# Discussion Regarding Triangular Calibration

**URL:** <https://forums.maslowcnc.com/t/discussion-regarding-triangular-calibration/5960>\
**Category:** Technical Details\
**Created:** [August 19, 2018, 12:39pm UTC](https://forums.maslowcnc.com/t/discussion-regarding-triangular-calibration/5960 "2018-08-19T12:39:04Z")\
**Posts on this page:** 1\
**Showing post:** 44

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**Author:** ![madgrizzle](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.maslowcnc.com/madgrizzle/32/1372_2.png) [@madgrizzle](https://forums.maslowcnc.com/u/madgrizzle)\
**Post date:** [August 24, 2018, 1:58pm UTC](https://forums.maslowcnc.com/t/discussion-regarding-triangular-calibration/5960/44 "2018-08-24T13:58:48Z")

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> [@dlang](#):
>
> The distance between the motors can be measured with a tape measure. This should  
> be done while under tension and while not under tension to make sure the  
> measurements match (if they don’t, something is flexing, fix it). This is a  
> critical value, so multiple measurements to average and/or throw out an outlier  
> is a good idea.

I measured motor spacing from outside edge of gearbox to outside edge of gearbox and subtracted 40.4 mm (what is reported to be the compensation amount to get center of sprocket to center of sprocket measurement). The measurement was made with the sled attached and as high up and in the middle on the workarea I could get it. I ended up with 3602.6 mm, which I used for chain compensation and was the motor spacing value used during the calibration cuts.

With rotational radius (139.82) frozen but motor spacing allowed to adjust , I get an RMS error of 0.312  
Cut 1-4 errors: -0.495, 0.092, 0.3691, 0.0  
Motor spacing ended up at 3607.818

With rotational radius (139.82) and motor spacing (3602.6) frozen, I get an RMS error of 2.023  
Cut 1-4 errors: -0.702, -3.6897, 1.0953, 1.0

3607.8 - 3602.6 = 5.2 mm and is pretty significant. Hard to imagine my measurement is off by that much or a tape measure would be that inaccurate especially since I’ve measured the same value multiple different times. It’s also a bit difficult to imagine that much inaccuracy would come from the sprockets not being perfectly at 12 o’clock (they were at least pretty darn close).

So, adjusting only the Y offset and chainSag just doesn’t work well… at least when chain compensation is used… though I suspect the same would be true if they weren’t used.

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