Smallest Practical Bits for CNC Cutting Work

CNC owners discuss how small a bit can be and still perform cutting tasks well. September 25, 2014

We'd like to cut our grain-matched slab doors and drawerfronts on our CNC instead of our sliding tablesaw, but would need to use a smaller bit than our 3/8" downsheer - such as a 3mm or other. We use 3mm reveals between doors, and 1mm edging so we have up to 5mm of area to cut with. Will a 3mm bit work? If so, where would be a good source for that?

Forum Responses
(CNC Forum)
From Contributor C:
Most 3mm (1/8th) bits have short cut depths. If you use one with a 1" DOC and a good bit slower there is no reason you cannot do this. It may snap a few bits finding the sweet spot. I regularly cut sintra and P-lam inlays on wood this way.

From contributor M:
Three mm is pretty small for deep cuts required for drawer/door fronts. If you can sacrifice a little loss of material, I would recommend a 1/4" bit. Those will generally have a deep enough CEL for standard front thicknesses. 3/16" diameter bits are available with 3/4" CEL's but you might have to specify as the standard is 5/8". Also see if 5/32" bits can be had with a longer cut length. Check Vortex for standard tooling.

From contributor L:
I'd say 1/4" is the smallest you want to go and still get a good cut depth and speed. That little bit of kerf isn't going to make much of a difference in the grand scheme of things. If you use anything smaller you'll have to do multiple passes at a slow feed rate and even then 1/8 is as small as you can go and still cut anything thicker than 1/2 inch.

From contributor A:
These 5mm compression bits are used by guys who make casework parts on small light machines like a shop bot, without a tool changer. They have the advantage that you can drill all of your shelf holes, cut cabinet perimeter lines (often but not always in two passes) and pocket for back or other assembly dados without changing tools. Pretty slick actually if you have low sheet volumes. That being said, Vortex will likely make a 5mm compression bit custom, they are very helpful there. You could have a 1/4 inch bit sharpened if it is only a couple of sheets of material for occasional use, but bits sharpened that much work less well than new ones.

From Contributor D:
For anyone using the 5mm Centurion bits what's the tool life like?

From contributor O:
I use 6mm Centurion compression bits (as well as their other larger sizes) and I'm very happy with them. They are inexpensive so buy a few and try them.

From contributor O:
Correction that is 1/4" or 6.35mm as we call it, haven't tried the 5mm yet but now I know they have added a 5mm to the range I will.

From contributor W:
Amana Tool makes a 1/8" compression spiral with a 13/16" cutting length. I have wanted to try one of these for the same purpose but was worried about bit deflection and breakage.

From the original questioner:
I'm going to call up Vortex and Centurion and see what they recommend; we'll probably test one and see what happens. We will also test the results if we move up to a 1/4" bit and see how the slightly un-aligned door next to drawers looks in the grand scheme of things.

From contributor Y:
The finished parts you show are super. One way to prevent the bits from snapping or being damaged is to reduce the vibration in the material(s) while making your small, narrow and intricate cuts. Are you using MDF or LDF as your spoiler or flow through board?