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Help with chain calibration

I’ve had a number of accuracy issues lately, so I am going back to zero to double check everything. I spent about an hour with a level and a laser level shimming one side of my frame to make it as perfectly level as possible. I spent about 2 hours in the calibration procedure and am I am not making any progress…

I am stuck on steps 1/2 of chain calibration. I can position my chain links (I use a zip tie and pull it tight until they just touch one another) in the dead center of the top beam, +/- some very small amount. I am not sure how to get it exactly center, as I don’t have a way of verifying that the motor sprockets are in an identical position - my eyes are not that calibrated. I am certainly within a 1/32" of an inch though. Just to double check, I counted the number of links on the chain from the same position of both sprockets and its the same #.

When I then move Y- to give the chains slack, over ~36" of the board, they seem to drift to the left approx ~1.5chain links worth.

Thinking this was a centering error, I went back and repeated the previous step. I did this multiple times, always with the same result. I finally counted the links and the RH side had 1.5 more chain links than the LH side.

What would cause both motors not to move an equal amount during this part of calibration?

M2 kit, latest firmware, latest version of Makerverse.

I am a bit ignorant when it comes to the Maker Made calibration process, they have the chains meet in the middle?

I show the process when I went through it in this youtube video. Hopefully that might help you some.

Thanks @Orob
I had watched your video previously. Its pretty helpful, but you are showing basically what I have repeated 50 times at this point, except for a minor difference in the way you ‘pin’ the chains together*. Its possible there is a small amount of error in this step, but it is centered and should still unwind each motor equally.

  • On a related note, I would like to know what math happens behind the scenes at this step, as the cotter pin orientation can impact this, or pinning them together like you did can. I zip tied mine together, which is very consistent for identifying center, but the distance is likely a 0.030" or so closer than if I used the cotter pin? I’d love to just measure the distance between the last hole on each chain at this step with a pair of calipers and put that in.

I don’t know the answer to your question. I think it might be interesting to know, but if you got a piece of string that was 1651 mm long and drew an arc on the waste board from each motor, you would be able to pinpoint the center line and the draw a vertical line to the true center. Which should be 2feet from both top and bottom of the spoil board. Drive the sled there, click reset chains. As long as your y motor offset and motor spacing measurements are taken in the correct plane, you should be close enough to proceed. I prefer the webcontrol holey calibration over the makerverse version of the chain centering deal, but I got them both to work reasonably well.

I pinned the chain that way because it clips that way in the ring. Actually one link up from there.

That string/arc idea is a great one. The number would be different depending on your motor offset & motor distance, but relatively easily calculated. So you are saying, just skip the chain centering step, if I can nail the true center of the board? I’m certainly willing to give that a try. The string arc seems like it would be less error prone, but the offset from the face of the board to the motors (Z-height basically) could introduce some issues.

My concern is that when traveling vertically to let the chains slack, it appears one motor moves more than the other - I don’t see how calibration would fix that, but I am not 100% sure.