Breaking bits like crazy since Shapeoko2 to XCarve upgrade


I’ve been using my Shapeoko2 for more than a year now and I never broken a bit during that time. I was using a Dewalt DW660 spindle and everything was fine. Now I upgraded to XCarve 1000mm with the 300W spindle, ACME rod, NEMA23 motors, limit switches and drag chains. I also upgraded to GRBL 0.9i (with shapeoko 2 default values). I changed the step/mm value of the Z axis to match the spec of the ACME rod. I also verified that all step per mm settings are correct by measuring the actual axis movement relative to the command. As for the acceleration settings I kept the default values. The homing cycle works, EASEL can start and stop the spindle, functionally everything looks fine.

Here’s my GRBL settings:
$0=10 (step pulse, usec)
$1=255 (step idle delay, msec)
$2=0 (step port invert mask:00000000)
$3=5 (dir port invert mask:00000101)
$4=0 (step enable invert, bool)
$5=0 (limit pins invert, bool)
$6=0 (probe pin invert, bool)
$10=3 (status report mask:00000011)
$11=0.050 (junction deviation, mm)
$12=0.002 (arc tolerance, mm)
$13=0 (report inches, bool)
$20=0 (soft limits, bool)
$21=0 (hard limits, bool)
$22=1 (homing cycle, bool)
$23=3 (homing dir invert mask:00000011)
$24=25.000 (homing feed, mm/min)
$25=250.000 (homing seek, mm/min)
$26=250 (homing debounce, msec)
$27=1.000 (homing pull-off, mm)
$100=40.000 (x, step/mm)
$101=40.000 (y, step/mm)
$102=188.976 (z, step/mm)
$110=5000.000 (x max rate, mm/min)
$111=5000.000 (y max rate, mm/min)
$112=500.000 (z max rate, mm/min)
$120=250.000 (x accel, mm/sec^2)
$121=250.000 (y accel, mm/sec^2)
$122=50.000 (z accel, mm/sec^2)
$130=500.000 (x max travel, mm)
$131=500.000 (y max travel, mm)
$132=100.000 (z max travel, mm)

Now the problem I have is that even if I lower the feed and plunge rate 50% lower than I used to, I can’t run a single job without breaking a bit. I even checked in EASEL to see if my feed rates make sense and they are even lower than what it uses by default for any given material.

The bits seems to break more easily during drill operation (no x and y movement). I broke a 3/32" bit by drilling 2.4 mm deep in a carbon fiber plate using 0.4mm stepdown and 100mm/min plunge rate. When it breaks it really sound like it is bending either because the Z axis is not straight or the plunge rate is way too fast. I checked that the Z carriage is square relative to X and Y axis but I do not have a way to see if the actual bit is straight.

Now except for a defective spindle that have excessive play in the bearings, I see no reasons why I can’t run a single job without breaking a bit. Is there a way to verify that?


I don’t have a lot of experience yet, but one thing I noticed right away is how stressed my bits sounded with a high plunge rate. While I’ve worked up to much faster feed and jog rates, I keep my plunge rates to 10ipm or even 5ipm depending on material, which can range from MDF to maple.

My spindle is dead square to the board in both X & Y axes.

Are you using bits that you had before, or, the ones from Inventables?

@Jean_marcGendreau do you still have your Dewalt DW660 to test to see if that makes a difference?

Yes I’m still using the same bits. For carbon fiber I’m using a diamond cut bit with a fishtail tip and diamond coating (they are expensive but usually very durable). For acrylic, I’m using a standard carbide single flute end mill (as sold by Inventable).

@Zach_Kaplan , Yes I still have my DW660, but I have to dismantle the Z axis in order to change the spindle. I can do it to see if the problem comes from the 300W spindle but I will have to find a more permanent solution because the DW660 spins way too fast (30000 rpm) for acrylic and most plastics. It’s great for carbon fiber and wood but since the speed is not adjustable I can’t do plastic with it.

BTW, I managed to carve a carbon fiber part with the 300W spindle but I had to use a plunge rate of 50mm per min and a feed rate of 100mm per min (that is 5X slower than my conservative settings that I was using before the upgrade). Even with steps of only 0.4mm it made horrible noise when the bit was moving. I’m pretty sure that even under a very light load the spindle can’t be anywhere near 12000rpm. Unfortunately I do not have the equipment to measure the RPM.

The torque on the 300W is far less than the 660. I was wondering if that was causing the bits to break.


I understand that the 300W spindle has much less torque than the 660 but I would at least expect it to be able to cut something at a reasonable feed rate. The 660 spins at 30K rpm and the 300W spindle at 12000 rpm. Normally with the 300W spindle I should be able to get a feed rate that is 40% of what I can get with the 660 but it’s not the case now. I get 20% and I should probably lower that because the cuts are rough and the bit makes really bad sounds while cutting.

I tried to cut acrylic using EASEL with the default parameters (for acrylic) of 20mils per step, 25 inch per minute and it broke the bit. To do the job I had to lower the step to 10mils and 20 inch per minute. And even then it sounded like there was too much pressure on the bit.

Anyway, I will put back the DW660 as soon as I’m done cutting Acrylic

I switched to the single-flute, up-cut for acrylic, and, it works great with Easel defaults.

Are you using the x-carve 300W spindle? If it’s the case, my spindle is defective because I’m using the exact same 1/8" upcut single flute bit when I cut acrylic.

Yes, I am.

I finally removed the 300W 24V spindle and replaced it with my DW660. And I’m no longer breaking bits. It looks like my 300W spindle can’t maintain it’s speed even under very light load and that’s what cause the bits to break. If the bit doesn’t cut enough material while it’s moving it will break as the accumulated uncut material will bend it. The problem here is that this happen when cutting acrylic with a step of 20mils and a feed rate of 25 inch per minutes which is extremely slow. I’m really disappointed with the performance of this spindle even a dremel does better than that.

Hmm. The Easel defaults work really well for me and acrylic.

Are you sure there is no play(looseness) in the rollers for the Z and X carriages. You should be able to pull up any corner of the X carriage without feeling the X carriage move at all. If it can move and you plunge a drill, that will force the carriage up, and it will rotate around the tight end and rotate the drill away from the Z axis. If the drill is deep when this occurs, you could break the drill.

The Z has only two adjustable rollers and is easy to snug up, but the X has four adjustable rollers. I spent at least an hour adjusting and re-adjusting for no play and not too much drag along X. Worse, I had to partially disassemble the XZ assembly because I had it all together before I realized I could not get an Allen wrench where I needed it.

This may or may not be what’s happening for you, but I just upgraded from a Dremel 4000 to the 24V spindle and had tons of problems initially. Turns out, the spindle had lots of runout; though the collets are advertised as having 0.6 mil runout, the cheap spindle and collet adapter increased that to 5mil for me. I only tested pcb milling, but the large runout may be causing bits to break. You can measure the runout on a bit installed in the spindle to check for this.


No, there is no play at all for the rollers for the Z and X carriages (nor the rollers for the Y axis either). And all the axis are square. Since I put back my DW660 I had no issues at all (except that the DW660 is loud as hell, that’s why I replaced it with the 300W 24V spindle).

So it comes down to two potential issues, my spindle has excessive runout or it has less torque than it should causing an excessive rpm drop under load. At this point I think I’ll try to return it because I broke about 100$ worth of bits with it and I do not have the equipment to measure the RPM or the runout. But I’m sure that it’s the spindle that cause the problem because other users are able to carve Acrylic with it using EASEL’s default parameter and I can’t.


What method are you using to measure the runout? Do you need special measuring tool to do this?

The preferred method it to use a dial test indicator that reads to a half thou. You need a way to hold it to the machine table and set it so it just touches a straight round pin in the collet chuck. then rotate the spindle by hand and watch for change in the reading.

Now if you do not have a dial test indicator there is another method. Put a straight round pin in the collet. Take a block of hard wood that you know is square and clamp it to the table. Now using a set of feeler gauges move the spindle till you can just get a 10 thou feeler gauge between the pin and the block. Now rotate the spindle by hand slowly and check the feel of the feeler gauge. If it gets tighter change to a thinner feeler gauge till you find the one that has the same drag as the first. The difference is half you TIR (total indicated run out) If it gets looser then increase feeler gauge thickness.

This method takes longer to do but can give good results with limited equipment.


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I am borrowing a crazy accurate dial indicator that can be positioned as DavidSohlstrom mentioned. Since the machine isn’t as rigid as a full size CNC, and I had the base of the dial indicator on the workbed, you need to be very gentle rotating the spindle to not deflect the gantry.

I hope that once fixed the runout problems do not reappear due to loads from typical bit changeout.

See this post. Have the same issue with old controller to Carve upgrade…