Can't get passed the Extend Chain to Sled step


Please, any assistance is greatly appreciated.

When I successfully complete the measure chain calibration step, I then remove the left chain from the left and right sprockets and I place the chain back on the left sprocket. Note: the sprocket goes clockwise when extending the chain for the measurement step.

I then select the Chain off Top configuration and continue to the next step. I attach the left chain to the left sprocket, assuming that the sprocket will go clockwise, and click Adjust Left Chainand the sprocket goes counter-clockwise and my chain falls off.

I successfully calibrated the setup and was able to make the test cuts the first attempt, and I was able to make some cuts with the temporary sled. Then when I attempted to re-center the sled, I’ve experienced this problem. I’ve attempted to calibrate it about twenty times now and I’ve attempted different variations to make sure I’ve covered all my bases.

Anyway, if anyone has had this issue or has any ideas, I appreciate it.

do not remove the left chain, it’s slightly faster to retract the chain than to
feed it out, so the current process is optimized to do that.

I think that what is going on is some confusion about the chain feeding over the top vs over the bottom. Both techniques will rotate the same way for the step which measures the distance between the motors, but then they switch to rotating in opposite directions.

It looks to me like you are set up for the chain over the top direction, and you noted that in the picture so I’m sure you are clicking the correct button during the calibration process.

Will you do me a favor and check to see what the setting under Advanced Settings says for the chain feed direction?

Thanks for the responses. I was able to successfully calibrate!!. After I successfully measured the motor distance with the chains I took the left chain off the right sprocket only, and let it dangle. I then clicked Adjust Left Chain and the left chain retracted to the correct measurement. Then I clicked the same button with a different label called Extend Chain. I don’t believe anything happened but wanted to check if this was required (it doesn’t seem to be).

I then put the right chain back on the right sprocket, just like the image. I clicked Adjust Right Chain and the label automatically changed to extending and the sprocket extended the right chain to the correct length.

I also took note of all my parameters so I can easily bypass these steps next time.



you also need to mark what link on the chain is on the top pin of the sprocket
after they are extended so that you can put it back in the same place next time
(it doesn’t matter which sprocket pin is stright up, but it does matter which
chain link you put over it)

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This is a vary important step. Maybe marking the link that gos with 0:0 should be in the calibration process.


The old process was to mark the link that went with the 1650mm chain length.

I’ve argued that we should find a position as near the center of the workpiece
as we can that has the sprockets with one tooth straight up and mark that point,
possibly even calling that 0,0 (accepting that we will be off a few mm from the
true dead center of the workpiece)

what do people think of that idea?


Using a set value that isn’t related to the frame geometry has the benefit of making those marks work with any changes one makes to the frame. 1650mm was chosen for the top-feed 4’ x 8’ arrangement, and also works for the bottom-feed and triangular setups. It it users with frames that are larger or smaller than 4x8 that the ‘Return to Zero’ step is needed before attaching the sled.
Changing the value once the ‘king link’ is painted means removing that mark and re-running the whole chain calibration. If the value is kept the same, the marks need not change, and the chain calibration need never be repeated.

one problem with using a set value is that that may not actually connect to the
sled, or may leave the sled on the floor, depending on your machine dimensions.

In addition, the current value isn’t actually an integer number of teeth, so
when you reset, you are off a bit

And if anyone ever has a need to use different size chain, the fixed value won’t
work for them.

And finally, with chain tolerance and chain sag taken into account, the no fixed
distance is going to actually map to an integer number of teeth.

all good reasons for doing an arbitrary number of full links decided on by the
machine builder rather than an arbitrary fixed distance.

“There’s a setting for that!” :wink: See ‘Advanced Settings → Extend Chain Length’. Users with a custom configuration can customize this value as well. The default value is set for the standard machine size.

After ‘Return to Center’, it is guaranteed to connect to the sled. One more click. Or change the setting, as above.

The error is minor (1mm). If this troubles you, change the setting to 1651, which is 26 revolutions exactly, or pick some integer multiple of 6.35 - the amount of chain payed out per tooth of revolution.

When adding length to the chain, I added it to the slack tail end to avoid needing to recalibrate. If by new chain, we are talking about a new chain with a different pitch or a full replacement, re-calibration and a new mark will of course be necessary.


That just got added to GroundControl, so unless you have latest from source you won’t see this. Otherwise you will have to wait for next release.

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And thank you @LakeWorthB, for adding it. :grin: A great contribution :+1:

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