What could be the cause for different depths when Rest Machining?

I’m cutting a pocket using Rest Machining and the second cut is slightly deeper (-0.01~). Image below.

I pretty sure I have the toolpaths configured correctly:

  • Path 1: 1/4" end mill, depth 0.25"
  • Path 2: 1/16" end mill, depth 0.25" - Previous Diameter: 0.25

Both tools are set firmly with wrenches, so there shouldn’t be any detectible runout, BitSetter measures every tool when it should and the difference is consistent from run to run.

I could just adjust the second toolpath to cut less deep by the amount it’s off to make it look right, but obviously that’s not the solution.

I use Rest Machining quite a bit and haven’t seen this before.

Thanks for any recommendations.

Error when changing tools, or the larger tool deflecting up and not cutting as deeply.

Best approach for the latter is to set the Depth Per Pass so that the number of passes results in the final pass removing a very thin thickness, so if for example, cutting to a depth of 0.5" and the Depth Per Pass is 0.125" resulting in 4 full depth passes, instead, change the Depth Per Pass to 0.124" which will result in 5 passes, the last of which will remove only 0.004" of thickness.


I’ve sometimes created a separate finishing pass to cut 0.01", but haven’t tried adjusting the depth of cut to manipulate the final pass. I’ll try that for the next run.


What could cause the larger tool to deflect up? It is a downcut end mill, so clogging at the bottom? I’d be surprised if that’s it as I’ve got strong dust collection and am using the default speeds/feeds, so I’m not being aggressive in clearing the 1/4" pocket.

Check your bearings?

Best thing to so is to install a probing pin, power up, grab the tip of the pin and try shifting it — it should be rock steady — if it isn’t, investigate any aspect of how it shifts.

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Will do. Thanks again!

I recently replaced my router and have been very pleased with the improvement. I guess I didn’t realize how bad it was.

I bought the rebuild kit for the old one but have not swapped that in yet. Maybe this weekend. It was only $45 for the bearings and armature from e replacement parts.

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Which Z axis do you have? If a Z Plus, the anti-backlash nuts DO wear out, and will give you vertical slop on Z.

With machine on, spindle off, try to move the spindle up-and-down by hand (but not so hard as to overpower the stepper).

If you have a dial indicator, you can:

  • set up the indicator to measure the vertical movement on Z
  • Using the finest movement interval, bring the Z down until the indicator move.
  • Now move the Z up, and see how many increments it takes before the indicator moves.

Now do the same thing AGAIN, except go up first then down.

I have a Shapeoko 4 XL with Z-Plus. The spindle (Makita RT0701C) seems very solid, there isn’t any play in any direction and all attachments are firm. If I really push up on it the whole assembly will torque agains the V-wheels on the gantry, but I really have to push on it - way more than seems like normal resistance. The V-wheels are all in contact with the gantry rails and tightened as specified in the assembly instructions.

I will try the indicator movement sequences you listed. Thank you!

Have you taken it apart yet to see how it looks? Amazing the difference, and glad e replacement parts worked out!

Not yet but it is on the list for this weekend.


I finally got to the replacement of the motor and bearings. It took maybe 15 minutes. It was all smooth.

There was a plastic cup around the lower bearing that wasn’t shown in the you tube video I watched but I just pried it off and moved it over.

One of the four screws holding the casing onto the plastic cap would not cinch down. I think the hole in the plastic housing is worn out but the other three are good and tight.

I didn’t put it in the CNC since I already bought a complete replacement. I did turn it on and it all seems good and the shaft is not wiggly like before.

Now I have a handy spare for $45.


I have a Dewalt 611 router and bought a second one with the plunge base and fixed base. It is my spare but my Dewalt is so reliable hopefully I wont need it. Better to have it and not need than need it and not have it.

You might shop around for a plunge base for the Makita (works on the C3D router) and use it around the shop and still have a spare. I find the plunge base does both the plunge function but also as good as the fixed base and more versatile. Dont let it collect dust or be forgotten in a cabinet.

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I’ve had differences in rest machining or v-carve toolpaths before. The times I’ve experienced it I was able to trace it down to the material deflecting, vibrating, or warping. Even wood has stresses in it that can cause the material to move weird after material is removed.

Just one possibility. :slight_smile:


I have 2 or 3 other routers for handheld use including a 20v Dewalt trim router and a full size Dewalt. I am perfectly happy holding this one in reserve. :blush:


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