Dangerous! Snapped chain!

I’m Making pocket Letters .37"deep in to the acrylic… for a Ballroom Dance Competition, DBDC
The Letters will sit on a base with LED lights that will reflect on the unpolished acrylic.
It should look good.

To give you an idea look at LED EXIT sigh … That is the look that I’m goin for.

Cheers

2 Likes

@bar @blurfl @dlang @mooselake , what would be the max stepdown before having a chain snap? I know there are so many variables; feedrate, material, flute length, etc… would seem like something would give way (motor gear, pcb or chain) if trying to cut through thicker material in one pass.

I’m not much help on that, I’ve never tried for deep cuts. I usually use shallow ones hoping for better accuracy. Accuracy is higher on my list than speed.

1 Like

Yes, I’ve always set the stepdown as half the diameter of the end mill.

1 Like

the tensil strength of the chain is ~10x the max force the motors put out. I
would expect the motors to stall and stop moving LONG before the chain is in any
danger.

David Lang

3 Likes

please see the pending edit here -

If you don’t want to back up a link - I’d use JB weld to glue the end together. I still suggest just backing up a link.

Thank you

1 Like

I’m not sure I would trust JB weld, applied properly it would do the job, but
you have no way of knowing if it got a really good grip on the material until it
comes apart.

David Lang

I’ve suggested the best method, this is a stop gap if not following the best method.

Your milage may very.

Thank you

I like the idea of inserting a small bolt into the last open part of the chain. This would mean there’s no geometry change to a calibrated machine, and no need for any adjustments, though if I understand right the only change is a quick adjustment in ground control to simply shorten the defined chain length?

Another problem with adding a bolt to replace the missing pin is you will likely not clear the gap in the carriage that the chain passes through, making for slower sled removal if/when you need to do that since the bolt needs to come out too. An alternative might be a rivet, which can be hammered flat and should clear the opening in the carriage.

If you back up one link on the sled couldn’t you simply skip the chain ahead one link on each sprocket to compensate?

3 Likes

Yes you can.

Not wanting to redo my chain positioning at the moment, I found an M2x8mm bolt and nut fit perfectly in the hole at the end of the chain. Better safe than injured!

5 Likes

For the record, the wood triangulation kit does NOT have this problem (and never has).
These are images from the assembly instructions:
.

That’s about as clear as I could get with how to insert the cotter pin…

The cotter pin that comes with the kits is much longer than this and is easily inserted/removed through the two arched holes for easy chain detachment.

While I was testing linkage strength my chains easily took well over 95 pounds each (and I was never able to break a linkage either :wink: )

8 Likes

Ok, I thought the pin was being inserted the other way (and I’ll bet that a
bunch of people are using the original pins going the other way, there hasn’t
been anything before now to say that they shouldn’t, and it’s easier to do)

David Lang

2 Likes

I totally agree! I never thought of it as a problem until now either. But it makes total sense.

Has this still been working well for you? Can you provide a picture? Does it interfere with the cotter pin? I am guessing that you have one of the ring kits, but perhaps I am wrong on that. I suppose your fix would work for any connection method, though, no?

I haven’t had a chain fail, but I’d rather avoid the issue than learn from it first hand :slight_smile:
Thanks

The pins are just over 2mm, so a M2 bolt will work well, if you get one just the
right length (or cut it down) it should not interfere with anything.

But just moving everything one link works as well.

David Lang

1 Like

+1 to what @dlang said. Moving everything 1 link works fine (feed the second link over the vertical sprocket when feeding chains and then put the Cotter pin through the second link). I used the M2 bolt until the next time I reset chain lengths, then I moved to using the second link. Using the 2nd link is a simpler solution and doesn’t require extra parts

2 Likes

Thanks @dlang and @johnboiles. I will plan to move the chain once link when next I get some time.

Out of curiosity, does anyone if this something that has been added to the calibration procedure? It seems like a good practice for everyone considering the potential for damage and injury in the case of the hollow link snapping during a cut, as well as the ease of adding it as a step in the initial calibration.

The calibration procedure in GroundControl? I don’t think so but I haven’t opened GroundControl in months because of WebControl. It would be great to update instructions about this

1 Like