Centroid Community CNC Support Forum

I had a situation where volumetric compensation was very handy, and quite effective.

I'm turning square wood blanks down to dowels on my rotary axis using continuous turning. Usually when I'm doing stuff on the rotary axis it's artwork and accuracy isn't necessary. With these dowels, I need them to be pretty accurate. I found that the difference in dowel diameter from the headstock end to the tailstock end was off by 0.026 inches, which is pretty large. The tailstock on my Avid rotary setup has some adjustment capabilities, of course, but the adjustments are sort of fiddly and not very objectively measurable on the tailstock live center. I did what I could but just couldn't get it dialed in very accurately.

I went through the process of 2-D volumetric adjustment as published so far. This is pretty simple as there is only one axis to adjust for the rotary setup. I measured the difference in dowel diameter at one inch intervals from the headstock. This diameter difference is twice the adjustment needed in the Z-dimension. So, I divided by two and entered the values in the X-Tab file, interpolating for the half inch values that table requires. I turned a few more blanks and found this worked really well.

Here's a table of the results: The only downside to this approach is the X-tab table is applicable to the rotary axis setup, but will mess things up on the router. I'll just make two X-Tab tables for each setup and swap them as needed.

thanks, this feature has been on the back burner for a while now, hopefully we will get back to working on it some more soon.

ok moving to the front burner now!
does anyone have an example Renishaw (or any other brand) VC compensation file/table, i'm curious as to the format they use.

As someone with a welded base and no CNC to lay out all the holes for the rails and plates (chicken and egg problem), and as much as I'd like to say that my beloved optical centerpunch is perfect, I am really looking forward to this. I hope I can just throw on my 12" $40 amazon granite plate against the dowels on the Saunders fixture plate, tell it to probe, and fill out the table for me.
Not just because I am lazy, but because maybe, if there is a crash, or a pull (drawbar not releasing the tool fast enough, this has been a problem) and yanking the rack and y base plate upwards, I'd like to easily run a calibration and get a cup of coffee rather than go through and tap and shim things into place.

713cnc wrote: ↑Wed Nov 27, 2024 5:12 pm As someone with a welded base and no CNC to lay out all the holes for the rails and plates (chicken and egg problem), and as much as I'd like to say that my beloved optical centerpunch is perfect, I am really looking forward to this. I hope I can just throw on my 12" $40 amazon granite plate against the dowels on the Saunders fixture plate, tell it to probe, and fill out the table for me.
Not just because I am lazy, but because maybe, if there is a crash, or a pull (drawbar not releasing the tool fast enough, this has been a problem) and yanking the rack and y base plate upwards, I'd like to easily run a calibration and get a cup of coffee rather than go through and tap and shim things into place.

yeah that is one option in the works!

As a user of a Lathe with fixed headstock (alignment is pinned) this feature will be very handy for removing taper.

Great work, I really enjoy using your products.

I used an earlier version of volumetric compensation to remove taper from my rotary setup (y mapped to a). It worked great then.
I'm on version 5.3 now and can't seem to get volumetric compensation working. The instructions seem to be a little different than what I'm seeing on the screens, and there are two other aspects that don't look right (and different from before).
First, as I go into the M Comp table I get a message flashing up (very briefly). Message is "The A axis table cannot be created because of invalid travel limit settings.". The travel limit setting for the A axis are 0 and 0, which seems right (?).
I also notice that when I go to the motor settings I can't set A axis to Y (as in "yes", it reverts to N when I do a full reboot on the Acorn). I also don't get the message "Beta Volumetric Compensation Active"
Any ideas about what I might be doing wrong?

If you want to compensate taper from A it will not have anything to do with the rotation of A, it is only a function of XY and XZ movements and the alignment of the rotary A to X and Z.

Get the XY and XZ compensation ok and dial in the A Axis with an indicator along XY and XZ.

Uwe

Thanks Uwe.
I found my problem. I did not format the new x.tab file properly.

I still don't have this working properly.
The cnc-x.tab table seems correct. X,Y,and Z are set to "Y" in motor screen. I get the message "Beta Volumetric Compensation is Active". Should work...

I can't measure any difference when I apply the compensation table. When I look in the PID I see counts for X as I jog the axis, but I don't see any applied values for Z. It appears none of the Z values are being compensated correctly.
I don't know if it matters or not, but the M-Comp screen for the X axis is exactly the same as it was before I created the reformatted cnc-x.tab file.

Any ideas where this might be going wrong?