Fully Calibrated but Oblong Circles

Posted in an old thread figured I should move it to a new one.

Need a little more help, I have now run the calibration routine 4 times. My dimensions on the last one were almost perfectly matched, 1930mm and 1929.5mm. I set to cutting a new sled because I have a new dust collection design I wanted to try. Nothing I cut is a proper circle, I need three 9" circles and in the left right direction, they are correct, in the up down direction they are off almost 1/2". What am I doing wrong?

Thank in advance.

Where on the plywood was this piece cut?

Could you zip up your groundcontrol.ini file and the .nc file for this cut and upload them? Let’s see if we can find the answer.

I was cutting a small 2’x4’ sheet and I started in the upper 12" of the machine but right in the center, left to right.

I will send both the ini and the nc files when I get home. I am hoping you tell me its something in the gcode…

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So with respect to the overall maslow, I assume the 2-foot by 4-foot sheet was centered on the maslow and therefore the the cutting was close to center overall (just up and to the right of center)… correct?

What process/applications did you use to draw out the sled and create the nc code?

That is correct. 2x4 was centered and the program started in the upper right corner of the 2x4 sheet.

I used Fusion 360 to model the parts and generate the gcode. I am a total n00b with respect to CAM but I am pretty proficient with 3D modeling. One lesson I have learned with Fusion is you need to turn off helical moves which I did.

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Well, if your sled was a circle in Fusion 360 I’d expect the nc code to come out as a circle, but we should be able to check it. I just seems like calibration is off.

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Sadly, I am sure that is probably the answer. The calibration process and I have become close friends.


Are you by any chance using one of the linkage kits?

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Yes I am. Logan’s wooden linkage kit.

For good measure here is my ini and nc file.

groundcontrol.ini (1.3 KB)
Sled Rings.nc (36.9 KB)


Interestingly enough, it looks ovalish in a nc viewer. trying to find my other programs I’ve used to visualize it.

Nope… ripped it to a dxf and its round… not sure why it looked elongated on ncviewer


Honestly, this would be really great news. I certainly didn’t draw an oval but maybe the output to nc is getting lost in translation.

Looking in the .ini file, the distance ‘motoroffsety’ is 530.6mm/20.89in That is more than the default 463mm/18.22in, though not way out of the ballpark. I think that default value is for the original frame, I’m not sure what the value is for the newer frame.
It also looks like the shapes were cut from the upper half of the center of the sheet, two at the top and one below them. Is the lower one distorted the same amount as the upper ones? I might expect to see that one closer to ‘true’…

My frame is a tad taller than stock. I was attempting to go as tall and as wide as my space would allow in order to reduce the extreme chain angles at the bottom corners.

I did not allow the whole set of cuts to complete however, it did get one depth cut on the one closer to the center. I think it was still distorted but I will lay the one on top of the other and confirm.

This disussion does make me think of a possibility. I had to purchase some extra #25 chain so I could go the extra width and height. I didn’t buy it from the Maslow store because I bought it many weeks before I received my kit. I wonder if the chain pitch is actually a little bit different.

I did this too. I arranged for the new chain to be on the slack end, but I don’t think it matters.

Here’s a test you would make: move the sled to the center point of the work area, make a pencil mark at the place where the top of the sled meets the work area, then use the arrows to move the sled up 6 inches and make another pencil mark, then another 6 inches and a pencil mark, until you moved 18 inches total. Then get the sled out of the way and measure the distances between the pencil marks - what are the increments? Are they the same? Maybe repeat in the downward direction…


Sounds like a plan. I will get to it.

I am in the process of recalibrating with v1.09 and then trying your instructions.

I deleted the ini, wiped the eeprom and took 5 lbs of weight off my sled.


Well…still failure. Calibrated 3 times and my 1-2 and 3-4 measurements were 1930 and 1930.5 respectively.

I moved the sled out 18" in all directions and made pencil marks on the sheet of plywood. By my ruler, these marks are all 6" up and down and left and right. Made a quick nc file that cut 3 circles. A 10" one dead center and the two in up 6" down from the top edge and 16" from the center.

The 10" circle that was centered is exactly 10" wide but 9 15/16" tall. My two 6 inch circles are similarly oblong exactly 6" wide but 5 13/16" tall.

I feel like I am losing my mind.

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what were the results of calibration? (rotation radius, etc)