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View Full Version : slightly OT, spinoff of Pyramid Project thread



Wirecutter
08-25-2005, 05:04 PM
For the pyramid project for AZSORT's kid, some mentioned using various plastics, polycarbonates, etc. I made part of an enclosure for an electronics project from plexiglass - my question concerns bonding.

I used the common solvent glue, and frankly, it didn't look as good as I'd have liked. It was really tough to apply the stuff neatly, yet fast enough that it wouldn't dry out before I mated the parts together.

My question is this: I've used MEK (Methyl-ethyl-keytone?) for solvent bonding of other plastics with some success. Anyone here have experience using this on plexiglass or lexan? I'm looking for a decent, but not necessarily bullet-proof (billet proof? http://bbs.homeshopmachinist.net//biggrin.gif ) bond that is as transparent as possible. I'm curious how it compares with the more ordinary bonding compounds. Thanks.

-M

sauer38h
08-25-2005, 05:34 PM
Yes, MEK works on arcylic plastics (Plexiglass, Acrylite, etc). Lexan, a polycarbonate, is different stuff altogether and I haven't tried to bond it with MEK.

I wouldn't expect MEK to have any magical properties that the regular acrylic solvent doesn't have. That is, if the joint looks crummy with solvent, it will look crummy with MEK. If your parts fit well on the edges you can hold them in place with clamps or whatever, and apply the solvent or MEK to the joint. Capillary action will pull it in. That's probably the neatest way to make a bonded joint, but you'll need close-fitting machined edges, rather than sawn edges.

RPM
08-25-2005, 09:25 PM
I do a lot of work with plexiglas, and those joints you can see through are always priceless. There's several ways to improve your joints, first they must be pretty flat, and sanded to 220 grit with wet and dry. Clean with alcohol before assembly. Secondly, if you are clamping two pieces together, or taping them together with masking tape, you need an air space for the IPS3/4 to flow out properly. If both surfaces are compressed together, the glue will bond in the first tenth of an inch, then can't get any further. Try putting a 3-4 thou METAL shim in the joint, or perhaps two in a foot length, put in your glue, then pull them out pretty quickly before the glue sets up. If you leave them in too long, they'll have to be cut out :-)
Once the shims are out, you can fill in the new hole with glue, and the gap will disappear.
Of course, the pros use annealing at about 160 degrees F for a few hours, which improves joint strength and also hleps a glue joint look better. Hope this helps
Richard in Los Angeles

darryl
08-26-2005, 01:21 AM
The other bonding agent is methylene chloride. I don't recall now if it's better on lexan than plexi, but I know it's pretty noxious.

Wirecutter
08-26-2005, 11:13 AM
Thanks, all.

Yeah, I've heard of methyline chloride, and I think I've smelled it. You're right, it's nasty. So is MEK, though. Definitely an outdoor job.

RPM - When I was forming the box, I experimented a little with heating, but the oven was a disaster. I think that water absorbed in the plastic expanded, creating lots of bubbles. That part got scrapped. Cut another, and I ended up forming it by clamping it between blocks of wood and very carefully waving a propane torch over it. The box top came out well, but not so well when gluing the front panel, hence my question. I'll try your suggestions, though. Thanks.

bob_s
08-26-2005, 03:55 PM
I've always used just plain acetone to bond acrylic.

Davis In SC
08-29-2005, 12:44 AM
<font face="Verdana, Arial" size="2">Originally posted by Wirecutter:

For the pyramid project for AZSORT's kid, some mentioned using various plastics, polycarbonates, etc. I made part of an enclosure for an electronics project from plexiglass - my question concerns bonding.

I used the common solvent glue, and frankly, it didn't look as good as I'd have liked. It was really tough to apply the stuff neatly, yet fast enough that it wouldn't dry out before I mated the parts together.

My question is this: I've used MEK (Methyl-ethyl-keytone?) for solvent bonding of other plastics with some success. Anyone here have experience using this on plexiglass or lexan? I'm looking for a decent, but not necessarily bullet-proof (billet proof? http://bbs.homeshopmachinist.net//biggrin.gif ) bond that is as transparent as possible. I'm curious how it compares with the more ordinary bonding compounds. Thanks.

-M</font>

Never use any hydrocarbons or solvents on Lexan (Polycarbonate) Mere vapors of any solvent will induce stress cracking & eventual crumbling of polycarbonate... Last year, I did a R&D project that needed a Lexan box to enclose some electronics.. I assembled it out of 6 panels , cut & milled to size, of 1/4 thick Lexan sheet. I went to Travers (Right down the road, luckily) & bought some adhesive for plastics, made by Devcon... It was in a 2-part syringe... worked great !!!