-2013 by Vogelzang]

smaerd - 10-1-2013 at 16:59

Alright watson I'm looking into these rotary seals now because the only offer I was given for machining this ball joint was $100. So maybe using this aluminum pipe will have an advantage with this idea.

The problems I'm seeing is finding a way to mount something like this and where to actually buy one of these. They may be off the shelf but I am having a hard-time finding anything but technical data about them, not even a ball-park of what I'd have to spend to get one. I'd really appreciate a hand here. There's also a million different kinds and I have no idea which is best for this application. I'd assume a teflon constructed one suited for low pressure applications. Or something like this: http://www.kalsi.com/rotary_seals.htm
but a lot smaller. Again though I don't know how I'd get that into my aluminum pipe unless I pay a machinist $100.

Also on the side note, a friend told me that the reason why my capicitor exploded was because it was polarized and the back EMF of the motor I was trying to 'smooth' created a negative voltage spike. The motor is fine and the power supply has been replaced I'll likely get a non-polarized capacitor off of mouser eventually.

[Edited on 11-1-2013 by smaerd]

watson.fawkes - 10-1-2013 at 17:02

Quote: Originally posted by smaerd

not even a ball-park of what I'd have to spend to get one.

Call a local supplier of hydraulic seals. Every place with any industry at all has one.

smaerd - 10-1-2013 at 17:23

Actually nevermind I just got a message from a fellow chemist who offered to help me out with the teflon!

smaerd - 22-1-2013 at 15:08

Latest update. Found this great guy on another forum who machined these pieces out for me no problem. He did an amazing job. I tested the ball joint with a little grease and it holds a vacuum without issue, even while I rotate the part and wiggle it around.

He said to let him know if I needed any more paid work. So I figure if anyone on here is having any issues and wants to build their own I could connect you with him. Was kind of thinking about making a kit on one of those project websites once I build this up do some testing and see how it all runs! Which will be, tomorrow! Finally seeing the end of what was only a dream a year ago

.

I will also be doing some tests timing how long it takes to remove 25mL of solvent under various conditions. See just how efficient this puppy is.

smaerd - 23-1-2013 at 07:37

Well the build works great or it did. I realized my rotor was slightly camming because I had accidently man-handled the pillow block bearing onto the shaft. It was still holding a vacuum but having the glass ball joint wiggle up and down slightly annoyed me. So I dismantled it and tried tapping the bearing back into place with a screw-driver and a hammer... Dinged the bearing shield pretty good now its a fair amount harder to rotate. So I need a new pillow-block bearing but, it does work. Holds a vacuum just fine and was ripping ethanol/methanol mixture no problem at all.

I'm going to conclude the building plan updates because the build is a success and work on a finalized write-up. Thanks for all of the advice along the way everyone it meant a lot and I couldn't have come this far without science-madness. After I make a finalized write-up I will only make updates as to the condition of the device over-time. Such as what parts have broken after 6 months.

[Edited on 23-1-2013 by smaerd]

Organikum - 24-1-2013 at 23:17

Great that you got it going finally! Congrats!

How much did the guy charge you for this nice piece machined PTFE or how much would he charge? And do you know on which kind of machinery with what tools he made it?

regards
/ORG

smaerd - 25-1-2013 at 05:28

20 dollars for two ball adapters(I sent the material), I'm not sure how much he'd charge the next person looking for the same thing but I could ask him. Or I could give you his account on another forum and you could message him. He says he owns a small machine shop I think in Ma USA. He said working with Teflon was easy and that this project was not a big deal at all. I know he has a lathe and that he was working on machining stainless steel but he was saying that this was a pretty difficult project for him. Not sure exactly what he was doing though.

New pillow block bearing is on its way should be here on Monday which is when I'll be posting the results of the tests in the pre-publication area.

EdMeese - 26-1-2013 at 08:59

i'm also interested, my vintage early 80's IKA Werks rotovap needs parts I can't get any more, and can't afford anyway :-(

smaerd - 26-1-2013 at 09:27

The finalized write-up is here: http://www.sciencemadness.org/talk/viewthread.php?tid=23139

Got the new bearing today and it works great. I think the last bearings bore was actually smaller then 1" which is why I had to try so hard to get it on the shaft, while damaging it in the process. I'd love to see other people add onto my design or come up with their own! All I really need now is to dedicate a cheapy (walmart) hot-plate, a metal bowl(ran the trials using a corning plate and a stainless steel measuring cup hahaha) and build a stand for it out of some 2 by 4's(wood size) and hopefully it will be a permanent fixture for my lab. Tax-returns should cover that expenditure

.

PM me if you want to contact the person who helped me with the machining. Or check a local 'hack-space' or craigslist or machinist forum.

Edit: if after 6 months of use or so and it holds up I may start selling kits.

[Edited on 26-1-2013 by smaerd]

radagast - 26-1-2013 at 19:25

Terrific work. Although I already have a Buchi rotovap, I may try building one of these because I like the idea of a modular piece of equipment that you can repair yourself.

akok - 8-8-2016 at 04:17

Smaerd that's a good project and effort on this rotovap!!! But it can be unproved a lot if we can find someone with 3D designing software skills. Many parts can be made cheaply by 3D printer if there is a 3D design. Let's try to find someone that it can an upload an .stl file of the project on thingiverse.com
I believe the following pdf manual would be a good guide for a designer to replicate the basic mechanism. http://www.lasallescientific.com/products/heidolph/BAL_LARO4...

FYI his is a example of magnetic stirrer.
http://www.thingiverse.com/thing:632714