Parts bigger at the bottom than the top

Hello everybody, I just finished setting up my x-carve 500mm version and I’ve done a few runs so far as I get used to the machine and how it works. I have all the v-wheels set nicely, the stepper current seems just right and the machine is nicely square. However, when I took my calipers to the parts I’ve made, I noticed a strange deviation. At the top of the part it’s accurate to what I made in CAD, but at the bottom it’s wider by just about .007 to .009. It’s over a distance of .710 as well. Its very slight, but I could see it being an issue if I choose to make interlocking parts.

How do I solve this, is it a mater of the X gantry not being square to the bed front to back, or is it something like deflection with the bit? I only take about .04’’ passes at a time with an upspiral bit on a DW611, so I doubt it’s the latter. Any insight or experience would be very helpful!

In order for the group to help you we need more information.

end mill size, number of flutes, carbide or HSS
DOD (depth of cut)
WOC (width of cut)
spindle speed
stick out of end mill from collet
feed rate
plunge rate

Then the group can help.


Sure! In order, its as follows

.710 Baltic Birch plywood
.250’’ solid carbide double flute bit. .250’’ shank
.04’’ depth of cut per pass.
.250’’ width of cut.
30,000 rpm spindle speed (It’s the DW660, not DW611, sorry!)
1.25 to 1.375 of the bit is exposed
34 ipm feed
10 imp plunge.

Are you able to post of picture of the material that was cutout? It sounds like maybe a run-out issue, but I would think that problem would be uniform through the entire cut.

Other than you feed rate being a little slow I see nothing that would cause the problem you are seeing. The end mill is not deflecting in the collet from to much load.

This would lead me to think that you have a mechanical problem of some sort. If the z axis travel is out of square then the part should look like the leaning tower of pszza.