Lathe bed (South Bend 9) raised scratch and ding - repair options ?

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dansawyer

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The machine is a mid 1940's South Bend A. It shows moderate wear and will likely turn out to be serviceable. It was very dirty and filled with chips so I am removing the tail stock, apron, saddle, gear box, etc for cleaning. The bed is now clear and has two immediate issues, first the flat that the tail stock rides on has a raised scratch, and second there is a raised ding on one of the saddle v's about 6 inches from the end.
The ding is about 10 thousands high and 30 thousands across. the total raised area is about 30 by 30 thousands. The ding is on the high point of the V, the hole is on one surface and the raised area of the other. My thought for this is to grind off the high point. Is the best plan? What are alternatives? (I have placed the cleaned saddle on the cleaned bed with plenty of oil. The feel is smooth and consistent. When the saddle reaches the ding there is a definite hitch. )
The scratch runs nearly the entire length of the bed. It is relatively light but the raised portion is definitely feel able with a finger nail. There have been two mentions for this one is filing and the second is a hone. I am totally stuck on this one. What is the best method of removing the raised edge of a scratch? I have no idea on what to do with this, suggestions are appreciated.
 
@dansawyer,

First, Welcome to the Hobby-Machinist!

Great idea to open the lathe up for a good cleaning, you never know what you'll find in there.

dansawyer said:
My thought for this is to grind off the high point. Is the best plan? What are alternatives?
Click to expand...

I would hesitate to get a grinder anywhere near my lathe bed. It's too easy to have a little slip or distraction and do more damage than repair.
I second the idea of getting a nice flat sharpening stone and slowly working on the raised portions.

You say the "scratch" runs the entire length of the bed. Is it really a scratch like a nasty chip got under the carriage and was dragged back and forth?
Or is it just a "wear line"? Does it line up with the edge of either the carriage or tailstock?

What condition on your "wipers"? (the little rubber V's that keep swarf out of there)
Does this machine have the old flat belt?

-brino
 
raised scratches and dings can be stoned with a fine arkansas stone. you press very lightly, just enough to keep the stone level, and let it take out the high spots. It will leave inconsequential scratches visible in the light - these are very tiny and provide a place for oil. Remember to use lots of lubricant such as varsol, and keep cleaning as you go.
 
brino said:
@dansawyer,

First, Welcome to the Hobby-Machinist!

Great idea to open the lathe up for a good cleaning, you never know what you'll find in there.



I would hesitate to get a grinder anywhere near my lathe bed. It's too easy to have a little slip or distraction and do more damage than repair.
I second the idea of getting a nice flat sharpening stone and slowly working on the raised portions.

You say the "scratch" runs the entire length of the bed. Is it really a scratch like a nasty chip got under the carriage and was dragged back and forth?
Or is it just a "wear line"? Does it line up with the edge of either the carriage or tailstock?

What condition on your "wipers"? (the little rubber V's that keep swarf out of there)
Does this machine have the old flat belt?

-brino
Click to expand...
Thank you for the detailed follow up. Everything is off the ways and covered. I was not too concerned over grinding, but your point is correct. It would be a shame to spread abrasive all over. I will try the stone.

Yes, scratch is like a nasty chip got caught and dragged. It is well defined and does not look like a wear line. It is in the center of the flat way that the tail stock rides on. That is a fairly broad surface, it would be nice to have it cleaned up. There is no evidence that it has caused an issue with the tail stock itself. Based on this is using a stone still the best approach?
I have not checked the wipers yet. The saddle is off so it will be easy to check them.
The machine has the motor mounted under as opposed to in the back. The pulleys are flat. I believe it is a 6 speed. (All the drive gears are in good shape and when disengaged the spindle feels smooth. I have not checked backlash yet.)
 
Lacking pictures, and going strictly by your description of the problem, I would definately use a stone to remove the high metal. I would definately not use any kind of powered grinder or sander.

Bear in mind that there may be a matching scratch or groove on the face that slides on that surface that needs to be stoned also.

We stone the faces of the chucks on our cnc vtl machines at work between every setup... lightly, just 'feeling' for burrs or dings. If any damage is found, the stoning is done more aggressively until the high metal is removed.

-Bear
 
Beds can be quite worn and still make lots of good parts, so use the stone gently, don't take off too much material, just aim for smooth
be sure to wipe the bed carefully afterwards to remove abrasives, and apply oil or goose grease of your choice
(No geese were harmed making this advertisement)
 
What your describing on the inside V of the saddle way is called "The South Bend Ridge" On all South Bend lathes that are worn and have it especially up by the check where it is used 90% of the time. It is caused because the saddle way (opposite side that wears there) has an under cut that never hit's there. That is original way surface, so if it is .030" deep your machine bed is worn that much. If the bed is worn .030 the saddle is worn that bad too.
If you just going to use the machine to turn short shafts and not use the tail-stock and you don't need a very accurate machine then file off the ridge and use it. Same goes for the tailstock burr. file then stone it flat.

Now if you expect to hold say .001" and use the tailstock you need to get the bed machined, then scraped then put Turcite a wear strip material under the saddle to bring the centerline back to the original centerline.

You have some other issues too...the feed screw near the chuck, the feed screw bushings in the saddle are worn, the feed rack is worn. .030" is a lot. How much backlash is in the cross-slide screw and nut?

So can you live with the lathe cutting a big taper up by the chuck? File it after you turn it? Let me know and I have some more info I can tell you.

I found this old thread....shows a few pictures and a drawing. That guys ridge is on outside.
https://www.hobby-machinist.com/threads/southbend-9-x-48-how-worn-is-too-worn.11351/
 
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I find a flat scraper to be the easiest tool to use to remove burs raised by a ding, very easy to control and only takes raised metal down flush with the base.
 
Another old trick of the trade for pushing in scratches must be done soon after it happens by using a smooth faced ball peen hammer face and you rub it over the top pushing the metal together. If it's old it will have crud and rust in it, so you need to clean out the scratch first. A wide flat scraper in the hands of an unexperienced scraper can cause worse scratches if you tip the corner into the scratch. If your careful try pulling the scraper backward and not push it. :)
 
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