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Discussion Starter · #1 ·
First of all, I'm sure everyone asks this kind of question, but my search didn't turn up much. It seems to me there should be a pinned thread on the subject?

My long awaited CNC router is finally ready to be picked up! But I don't have any cutters for it yet.

I want to be prepared to do most things, from 2D cutting to 3D carving, all on plywood/ MDF/ HDF.

My machine is a ShopSabre 23, which has a 5" gantry (spindle lifts up 6" above bed) and a 1.7kw air cooled spindle. It comes with 1/8, 1/4, and 1/2" collets. Cut speed is around ~300ipm. (I don't know if the machine's specs will affect bit selection all that much, but just in case.)

Simply put, what are the types of bits that are essential and most useful? Also, what bits are not very useful?

Also, what shank size should I pick? Is there a rule of thumb for deciding? I will have up to a 1/2" collet, but I don't know if/ when the larger diameter shank is a good idea?

If left to my own devices, I would just order few down cut bits, compression bits, straight flutes, bullnose cutters, tapered spirals, etc. I do plan to buy a 2.5" fly cutter w/ inserts, but I haven't decided on anything else yet.
 

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For clean cuts in plywood a downcut spiral bit, 1/4"d or 3/16"d. In hardwoods upcut spiral bits usually do fine. For 3D carving the finish passes you'll need ball end bits. The smaller the bit then the finer the finish, but also the longer the job will take. If you've got a heavy duty machine rather than a hobby machine then 1/2" and 3/8" diameter bits can also be handy rough cuts and large pockets.
 

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Discussion Starter · #3 ·
For clean cuts in plywood a downcut spiral bit, 1/4"d or 3/16"d. In hardwoods upcut spiral bits usually do fine. For 3D carving the finish passes you'll need ball end bits. The smaller the bit then the finer the finish, but also the longer the job will take. If you've got a heavy duty machine rather than a hobby machine then 1/2" and 3/8" diameter bits can also be handy rough cuts and large pockets.
Thanks. The machine is a bench top size (30x40" bed), and it is built like pro machines. Welded steel frame, servo motors and ball screws on all axis, etc.

Have you bought bits you thought you needed but ended up not using? Or bits that were surprisingly useful?

Is breaking bits an issue? I know that will depend on rpm, feed rate, and depth of cut...but as a newb I'm wondering if I should worry about having multiples on hand.

I'm just trying to anticipate what bits I am likely to need, so I can have them on hand when the need arises. My project has been on hold since March, which is when I realized the only way forward was for me to buy my own CNC machine. I want to be as prepared as possible when my machine is finally ready to go. (Hopefully in 2 weeks, but anything could happen...)
 

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I generally buy bits as I need them. Turn around is usually only 2 days max where I live. Those bits I use regularly I try to keep 3 of on hand. When one seems dull or chipped or broken I order another, but obviously have a spare I can use while waiting. The third is a spare of the spare, and is there just for peace of mind when what I'm doing has a deadline and I can't afford 2 days of downtime. I don't often break a bit. I've only broken tiny 1/16" end mills in use. Other sizes get broke trying to cut through steel clamps or plow into the bed, etc. Yes, you could break one feeding too fast through hardwood taking too much off in a pass. The software I use defaults to 1/2 the bit diameter per pass, and 40% stepover when clearing an area. Both these can be overridden for any cut. I can also dynamically slow down feed speed as a job runs If it sounds too aggressive.

Bits I use most are 1/4" and 3/16" spiral end mills, both upcut and downcut. I'm most often cutting joinery for student furniture designs though. My machine is a Probotix Meteor and not too heavy duty. I like the 3/16" bits over the 1/4" bits wherever they'll do the job. I use 1/4" bits when I need extra depth. I keep 1/8" and 1/16", as well as 5/16", 3/8", 1/2", 5/8" end mills too, but only use them for pocketing or rough cuts when their size best matches what needs to be cut. I keep 1/4", 3/16", 1/8" ball nose bits, and a tapered ball end bit for deeper 3D cuts. For simple slopes I use the larger ball end. For fine contours/detail I'll use smaller bits.
 

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I started with a 60 degree v bit, a 1/4 down spiral, and a 1/8" ball nosed taper, plus all the router bits I had accumulated over the years. It really depends on the project what you are going to need. I ended up needing larger spiral bits to hog out material in the bowls I was making, as well as a bowl bottom bit for finishing the bottoms.

I have broke a few bits, mainly because of human error. It happens. all it takes is not setting your safe z clearance, or resetting your tool zero when changing a tool, or running into a clamp.... lessons you hope to only need to learn once.

Things that have stopped me cold were needing brushes for the router motor, needing a flexible coupling for my Z axis; things which only failed with a tight deadline on a weekend.... I now have a little supply of spares that I keep on hand.
 

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Discussion Starter · #6 ·
So just to update, I ordered a few bits. I didn't go too crazy, as the price is a bit sobering. But at the same time, the investment is a waste if I handcuff myself by cheaping out and not buying the cutters I need.

Mostly I got 1 of each, except small ones that seem more likely to get damaged. They all seem reasonable for what I'm trying to do. I'll try to remember to update this list as I go.

2.5" fly cutter/ spoil board cutter w/ carbide inserts (I got the vacuum table option, so this one was kind of necessary, though expensive)
1/4x 1 1/2" ballnose
1/2x 1 1/2" ballnose
1/16 x 1/4" ballnose (2x)
1/4x 1 1/4 down cut spiral
1/4 to 1/18 ball nose tapered spiral
1/4x 7/8" compression
1/8x 7/8 up cut spiral (2x)
 

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Discussion Starter · #7 ·
Has anyone ever come across a 3/16" or 5mm tapered spiral bit? I'm looking, but haven't seen anything. I don't care what the shank diameter is or the cutting length, but ideally the overall length would be 3.5", but no longer than 4".

I am cutting contours, not fine detail. So the larger diameter bit would give a smoother finish and allow a larger step-over.

I'm searching right now, but the bits I'm seeing jump from 1/8 to 1/4" (or 3mm to 6mm...which is effectively the same sizes.)

When I first started looking at bits, it seemed the selection of bits was endless. But now I'm looking for something specific and I can't find it.
 
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