Why use 1/8" bits with 1/8" collet

I’ve had this question for awhile, and now since im out to replace my first set of bits I was wonder why should I use different size collets when I could mostly keep in my 1/4" collet and just buy 1/8" bits or smaller with a 1/4" shank. I know the 1/8" shanks are a little cheaper but is that it, is there anyother pros and cons?

I prefer my 1/8 bits with the 1/4 shank. It makes my life a little easier.

The drawback for me, at least, is that I keep dropping them, and they break. UGG. The 1/8 bit shears right off the 1/4 shank. So far, I have lost 2 bits to my clumsiness.


I agree with @SDGuy. I hate changing collets even though it is quite easy. If replacing your bits just get 1/8" bit with a 1/4" shank. I bought a 1/8" down cut bit from Grizzly that I use a lot.

I also have a groovee jenny 60 degree down cut bit but they make other bits that are equally as good.

Carbide3d bit are good and competitive but there are a lot of other bits out there to explore. What I do not recommend for a Shapeoko are the compression bits. For a compression bit to work properly you must make a full depth cut for it to work properly. Most Shapeoko machines do not have the power to take full depth cuts. People here on the forum have tried them but have been disappointed with them.

Depending on the age of your collet C3D sells Makita/C3d precision collets and you should have a spare on hand. I like the elairecorp collets.

They make both SAE and metric collets so you can extend your bit usage if you want to use metric bits.

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There are compression bits that can work with Shapeoko-class machines, they have a very short upcut region so that a ‘normal’ DOC still cuts as compression. Even though a thicker cut requires multiple passes, you still get the benefits of a compression bit - clean surfaces both top and bottom.

The ‘Jenny’ bit is such a bit, I have had good success with it in both hardwoods and softwoods. A DOC of 0.110 (or more) will cut as a compression.


For the compression bits, is that because the stepper motors don’t have the torque, or because their router doesn’t? Im working with a 2.2kw 80mm spindle from Pwncnc on a S5. I am still new where i don’t fully understand feeds and speeds enough to make deep cuts. But i can tell my spindle never has any issue, so i feel i could push it harder but im still afraid of breaking something so im sure my cut times are longer than they should be

One thing to consider is that if you have a 1/8" shank bit, you can go deeper then the usual 1/2" cut height if needed. Usually not able to do this with a 1/4" shank bit


You should buy some cheap bits and test what speeds you can achieve. I’m on the 1.2kw spindle and cut 200 IPM and 100% diameter DOC with a 1/8th. A little slower with a 1/4 bit.

Wow im going extremely slow, i dont think I’ve gone above 60. But thats because im usually cutting smaller things and im worried about my motors constantly slamming to a sudden stop to move in a different direction. Is that something to worry about our does the machine now its limits and will slow down before the motors reverse.

I’m pretty sure it’s programed into GRBL. So the stops do decelerate before coming to a stop. Movements are not instant they speed up and slow down based on the acceleration profile.

I changed my acceleration parameters by half. I found it helped a little to get better surface finishes.

I am sure running 200IPM is harder on the machine than 60, but I’m not sure how much harder. I suspect the machine can handle the speeds well.

If you do run into issues when testing you speed numbers, make sure to tighten the couplers. That was the first issue I had when testing speeds. The machine came with screws that were not tight at all.

There’s not a single mention in this whole thread about what “machine” any of you are using. Feeds and speeds are “machine” dependent especially when one is looking for maximums.