Acrylic Gearbox Sideplates

[Mike Wittman]

Hi Andy, everyone so far is right. Avoid Acrylic. It is far to brittle to use for a gearbox. In addition, laser cutting will introduce its own stress into the material making it more prone to crack or break. What you gain in structuring your cuts you loose in how the laser affects the material.

I like what squirrel suggested. Make a template and use it to machine your Polycarbonate (PC). I often laser engrave Polycarbonate and then machine to the line. It is also nice for picking or marking center points to drill.

You can cut PC with a laser. You usually need a high wattage laser to do it however, it can be done with multiple passes. It is a very messy process making lots of smoke, leaving lots of residue and also charring the edges of your material, but it can be done.

There is an alternative material you may want to use. It is called PETG. It's properties are somewhere between brittle Acrylic and durable Polycarbonate. The advantage of this material is that it will laser cut cleanly. It can still crack and break, but it is deffinately going to hold up better than Acrylic.

[tennispro9911]

This may or may not be the right place for this question, but for Transmissions, what are people's opinions on the pros of cons of Polycarbonate vs Delrin vs Aluminum. Those seem to be the most popular materials for transmission construction. We are in a similar position as AndyB, except we also would be able to get material waterjetted, which makes it much easier to use polycarb or Al.

[AndyB]

Well, aluminum is the traditional material. It's probably the safest. I got the idea of using a plastic from 254/968. (They use delrin, I believe). The only gearboxes I've seen that use lexan side plates are the AM Toughbox's.

[tennispro9911]

I know 254/968 used delrin. I was utterly amazed at their gearboxes a year ago at champs during my rookie season. I am still utterly impressed although (slightly) less incredulous. Lexan is a material our team has used a lot. In my opinion, its a great material and its never cracked for us, which is great. We've bent .25" thick pieces back to touch the other end of the 3'ish long piece and it just shot back into form.

[Dick Linn]

Maybe you could use some of this surplus MIC-6 aluminum jig plate in 5/16" or 3/8". The price is right: http://www.sandsmachine.com/alumweb.htm

The deal with jig plate is that it doesn't do funny things like warp like crazy when you machine it - it is very stable compared to regular plate.

Someone near Roseville, CA ought to get S&S Machine as a sponsor!

[MrForbes]

Originally Posted by tennispro9911

This may or may not be the right place for this question, but for Transmissions, what are people's opinions on the pros of cons of Polycarbonate vs Delrin vs Aluminum.

Steel is best!

[Dick Linn]

Actually, cast iron is probably better for transmission casings. Doesn't do much for gas mileage, though.

[NickE]

from what i've seen, delrin works fine if you keep it solid (no pocketing)

if its just a solid sheet with only necessary holes cut out, it should work fine

[ajlapp]

I definitely wouldn't recommend acrylic for most robot applications, but I did recently have the chance to work with both cast and extruded acrylic.

I found the cast acrylic to be closer in machinability and performance to polycarb and it is significantly cheaper.

A call to you local plastics supplier can offer lots of insight and alert you to materials that you may not know about.

My local supplier here in Michigan is Total Plastics.