Need a few suggestions for milling plastics.

[macdarren]

Hi All,

I generally work in metal, mostly AL, but of late I find myself cutting some things that are near the end of the production and fairly pricey to replace so I thought if I could find a less expensive practice material I could do some trial runs before committing an expensive piece of stock. In the past I have just used .1 inch AL plate to test my tool paths and it works ok, not the cheapest but not bad. However I always thought it would be nice if I could see through it (transparent AL not withstanding) I am often trying to fit a milled piece to something that exists already and being able to hold up a clear template would allow me to easily see where I might need to correct something.....

Anyway I found the 'perfect' cheap material that we all probably have laying around that being CD jewel cases, they are fairly stiff and transparent. My problem is so far my attempts to mill or drill them have been failures. I really don't much about plastics or what type of plastic this might be but I need some pointers on the proper cutting tool and speeds. Generally I am using 3/32 end-mills and 1/16 drills for this work and so far the result is seems to be the point the mill must be getting hot. (I actually don't have the coolant running for the plastic parts so maybe that would help) What happens is I end up with a big glob of melted plastic on the mill or the drill. I am guessing I need to cut with a slower spindle speed or maybe I need some different tooling for plastics?

Any suggestions??

Thanks
Darren

[Chrliev]

CD cases that's a good idea...

Metal cutting tools are not sharp enough for cutting plastics the heat build up in metal is not enough to cause most metals to melt and metals also conduct heat away for the cut quickly but plastic has a much lower melting point and doesn't conduct heat at all so the metal tool gets hot enough to melt the plastic.

Use really sharp one or two flute tools and maybe some water in a spray bottle to keep the temp down. For drilling holes try brad point drill bits like the kind made for wood they are sharper and tend to cut cleaner, drill bits for metal have a blunt center point and tend to push the metal out of the way.

[fabelizer]

A Google search for milling plastics provided quite useful information, however, it is not specific, and specifics appear to be found with experimentation for a given material. It seems one of the toughest cuts in plastic is where both sides of the mill are in contact with the material, as that contributes to heating. This is due to the flex of the material allowing a cut to be made, but the cut edge has been slightly compressed, and re-expands for the other side of the cutter to rub against. Try starting with outside perimeter cuts as much as possible. It appear water is a decent cutting fluid for cooling, and highly polished cutting edges are preferred.

I would like to know what you find out, as yes, I have a few of those jewel cases lying about!

-fab

[runangolee]

A lot of plastics, especially decent cutting ones, can be a bit spendy. Delrin cuts well without coolant and can give perfectly accurate sizes/profiles if you want to go that route. the only time it seems to melt is drilling holes or in other tight spaces.

You might also consider wax. I've gone to wax in the past to test some expensive parts first. You can melt it down yourself if you want, but I know MSC also sells "machinable" wax that has some additives to make it crisper and have it cut better. I don't recall that stuff being real cheap either but at least its easy to reuse.

[RCaffin]

Originally Posted by macdarren so far the result is seems to be the point the mill must be getting hot. (I actually don't have the coolant running for the plastic parts so maybe that would help) What happens is I end up with a big glob of melted plastic on the mill or the drill.

That's not a good plastic for milling. It melts very easily.

Anyhow, rule #1 for machining plastics: do not use cutters which have been used on metal first. Use new cutters dedicated to the plastic ONLY.
Reason: cutting metal very slightly blunts the cutter edge.

Cheers

[louieatienza]

I've successfully used Onsrud 65 series super-O flute bits for most plastics. They come as small as 1/16" and cut pretty clean.

For more "melty" plastics I use a low-helix spiral-O. I try to keep my spindle under 6000rpm...