Bit Selection for a CNC Router

A shop owner gets advice on what bits he'll need for his new CNC router, along with tips on bit care and re-sharpening. August 30, 2005

I'm a commercial frameless casework manufacturer. What array of bits should I have for the cnc router that will be delivered to my shop in three weeks? To start we will be using blind dado construction with 32mm system holes for adjustable shelves. We will pre-drill for mounting plates, guides, locks, etc. The machine comes with a 5 x 5 drill bank, and 8 position tool changer with 2 collets each for 1/8, 3/16, 1/4, 1/2, & 3/4. Any help is appreciated.

Forum Responses
(CNC Forum)
From contributor C:
What I have found after a year of use is that the number one bit you will use is a compression bit, upshear/downshear. Our choice is a 3/8" diameter 2-flute compression spiral by Amana. This bit will cut 3/4" mdf and flake core material at a rate of 750 inches per minute at 16000 rpm and last about 100 sheets of just cutting out your shapes. As for your secondary bits, 1/2", 3/8" and 1/4" down shears to cut your mortise and tenons or dado's if required. I never use re-sharpened bits, only new ones. Re-sharpened bits tend to wear out in 20-30% of the time that a new one does and the cost of re-sharpening is about 30-40% of a new bit.

If your router uses a spoil board, you will need a bit to fly cut it. Ours is an Onsrude 4" diameter with replaceable cutter tips. As for drill bits, many schools of thought here are brad-point bits for line boring ends and v-point (optional) for through drilling partitions. Our router uses a spoil board (bleader board) and we keep it resurfaced after 20 sheets or so. I tend to keep 5mm brads (9 in the x+/- row) for line boring everything. The bleader board serves to back up the sheet good so as not to blow out the back side of the part.

Make sure you router manufacturer tells you what length drill bits your machine uses. Two main choices as I see it are 57mm and 70mm long.

From the original questioner:
My equipment supplier told me that I need to find someone with a Walter’s cnc grinder for the bit sharpening. Otherwise I won't get good results from my re-sharpened bits.

From contributor L:

In addition to the above post we use a 3mm bit in an adapter to peck holes for hardware that will be screwed on with #8 screws. It saves time at the bench by not having to measure. We also have a 25mm cylinder bit loaded for KD fasteners. Our main router bit is a 3/8" compression spiral and they work great, there are versions of it made with very short up cutting on the bottom so you can use them to groove. We also use an "O" flute 1/4" for cutting plastic sheet. You need to be careful with "O" flute bits because of inherent balance problems, check with you machine supplier for max rotational speeds if you use them.

We keep a 1/8" bit loaded in a tool holder but not in the changer for squaring out corners in some thinner work, leaves just the 1/16" R. Get spare collets, a couple of 10mm for loading odd boring bits in the main spindle, we’ve also got a ¾” collet used when deep heavy cuts are required in 3” UHMW.

Get several extra tool holders so you don't have to take the occasionally used cutting tool in and out and touch it off again. We've got an Andi and just installing a Komo. Let us all know how it goes with the new machine.

From contributor M:
To the original questioner: It sounds like you have the same boring head as us, 5x5. One thing we found is that with such a limited number of bits this will hold we simply use all through bores on the 5mm bits, the more 5mm bits you can fit into your configuration the faster you will produce nests that contain end panels which in my experience are the ones that eat up your time.

From contributor G:
I suggest the following:

CUD-375-3 3/8 x 1" compression 2+2 flute. This tool is used cutting out your 4 x 8 sheets (nested).

CD-250 (1/4) CD-500) (1/2) for you dado cuts
0500-RH(LH)70 right and left hand brad point drills. Use 70mm.
0800-RH(LH)70 right and left hand drills , again use 70mm.
CII-100-123 4" spoil board Insert tool (you will need a 3/4" collet)

This is your basic setup. As you get more used to your machine you will be using a variety of different tools. COURMATT will provide you with the feed speeds vs. rpm's on all tools sent.