Compression bit

I bought my first compression bit from whiteside and I figured i would try it on a project using 1/2 birch ply wood. I grabbed the tool data off of whitesides website, I noticed the feed rate was over 400… I dialed it back to 400 hundred, and started cutting. The project had a bunch of short tool paths followed by a large cutout. Once the cutout came the screen on the onefinity started cutting out and then it skipped a few lines of gcode. Project ruined.

Changed out the wood for round 2. I figured the current draw from the router on a big fast cut was two much to be on the same circuit as the onefinity. So I got an extension cord and put the router on a different circuit. I also reduced my feed rate to 200 to see if I could get round 2 to completion. Screen stopped flickering but on one of the cut outs seperated the top ply.

My questions are what feed rates and plunge rates should I use for a compression bit?

Did the compression bit cause the top ply to separate or was it a bad spot in the plywood?

Plywood is not a great wood to work with. Most likely there was a bad spot in the ply somewhere. Depends on the quality of plywood.

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I know that pretty much everyone loves their compression bits, but my first couple runs with them were less than ideal (cutting HDPE). Yes, it gave me a cleaner top surface, but overall it didn’t cut nearly as well as a standard upcut bit and the sidewalls of the cut exhibited chatter. Instead of evacuating the chips like a normal upcut bit, the downcut bit actually compresses the chips down into the cut pocket. This was evidenced by the nasty crunching sound I heard when using it. It was only cutting about .060" deep at a conservative feedrate. This was a 1/8" bit, and I may have bought a cheap brand of them. But as an old-school machinist, I could definitely see & hear that it wasn’t a proper cut. Maybe they do better in wood.

I use 1/8th compression bits when I make my monograms. In 1/2 in plywood (.46 thick), I usually run it at 100 imp and .1 DOC. The trick I found out was to turn off the dust collection and use the dust boot as a broom to sweep the chips into the tool paths, essentially locking in the pieces. When I was using the dust collection, the smaller pieces would sometimes lift up and rattle around before getting sucked up. Sometimes these pieces would damage the top layer of plywood and once even broke the bit. My 24in Monograms usually take less than 25 minutes to complete. I successfully made about 10 of these before Xmas using this method, all with one bit.


Very nice. How did you post the picture on your post ?

@Eddie - you can upload pictures by uploading them from the menu. Looks like a hard disk with an arrow coming out of it.

Thanks. I’m old but learning new tricks everday😎 I see it is in a post or reply.

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Here ya go Eddie.

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Thanks, ! Seems to work :sunglasses:20210107_202758|375x500

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You can also just drag and drop the picture into the message box.

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