New Machine Build- 3/4" dark gray machinablePVC sheeting for a build?

[coloradonewbie]

I'm gathering materials for my CNC router build and had a question about using plastics instead of plywood. The plans call for 3/4" 13 ply birch plywood that I understand is a very stable building material with no voids between the layers.

We've been playing around with some 3/4" gray PVC sheet material at work to make fixtures for fabrication and thought it looked stiff and strong enough to use for my router build. The full cutting area of this router is only about 28x16x5 so there would be very little sag factor.

I believe this stuff can be tapped and would hold a screw in the threads. Also, the plans call for PTFE supports for the head assembly with aluminum plate pieces for the Z axis. I was thinking about building the whole thing out of this gray PVC material.

Anyway, I was wondering if anybody has played with that material or suggest an aluminum replacement for the Z axis as aluminum is a bit harder to drill, tap, etc. and costs more.

Thanks in advance for your reply

[eloid]

Becareful in what material you choice and use where, Some plastic can develop Lots of static charge. ie if you hear a static zap but dont see it thats ~2000v, if you see it and feell it that ~5000v any thing under 200o volts you typical dont see or feel which can..... still kill all electronics. I would check the attaction of wood chips / saw dust to the plastic....etc You May find a issue..with your bearing woth attacted to dust.... Do some home work and it will help in the long run, some plastics are great.... others are generators of esd..... remember you cnc will be moving back and forth 100-1000's of time
in a given x,y direction.... which can build a static charge easy...

[coloradonewbie]

A static build up never even crossed my mind. That's why I'm asking the experts. So they use HTPE or PTFE for some carriage parts on a lot of home builds, (don't know if the abbreviations are right), do they not build a static charge as well, or because the rest of the machine is wood it doesn't transfer to the electronics?

I don't mind building the body and table out of wood, that's what I do, but I'm really trying to get away from all the aluminum work on the carriage and Z axis as I'm no machinist and it's got me a little worried if I can do it or not.

[eloid]

Originally Posted by coloradonewbie A static build up never even crossed my mind. That's why I'm asking the experts. So they use HTPE or PTFE for some carriage parts on a lot of home builds, (don't know if the abbreviations are right), do they not build a static charge as well, or because the rest of the machine is wood it doesn't transfer to the electronics? I don't mind building the body and table out of wood, that's what I do, but I'm really trying to get away from all the aluminum work on the carriage and Z axis as I'm no machinist and it's got me a little worried if I can do it or not.

Im not sure if the mention plastic are static generators... do google with htpe esd issues .... I would recommend contain all electronis in metal box, with a single common grounding point in the box, and star out from there to...
ie the metal frame of the cnc or x,y,x caragie etc if the body is wood.

You may find the plastic is ok, ie if the plastic is more of neutral and doent attract static ie more of dissaplative plastic...its bleed off and charge... note it not "conductive " but doesnt hold a charge...

[coloradonewbie]

I've already purchased the Xylotex 425oz 3-axis stepper kit with the pre-made controller box and pre-wired cables. Don't know how that will effect the common ground for everything.

[Geof]

Almost certainly too flexible and also too much thermal expansion just with changes in room temperature.

Don't be nervous about working in aluminum there is no reason you could not make practically all the parts just with hand/power tools, a bit of creativity and advise from people here.

[Drools]

Just a note on your Birch Plywood, the type you want is Baltic or Russian Birch plywood (maybe more names for it). The laminations are thinner and supposed to be void free. This wood is quite nice and very strong. If I had the choice I would use it over plastic.

[eloid]

Originally Posted by Drools Just a note on your Birch Plywood, the type you want is Baltic or Russian Birch plywood (maybe more names for it). The laminations are thinner and supposed to be void free. This wood is quite nice and very strong. If I had the choice I would use it over plastic.

Baltic and russian plywood are very stable due to the high number of laminations (5 or more layers) etc...

If you you planing to make one machine.... and the budget permits $?
I would make the critical structual parts out of aluminum ( ie gantry/ and racking brackets and other bearing mounts out of aluminum with 8020 extrusion..) if you need more than one part...
make a 1:1 template of it, and use a router with collets to cut the aluminum with shallow multiple cuts)

When you machine is made tested and running you can always. make improvements and add ons with your cnc for parts...

[coloradonewbie]

Thanks for all your great advise. I do use 1/8" Baltic birch plywood for artwork that I do in wood. It's very clean and void free. I'm sure the 3/4" is awesome as well.

I think I'm going to build the first one out of plywood and aluminum, then making plans for a 4x4 extruded aluminum table or possibly start gathering parts for a Joe's Hybrid.

I didn't know plastic expand and contract so much with temperature. I would have thought the plywood would be worse at that of the two materials.

Not really worried about the aluminum that much. I have a friend at work that's pretty good on a manual mill too. He will help with the carraige and z-axis parts. Still can't find a great source for aluminum plate, 1/4" and 1/2" that isn't crazy expensive. The parts aren't that big. I know it costs more for a larger chunk of plate, but I could probably pick what I need out of a scrap barrel.

Here's a pic of the plans I'm building in the attachment. I'm sure you all have seen this one a million times from eBay. Has anybody here built this one, and what are you calling it in the forum threads?

[ger21]

Wood does not expand and contract with temperature. It moves due to moisture.

[coloradonewbie]

That makes sense. Thanks for the input. I'm excited about getting started now. Got movement from the steppers last night with my Mach 3. It's all uphill from here! =)

[eloid]

Originally Posted by coloradonewbie Thanks for all your great advise. I do use 1/8" Baltic birch plywood for artwork that I do in wood. It's very clean and void free. I'm sure the 3/4" is awesome as well. I think I'm going to build the first one out of plywood and aluminum, then making plans for a 4x4 extruded aluminum table or possibly start gathering parts for a Joe's Hybrid. I didn't know plastic expand and contract so much with temperature. I would have thought the plywood would be worse at that of the two materials. Not really worried about the aluminum that much. I have a friend at work that's pretty good on a manual mill too. He will help with the carraige and z-axis parts. Still can't find a great source for aluminum plate, 1/4" and 1/2" that isn't crazy expensive. The parts aren't that big. I know it costs more for a larger chunk of plate, but I could probably pick what I need out of a scrap barrel. Here's a pic of the plans I'm building in the attachment. I'm sure you all have seen this one a million times from eBay. Has anybody here built this one, and what are you calling it in the forum threads?

what did you draw/ cad this up in? nice cad work...

you may need to stiffen up the gantry you may get rack side to side motion when you cutting under load... maybe add a 2 horizontial member ( 1.5 x2 support) running in parallel with you rails but in a way the dont obstruct you travel horizontally with you z or x ... not sure how thick your 2 vertical supports are
for your gantry? maybe try laminate some more wood in the center of them...

nice clean design...