Fully Calibrated but Oblong Circles

there isn’t a simple relationship.

no, inside to outside (so that the bit diameter doesn’t matter)

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Hey ArnoldCP…
Is the chart/spreadsheet you posted in #138 available somewhere… I ran the Calibration Benchmark, but do not know what to do with it.
Thanks for your help!

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Today I had great success. I tried the calibration again but this time I took the measured number between the motors and divided that by shaft centre to shaft centre. As measured by me was only 2 and a bit mm different from the maslow but slightly longer.

So I took my two numbers and divided my number by the maslow number and came to the conclusion that my chain pitch was off a bit. Setting things up with my measurement and then chain correction I got a 1mm difference in width from one end of the 6ft growth ruler. My best results yet!

My magic number is 6.349mm

Thanks again everyone for all the brain storming in this thread. I think its what spurred me on to experiment.


That is my number as well, 6.349mm


The spreadsheet was in the calibration routine thread. I think @MeticulousMaynard posted it?

EDIT: In this thread!

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I would have expected you would need to increase the chain pitch if your measurement was greater than Maslow’s measurement.

I did too, I tried that first actually because I took the percentage difference and applied it to the 6.35 first. It was not a pretty result.

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So, I recalibrated using v1.11 of firmware and GC. I measured the motor spacing using a steel rule and the Maslow chain stretch process. My measurement was 3009.9, whereas the chain stretch registered 3001.9 mm.

I used my measurement, along with rotation radius of 138 per a note I read from @bar . After running through the entire cal routine, including the triangular test cuts, the data summary reported the radius as 140.7.

Doing my circle tests, the are still pretty much dead on in width, but generally shorter in height. Ones in the center and towards the top a little worse that bottom and sides.


The large center circle is 1/8" off vertically, with the smaller one inside about the same.

Here is the .ini file…

groundcontrol_4-21.txt (1.5 KB)

Should I use the Chain Stretch result instead?



Your results are very similar to my original results when I started this thread. I have gotten down to about 1/16" vertically on a 10" circle in the center of the sheet.

I think you really want to use your measured value not the chain stretch value. You are more accurate at this point. You might backup your .ini file and adjust your chain pitch. I am calculating your pitch closer to 6.366mm (which seems too long). Ideally, your measured value should match the chain stretch value within a few hundredths.

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So, looking at my .ini file, it shows 6.35 for the pitch value, which I assume is the default. In recent posts on this thread, it looks like you used 6.349 as your “magic number”, which is a pretty small adjustment, and smaller than the default. As you note, since my measuremen is longer than the Maslow chain stretch value, the actual pitch also has to be larger. What would you suggest I start with? It seems like a lot of other machine calculations depend on this as well.

Thanks for your attention on this!


The way it worked for me was



Now 6.345 was too little in my test case so I guessed at 6.349 and it is a marked improvement.

Maslow thinks it is closer together than reality because the chain is actually a bit shorter than it is using to calculate right? I also note that I’ve never seen my top bar flex like in practical use like it does when measuring with the chain.

So when I had my numbers I then did the triangle cut pattern again to finish the calibration.

I hope that made some sense

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Yes, I think @Jon used 6.349 mm I mistakenly said that was my magic number, mine is actually 6.359 mm. In your case your case and mine, Maslow thinks your motors are closer together than they actually are so your chain pitch must increase. In @Jon’s case his Maslow thinks they are farther apart.

There are two ways to adjust this value in the settings, in 1.11 you can actually use a percentage error for the right and left chains independently or you can manually change the chain pitch.

To be honest, I have never actually measured my right side chain so I don’t know for a fact that it has the same error as my left side chain (that you use for the stretch measurement). It is something I need to test.


Thanks for that @arnoldcp… I was definitely confused. Maybe I still am.
I guess I should Maslow measure both sides as well. To be clear, in our case, with the chains longer than the Maslow thinks, the percentage error would be actual dim / Maslow dim, in my case 3009.9 / 3001.9, or 1.002365. Is this the value that would be entered for percentage error? Or the opposite?

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That calculation is correct. I will say the difference between your measurements and the resulting error percentage seems high. The published spec I have seen on #25 is +0.15% which should give you a maximum chain pitch of 6.359525 mm.

You said you planned to measure again, that’s a good idea. Because it is so hard to measure center of shaft to center of shaft another member determined that if you measure from the outside of the gearbox to the outside of the gearbox and the subtract 40.4 mm. You end up with the proper distance between the shaft centers. You may want to attempt that as well.

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OK. I remeasured the motor spacing to the outside of the gearboxes. Assuming that the 40.4 mm correction is correct, my spacing is now 3006.012. Previously I measured from the right side of the R chain gear bushing to the right side of L chain gear bushing. I will try the new calculation.

Also, for yucks I entered the 1.002365 value into the Left and Right chain tolerances. I then needed to do the 12 o’clock routine due to loss of chain length error… The gear rotation adjustments were all screwed up (Large distances, wrong directions) until I returned to the 0 settings.

I also measured the left and right chains using the Maslow chain tightening, and got the following:
L - 3001.8
R - 2997.15

So, it’s Duck Soup to me…

I will try the 3006.012 distance number and cut a circle, and then, if necessary, try fiddling with the pitch settings.



Used the 3006.012 top measurement, ran through the calibration and the triangular cal cuts. My 6" circle was 6" wide x 5 7/8" high. Made several adjustments to the chain pitch, ending up at 6.368 mm, which yields some perfect 6" circles, and several that are either 6" wide x 5 31/32 - 5 15/16" high or 5 31/32" w x 6" h. Maybe this is as good as it gets? I have just run the Benchmark Cal cuts, and we will see what that yields.

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What speed do you cut circles at? I found they are more round at 500mm/minute than at say 900. Ju still another thought from the peanut gallery

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so this tells me that the chain tolerance is different for the two chains,
calculate it for each one separately.


Regarding the separate chain tolerances, how would that be calculated? For instance, on the left side, the ruler-measured distance is now 3006.012, with the Maslow measurement at 3001.8 I am assuming the value would be entered into the Chain Tolerance section for the left chain. And, what value should be used for the motor spacing? Seems like it would need to be the actual number.

Note that I tried dividing the Maslow number by an earlier slightly larger ruler measurement, using the Left side value for both chains (1.002365). This change made adjusting the 12 O’clock position impossible (large movements, often in the wrong direction.)

Thanks @dlang