One thing I found is that I bought extra collet nuts so I dont have to pop out the collet ever time I want to swap from 1/8" to 1/4" bits. Only $10US and saves additional wear and tear and time if you are swapping out alot.
sorry for digging a one year old thread out…
I was wondering how long bits should be with the SM 2.0 CNC, I plan to cut a bowl out and need something like 40mm in depth. I was thinking about a bull nose bit and getting a 1/4" collet (or 6mm). There are bits with a total length of 76mm, but… can someone give some advice if this is ok with the SM2? The material is wood (Paulownia, which is really soft).
I successfully used a 60mm long bit with 32mm cutting length (6mm diameter) with spruce and oak. Details see here:
thank you, I will give it a try with a 42mm bit then.
btw: nice job on the garage remote
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It’s not really the length of the bit that matters as much as the amount of contact that it has with the wood. So if you’re doing something like hollowing out something you can go as deep as your bit allows. But if you’re trying to cut out a contour or a slot where the bit is making contact on both sides then it can only handle 10-12mm deep. So to do deeper cuts you have to set up boundaries or silhouette so that it does an inner and outer path.
I’ve also found with some rougher grained woods like oak, that even if it’s cutting a single edge that once you get more than 30mm of edge contact, that it will sometimes have problems. So as I go lower, every 15-20mm or so I actually increase the radial stock to leave slightly: .1-.5 mm. Usually it’s not noticeable and easily sanded out. (Depending on the object/paths I also will decrease the boundary size slightly to do the same thing on the outer cuts.) Smaller diameter bits, like 3/175mm will have less issues than 6mm.
Also be aware that with a longer bit, any play in your axis will be magnified, and it will cause more stress on the bearings. So you need to make sure they’re tight and may have to adjust them more often. And you may want to slow down your milling speeds from what you would use with a shorter bit.
Lastly, make sure you’re vacuuming or blowing away sawdust, because as you get deeper it will get compacted and the bit may get stuck. Using an up-cut bit will help reduce the chance of this.
-S
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Thank you for your advice!
I don’t want to cut out the bowl from a solid piece of wood, I already have bowls that are simply cut out or carved out very poor - I just want to improve them… make them round inside and flatten the bottom, later I will try to use the rotary tool to make them round on the outside and carve some pattern … if everything goes fine, I can send pictures. That said - I think I should not get in trouble regarding what you said - I manually vacuum the sawdust every now and then (like everytime when I think it is too much dust). The only concern I had was the stressing of bearings like you mentioned. I will try and go slowly - as many users said, you can hear pretty well, when the machine/bit reaches its limits.
I bought SM2 back in 2020 (I think) and this is the first time I try out the CNC - pretty fun 
now my project is … almost … finished - thank you for your suggestions, I used 6mm-bits with a 42mm blade without problems. I carved 1mm deep with workspeeds between 500-700mm/s without problems, again: Paulownia is a very soft wood. For the filigree patterns I used the Groove V-bit (Snapmaker) and I am pretty satisfied with the result. Still, I learned a lot about CNC carving as well as working with Fusion 360 (first time I used it, I thought I will never get used to it). So again, I appreciate your answers and tipps. Thanks, especially to Hauke and sdj544
and as promised - some pictures of my ‘project’ - I thought I put it on Snapmaker Showcase: