Question about cut quality in Polymers

[johnm]

Folks -

We've been "fixin'" to cut some small parts out of 1/4" polymer sheet, with logo engraved into the face of the part.

I am getting "whiskers" in these cuts and it's driving me nuts! I am using a new 90 degree V bit, and changing cut speeds from 1 to 3ips doesn't really change anything. I am running 13k rpm with a spindle.

I have used a heat gut to condition the surface, but have to many whiskers to have this be viable. I've tried using duct tape to lift them off, and it helps, but still too many.

Is this the nature of polymers? I could sure use some help - I have a large order riding on being able to cut quickly and cleanly - I don't want to do hand work on a zillion parts.

Thanks in advance for any assistance.

John Moorhead
Lakeport, CA

[stevem]

What type of plastic are you cutting?

Is your V bit carbide, or HSS?

[richards]

By definition (from Wikipedia) polymers are going to leave whiskers:

"Polymer is a generic term used to describe a very long molecule consisting of structural units and repeating units connected by covalent chemical bonds. The term is derived from the Greek words: polys meaning many, and meros meaning parts [1]. The key feature that distinguishes polymers from other molecules is the repetition of many identical, similar, or complementary molecular subunits in these chains. These subunits, the monomers, are small molecules of low to moderate molecular weight, and are linked to each other during a chemical reaction called polymerization."

[johnm]

Steve -

I don't know, really... This is the stuff, all it says is that it's a polymer. It isn't as hard as an acrylic, but it is harder than PVC.

Here's the link:

http://www.tacomarine.com/cat--Marine-Lumber--marinelumber.html

We are cutting a logo into the surface of a 1/4" sheet, and going .007 deep.

I am using a new carbide 90 degree bit. Hope someone can offer some advice. If the problem is inherent to polymeric plastics, I won't sweat it - we just haven't cut this stuff before...

TIA

John Moorhead

[richards]

John,

I should have added in my previous post that I've never had any luck cutting polymer plastic. There's probably someone who knows how to do it, but I haven't found a way. Just like you, I've tried various feed rates and spindle speeds, but the whiskers keep growing. I have NOT tried misting the cutter to keep re-melt to a minimum and I haven't tried a vortex type chiller either. Maybe something along those lines might help.

[elcruisr]

Well, the first problem is that v bits and plastics are a poor match. Y
The tool geometry is wrong. I can get away with small shallow cuts but anything more usually is problematic. That's why plastics bits look different than wood bits. I don't know of anyone making a plastics geometry v bit. You can get away with it in some plastics like Sintra but other plastics are very unforgiving.

Eric

Eric

[gerald_d]

Maybe a wild thought, but will flame polishing help? Solvent? link (http://www.dynalabcorp.com/catalog_polishing.asp)

[knedert]

Gerald -

Well, yes, I have, sort of... As I noted in my opening post, I used a heat gun, and had too many whiskers to start with for that to be viable.

Thanks for the link tho'!

Cheers,

John Moorhead

[georgew]

Gerald

Cutter geometry may be the problem as Eric stated. If you have a 1/4" collet you can use engraving cutters from companies like Antaries and Crown that are designed to engrave into plastics. Check out Artisan Engraving Supply co 1(800)462-7117. They have 1/4" short stub cutters that can be used in a bottom load spindle, and they can grind them to your point size.

George