SB 9A Lathe Excessive Bed Wear?

[Surprman]

My research when buying a lathe indicated that South Bends (and maybe all lathes with V-ways) primarily wear on the face of the way not the peak.
Based on the fact there doesn't appear to be a significant ridge at the top of the ways you are probably good to go.

I agree - my bet is that the lathe was used in some way that beat the crap out of the tops of the ways under the chuck/faceplate. They probably ground off the tops because they figured it would not effect the accuracy much due to the V ways.

Rick

 

[twooldvolvos]

My research when buying a lathe indicated that South Bends (and maybe all lathes with V-ways) primarily wear on the face of the way not the peak.
Based on the fact there doesn't appear to be a significant ridge at the top of the ways you are probably good to go.

That is my understanding too. I read that the carriage does not actually run on the top of ways. If that is true, the cause of the missing peaks on this lath must have been caused by something else as has been suggested in the replies.

 

[malleusmagnus]

The wear (or ground-in clearance, as you will) on the tops of the vees, is indeed in the length that a gap bed lathe would have it, as @Papa Charlie noted. Also, @DavidR8 is correct, the saddle contact is on the vee face; the flat on the tops of the vee ways is clearance. What's more important is the flatness and parallelism of the vee faces; that isn't something that's easy to discern from a photo.

You will likely be told that the faces, and flats adjacent to them, have to be ground flat within X amount, but I can tell you it very likely wasn't that good when the lathe was new. These lathes were not instrument quality lathes, they were sold as light duty lathes that could be used to produce good work. When your's was new, there weren't commonly available sets of measuring equipment that read in the millionths; most toolroom work back then, and even much later, was just a little better than cut to fit and paint to match. The quality of a machinist was measured in how quickly he could adapt to the inaccuracies of any machine he was put on and still make parts to print.

As a reference point for both assessment and reconditioning, you really don't need much more than 90% of the surface area of the ways to contact the saddle in any given area to be able to produce good quality parts. You'll be able to find any number of people who scrape bed ways, either professionally or as a hobby, who will argue this point, but this is a fact.

FWIW, I'm also a mechanical engineer and former machinist, and I used to work for a very large, reputable, machine tool rebuilder, so my rebuild assessment comes from a commercial, for profit, context.

 

[malleusmagnus]

You filed away the dings. What else did you do to the ways? I have to agree that if you ended up with a nice SB9B for $1000, I think you did OK. Most of us can expect to put in a bit more, over time, for QCTP, various extra goodies. I plan to add on a Chinesy DRO kit, and I fancy trying out a YouTube project to make up a nice steady rest, starting with a pair of disc brakes discs (OK then - disks).

My SB9C has not got significant wear on the ways. Only the paint job colour puts me off. The tops of the ways look a bit rounded, but in fact, are not a wearing out surface, and are in fact a great reference. The same goes for the SB9A way tops, even though the ways are more worn.
You can see in the picture in post #13 how I measured from B to E to check it out from original placed surfaces. I now know that I can put a parallel, or a level straight across it, and take out twist, and verify alignment. It's very handy.

If you really want to check out the ways ..
The Kingway alignment tool is covered in other threads in HM. I had thought to try and make up my own version, because it can be done entirely from turned parts and some easy Aluminium extrusions. I have a pair of (Chinese again!) 100mm levels, and those knobs can be had from eBay.

Rex Waters lashed up what he called his "ghetto" Kingway by clamping to a level a bit of metal to which he had epoxied a couple of washers to touch to a unworn reference surface. There was also a leaned over loose gauge block involved.

View attachment 350171 - - View attachment 350173

For convenience to those interested, I put the info I have all together here. The original patent US2761217 does explain all the various ways this kit can be used, but various improvements have been figured out since, and many versions are now easier to make. The example set of dimensions are in a text file that originated from a UNIX-Type OS, so I do hope it displays OK in a Windows based system. It seems OK here on NotePad. If there are problems, I can put the text direct in the posting.

The best is to search on YouTube. There are videos of measuring kit that look easy enough for beginners as a project.

[Edit: The explanation from @mikey seems exactly right]

You gotta love Google Patents...