[slamman]

I am trying to calibrate my router table with mach3 and am having some difficulty. When I calibrate the machine under no load i.e. a center chucked in the spindle moving freely over a framing square to measure travel my x axis is dead on over the length of the table. However as soon as I cut something my cuts seem to be 1/16th off.

Any suggestions as to what would cause the error when cutting? Could there be backlash that is only realized under cutting load? This happens even at very light depths of cut. I have checked the size of my bit(s) and that doesn't seem to be the problem.

My axis are servo driven rack n pinion.

Any suggestions would be greatly appreciated.

SlamMan

[jckstrthmghty]

I am trying to calibrate my router table with mach3 and am having some difficulty. When I calibrate the machine under no load i.e. a center chucked in the spindle moving freely over a framing square to measure travel my x axis is dead on over the length of the table. However as soon as I cut something my cuts seem to be 1/16th off.

Any suggestions as to what would cause the error when cutting? Could there be backlash that is only realized under cutting load? This happens even at very light depths of cut. I have checked the size of my bit(s) and that doesn't seem to be the problem.

My axis are servo driven rack n pinion.

Any suggestions would be greatly appreciated.

SlamMan

Could be backlash or missing steps? Is the offset consistent? Happening no matter where you cut on the table?

[vtx1029]

Or maybe your selecting the wrong cutter?

There is also a check for missed steps tool in Mach 3.

[Phife]

machine flex?

a framing square is not a proper tool to use for calibrating the steps/inch..

We need more info, any pictures of the machine?

loose coupling? does it do it in both X and Y or just one direction?

[Deep Groove]

One thought -- are you sure you have the correct offset for the cutter? Remember, for a 0.125 tool, it will offset 0.0625 (1/2 diameter). Could this be what you're seeing?

[slamman]

Thanks for the responses.

I have experience on manual mills. Mostly bridgeports. So I have experience with the normal measuring tools. I also have experience on a VMC albiet not a ton, but enough to know tool offsets and such.

None of the setups I have come up with can measure the entire width of my table using a dial caliper, and the point I was trying to make is that the table is calibrated to the point where measuring 40+ inches of travel along the x axis with a square shows no error at all. The initial calibration was done using a dial caliper at much shorter lengths. 1/16 would be very noticeable even on a square. I am getting a consistent 1/16 shy cut whether the cut is 10 inches or 30+ inches on the x axis.

I have recently gone through and checked, tighten and thread locked the pinion gears attached to the servo shafts as there had been some play. All now seems very tight.

I would expect backlash to show up even when not cutting but I am trying to get other peoples experiences to see if that is an incorrect assumption.

I don't know where the missing step tool is, but I will look for it.

I am sure about the cutter as defined in the CAM software. The error is very consistent and across all cutters. I use sheetcam to export gcode on this machine...and Mastercam on the VMC. I am considering trying to get a post setup for Mastercam to try using it and see if that changes anything. When calibrating I use direct MDI input so possibly error is being introduced by the CAM software. Also I am not very familiar with the working of Mach3 as this machine was setup before I started using it, so possibly there is some offset inside Mach that I am missing that causes the problem, but I would think it would show up when I am testing as well.

I will try to get some photos and more info asap, but I am not around the machine right now. I have just tried everything I can think of, but I am aware that I have alot to learn about the setup on these machines.

As always all suggestions are greatly appreciated.

[slamman]

I put a 2" dial indicator on the machine and checked the calibration again. It is within .003 measurement. With the worse readings on the shortest movements i.e. If I move the x axis 1.75 inches and to x1.75 and then move it from x1.75 to x.5 this is where I get the most error, but the move from x0 to x1.75 was dead on.

With this in mind I wanted to check some cutting under load, so using the wizards biltin to mach3 I made a 1" circle pocket and a 2" square pocket. Both of these resulted in pockets that were roughly .010 under sized in both the x and the Y. The circle had a little more error in the x of .015. I can live with .010 error on this machine, but I still need to make some bigger cuts and see if the error compounds up to the 16th of an inch I have been seeing.

I have some photos and I will upload them as soon as I can find a usb cable to get them off my phone.

Any tips or suggestions are always appreciated.