Try a second pass on the finish cut. Or you can always set the axial Stock to Leave at a negative number to increase the size.
Is your 6mm cutter actually 6mm cutting diameter? Sometimes they are a bit smaller.
Hi All,
I have built a custom CNC router.
In external features (e.g. bosses) I manage to hit tolerances of +/- 0.05mm
In internal features (e.g. holes / pockets) I get a poor tolerance of negative ~0.2mm (they always come out smaller than designed).
Anyone has any suggestions about why that might be?
Some details of the machine:
- Aluminium extrusion frame built
- Ball screws + Linear rails (cheap aliexpress stuff)
- 2.2kW spindle
- Closed loop NEMA 24 steppers
- GRBL controller + UGS + CAM in Fusion 360
- Tested material: Delrin
- Cutter: 6mm single flute
Similar Threads:
Try a second pass on the finish cut. Or you can always set the axial Stock to Leave at a negative number to increase the size.
Is your 6mm cutter actually 6mm cutting diameter? Sometimes they are a bit smaller.
Jim Dawson
Sandy, Oregon, USA
I do repeat passes on very feature of importance to make sure that tool/machine deflection is kept under control.
I have not measured the endmill size precisely yet. If it is undersized does that explain the issue?
If you kknow it's always out and is always out by this amount.
Easy way is to set 'stock to leave' in your cam as negative -0.1mm.
Now it will remove an extra 0.1mm of material all around the iinner diameter bringing it to tolerance without effecting anything else.
Yeah it's pretty consistent so far (same cutter - same material).
I have been doing the negative stock to leave trick with success.
However I do want to find out what the root cause of the issue is
Thanks!
So I have some interesting results.
I measured the diameter of my tool using 3 methods.
1. Taking a pass on the right hand side of stock, then left hand side. Then measure the part across the cut faces -> calculate tool dia.
Result: tool is 5.85mm
2. Indicate the tip of the flute with reference to the tool's shank diameter (which was measured exactly 6mm)
Result: tool is 6.05mm
3. Cut a slot with the tool and measure the slot width.
Result slot is 5.98
I am not sure which method is more trustworthy ?
Any interpretations of those results?
I think #1 is the most accurate. This takes into account any tool runout and machine/tool flex.
Jim Dawson
Sandy, Oregon, USA