Being driven insane by an offset problem!

[Cold Fusion]

Help me! I've been getting a repeatable error from every single part I've cut. The size of the parts and holes are all perfect to the .001 but the position is off by exactly .025in every time. This ONLY occurs on the X axis. I'm getting no backlash marks in the part. I'm using a custom post with Onecnc and Mach2.

Attached is a g code of the part I just cut.

[kong]

Are your tool tables correct? Just a thought, sorry, I'm in a rush

[Cold Fusion]

I'm offsetting everything in Cam and having Mach2 follow the paths with no additional offset.

[wms]

Andrew,

A quick backplot of your codes shows everything is OK with the code. As shown below.

You need to check the Zero position setting to make sure they have not been changed to something other than Zero.

Then I would start looking at your work offsets at your controller.

[Cold Fusion]

Maybe I should try to reinstall Mach2. My OneCNC settings are all 0,0,0.

I think that I have all the offset options on the controller turned off. Remember, this is only happening on the X axis, not the Y or Z. I would think that if there was an offest problem it would affect the whole system.

I'm notcing that the problem seems to be happing between toolpath cycles, not during them.

[wms]

Andrew,

Sorry I don't have a clue as to how a Mach 2 control operates or it's features.

I did notice that you have a G54 called out on line N100 for your first tool change but No work offset for your second tool change. I have no idea if that matters as for most controllers the work offset is modal. Just a thought.

As for it only affecting the X axis, it could be that is the only value that is different in the offset table of the controller. Again sorry I don't know more about your machine setup.

[Cold Fusion]

It's a PC based controller. My tooltable is completely blank.

Not likely on the G54 but I'll give it a shot.

[JRoque]

Hi there,

Check your step per pulse on your drives and Mach2. Is X and Y set equal?

Later,
Julio

[HuFlungDung]

Make sure that your work offset for the G54 coordinate system offset, is zeros for all three axis to start with.

I'm not sure what kind of command in Mach2 ensures that your machine returns to exact home for the toolchange. Do you know if this logic is in place, and working? Relying on limit switches to find home is not the best method, IMO, because the repeatability is suspect. An encoder index is the best.

If you do use a G54 work offset (someday), you might have to take the precaution to cancel it with G53 before returning to the tool change position. It depends on the smarts behind the controller software.

[Cold Fusion]

I triple checked the pulse per inch amount and it's perfect.

For a toolchange the machine rises to Z Rapid and remains in the same XY location.

After looking over the mechanicals of the machine I found something interesting. Even though I am getting .0005 accuracy with a dry run, when cutting the gantry is skewing about .02. I knew about this problem and had ordered the materials for a proper bridge but for some reason it had slipped my mind while troubleshooting. After getting my double deck 2 inch aluminum slab/gantry setup I'll post again with new results.

[Cold Fusion]

Problem solved!

It turned out to be my router mount. Since I was using a single 1 inch thick clamp style mount it was deflecting back and forth in the X axis of direction when cutting. Now that I've added an upper brace the surface finish is amazing, feeds are way up, and I'm not getting that little error.

A roughing pass with a 2FL with .01 left for finish and a 4FL for cleanup works great for 6061. The finish is comparable to some of the "real" cnc parts I had around here.

[Ken_Shea]

The finish is comparable to some of the "real" cnc parts I had around here.


Excuse me Andrew, but what you have is a real CNC machine