SB underdrive removal

[hudstr]

Hi all, I am trying to remove the underdrive assembly because there is a lot of wear in the cone pulley shaft. The lathe is from 1939 so the design is slightly different than the videos or info i've been able to find. It uses plain bearings that you oil instead of ball bearings of the "newer" designs. I'm trying to remove the shaft that holds everything in, part 2548 in the parts catalogue. (same design but the 11" only has 3 pulleys instead of 4 for the 13" or 16")



It should only be held in by a set screw, but I am unable to fully remove the set screw. I can rotate the set screw about 200 degrees, but something binds up and it wont turn more. I've tried removing the paint, dremeling back the top if the threads got damaged somehow, I've tried an impact gun, wrench on a screw driver. Something just doesn't add up because I can't think of a reason why it would rotate 200 degrees but is not able to come out. Any ideas appreciated. The shaft is loose, i am able to rotate it and move it back and forth about 1/4" so that isnt the issue.

View attachment VID_20201231_192333216.mp4

 

[Jim F]

Penetrating oil and heat.

 

[hudstr]

I think i just realized what the problem is. I think the last threads on the screw have been deformed by the shaft moving so it binds up when I turn it out and the threads of the screw engage the threads in the base. Looks like drilling is the only option now

 

[markba633csi]

I think you are correct, you'll need to drill it out and possibly re-tap the hole for a larger size set-screw depending on how much thread damage there is when you get done
-Mark

 

[Technical Ted]

Looks like a slotted head set screw. I have one of those impacts that you can put screwdriver bits in and hit with a mallet. I think you can pick these up pretty cheap at Harbor Freight. My 15" lathe is the same type of design. If you're lucky it will have bushings you can replace. Mine is from the early 30's and they bored the cast iron base and no bushings were used. Mine was worn so bad the lathe couldn't be used and not having a milling machine at the time I ended up making a replacement base out of angle iron and used pillow block bearings instead. Been working fine for 40 years! Just don't forget to grease the pillow blocks every so often.

Ted

 

[hudstr]

yeah I tried the impact you hit with a hammer first, unfortunately I wasnt really able to get a good hit on it lying upside down and contorted to reach under there. I'm just going to drill it out and tap it for a larger size. It has replaceable bushings but even the cone pulley shaft is worn about .050" so i suspect it went a while without being oiled at some point in its life.

 

[zuhnc]

I was going to suggest someone might have replaced the set screw with a different type of point on it, and tightened it down so much the threads deformed. Tight quarters in there. I have my complete underdrive out, trying to rebuild the motor. Good luck with the drilling. One needs eyes on the knuckles to see what is happening! A left-hand drill bit might make things easier. zuhnc

 

[hudstr]

After much frustration I got it out, but as Ted said, it appears they just bored the cast iron. I'm now weighing my options on how to fix this. One option for fixing this is find someone to bore it out larger, make a new shaft, but this will also require boring out the step cone as well. I could try to bore out the bushing completely to put in roller bearings, like the later designs as shown in this video. This way I think i could get away without boring the cone pulley.

I am probably going to find someone or a shop to do this because I dont own a mill, and while I do have access to mills and lathe at the school machine shop, I don't trust myself to not mess it all up.

Any other ideas which could be better or easier or cheaper are more than welcome.



I also found the pin that holds the motor belt pulley on the shaft hiding on the inside, you can kinda see the outline from the dirt.

 

[Technical Ted]

When I got my 15" SB 40 years ago, I didn't have any other machines either, but my dad did have a welder. We made a whole new assembly from 2"x2" angle and used pillow block bearings for the shaft. Works great to this day forty years later! Just have to give the pillow blocks a shot of grease once in a while. We replaced the shaft with a piece of cold roll steel.

Ted

 

[sdelivery]

I think i just realized what the problem is. I think the last threads on the screw have been deformed by the shaft moving so it binds up when I turn it out and the threads of the screw engage the threads in the base. Looks like drilling is the only option nowView attachment 349583

Exactly, use a bushing like below and a center drill then a standard drill.