Shopsmith Forums

Yes I know it is quite bad!

If making a 'new' one, let me give you an alternate design to the threaded shaft/nut/...

I think a retaining clip on both ends of the eccentric/bearings will work.

JPG wrote: ↑Mon Feb 21, 2022 10:50 pm Yes I know it is quite bad!

If making a 'new' one, let me give you an alternate design to the threaded shaft/nut/...

I think a retaining clip on both ends of the eccentric/bearings will work.

Brilliant minds run in the same gutter. My plan if I do it over is a double snap ring between inner bearing and the pulley sheave and on the outside, I was thinking either a fine pitch thread with locking washer or another pair of snap rings. Don't need or want any axial load on those ball bearings. We'll see what the chrome shop says. It might be cheaper to just chuck up the 5/8" shaft and cut the snap ring grooves and the keyway, and be done with it.

Yep! I have tried to get 5/8" shafting with a 1/8" keyway, but have not been successful.

Why double snap ring?

The idler sheave does bear against the front snap ring - that why double? If so I do not see a need for double at the aux shaft end.

Double snap ring at idler sheave end will cause displacement along the shaft axis.

JPG wrote: ↑Tue Feb 22, 2022 3:40 pm Yep! I have tried to get 5/8" shafting with a 1/8" keyway, but have not been successful.

Why double snap ring?

The idler sheave does bear against the front snap ring - that why double? If so I do not see a need for double at the aux shaft end.

Double snap ring at idler sheave end will cause displacement along the shaft axis.

Well, not sure if you will believe me, but a snap ring is designed to hold lateral or axial pressure against one direction, not both. I think there are snap rings which have a bi-lateral design and are setup for pressure in both directions, but I'm not going to find that at Granger or McMaster Carr, and would have to order it special. The end of the shaft that faces outward where the threads are on the eccentric could get away with a single snap ring, as it is squeezed by the pinch bolt and won't go anywhere as long as the inner race doesn't move, but the inner snap ring location was incorrectly designed using a C clip(mine was completely missing) to separate the bearing race from the sheave. It was under-sized, and over-stressed for that application, although given that they lasted many years, I guess it could have been considered acceptable.

In the same theme, my commentary on the vacuum system engineering shows up the same way on this shaft. Wrong bearings, wrong C clip, wrong captive method. This is not a complaint, as the entire system of the Mk VII has stood the test of time. But - it could be better in some respects. We've also seen this in the plastic cam follower. Small mistakes were made, and over time have been corrected. BTW, the added width offset will be taken up by moving the eccentric out 3/32" to maintain the sheave alignment.

OK, I've got bad news, and then badder news. First, the hard chrome shop can't help us for a ton of different reasons. Threads won't plate right(told him we didn't care), grooves too deep, unable to machine after hard chrome, porous surface, and on and on. He recommended just make new shaft.

So, I got down to the shop to do some practice keyway cuts, and my mill went Tango Uniform with the X axis motor crapped out. I don't know if it's the motor, or stepper drive, or controls or whatever, but my option is to try cutting it by hand, and that's a mega-hassle.

My next approach is to take it to my drunk A&P mechanic and find a few hours when he is marginally sober and can use his mill and lathe to make a couple. Will advise on that. He's usually three sheets by noon, so if I catch him or wake him up early might get it done. Will see.

I have bar stock, working on it on Tuesday. Will make 3 rods, 6.5"x5/8" with threaded end and 3/16" keyway, with two notches for snap ring.

If anyone else has a Mk VII, and wants a rod we'll have a spare. If someone needs a Mk V intermediate rod I can do that too.

I may be wrong but isn't the keyway 1/8" wide by 1/16" deep to correspond to the keyway in the sheaves. If you do 3/16" the sheaves won't fit.

redleg wrote: ↑Thu Mar 03, 2022 9:01 pm I may be wrong but isn't the keyway 1/8" wide by 1/16" deep to correspond to the keyway in the sheaves. If you do 3/16" the sheaves won't fit.

You might be right. I'll measure before I mill. It looked 3/16 to me.

It is 1/8" x 1/16" deep. I think the threads are not necessary. Clip slot inside and outside is sufficient(IMHO). Realize the 'threads are acme threads, not std threads. Obtaining an acme nut would be problematic. With std threads I think two jam nuts would suffice.

I ordered a 5/8x18TPI die. I'll thread them and we can use a castle nut with a cotter pin. Still haven't fixed my mill, but will work on it later this week. The end shaft on the orig has a flat grind. I think it was designed so that the spinning tools could be mounted out there. Wonder if we want to grind that again? Won't take but a few min once the threads are cut.