Help with backlash

[wdp67]

Hi again everyone. I am running into a little problem. My cnc'd mini mill has the stock leadscrews. I am using Mach 3. I am trying to cut out a circle in a peice of stock. The circle comes out looking like a circle but I can not get it to cut to the right diameter. I suspect it is a backlash problem, but am not sure. I have checked the backlash and have entered those figures into the backlash compensation. I can measure the cut out in several places and it seems to be fairly consistent in size(within .002-.004), but it always comes out about .015 smaller than it is supposed to. I have checked my drawing and it is the correct size. Any suggestions?

Also what have you guys done for backlash, using the stock leadscrews and nuts?

Thanks!!
Walt

[Robin Hewitt]

Originally Posted by wdp67 it always comes out about .015 smaller than it is supposed to. I have checked my drawing and it is the correct size. Any suggestions?

Presume you are cutting uphill. If you cut down hill it might make it .015 larger.

As you have removed backlash from the equasion it probably means the cutting side load on the tool is flexing the machine somewhere.

If you repeat the finishing cut does that fix it?

[cliveastro]

Are you sure of the diameter of the cutter and Robin suggest to do one or two spring cuts.

Clive