Need help with South Bend 3-jaw scroll chuck.

O

Old Rivers

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I have a 5" three-jaw South Bend scroll chuck I am trying to dismantle for cleaning The chuck is very dirty, but has some external but no internal rust.
I got the back off the chuck, which uncovered the three screws which I removed.

Here is my problem: I need to remove the scroll pinion next, and there is a very small slotted setscrew located near the chuck body OD (see photos). I can only turn this screw a few degrees before it becomes impossible to turn.
I rotated the pinion as I attempted to remove this screw, and discovered that when I apply CCW torque to the tiny screw the pinion rotation becomes more difficult. The pinion will move very slightly when I try to loosen the tiny screw. When I turn the little screw CW, the pinion will turn freely as the interference disappears.
Does anyone have an exploded view of this chuck, or any suggestions? How do I remove this tiny screw?
Thanks for any suggestions.

Bill

chuck back1.jpg

chuck back2.jpg
 
Sounds like the pinion may have to be turned to a specific orientation to remove the screw. Screw may have some kind of cam to it.
PS, never done this, just going by what you described.
 
GrayTech said:
Sounds like the pinion may have to be turned to a specific orientation to remove the screw. Screw may have some kind of cam to it.
PS, never done this, just going by what you described.
Click to expand...

GrayTech,

As I mentioned in my post I did try what you suggest, I rotated the scroll pinion through at least one revolution while trying to loosen the setscrew.
Setscrew remains stuck.

Bill
 
The set screw probably has a bur on it that hits when you start to loosen it.
 
Bill, that little screw is a shoulder screw. The shoulder runs in a circumferential slot in the pinion body; this keeps the teeth on the end of the pinion engaged in the scroll. There is nothing that should interfere with this so if the screw is stuck then I'm going to guess that the shoulder screw is bent. When you turn it, it is taking up whatever space there is in the slot and it binds.

Unfortunately, I know of no way to remove the screw other than to try and force it out. If this were me, I would make a hardened bit that precisely fits the slot - square like the slot, not tapered like a screwdriver bit. I would put that hardened tool in the chuck on the mill or drill press, clamp the stuck screw under it and use controlled torque to turn it out. You won't have many chances at this so I wouldn't just use a regular screw driver on it.
 
mikey said:
Bill, that little screw is a shoulder screw. The shoulder runs in a circumferential slot in the pinion body; this keeps the teeth on the end of the pinion engaged in the scroll. There is nothing that should interfere with this so if the screw is stuck then I'm going to guess that the shoulder screw is bent. When you turn it, it is taking up whatever space there is in the slot and it binds.

Unfortunately, I know of no way to remove the screw other than to try and force it out. If this were me, I would make a hardened bit that precisely fits the slot - square like the slot, not tapered like a screwdriver bit. I would put that hardened tool in the chuck on the mill or drill press, clamp the stuck screw under it and use controlled torque to turn it out. You won't have many chances at this so I wouldn't just use a regular screw driver on it.
Click to expand...

Mikey,
Makes perfect sense.
I'll attempt the solution you suggest.
Thanks,
Bill
 
Soaking it in some Kroil or other lubricant first wouln't be a bad idea either.
 
With those 3 screws out you should be able to remove the back cover and see the scroll- maybe you can clean and reassemble without
needing to take the pinion retainer and pinion out? Assuming you can't get that stubborn screw out..
Mark
 
markba633csi said:
With those 3 screws out you should be able to remove the back cover and see the scroll- maybe you can clean and reassemble without
needing to take the pinion retainer and pinion out? Assuming you can't get that stubborn screw out..
Mark
Click to expand...

Mark,

Yes that tiny screw is stubborn... my home made extraction bit failed to remove it.

For the life of me I can't figure out how to expose the scroll. I have removed the chuck back cover (with the spindle threads), and then removed the rest of the screws which are covered by the back plate. How do I remove the scroll back plate which is slightly recessed inside the chuck body?
The pinion fits in between the scroll and this recessed back plate, so I don't see how the pinion is interfering with removal of the plate. There is no rust, and I've oiled everything. My photos in the first post show this inner plate.
I'd love to see an exploded view drawing of this chuck.

Bill
 
If this is a Cushman style chuck, the split is mid body and not at the back plate.
 
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