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Repair or replace?
- Thread starter Elektrishun
- Start date
FatherWes
Wes
When assessing risk, I like to try to put things in terms I can relate to.
10 inch diameter sheave spinning at 1750 RPM means the outer edge of your sheave is doing about 50 mph. If it's 3600 RPM, it's about 100 mph.
I've been hit in the forehead by a bee while doing 60 mph on a motorbike. Sure glad it wasn't a few ounces of steel.
I'm trying to understand what would have caused those cracks in the first place. My guess is this is not steel, it's cast iron (maybe nodular iron), and I'm guessing it was pressed on. Does it run true, or does it wobble?
Failure would likely mean one of the small chunks flies off from adjacent to the shaft (where the visible cracks are). Their velocity would be much less, so that's good. But, what the rest of the sheave does after the hub comes apart is anybody's guess.
This has a skookum belt guard around it, right?
10 inch diameter sheave spinning at 1750 RPM means the outer edge of your sheave is doing about 50 mph. If it's 3600 RPM, it's about 100 mph.
I've been hit in the forehead by a bee while doing 60 mph on a motorbike. Sure glad it wasn't a few ounces of steel.
I'm trying to understand what would have caused those cracks in the first place. My guess is this is not steel, it's cast iron (maybe nodular iron), and I'm guessing it was pressed on. Does it run true, or does it wobble?
Failure would likely mean one of the small chunks flies off from adjacent to the shaft (where the visible cracks are). Their velocity would be much less, so that's good. But, what the rest of the sheave does after the hub comes apart is anybody's guess.
This has a skookum belt guard around it, right?
My very first question on reading this was: What caused the cracks to happen?
The pulley is cast iron no?
This tapered pin is...... ?
If it is tapered, is the fattest diameter of the pin bigger than the hole? Could it have been tightened enough to initiate cracking?
I don't think all these radial cracks suggest overloading of the pulley shaft or relative movement between the pulley and shaft. However, they could be formed by overtightening the tapered pin.
I think the reason for a tapered pin is to take up all the clearance in the hole so that the pulley cannot move relative to the drive shaft. Likely, the first design was a straight pin. That was changed to a tapered pin when the hole started to wear from relative movement of the pulley and shaft.
But I'd bet there was a tightening spec on that pin. Either for driving or torque.
I think those cracks are from overtightening the pin - either driving it or torquing it.
I'd favour an exact fit shear pin over a tapered pin.
I also like @Darren's collar idea. But when you make the collar keep in mind that these cracks are likely caused by the pin not by the shaft load. So the collar should be installed and tightened before the pin.
I don't think brazing or welding will help. The expansion caused by the pin must be dealt with or it will just crack elsewhere.
Do you have an owners or Service Manual for that machine? If so, look up that pin and the install procedure.
I could also be all wet. But those are my thoughts on it without the benefit of being there.
Elektrishun
Member
Guard is on left of first picture.
You can kinda see it in place in the second picture (back left corner).
Elektrishun
Member
I found some basic information but nothing too detailed about the tapered pin. Knock it out and put it back in is essentially all of the instruction.
If the crack is there, then there must be some load on the metal. Unless it was dropped on the floor or hit with a hammer, that load comes from the pin somehow. The idea that the pin has simply been overtightened makes a lot of sense.
I wouldn't be too concerned about it for 2 reasons. First there is a lot of metal and the force from the regular shaft load can't really act on the cracked section. For it to fully fail, the pin would have to pop out a wedge shaped section and there should be a bearing that makes that difficult.
Second if it does fail, you expect a loss of power and not much else. Even if the guard is off, the fragments won't a ton of energy and it would be a fluke if they hit anything. Something like large chips
I also agree that a roll pin is a much better choice. and if you are worried about it, drill a new hole. The part probably has a lot of life left if this is the only damage
I wouldn't be too concerned about it for 2 reasons. First there is a lot of metal and the force from the regular shaft load can't really act on the cracked section. For it to fully fail, the pin would have to pop out a wedge shaped section and there should be a bearing that makes that difficult.
Second if it does fail, you expect a loss of power and not much else. Even if the guard is off, the fragments won't a ton of energy and it would be a fluke if they hit anything. Something like large chips
I also agree that a roll pin is a much better choice. and if you are worried about it, drill a new hole. The part probably has a lot of life left if this is the only damage
Elektrishun
Member
That would be appreciated. Thank-you
Elektrishun
Member
I have a Dayton brand, 2 piece, shaft collar clamp on order for next week.
Thanks to everyone for all of your input and suggestions.