Compression Bit Advice

[dcrowder]

I've purchased one of these 3mm dia. compression bits from Wealden's..... http://www.wealdentool.com/acatalog/Online_Catalogue_Compression_230.html

I've cut into 6mm Plywood with a DOC of 4mm and also cut 4mm Plywood wih a DOC of 4.2mm single pass... the full depth cut worked but I didn't intend to do the full depth and was concerned about breaking the bit so slowed everything down. I wasn't too impressed by the cut finish although I'm sure this was my fault because the cut in the 6mm plywood was really nice with little sanding required.

Can anyone offer me any advice on the depth of cut I should be aiming for? Maybe I'm pushing the bit too hard? Somewhere I saw recommended DOC to be half of the bit dia but in other places I have seen people cutting deeper than the diameter of the bit. I also saw a video cutting 18mm ply with a 3mm compression bit in 4 passes which suggests that I could get away with 4mm DOC.

Also the compression bit cuts really noisy compared to my up cutting bits - is that normal?

Cheers - any other advice appreciated!!!!

[Ger21]

I've never used such a small diameter compression bit.
I'd probably make 2-3 passes, and a full depth finish pass, which should improve your cut quality.
In most cases, if the bit is making a lot of noise (screaming?), it's because you're feeding it too slowly.

[dcrowder]

Cheers for the advice Gerry, the bit was definitely 'screaming'... I was feeding it slowly because of the DOC being 4.2mm for a 4mm sheet and me worrying about snapping my new bit due to its length.

Can you tell me if what I've read about the DOC being half the diameter of the bit is true? I've had success with cheap Chinese carbide up cutting bits, cutting deeper than their diameter and everything seemed to be coping.

[Ger21]

Can you tell me if what I've read about the DOC being half the diameter of the bit is true?
No, not for wood.

For bits 6mm and smaller, I use DOC = Diameter.
Once you get to 10mm, you can easily use a 20mm DOC. The material makes a difference, though. Feedrate as well.

[dcrowder]

No, not for wood.

For bits 6mm and smaller, I use DOC = Diameter.
Once you get to 10mm, you can easily use a 20mm DOC. The material makes a difference, though. Feedrate as well.

This answer is worth 1000 googles! :beer: