Wrong cut

[bcsstefan]

Hi all!

I have a "small" problem with my DIY CNC. For some reason, I'm not able to get the right dimensions when I cut a 40x40 mm square in wood. I get 40 mm when I cut along the wood fiber and 39.7 when perpendicular to the wood fiber.I have tried to reduce the cut deep from 2mm to 0.5 but the result is almoust the same.If I cut in mdf ,I will get 39.8 mm on one axis and 39.9 on the other(so here the differences between the axis is smaller).
The backslash on all axis is less than 0.03
The deflection is around max 0.04-0.05mm when 15 kg applied on each axis
I'm running Uccnc with ETH400 and on each axis, I have a DM856.
Also 2.2 China spindle+VDF "NowForever"(China)
The cause of my problem can be the high noise made by the VDF. Probably I'm losing steps (when high cutting force), but I'm not sure about it.

Any idea?

THX
Stefan

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[skrubol]

What size bit are you using? How much stickout?
How are you measuring the deflection under 15 kg load?
How are you holding the workpiece?
I don't think it's lost steps. you'd see some stairstepping probably. You should be able to determine if it is by referencing the spindle position to something very accurately, running one of these cuts, then seeing if the spindle still lines up to the reference.

It may just be how the wood cuts. The edge may get pulled into the cutter as it's cutting.

[awerby]

If it's important that the size come out correct, adjust the drawing to cancel out the errors and run it again, in the appropriate material.