In looking into the ‘What is correct chain pitch’, I found that my chains are slightly different lengths.
After hanging the chains from the rafters, I find that my right chain is almost 2 mm longer than my left chain, judging by the 2.3mm pin in the end link:
Looking at the place in the chains that sits on the top tooth for ‘Manual Chain Calibration’ at 1650mm from the sled end, it looks like the right chain is nearly 1mm longer - again based on a 2.3mm pin diameter:
Note that the chain that is longer is not the one stretched for measuring between motors.
Interesting, but I’m not sure there’s anything to do beyond getting some more chain. This doesn’t seem like something software could be expected to handle.
That is really interesting, and that distance is enough to be significant. Does it seem like the error is the result of small accumulation of manufacturing tolerances over the length of the chain or is there one spot where one suddenly becomes longer?
We tried to choose the best quality chain we could find, but we are using our chain for a more precision application than it is normally used for.
I will test two brand new chains and see if they show the same discrepancy
I tested two new chains and I can confirm that they do begin life the same length
According to data sheet of ANSI #25 correct would be 6.35mm
For tolerances you should look-up the specs of your chain brand
Would be good to also have these datasheets on github of the materials used on the stock design to have a good reference. Chain and sprocket
I didn’t mean to cast aspersions on the stock chains! I’ve had several runaway events and lots of chain jumps, these chains have had hard use since day one . I’ve put serious miles on those chains!
It does seem like something that folks setting up to do accuracy testing should at least hear about though, because it captures one of the unspoken assumptions about the system under test.
I wouldn’t have expected chain growth either
You think it would it make sense to put the work piece a bit lower on the frame?
To me it seems that the forces are higher on the top. So placing the work piece lower would reduce the workload on the chain a litle.
i don’t think any changes are called for beyond the occasional PM to check my chains
@vertex where on that data sheet are you seeing the tolerances?
nowhere on that sheet… but i would thing there are tolerances documented by some companies
It may be pertinent then for anyone doing the linkage accuracy tests to measure the lengths of the chains in the manner you have, and record them in the sheet I created. That will do two things for us. First, it will give us a data sample to show if the chains are noticeably stretching, and if so, what conditions might be cause it. For instance, I have a 40 lb sled and I’ve also experienced a fair amount of chain skipping. The other is that it would give us more data to cross-reference if one person’s machine is significantly less accurate than others.
I can add that into the sheet if we want to it.