The router kill switch is definitely going to happen, going to Rockler today. I was going to put this on the side of the Maslow but now I know that is not a safe enough place to put it. It must be in front of the cutting plane, ideally right next to the operator’s spot. A related question though-.if the router was cutting while moving and I kill the router power then the bit gets caught while the sled can keep moving. Seems like it could ruin other things (calibration and/or the motors). Has anyone hacked Ground Control/Arduino to add a physical stop switch also so the motors stop also?
On the chain strength- I’ll move to the second link but have three questions: a) When re-calibrating chain lengths, should we add one chain link (use second link) each time since Maslow is assuming we are using the first link? b) what is the rated strength of the chain?, and c) is the last link actually weaker because the pin is not in the link?
Trying to answer my own questions:
a) Yes? Right?
b) Some googling shows tensile strength of #25 roller chain should be around the 800-1000 lb (lbf?) mark (www.usarollerchain.com). But sites like McMaster show standard #25 chain having a “working load” of 85 lb. (https://www.mcmaster.com/6261k171). Obviously these are different ratings, but I’m not sure how each is measured. Assuming the router and sled weighs ~20lb (90N) and doing some trigonometry, the tension on the chain should really be less than 3x this (about 60 lb). A factor of safety of 5 would be appropriate as there may be additional forces (Bit grabbing, unequal chain tensions, etc) at play. So if the strength of the chain is indeed ~1000 lb - it should be fine. But if the failure is 85lb “working load”, then it is totally a concern.
c) I haven’t quite wrapped my head around the force diagram of the chain/pin/roller/bushing yet. But I think it’s related to the question above in that there could easily be different failure ratings for tension on the chain (the pins take the load) vs the force going over a sprocket (the rollers take the load). The cotter pin through the roller in the carriage seems like the same loading case as the roller over the sprocket - crushing the rollers. And I would assume both locations should be nearly equal given the tension on the chain is everywhere. The pin in the second link might not be add strength since there’s a tiny slop in the roller/pin/bushing mechanism. However it might be an excellent “backup” mechanism if the roller were to fail. Or the roller might be bending a little bit, removing the slop and indeed stiffening the joint with the pin.
As a second failure mechanism, from the attached picture you can see that the linkage side plates splayed (looks a little like a “Y”). It could be that happened as the roller tore out, but it could also be that the side plates splayed first due to torsional forces and the assembly slid apart. This probably would be helped by the roller side pins in the second link, but not significantly as those are not supposed intended to take shearing force, either.
I don’t know the answer, but all I’m saying is perhaps this area needs more thought before assuming moving the link up a spot is the solution.