What's a good plastic(like) material for prototyping?

[brebey]

I've just finished my first CNC router, but now I'm having trouble finding a suitable material to machine.

I'm making prototype cases for an electronic gadget that I'm developing. What I need to do is make these in 1-off or small-batch runs for evaluation, testing, demos, beta sites, etc. These will later be commercially manufactured, but right now I need an inexpensive material from which to make cases. We are a very small company, funded completely out-of-pocket, (and we have very shallow pockets).

The cases will be on on the order of perhaps 4x6 or 5x7 rectangular, and 3/4-to-1-1/2 inches thick. Think along the lines of a PDA cabinet, or a remote control, or a multimeter, or something like that - a thin-walled shell with electronics inside.

Is there any kind of plastic that's suitable for machining (read: machines clean, without melting) that might be suitable to my task and be affordable? Garolite sounded like an excellent solution, but it's horribly expensive - a 36x48 sheet of 1" G9 is $1,400!

That's a far cry from a 48x96 sheet of MDF for $35.

Isn't there something in the middle? Something that I can make usable parts from that's affordable?

I've ordered some machinable wax just for early-stage test-cutting, but even that cost me $172 delivered for two 15x15 sheets.

Any ideas would be appreciated. I'm at a loss.

[mxtras]

HDPE is the most economical solution with aluminum a close second. I looked at about 20 different materials, got quotes and built a spread sheet based on price per cubic inch since volume is what you are looking for. Cutting performance, availability and stability wer all evaluated and I chose HDPE.

Keep in mind HDPE reacts to humidity so if you are looking for absolutely perfect dimensional stability over the course of a few days, it might not be for you.

Scott

[One of Many]

I think you would be better off vacuum forming the shell and using the router to make case half molds. Then use the router again to trim, drill and shape holes etc. A small home built former would benefit you greatly.

PVC or styrene sheet would be my first choice on the cheap. Then you could go to an FR(fire retardant) rated ABS once in production. These can all take gluing. Like internal mounting blocks, structure or mating surfaces to create a shell not moldable otherwise. They also cut nice and clean with the proper feed rate and standard single flute carbide router bits. Even if you didn't form it, you may be able to route flat patterns and mock up a box. Hydrofurane is a very thin solvent(stinky stuff) that will leach into tight fitting gaps and melt these materials together. A little goes a long ways applied with a small blunt syringe tipped bottle. It is not anaerobic ester like superglues, so it does not craze the material. It just dissolves the materials together and evaporates.

Not to discount MXtra's suggestion (He's a good egg LOL!) The biggest problems I have had with HDPE is its thin section instability with temperatures and not much sticks to it, so most glues are out. If it does hold, it may not be solid if the material grows or flexes much. Thermal forming it or machining it in thin sections highlights many of those issues too, but there are places where not much else will fill its positive attributes.

DC

[High Seas]

brebey
My little company is in the same "boat" so to speak - thats why I got into cnc machining to start with

And now I too need to :

Originally Posted by One of Many I think you would be better off vacuum forming the shell and using the router to make case half molds. Then use the router again to trim, drill and shape holes etc. A small home built former would benefit you greatly.

Vacuum forming resin and fiberglass over molds would be another option - use the shop vac and no heaters required.

Acetal/delrin might be a posibility and I have considered using nice timber-bits (teak, black walnut, ebony, etc) as milled case materials - thinking they might look a bit more elegant and with the right fittings might even get more for them! Can you imagine what Brookstone would ask for a stylized teak calculator?

Best of luck and welcome to the zone!
Jim

[Mjolnir07]

Heya Sir...the one off stuff the other guys may know more about. But as for small runs etc...you may want to look into making your one off then molding and casting it in resin yourself. I have done and do alot of this stuff but geared towards tabletop gaming and plastic models. It was alot of hit and miss until I came across some of the best materials I have ever used.

There is a company called Smooth On, tossed a link in below. I have personally seen thier material in the tunnels at Disney in Florida on a tour I took, so I think that speaks volumns for thier stuff. They have a huge range of products and it is all nice product. You can order test kits for like 25.oo or so of any type of material. Browse thru maybe something will suit your needs.

I will go out on a limb and say that the Dragon Skin mold material has lifted off etched glass highlights in molds I have made, can be stretched and abused and always returns to it's original shape...../shrug might help, might not, good luck!

http://www.smooth-on.com/

[svenakela]

Sometimes people tend to forget a superb material. Wood.
One of my biggest moulds was made from plywood. It was a uge planet gearbox cover.

I've been working a lot with a material called "Ureol". It's very common in the prototyping industry. It cuts easily and have good mechanical properties. We also made a lot of plugs for aluminium plaster moulding. After milling we clear coated the surface and polished it, the plug could run hundreds to thousands of copies without loosing tolerances.
If it's more economical that HDPE I don't know, but check it out.

Regards,
Sven

[mxtras]

My suggestion failed to give substantial regard to the entire prototyping process. You guys are correct - HDPE would be tough to glue. BUT - until you have the shape/size/parting lines nailed down, using the cheapest material is attractive. Once the shapes and cutting program is good to go, then migrate to a more suitable material for the final prototype and then make a mold and go for the vacuum formed skin.

I see all prototyping as a progression of an idea, and many times after the first one is complete and operational, changes are desired. HDPE offers a very cheap way to make this happen without tears when your first three shapes fail to meet your exact expectations which seem to change as you progress.

Good points, guys.

Scott

[martinw]

Originally Posted by brebey I've just finished my first CNC router, but now I'm having trouble finding a suitable material to machine. I'm making prototype cases for an electronic gadget that I'm developing. What I need to do is make these in 1-off or small-batch runs for evaluation, testing, demos, beta sites, etc. These will later be commercially manufactured, but right now I need an inexpensive material from which to make cases. We are a very small company, funded completely out-of-pocket, (and we have very shallow pockets). .

Dear brebey,

My tiny company is , pretty much, going through the same birth process.

We took the view (and it may well be wrong) that machining easily available existing enclosures, and adapting our "guts" to suit the box is a pretty good start. There are vast numbers of display-type enclosures available.

If you can lay out your pcbs , to take the fixing points on the enclosure, you save a load of trouble.

Last point... shop around for similar off-the -peg enclosures, and see what the supplier will quote for custom machining by them. You may be surprised....

We considered two pretty much identical boxes. Supplier A quoted £26 plus £13 for putting 21 half inch tapped holes in one wall. Supplier B quoted £13 for the box, and £1 for the machining. I could not believe it when I read their e-mails. Another thing you really should consider is is it actually worthwhile doing any machining yourself on a standard out-sourced enclosure.

Think of the sequence.

1) you get sent the enclosure
2 you unpack it
3) you machine it
4) you get rid of the swarf and cutting fluids
5) you have to store it before it goes for assemby.

If you get the box supplier to do that, you go straight to stage 5.

Another thing, if you screw up the machining, you have a trash box at your expense. If the box supplier screws up, you don't pay them.

We went for polycarbonate, and ABS as a slightly cheaper alternative. Identical enclosures though.

Bear in mind that just because you have the ability to machine in-house, and it might be fun, it might not make economic sense.

Good luck with the birth,

Best wishes,

Martin

[martinw]

Dear brebey,

BTW, those enclosure prices were for an initial batch of 25, from UK suppliers, not thousands from China.

Also, since I very much doubt that we will be commercial competitors in the same product sector, you should seriously consider getting your prototype pcbs out-sourced, even at one-off levels.

There are people who do a single though-hole , double-sided, 100 by 160 mm Eurocard , complete with etch resist and component ident prototype, in Europe for about, I think, less than £20. I cannot remember where, but it's posted somewhere on the Zone. At that price, I think it might be a good idea to put my ferric chloride etch tank into a long deserved retirement . Just send them the gerber and drill files..and wait.

Good luck.

Best wishes,

Martin

[brebey]

Many thanks to all of you! I really appreciate the direction; that gives me lots to work with.


Scott, thanks for the HDPE suggestion. I didn't even consider it as a possibility.

DC, It looks like PVC is relatively inexpensive, too, and is available in plenty of size options. I can't find styrene in anything but thin, rolled sheets, though. Do you know of anyone who sells machinable sizes - like in the .75"-1.5" thick range?

Oh, DC and Jim? Thanks a lot (read with dripping sarcasm...) for pointing me to vacuum forming. Just what I need - yet ANOTHER obsessive hobby that I'll spend countless hours and dollars building the machine for, only to turn it on and immediately declare "Hey! This is REALLY cool! I need to build a better one of these." (That's exactly what happened with my CNC router. This is getting expensive!) ;-) Seriously, though...thanks so much for the help. Vacuum forming might be the way to go after all. I'll research...

Martin, yea - I knew from the onset that outsourcing PCB prototypes was a no-brainer, especially given the size of the traces on some of the components I'm using. I use AdvancedCircuits.com; they do 3 pcs for $99 US. Can't beat it! Regarding the case prototyping in-house vs. outsourced, at this point it's a matter of principle: I AM GOING to make at least ONE in-house prototype case if it kills me! Maybe after that one I'll outsource the whole thing, but dangit, I WILL NOT BE BEATEN by my inability to make a 5" square box! ;-)

Yea, Sven - you're right. Wood is actually pretty good, and free. I'm a homebuilder and a professional trim carpenter/cabinet builder (that is, while I'm not being a software and electronics engineer making electronic gadgets), so I have an ample supply of maple, Brazilian cherry, oak, pine, and poplar material. Trouble is, it burns easily. You're right, though - wood's a pretty good option for a lot of things!

Thanks again to all of you!

[mxtras]

Check with McMasterCarr for a pretty decent selection of plastic materials. I would not suggest PVC - it has static issues and I think it sucks to machine. Just my opinion.

Scott

[Mjolnir07]

Ok so like I need to drive my pickup out to you and loadup on all your hardwood scraps for my Intarsia stuff...RoadTrip!

Sorry I was so far off base with my suggestion I was way out of my league there but it has been interesting reading about all this none the less, good luck with it all and i hope we get to see pics when it is all finished!