Mark VII Idler Shaft Damage

[GerikBensing]

I'm rehabbing a Mark VII unit I purchased recently and one of the issues I found was that the idler shaft that holds the eccentric bearing had a lot of play in it. Disassembling it I found the shaft has worn away from where the bearing is supposed to ride.

Idler Shaft Bearing Surface.jpg (366.47 KiB) Viewed 847 times

Does anyone have any advice on if there is a way to repair this? I've done some research and found there is an epoxy or special welding machine process for shaft repairs in general and put out some feelers locally if anyone offers such a service. Of course, the easiest thing to do would be to replace it but this is a Mark VII only part and I can't seem to find a replacement. It looks like a Mark V idler shaft is similar, but I don't believe it's similar enough from what I can tell.

I have a full video of my Shopsmith Mark VII teardown as well. Video showing this part wobbling is at 8:54.
https://youtu.be/vNvNrkP6sOQ?t=534

Any advice would be appreciated!

[DLB]

I'm not a Mark VII guy, but since they haven't weighed in... There have been threads with similar problems. One member adapted a Mark 5/V speed control and in the other the resolution isn't clear:
viewtopic.php?p=311335#p311335
viewtopic.php?p=294730#p294730

While the Idlers are significantly different, it isn't obvious to me why a Mark 5/V Idler would not work. The obvious differences are in the attachment of bearing to shaft, but as long as the bearing and shaft fit together this isn't necessarily a problem. From my non-Mark VII perspective, adapting the entire M 5/V speed control seems good as it eliminates another known problem area, the speed control cam. Though I don't love the new style, the old style Mark 5/V Idlers and bearings are relatively bomb-proof.

There are multiple methods for metal deposition as you describe for a potential resolution, and also epoxy based solutions. I would think that finding a machine shop that can do this and rebuild the shaft should be okay, not necessarily inexpensive. Similarly a machine shop could make a new shaft, also perhaps a bit expensive. IIWM I'd want to definitively rule out using or adapting an old-style Mark V/5 shaft first because intuitively that seems easier and less expensive. I would guess that the Mark VII experts already know why that won't work.

Good luck!

- David

[GerikBensing]

Yeah, adapting it to a Mark V speed controller setup crossed my mind when I found that post. I'll have to pull the idler shaft out of my Mark V and see just how different they are.

It seems like a new (used) Mark VII idler shaft would be ideal but I've not found a source for one yet. If I had a metal lathe doing the fancy shaft repair epoxy would probably be pretty quick and easy, but alas I do not own one and don't know anyone who does.

[miken]

I have a lathe and a mill and would be happy to help, but I don't have any experience with an epoxy style fix. I would assume it would need to be turned down considerably in order to get a decent build up thickness, and probably would need to knurl it for epoxy adhesion? If it was my problem, I might try turning it down and press on a new sleeve. Then turn that to match the o.d. it should be. That would require rethreading the end to a smaller size. I cant remember if that keyway on the threaded end is needed under the eccentric? I'd probably give that a try first, and then just make a new one.

Spray welding is the fix for this, but I think the cost would be an issue.
Mike

[Edit] after thinking more about this, I would turn the worn area under the bearing to a specific o.d. then create a two piece split sleeve that you could assemble one piece on each side as you push the bearing into place. Like shimming under the bearing.

[JPG]

1) the MVII idler shaft bearing is entirely different from a M5/V but is similar to the new two bearing version now used on the M7..

2) The spacing of the MVII bearings is different.

3) The threaded portion of the MVII idler shaft only serves to accommodate the nut which provides a positional stop for the bearing 'assembly'.

4) The turn down/two part sleeve scheme would likely work for the excessivly worn location where one of the bearings was originally located.

5) A similar scheme would likely be needed where the second bearing was originally located.

6) An issue not mentioned is the wear to the edge of the snap ring groove that positions the inner bearing and limits the idler sheave travel towards the bearing.

7) I think a suitable replacement could be made from 5/8" shafting by someone with an engine lathe and and ability to add a 1/8" keyway and drill the key end hole/dimple and create the snap ring groove. A second groove could serve to limit the bearing assembly movement towards the shaft end thus eliminating the acme threaded end/nut/retainer. Lastly the flat for the coupling would need to be machined.

[tomthank]

This content is like a beacon of truth shining brightly.

[miken]

JPG, you are correct. I pulled my idler to have a better look. It would be far easier to just make a new one than deal with the tolerancing of a split sleeve and a fix for that eclip groove. I believe it is only a piece of 5/8" ground drill rod, and I just happen to have a 1/8" keyway cutter for the horizontal mill. The threads on the end don't need to be acme. I could single point cut a 5/8-11. I already have an eclip grooving tool I ground for another project.

[GerikBensing]

Miken, if you think it'd be easier to simply remake this shaft, I do think it's the better option. Sounds like you have the tools necessary to make this happen. I'll send you a PM.

[JPG]

My clumsy measurements are: O/D 5/8", LENGTH 6 3/8", INNER END TO KEY STOP DIMPLE CENTER 2 15/16", INNER END TO OUTER EDGE OF E-CLIP GROOVE 3 3/4", E-CLIP THICKNESS 0.050", OUTER END TO BEARING EDGE OF RETAINING E-CLIP 1 1/4", INTERNAL BEARING SPACER 1/2", BEARING THICKNESS(EACH) 11 mm.

The key slot need only be flat to the inner edge of the dimple.

I say clumsy because adding everything up is slightly greater than 6 3/8"(6.416). ***

A tapered flat on the outer end would be 'nice'.


*** Closer examination reveals the 6 3/8 length is actually longer by about 1/32. The critical dimension is the inner edges of the e-clip grooves must be no less than 1.367".

FWIW an 'extra' idler assembly I have appears to have a groove cut at the end of the threads that would provide the external e-clip as suggested above however it is shallow so I suspect it is a relief cut for the threads. Perfect location though. ???

[miken]

Good info JPG, they cut the keyway using a slitting saw or keyway cutter, thus the reason for the keyway going past the dimple hole. It does a better job than using an end mill. Yes, my two idler shafts do not have outer eclips and I suspect as you noted they are really intended to be thread relief. Correct me but I think the threads are acme because the Jointer coupling lug is driven from this. The flat top threads are less likely to be damaged (flattened) by the lug. I'd need to think if I can grind an accurate acme thread cutter. Maybe your double eclip, no threads idea is best?