Plexiglass instead of MDF

[slickrick]

I'm thinking of designing my CNC to be made of Plexiglass instead of MDF.

What have you guys seen as far as flex and keeping tolerances when using plexiglass?

My CNC will not be that large. Probably 12x24 cutting area if that large. I'm planning on using 3/8" to 1/2" thick pieces depending on where they are located.

Personally I think that with MDF, I would have problems with the wood keeping tolerance because of the temperature changes it may see. My garage can go from mid 20's to low 90's in the same day. The humidity may not be that wide of a range, especially in the garage, but I know it copuld have some effect on the wood as well.

What are your thoughts on MDF and Plexiglass for small CNC's?

[ger21]

Originally Posted by slickrick Personally I think that with MDF, I would have problems with the wood keeping tolerance because of the temperature changes it may see. My garage can go from mid 20's to low 90's in the same day. The humidity may not be that wide of a range, especially in the garage, but I know it could have some effect on the wood as well.

Temperature won't really have any effect. Wood moves due to humidity, not temperature.

MDF is cheaper and easier to work. When the machine is built, seal it with a coat of thin epoxy (like West System or similar) and then paint it. You shouldn't have any trouble with humidity.

Look at at the MDF machines on this site. There's gotta be at least a hundred. Now see if you can find one acrylic machine (I think there is one here ).

[High Seas]

1. There is at least one very small mill/table unit built - as ger21 recalls - I seem to remember it as being not made of acrylic - but cutting board stock. A bit thicker, more rigid, and CHEAP as chips!

2. Also, there is a real sweat acrylic Foam Cutter a French fellow built. So tolerances are not a real problem - nor heat and humidity (room fluctuations).

3. The problem will be getting the framework rigid enough. Years back I built a 2x4 water-table flow bench (like a wind tunnel - but water and near 2D only). The challenge was getting and keeping the table FLAT. I bet the same would apply to the gantry. A lot of engineering (pieces/parts/glue) to get the beam stable and support your spindle.

4. I used Starboard - a plastic like material for the cars on X andY Axis, and most of the Z Axis on my SYSTEM2 - see members gallery. Easy to work with and plenty rigid. Drilled and Tapped well and has held its shape-- no glue required.

Gotta say - it would be very Dramatic looking!
Jim

[slickrick]

Thanks for the reply guys. So far I am not detered. This will be my first cnc, and I want to do all the design by combining alot of the ideas I have seen on here and adding that to some of my own.

I am pretty good at understanding the effects of design and hopefully I can design one that will be structurally sound. I think I can.

If I was making a larger machine, I would be doing this out of steel/aluminum, but since this is a smaller one, I don't think that I will have any problem with lack of ridigity.

[harryn]

It would certainly be a neat looking project to have it made from "clear" material.

The biggest challenge I have had with making items from plexi have been stress cracks. It does not take much force to start and propagate a crack from a tapped hole in plexi or acrylic. Polycarbonate might be better, but the price is a bit high.

There are many MDF systems here on the zone mostly because when new is pretty flat and can be cut with wood tools. I hate the stuff - mostly because I tend to break out edges and holes with my poor craftsmanship.

If your project is small, you might find it easier and simpler to make it from 1/4 in thick x 3 x 3 angle aluminum. That makes it thick enough to hold a threaded hole and rigid enough to not flex much. I am not sure what you want to build, but it seems like the smaller an object is, the more important tolerances are. Even my mediocre eyesight can notice remarkably small imperfections, and my wife and kids are even bigger critics.

[High Seas]

Gotta say - your idea and confidence has piqued my interest.
I'd consider using acrylic and thermoforming it to get a channel structure - gain some built in strength and some sweat visuals!

You can find a bunch of plastic cutting bits to help keep from tearing/cracking it. Or grind some yourself.

You could mount mechanicals etc inside the channel - sorta lokk like the old model of the "visible-man"
Keep on Keepin' on!
Jim

[syon]

if plastic is the way you would like to go, i would recommend using delrin 1/2" on the base, 3/4" for the gantry, and 3/4" on the z axis as well.

Plexiglas (acrylic) is very brittle, and at some point, due to lack of UV stabilizer, it will shatter.
Delrin will last for ever, and hardly flexes under a huge load (normally cutting aluminum, plastics, and other durables)

mdf, even if you coat it, the trapped moisture will eventually bubble the surface, creating an unsightly bed, frame, and quite possibly interfering with the overall integrity of safety of the machine.
I don't think it was meant to have one stay with this original material, but more to get them into the hobby/business cheaply, and progress to a more sturdier material.
JMHO