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Lathe bed re-grind dimensions.

plumberpieco

Cast Iron
Joined
Feb 27, 2010
Location
cleveland
I had originally posted this in the General forum and was advised to move it here. Thanks Iridium77.

I acquired a 9"B South Bend lathe that was going to be restored but the owner never got around to it. He had the bed re-ground and here are the only dimension's of the work done that was found with it .
lathe re grind.jpg
I had put a slight amount of bluing paste on the top slide and moved it across the bed and got a consistent transfer with no abnormal fit. The tail-stock base plate gave favorable results too. I had't checked the head-stock fit yet though. From what I interpret I would need to shim the feed rack and lead screw brackets down .005" to accommodate the changes. Figured I'd check to see if I'm on the right track.
Thanks Z

That was the original post and here is a little more info.
As Iridium mentioned in his reply about fitting the tailstock, headstock and saddle [ which I called a top slide in my original post] I thought I'd add a few more pictures. I know it's not good to assume anything but it would appear that the tailstock and saddle have been fitted to some degree as there is no appearance of wear that you would expect on an 80 plus year old lathe. There's bluing still on the saddle from when I checked it some time ago, I forgot to take photo's but can do it again at some point.

Thanks Z
south bend tailstock base.jpgsouth bend saddle.jpg
 
Do you have a question?

A bed grind is just the first step in the fitting process. From there the surfaces must be hand scraped for fitment issues and then scraped to "points". The points are the high spots left from the scraping process that actually contact on each surface. 20,30 and 40 points per square inch are common values we shoot for. Without the points the ground surfaces will have too much contact, with each other, and there will be too much friction. "Stick slip" is greatly reduced when the surfaces are hand scraped to 20 points and half moon flaking is provided ( low spots ) to hold the oil as the surfaces slide over each other.

Scrape the bed first and then work on the other pieces to make them fit the bed. If there was a large amount of grinding done you have a few ways to correct the geometry of the machine after the bed scrape. I think the most common one is to build the height back to the correct height by gluing a layer of wear resistant material, of which there are many, to the underside of the saddle and tail stock.

Steve
 
I would not get to excited with the bed measurements your showing us. Put the saddle back on and use a soft blow rubber mallet say a 2 or 5 pounder and tap the saddle top on the 4 corners and listen. if the sound is solid and doesn't ring or slap. The saddle matches pretty good, if not it needs to be scraped. If you want to hear the slap noise slide some paper under one end of the flat and then tap it, you will figure out what the sound is with and with-out. I will attach a link to a super forum written by a former member who we lost a few years back.

Many of those old SB lathes bed were planed and stoned and not scraped, others were planed and square cut for oil pockets and some of the newer machines were flame hardened and were ground. Plumber is green and assumes no wear, but on the tailstock you can see the unworn surface's. Plus the bottom of the saddle was originally scraped and there is no scraping now, so it is worn. Why is there 2 tail-stock bottoms?

A professional would never shim down the rack or brackets, that seems to be something hobbyists do. If it is worn .005" I would only square cut the bed and saddle. If he knew how he could 1/2 moon the unexposed areas or bottom of the saddle and tailstock. Also relieve the center of the front saddle ways .001 to .002 middle 40% as I bet it is high in the middle now.

Also grind in some oil groves in the saddle to help distribute oil down to the ways. Have to be careful how far you cut them in, so you the groove goes to the open air which would be bad news.

I have seen those beds worn .020" near the headstock and they still run so if it is low .005" that won't hurt a thing. If your a hobbyist you are more likely going to screw it up trying to shim it then letting it alone. In this forum we rebuild and repair this the professional way and not the Yahoo or Hobby forum way.

How about some pictures of the bed and the bluing on the saddle. Then check the taping. Try depth miking the tailstock ridge that can be seen unworn and worn on the bottom flat. You guys can tell him how to indicate the top of the TS base making it parallel to the cross-slide and bed...also how to check the TS quill and how it points. You guys know the drill. Rich

http://www.practicalmachinist.com/v...ki-lathes/sag-12-restoration-progress-237940/

http://www.practicalmachinist.com/v...ag-12-restoration-progress-237940/index5.html
 
Last edited:
Thanks guys, I had posted the two tailstock bottoms as a reference as the one is on a 9" SB that is in use and has wear and the other to show the apparent scraping marks with no wear. My experience with South Bend lathes is fairly decent as I have had several over the years and am well aware of the difference between their non hardened beds and flame hardened ones. I agree I am as about as green as it comes in respect to scraping and fitting these surfaces but I have a very good mechanical aptitude. Here are two pictures of the bed, I know they aren't the best but I have to use my phone. I can tell you this that the bed has definitely been resurfaced. I did set the saddle on the bed and give it a quick test as Richard had suggested and giving it a smack in the center gave an good thud and on the front corners it was the same. On the back corners I got a slight tink. I could slide a piece of paper underneath each back corner while it sat on the bed.

Now do I plan on giving this a full blown restoration? No. Do I plan on putting it on display and ogling over it? No. Thought it would be an easy project to do in my spare time at home. In reality I should get my 10ee and Hendey back in shape but they are not at home in the basement. I figure with the re-ground bed it might be worth the effort as most South bends are beat to death.
south bend regrind 1.jpgsouth bend regrind 2.jpg
 
Caveat: I'm very green as well.
Anyhow, if I interpret the sketch correctly, the saddle ways have been ground .013" down, not .005"
My concerns would be that, if I understand correctly, in general the slides under the saddle wear roughly twice as much as the bed, Therefore, even without accounting for the material that needs to be removed from the saddle for mating properly the bed (optimistically, let's say .003"-.005" vertically), the apron would be at least .025".030" lower than what was when the machine was new.
It's true that half of that drop built up during the years and you'd have correspondent wear in the bearings for the leadscrew. But, by suddenly increasing this drop, especially considering the design of the 9" South Bend, where you don't have any strong and reliable way to hold down the saddle on the ways, I'd be afraid that the saddle would be pushed up near the headstock by the leadscrew.
The "cheap and hobbyist solution" would be to shim down the gearbox (if any) and the leadscrew supports. The preferred way, at least by me, would be to build up the material under the saddle to bring back the apron to its original height.
As I warned at the beginning, I'm very green and my very limited experience should be considered hobbyist experience, where time and effort involved are of secondary importance.
It is also likely that I'm off from reality in considering the real effect of the leadscrew pushing up the apron and saddle near the headstock (if your lathe doesn't have a quick change gear box, I wouldn't worry too much).

Paolo
 








 
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