Situation: before calibration begins, we need an accurate measurement of the current chain lengths in order to achieve good calibration results. It is especially important that both chains are extended the same length.
Problem: the current “extend chains” is tedious and prone to wrapping, snapping, etc.
Proposal: in Makerverse, I’ve been working on an approach involving a cotter pin.
I will update this post to reflect the progress of the steps.
With the sled off, insert the cotter pin into the chains.
Ensure that the chains are of the same length. The best way to do this is to pull taut the chains using the motors with the cotter pin still in place, such that the cotter pin is in the center of the top beam.
Measuring each chain while it is slack is also fine. Just be certain they’re the same length to as high a degree of precision as you can manage.
Jog the motors along the Y axis (NEVER the X axis!!) until the pin can hit the exact top middle of the stock. Exert strong downward pressure on the pin. Be certain it is perfectly straight.
- Mark the chains. This will be the “reset chains” point.
- Do not move the motors again until validation is complete.
- Attach the sled to the chains.
- Makerverse calculated that the chain length should be 1968.146 (at the cotter pin point) based upon my motorOffsetY and distBetweenMotors.
- By plugging that chain length into a normal kinematics calculation for my sled, Makerverse says that once I attach my sled it should be at Y=302.8mm
- Once attached, the bit (end-mill) on the sled was measured to be located at Y=302.9mm.
- The sled is centered on the X axis and all signs point that the chain lengths are correct for Y pos.
- The entire process was quite fast; most of the time was spent simply attaching the sled.