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Author: Subject: Making an acrylic büchner funnel
Fulmen
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[*] posted on 29-3-2018 at 10:27
Making an acrylic büchner funnel


What do you do when you lack a piece large enough to make something? Here's one solution, inspired by 3D-printing (during assembly):

Buchner1.jpg - 96kB


The funnel will be 70mm and is made by gluing disks of 6mm SAN sheet together. It will then be machined internally before the top, filter disk and bottom are glued together. It can then be machined externally.




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aga
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[*] posted on 29-3-2018 at 11:23


Cool ! It's a solution for sure.

I guess it could all be 3D printed.

Easier as two parts, but i suppose glue would work to hold the disc in place.




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Fulmen
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[*] posted on 29-3-2018 at 11:25


Here's the sketch of the assembly.

70mm Akryl Buchner.jpg - 127kB

It''s beneficial to keep the glued area as small as possible by roughing out the parts before assembly. Since the glue is solvent based the drying depends on diffusion, reducing the diffusion path by a factor of two should reduce drying time by a factor of four.




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[*] posted on 29-3-2018 at 11:34


Quote: Originally posted by aga  
It's a solution for sure.



It will be if he tries to filter any strong solvents

As A kid I had a filter funnel made by cutting the top off a plastic bleach bottle. The "plate" was perforated zinc- which is not really inert enough.
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[*] posted on 29-3-2018 at 11:48


Chemical compatibility will be an issue in some cases, but I rarely work with aggressive chemicals. I will of course replace my broken ceramic funnel in time, but this was a simple and fun fix.



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[*] posted on 29-3-2018 at 11:52


Careful of thermal expansion. If each piece expanded a different amount, after a while it would eventually shake itself apart.
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[*] posted on 29-3-2018 at 12:02


Why would the segments expand at different rates? They are from the exact same material and glued together with SAN dissolved in MEK. Of course the bonds will be weak points, but they will only see compressive loads.



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[*] posted on 29-3-2018 at 12:14


Quote: Originally posted by Fulmen  
but they will only see compressive loads.


I'm not sure about that.
I think the bits that form the conical section will try to "peel" apart.
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[*] posted on 29-3-2018 at 12:37


Fair enough, there might be some bending loads on the segments in the cone. But it's only subjected to vacuum, and that really isn't much of a load. It's deliberately over-engineered for easy machinability, but I ran it through stress analysis and got a safety factor of 15. I think it will survive.



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[*] posted on 29-3-2018 at 12:48


It's a good practical solution Fulmen.

Nice one.




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[*] posted on 29-3-2018 at 13:03


Quote: Originally posted by Fulmen  
But it's only subjected to vacuum, and that really isn't much of a load.


The vacuum isn't a load at all, but atmospheric pressure is about a ton to the square foot.
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[*] posted on 29-3-2018 at 13:38


Details, schmetails.



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[*] posted on 2-4-2018 at 09:26


O ye, of little faith. Watch and weep:

Buchner.jpg - 88kB




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[*] posted on 2-4-2018 at 13:42


Quote: Originally posted by aga  

I guess it could all be 3D printed.

Easier as two parts, but i suppose glue would work to hold the disc in place.


I 3d printed mine in PLA+ (some kind of modified PLA thats not as brittle). In two parts to avoid the need for support during printing.
I didn't glue the parts together, as I only wanted gravity filtering. Worked a treat.

Pic is from my cad model (Solidworks)

buchner.JPG - 68kB




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[*] posted on 3-4-2018 at 01:40


Are these acrylics and PLAs solvent resistant? How are they with weak solvents like Methanol, hexane and IPA? Should be alright I suppose - good idea. :-)



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[*] posted on 3-4-2018 at 14:04


Quote: Originally posted by DrP  
Are these acrylics and PLAs solvent resistant?


Pretty easy to find out
Chemical resistance chart

There are half a dozen different polymers available for 3d printers, so it shouldn't be too hard to find one to suit a given purpose.

[Edited on 3-4-2018 by Twospoons]




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[*] posted on 3-4-2018 at 15:18


I wouldn't use SAN for any solvent (except water) or strong acids/lye. I made the funnel for recrystallization work, if I ever need to work with solvents I'll buy a glass funnel.



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[*] posted on 3-4-2018 at 15:32


I had some success using a 3" PVC end cap and drilling holes in a plate to fit inside the plate. The caps are available in 4", 6" & 8" as well and also in CPVC and ABS.

I posted pics in this thread of how I made it. I added a threaded hose barb and ran tubing to a vacuum flask, or placed the barb into a bung in the flask.

https://www.sciencemadness.org/whisper/viewthread.php?tid=61...
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