Basic necessary CNC bits

I’m new to using the CNC, and would like to get a few bits to do most of the basic functions with. In the class, we talked about some bits, such as the difference between upcut, downcut, compression, v-bits, o-flute etc, but there are so many options online that it’s hard to know which are any good and which will just break when looked at the wrong way.

Anyone have any recommendations (with links, perhaps) of some bits to buy or sets of decent quality cutters? Looking to do some cutting and some engraving, but not sure exactly which diameters will be needed. Could be useful to have a sort of compiled basic short list of links to bits to buy for CNC beginners. Hopefully this is not already created somewhere else and I am just missing it.

I know that @JoeN compiled a short list in this thread but I figured I’d ask and get a bit of a longer list with some more options.


What jobs are you thinking of? We all know there’s no “one general bit for all” of course, but it’s similar that there’s no small set of “general bits for things”.

O-flute and 2-flute upcuts in various diameters (1/8" to ~1/4"), 1/4" compression bit, 1/4" downcut 2 flute are pretty common. The 32mm dia Chinese V-carvers in various angles. That covers a lot.

But, the flute LENGTH is variable. More flute length than you need is not entirely better, it makes the bit easier to break. The o-flute and 2-flute upcuts have a range of flute depts. 1/4" compression bit comes in a couple of common variants, the important part is where the upcut-to-downcut transition point is.

There are o-flute compression bits, which are often way better. They were hard to find for a long time but now much more available.

Ball mills and tapers are typically for 3d carving.

I’m looking to do some MDF cutting to create templates, and perhaps some inlay work (either a 2-part inlay that fit together well and get planed down, or just a carved inlay that then gets filled with resin or something). For example, inlay cutting boards.

I think for these two operations, I’d just need a good endmill (1/8” or 1/4” compression) and a 60 degree v-bit. Agreed I need to do some more research on bit length. Perhaps get a medium length one to start.

Yep so like on inlays, it’s job-specific. If your big diameter is too large for the inner corners, the bit’s radius fillet may be a problem. If the diameter is too small it will take forever and you may be limited to a lot of shallow passes.

Gotcha, that makes sense. I guess best course of action will be to come up with a specific design and try to pick something more specific based on that. May also get a couple common diameters to play around with beforehand. Thanks for the advice

@gordoa40 You would be surprised that the list I made covers most of your cnc routing needs.

The reason for an up cut bit is you are not worried about material tear out. Materials such as plastics, and soft metals need as much material removed as possible. If don’t remove aluminum and over heat the bit. You get chip welding which is bad. It will break you bit. Plastics need as much material removed from the cut as possible also. If the material is left in the cut it can reweld itself in the kerf from the residual heat.

A down cut bit is great for pocket cuts into plywood. Plywood has opposing grains and will tear out if you use an up cut bit. The down cut bit is forcing the grain down into the plywood. A down cut bit has a con. If you cut through a sheet of plywood the bottom can have tear out since you are forcing the grain out of the bottom of the cut.

A compression bit is the best of both worlds in terms of plywood. The lower geometry is a up cut bit. The remainder of the cutting flutes is a down cut bit. You have to set your initial pass to be deeper than the up cut bit height. A 1/4" compression bit has 1/4" of up cut geometry and the remainder is a down cut bit. If you don’t account for that you will lots of tear out and a lot sanding to do.

I would look for Amana bits they are are high quality. You can start experimenting with lesser quality bits after you get the hang of cnc routing. I would recommend you get an 1/8", 1/4" bit diameter for most of your general purpose cutting. A 3/8" or 1/2" will give you more cutting ability to include rigidity, but cost more and might not serve your purpose right now.

Locally I would check out Sparktech in Round Rock or Dixie Tool Crib in south Austin.

Thank you so much, this is some great advice. I’ll be cutting 95% wood, at least for the time being, so I’ll definitely check out Amana and get probably 1/8 and 1/4” down cut and/or compression bit. Any suggestion as to min/max number of flutes? I assume 1-3 flutes max, but most I’ve seen are either 2 flute or o-flute, I think. Would either work fine?

For wood a 2 flute compression bit is fine. Download cnc cookbook Here to get you feeds and speeds correct. The feeds and speeds calculator is easy to setup. Correct feeds and speeds will help with less chatter and better cut quality. When setting up the cnc router in the program. Use a cnc router parts machine as an approximation for the Hackerspace machine. If you choose an $100k haas router. The f/s calc will spit out the wrong numbers.

1 Like