South Bend compound gib wear and adjustment.

[Ski]

Hello, I picked up a different compound for my 13" South Bend that included the compound base and gib. It is meant to replace a chewed up original. I would like to know what the proper adjustment procedure is for the compound gib? Or direct me to an explanation of the proper way to do this?
The gib,compound and base are all marked the same so believe they are all original mating parts. Scraping marks are clearly visible but unknown if they are original or something new. I noticed that when I assemble them to the lathe and adjust the gib in to the point of lockup and then back it off about 1 and 1/4 turns until the compound slides smoothly that approximately 3/8" of the gib will protrude from the back of the compound. That seems excessive to me. Can anyone shed some light on this? Thanks ahead. Ski

 

[Bob Korves]

The gib is possibly warped. Some of them are cast iron. Don't try to straighten cast iron! The 3/8" protrusion just shows the wear in the system... Taking it apart and really looking at everything carefully might let you find what your real issues are.

 

[Ski]

The gib is possibly warped. Some of them are cast iron. Don't try to straighten cast iron! The 3/8" protrusion just shows the wear in the system... Taking it apart and really looking at everything carefully might let you find what your real issues are.

The gib is bowed a bit. It is steel not cast. It is apart and clean and I scraped off any and all burrs and bumps. I will throw a indicator on it and check it without the screw on it with hand pressure. Thanks for suggestions. Ski

 

[Bob Korves]

Put some Prussian blue (High spot blue) on the sliding surface of the gib and the sliding surface on the side without the gib, slide the gib in carefully without moving anything, move the compound by hand (without the lead screw mounted) one cycle, and then carefully take it apart and see what is making contact and what is not. A sprung gib makes the whole operation more difficult, and also makes it difficult to set the gib properly. The best thing to do is to make or buy a new gib that is straight and then scrape it in to fit properly.

 

[Ulma Doctor]

gibs can be straightened, here is how ...
support the gib on 2 parallels with the bow facing up in a hydraulic press.
measure the bow as best as possible and press on the gib a bit more than the original error by a couple (few) thousandths and release
repeat this process until it is flat in reference to a surface plate or straightedge
i wish the best of luck!

 

[4GSR]

..................... I noticed that when I assemble them to the lathe and adjust the gib in to the point of lockup and then back it off about 1 and 1/4 turns until the compound slides smoothly that approximately 3/8" of the gib will protrude from the back of the compound. That seems excessive to me. Can anyone shed some light on this? Thanks ahead. Ski

If the compound is in near new condition, it is normal for the gib to stick out a bit. And 3/8" is about right. I always run my compound gib snug, not real tight. I only loosen it a little, maybe a 1/2 a turn from tight when using the compound slide itself to cut an angle on a piece. Even on cutting 60 degree threads, I leave it snug to very snug. 1 and a 1/4 turns to me is too much, way too loose in my book. Looseness in the compound causes abnormal wear in the compound slide from tool pressures. Tightening the gib keeps the tool pressures from bouncing the compound slide around. Ken

 

[Ski]

Thanks for all the tips gents! I did straighten the gib and that took awhile. Way better than it was. The adjustment tips are a big help as well. End result is it is smoother. I can run it tighter now and still be able to turn it. Thanks again . Ski