Slotted Nuts and Shifting

[sanddrag]

I just got a crazy idea but I don't know if it will work. Do two slotted nuts (sort of like castle nuts) fit together? If so, could they be used as shifting dogs?

[Cory]

would this be an example of such a slotted nut?

If the slots were wide enough that another one could fit it's protusion into the slot, then I don't see why they couldn't, as long as they didnt shear off.

Cory

[sanddrag]

Never seen anything like that before. I was referring to something more like this

I just don't know the dimensions on it and the hardware store is closed.

www.cbliss.com had one in Inventor but I couldn't open it after I downloaded it.

[Adam Y.]

Hmm... What is a shifting dog? If you want my opinion that picture bears a strange resemblence to a spider coupling.

[Tristan Lall]

We looked into using a spider coupling (2- and 3-jaw versions) as a low-hassle dog shifter. But we decided it was a bad idea after a little impromptu stress testing. We gave it a good smack with a hammer, and the jaw we were striking broke off. Then we hit it a couple more times, and it developed cracks in the hub. While it might work if you picked a large size (ours was small--less than Ø2"), and were gentle with it when shifting, I don't think it's worth the risk of fracture associated with them.
The sintered iron that ours was made of was brittle, but probably absorbed vibration rather well (but that doesn't help much in a shifter). Instead, we went with something vaguely similar, out of 4140 steel--that should hold up for us.
As for castle nuts, are they designed with enough clearance between the jaws to allow another to slip in? It looks like the slots are rectangular in the little diagram. Also, what do propose to do about the threads? I'd be wary of them unscrewing themselves!

[Adam Y.]

It sounds like you picked the wrong item. Those things are rated for torque that First robots will never see. I don't see that there is no problem in using them if you pick a properly rated coupling.

[Biff]

I have a pair of castle nuts on my bench that I got to fill out a min order with an online supplier of boat hardware. They do fit together as you would hope, but these are only 3/8" and don't fit in all rotational alignments possible. A little work with a small file and I'm sure they would. I have looked at them and wondered the same thing. There are most likley better choices, ie real shift dogs or ball bearings and sliding hollow shafts. The ones I have I wouldn't try and put real torque on, say near the final output, they are also stainless and were like 3 dollars each (filled min order) May be next year in a much larger version, Say 5/8, have a key way cut and the threads cleaned up, real steel, attached or welded to a hubless sprocket, may have the seeds for a chain based two speed. I will have to sleep on it.