[Newbie] Operating Screw Retainer Pin Disaster - SB 4-Jaw Chuck

[karlsangree]

Newbie Alert: good mechanical and fabrication skills but brand new to machine work.

I just purchased a '42 South Bend Heavy 10 and with it came two independent, 6", 4-jaw South Bend chucks, both in desperate need of servicing and gunked up to the point where they barely work. I found a couple YouTube videos of guys stripping these down, cleaning, lubing, and reassembling. There are 4 hardened steel pins that retain the 4 individual operating screws. In the YT vids, these pins were (somewhat) easily tapped out with a punch or small drift pin.

On the better of my two chucks (pictured below), these pins were pressed in so tightly that I had to fab a custom tool and then, with all my weight, force them out with my 2-ton arbor press. I am now ready to reassemble the chuck and these pins are so tight that I can't even get them started properly and I can barely force them with the press. It looks as if these pins need to be very accurately positioned (rotationally) so they don't bind the operating screws when the pins are fully seated and as tight as these are, I don't think I can make that happen.

I'm guessing that I need to reduce the diameter of these pins to give them a just slight interference fit, but they are hardened and I have no idea how to accomplish that with a lathe. Is there a way to deal with this, or is it time for a new chuck?

Jaw, Operating Screw, and Retaining Pin.
I am being careful to keep the groups of parts together as they came out of the chuck body.


Chuck Body.
The original sales slip shows that the lathe was delivered with a 3 and 4-jaw, so this may be an original.
It appears as though the work or tooling has been crashed into the chuck once or twice in the last 70 years.

 

[Braeden P]

very fine sandpaper might work dont take too much off.

 

[pdentrem]

Polish in the lathe which emery paper or something like 1000 grit backed up which a flat piece of wood. Or can use a whet stone. Just a polish will make a huge difference on pushing them in.

 

[karlsangree]

Thanks gentlemen.

I'll give the abrasive a try. And yes, I'll protect the ways

 

[woodchucker]

the pins can be turned on your lathe. Do you have collets?

put them in a collet, and take some silicon carbide sand paper (wet dry black paper)
put a piece of cardboard or cloth on the ways to protect it. Start with 220, or 320 , cut the paper into strips.
use wd40 as a lube.
hold each end of the paper and rock it back and forth, don't hold the paper on the pin with your fingers, you can lose them if you try pinching the paper on... if you need to touch, you do it open handed from the bottom...

if I wasn't clear let me know. Keep checking. move from 220 up to as high as you wish. Turn the pin around and get the end... leave it wider so it holds in. A taper might be a good thing.

 

[karlsangree]

the pins can be turned on your lathe. Do you have collets?

Yes, the lathe came with a complete set of 5C collets in 64ths. Great suggestion! I guess that's why you make the big bucks woodchucker . I didn't think of using the collets; I was just going to chuck the pins in my 3-jaw. My inexperience is showing lol

Any ideas as to why or how these pins got so tight? The YT videos I watched in preparation for the refurbish (with one exception) showed the men were able to easily tap their pins out and back in with a punch/drift pin and small hammer. I had to beat on the pins with a large ball peen hammer like a man possessed just to get them to budge. Afraid of damaging the chuck, I ended pressing them out with my 2-ton arbor press after grinding a tool to get past operating screws. then, the pins fought me all the way out. Now, I can't easily get them back in.

 

[woodchucker]

age... gunk, old oil, rust...

BTW you might want to clean the hole out too. I have a bunch of rods with slits in them. I can put sand paper in, and use an air grinder, or electric drill to clean the hole out. It doesn't take much..

whenever sanding on the lathe protect as much as reasonably possible.. the grit is bad for the lathe. but don't be afraid to use the lathe to do these operations... that's what it's there for.

 

[woodchucker]

Looking again at your part, see if 400 or 600 will clean it up, and the hole...
also I wonder did someone pean over the end and that's why it didn't come out?

 

[karlsangree]

Looking again at your part, see if 400 or 600 will clean it up, and the hole...
also I wonder did someone pean over the end and that's why it didn't come out?

There is no visible physical damage to the pins such as would be caused by hammering but I'll throw them in a collet and have at them with a dial test indicator and make sure there are no bumps.

I'm off to see my cardiologist this afternoon but tonight after dinner I'll slit up a 3/8" wooden dowel and use that with a strip of emery cloth in a hand drill to clean the body. I'll then set the pins in a collet and take care of them with a strip of emery cloth and some WD40.

Hopefully I'll have some good news before the end of the day.

 

[francist]

There is no visible physical damage to the pins such as would be caused by hammering

This can happen easier than one might think, I learned that the hard way quite recently. One a close fit such as a precision bearing and shaft or a light press fit it really doesn’t take more than a few tentative tap-tap-taps with a light hammer to swell the very end just a hair. Not enough to see dings or visibly deform anything but still enough to make removal decidedly miserable. The old adage “bigger hammer, bigger damage” does not necessarily bear true in all cases.

-frank