Mark V Pinion broke...

[Majones1]

I always think about looking for the cause and not just treating the symptom. Mine’s 67 years old, so hoping it doesn’t happen to mine. I do have a spare carriage so can easily replace that part if needed.

[DLB]

Looks to me like the ring/washer had a chamfer to match that of the pinion body and that connection is what failed. Def looks like they are two pieces when looking at the unbroken one.

It does doesn’t it. Is that washer glued or welded? It looks to me like the former. But either way, this may indicate there is a greater problem because it seems like they would not put so much pressure on the washer portion of this unit that it could eventually fail. I would think that the locking pressure should only be applied to the inner chamfered portion of the unit. I would look for how it seats in the carriage and if there is excessive wear on the pinion chamfers and the carriage seats they press against.

Mine isn't set up so I can't confirm, but I think the inner chamfer is in play against the table leg. But when using a lathe tool rest I think the washer is in play on the rear pinion, there is nothing for the inner chamfer to bear against. On top of that it takes a lot of pressure to really lock the old style tool rests with the spiral leg, which means quite a bit of pressure on this joint.

- David

[JPG]

Does it work without the flange on the rear? I am not sure what it does for the rear one.

[chapmanruss]

The Carriage Pinion P/N 501392 for the original Mark 5 and Mark V 500 is no longer available new from Shopsmith so you will have to get it used. I looked at one of mine from a 500 carriage yesterday after reading about yours breaking. To me that flange looks cast on and the only part not in the one-piece cast is the collar on the other end of the Pinion Assembly over the "teeth". I don't know if welding it is possible without obstructing some part of it. It is definitely an odd failure point.

The flange on the Pinion Assemblies keeps them positioned in the carriage casting. Without the flange the Pinion could move back and forth on the square rod anywhere in the carriage. Without the flange on the rear Pinion the whole raising assembly would be free to pull out of the Carriage. The flange on the rear Pinion is also necessary for locking the Lathe Tool Rest Post in the Carriage.

It may be possible to use the "broken" Pinion in the front position with the flange there for spacing since the locking action against the Table Post and Lathe Tool Rest Posts work against the angled edge of the Pinion and not the flange itself. Of course, you would need to make sure the broken Pinion Assembly is properly positioned in the front hole before inserting the Table Post or Lathe Tool Rest Post. Since I don't have a Pinion Assembly that is broken like yours to test this it is only a theory at this point.

[JPG]

My 'thinking' was that the table tubes would prevent the assembly 'moving in'.
Had not thought of the lathe rest. A second 'post' in the rear would suffice there.

Yes no tubes allows 'moving in'.

I think gluing the flange back on AND moving it to the front will work.

[ScotSunnergren]

My 'thinking' was that the table tubes would prevent the assembly 'moving in'.
Had not thought of the lathe rest. A second 'post' in the rear would suffice there.

Yes no tubes allows 'moving in'.

I think gluing the flange back on AND moving it to the front will work.

I have super-glued the broken pinion flange and swapped it with the front one. I think this may actually work! The front side has the handles pressing the flange against the carriage recess for it and does not seem like it would put stress on the join. On the front one it seems that flange washer is only to keep the pinion in place for the front post rack.

The rear one seems to bear the stress of th tightening of the carriage locking process.

It has locked down tight and I will let you know if I have any further problems with it... Of course I have a whole replacement carriage arriving tomorrow.... But I guess it will be good to have spares.

[benmcn]

I don’t know how well superglue holds up with metal long term, but I have seen JB Weld work really well for the type of repair you made. The wealth of information on this forum is amazing. Glad you got things up and working!