9A reverse tumbler gear assy - purpose of the "lock bushing" ?

[oztool]

I have a 9A lathe with the later plunger-type reverse tumbler assembly.
When the stud gear is mounted it does NOT line up with the idler.

This has been a great mystery to me for the past 25 years. However, yesterday I pulled the gear train apart for "regular" maintenance and, after comparing my reverse shaft with some advertized eBay parts, I came to the conclusion that I have the wrong type of reverse shaft:

........................ my part ..................................................................older bolt-type shaft..............................newer, plunger-type shaft (?)


I assume that the newer plunger-style shaft must be about 3/8" longer than the previous type to suit the new bracket which was longer - see comparison of the two brackets below:


old bracket 1 3/8" long ................................................... new bracket 1 3/4" long

The simplest way for me to make my stud gear line up with the idler would be to chop the extra length off the new-type bracket.

HOWEVER ... I know that the South Bend Engineer who designed the later plunger assembly bracket greatly increased the cost and complexity of the assembly by adding a special spring steel band and a circlip, which required lengthening the casting, and then more turning and grooving. Clearly there must have been a purpose behind this seeming madness.

The spring band (PT2585K2) is labelled "lock bushing", but it's hard to see how it would lock anything since it is at least 0.001" smaller than the bracket OD .
The circlip must serve to prevent the spring band from sliding off, but WHAT IS THE IMPORTANT PURPOSE OF THE SPRING BAND ?

Can anyone explain ? or even guess ?

 

[Rsty1]

Hello Adelaide!
142 views of your post & no replies. Well I'll take a stab just so you don't feel lonely...

Maybe it's adaptable to make it cross-compatible with other lathe headstock variants?

 

[woodchucker]

without seeing a picture of your lathe from 2 feet away, I am going to take a guess that your headstock is not mounted correctly.
I think you need to loosen it up and move it further out toward the left, so it does line up.

 

[DavidR8]

I agree with @woodchucker. I have seen this before and the headstock had in fact been shifted to the right causing the misalignment.

 

[oztool]

Hello Adelaide!
142 views of your post & no replies. Well I'll take a stab just so you don't feel lonely...

Maybe it's adaptable to make it cross-compatible with other lathe headstock variants?

thanks Rsty - you have somewhat alleviated my feeling of isolation !
So far I can't think of any better reason than yours for introducing this complex modification to the assembly. Of course the problem that it has caused for me is that I have a SHORT SHAFT mis-matched to a LONG BRACKET. The shaft and stud gear is therefore displaced to the right.

 

[oztool]

I agree with @woodchucker. I have seen this before and the headstock had in fact been shifted to the right causing the misalignment.

thanks Woodchucker and DavidR8 !
to date I haven't pulled the headstock off so I don't know how it could be made to slide out of its correct location. While that may conceivably be the reason for the stud gear mis-alignment, I think that the obvious reason is entirely contained within the reverse tumbler assembly itself i.e. the shaft is 3/8" SHORTER than the bracket. I beleive that I must have inherited a mis-matched assembly consisting of the old-type short shaft, and the new-type long bracket.

 

[woodchucker]

I don't think so. the head bolts to the ways using 2 bolts underneath the head. I would not modify anything other than moving the head.
Your tumbler looks normal.

 

[oztool]

I don't think so. the head bolts to the ways using 2 bolts underneath the head. I would not modify anything other than moving the head.
Your tumbler looks normal.

I will have a look at the headstock and see whether that could be the cause of the problem ... or perhaps the solution to the problem.
Although the tumbler does "look normal" (and works fine) you can see from the measurements in the photographs above, that there are two types of bracket. The new bracket is 1 3/4" long, which is 3/8" longer than the old one. The introduction of the longer bracket would have necessitated lengthening the shaft to maintain the original position of the stud gear. Therefore new and old bracket/shaft are not interchangeable. Using an old shaft in a new type bracket would offset the stud gear as shown in my photograph above.