Bit advice for cutting UHMW.

[gundog]

I bought the starter set with my new Shopbot. I will be cutting UHMW for the most part are there any bits that came with the starter set that will work for me?

I will be using a Milwaukee 3.5 HP router in the bot and the material to be cut is 1.25" thick. What size and type should I use?

The guys that were cutting my parts on a CNC router (big machine 7HP spindle) where using a 1/2" bit. That seemed to me like a lot of wasted material but I am new at this. I was thinking 1/4" or maybe 3/8"

These are the bits I have.

A collection of 8 high-performance router bits from Onsrud Cutter to start you off right with your ShopBot. Includes 1 1/4in planing bit, V-bit, straight bits, upcut and downcut spiral bits, roundnose tapered bit.
(#13699) Starter Bit Kit; PRICE $195

I also have a fair amount of standard wood router bits.

[paco]

That's a tad thick for a 1/4" CED tool bit but feasible (beware of flexing the tool). You are looking for O-flute(s) tools. Since it's thick and pretty stable (compare to say 1/8" thick of the same material), I'd go with a spiral up cut to clear the kerf. Check out Onsrud 63-700/750 serie (or the 800/850 for metric). I see an 1/4" CED X 1-1/4 and 1-1/2" CEL in both model (700/750 - hard/soft plastic - it's about the tip/tooth of the bit)... UHMW is a soft plastic. The 3/8" CED will definitely be more rigid but you'll need to find 3/8" collet for this router.

[knight_toolworks]

I would use the 3/8" thought there won't be as much bit flex as when I cut tropical woods it is still best for that deep of cutting. plus the larger bit will clear the shavings better and they get strange in that plastic. I need to cut a sheet on my bot. gonna be fun holding it in place (G)

[dana_swift]

UHMW and HDPE are both very similar materials, and both machine extremely well. Just start out gently and try all your bits.

Cut depth is a matter of repeating the cut while ramping down Z. When the bit is thin compared to its unsupported length I back off the depth-per-pass to keep flex from becoming too great of a problem. Look at your edge wall and see if it is acceptable for your application.

With both materials hold down can be tricky as these plastics are almost as slippery as Teflon. Screwing the material down to the spoilboard will work, and so will vacuum.. however it helps to have a HIGH vacuum and a lot of surface area to increase the friction. I clamp the stuff with great results, but then I have to be careful my path stays clear of the clamps.

I use regular up/down spiral wood bits with the material all the time and have had no problems there. However if the bit doesn't spiral the chips can clog the bit quickly.

Also I have had trouble with the material and very small bits .. like 1/16". I have broken more than one bit as mistakes in feed rate and chip load are really unforgiving. With 1/8" bits on up to 1/2" I have had really good results.

Good luck!

[gundog]

I ordered some new bits that were recomended by Onsrud tech support. Make sure you are sitting down when you order them wow they were not cheap.

They recomended the 52-700 series and the 52-704 for my application. I looked a little and found a source for $68 most places wanted over $80 for them.
Thanks Mike

[myxpykalix]

Michael,
Contact Fred at www.centuriontools.com (http://www.centuriontools.com)