.5" HDPE

[REG]

I've cut a lot of HDPE. I love cutting it; some of the easiest material to cut.
As others have mentioned, select a larger "clearance" bit and let the 1/8" bit square your corners of your pocket. As Ralph stated, re-check your step over. Step over is how much does the bit "step over" from its previous path. A 40% setting means that the bit moves over 40% from center and cutting 60% over the previous path. This sort of gets rid of the ridge caused as the bit picks up the grain of the wood.
Think of it like cutting your grass. One would tend to go over the last cut path a little so there is no stands between passes.

Now, HDPE is peculiar on a flat bottom. The plastic tends to melt rather than cut so this can leave tails if your movement is too fast (ipm) or the rpm too high. A sharp bit is a must for a smooth bottom pocket. Just test/experiment before running your project.

I have a few slabs of HDPE around the shop that I plan to make a router bit holding tray. Since HDPE doesn't absorb moisture it will make a perfect holster for my bit storage. I can oil the bits down right in the tray. Just need to come up with the "perfect" plan to sort the bits; i.e.: used, very used, V-bit, EM, BN and so on.....

Bobby

[Bobby_B]

Thanks for the help guys. I switched it to use the 1/4 bit and then i am going back with the 1/8 to fine tune the edge. This cut the 12 pockets from 4 hours to under an hour.

Bobby