9" SB lathe bed worn---options? (Metal content!! Long)

Terry, let us know what you find out about this. I am in the same boat as you.

My feel about a DIY regrind is that a lot of things can go wrong and the likelihood of ME succeeding in making the bed true, is not great.

i

If your time is worth a plug nickle, you're better getting off another machine and sending this one on down the road. Prices are really depressed right now. If you can afford it, hold on to this one till inflation kicks in big time. I think hobby machine tools will be a decent investment if you hold 3 - 5 years. Could be wrong.

If you have an attachment to this particular machine, bite the bullet and have somebody grind it.

Just my 2 cents

Karl

I have the same opinion, except that the space that they take is expensive. But, like you, I agree that they will likely rebound in price.

I could not agree more!

i

If there's lots of wear, the carriage and tailstock should be disassembled and cleaned (there could be grit embedded from past use).

I'm not sure what the best degreasing would be (I'd probably start with solvent and Scotchbrite pads, finish with paint remover, but what do I know?), but degreasing and a wipe down (old-style, linseed oil) would be second.

Then, assemble, lube, and carefully level and shim the bed. A few test cuts will tell you if the 'wear' is a functional problem. Maybe it's good enough as-is.

The glass-and-moglice treatment will give you smooth, but not necessarily accurate. Don't trust it.

As an optical engineer I can comment about the epoxy and glass technique as it is similar in concept to making replicated mirror surfaces from epoxy. The most proprietary part of the process is the release film and separation method. If you use an oil film, the epoxy stays gummy on the surface. If you use a spray-on teflon or silicone coating, the epoxy still sticks somewhat, and since the bond area is very large it can be very difficult to remove the rigid glass from the rigid epoxy. The companies that do this vacuum evaporate a very thin layer of some proprietary substance on the glass and then have a secret process to separate the glass. I have seen other mold-making techniques where compressed air is injected into the gap to help separate the mold. Perhaps this is what they do.

I wonder if a more-surefire way would be to apply the epoxy a little thick and then manually scrape it using the glass as the master flat plate. You can read up on hand scraping on the web. I would think it would be easier to scrape filled epoxy than steel.

Terry, There is no economical way of saving this machine. Scrap it for parts on eBay and buy a better 13 x 40 machine that is not used up. If you don't know how to do that, get tech support.. Both Iggy and Karl are correct. Steve

Moglice is often used in repairing Clausing Varidrives.

My attempt.

Are you going to try to use half a can at a time?

How are you going to repair the sadle wear? If the ways are worn, I would assume (dangerous) that the sadle is worn.

Dewitt seems to have exclusive rights to market this assuming you are in the USA.

I'd call them and run your idea past them.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

Steve Lusardi was the first guy to say it to me. It took me a year to believe him. Now I know that he is right.

i

Worth a try - do you have a trades school nearby who could be persuaded to take it on as a teaching exercise, or even enroll yourself for a term to get access to their (usually) industrial machinery. The instructors are nice people - teachers LIVE for the students who are actually interested in learning...and they dont have to be so paranoid about us mature aged students doing something stupendously stupid....

Andrew VK3BFA.

I milled the worn bed of my 6" AA/Sears lathe. The carriage is now ~0.030 lower and the half nuts don't line up with the lead screw. I had planned to install 1/32" brass shims under the carriage to raise it back but they caused too much play, and anyway I have a larger lathe.

If you have the room for it there is rough, messy work that can be done on a poor lathe to save the good one, such as turning cast iron, metal spinning, and lapping or polishing. The bed and leadscrew at the tailstock end may not be so bad.

jsw

The first question you should always ask yourself before buying old heavy iron; do I want a lathe/ mill/shaper or do I want a project.

Those old guys that built those machines were pretty clever and it seems unlikely I could second-guess them with a can of epoxy and a bunch of shims...

I did this on my Sheldon 15" lathe with pretty good results. I probably should have stopped there, but I wanted to make it "perfect". That took me an additional 20 months or something!

I used Moglice on the underside of the carriage. It works great, but is expensive.

Glass is not flat, way far from it!

It won't stick in thin films, it is supposed to be used in .060" thickness, minimum.

I believe this procedure will never work. It will put a layer of Moglice on the bed, but it won't be anywhere NEAR flat. You will then still have to hand-scrape the Moglice using spotting dye and a known-good straightedge.

It will deflect 20 thousandths just due to the pressure of pushing on the Moglice. No, if you apply spotting dye to a known-good surface plate and put a sheet of glass on it, you will be amazed at how NON-flat ordinary glass is. I have worked with surface plates, and made my own straightedges (I finished a Michael Morgan 25" straightedge) and then made a set of 3 right-angle plates. Also, glass is VERY flexible, so any force, or even its own weight, will cause it to deflect. That's why straightedges have a "spine" on their backs, to add the necessary stiffness to prevent bowing.

Devitt Machinery sells it down to 50g, I think. That isn't very much. It will cost you over $100 for the correct setup of materials.

Bottom line : If your tailstock ways are in good shape (usually are) then rig a toolpost grinder on the compound slide, which is rigged by an angle plate to the tailstock base. Tow this arrangement down the bed with a small gearmotor so it takes 5 minutes or so to complete a pass. Keep stepping down until it cleans up the whole length of bed, then repeat for several "sparking out" passes without stepping down.

Now, smooth the bed finish with a fine bench stone totally saturated with ATF or air tool oil. I rubbed two stones together to keep them flat every couple times. Now, apply Moglice putty to the bottom of the carriage. You may want to machine the carriage bottom so the moglice has sufficient thickness and the carriage ends up back where it is supposed to be. I didn't do this machining and really should have. I ended up putting a .010 shim betweent he carriage and apron, and that sorta works.

I drilled and tapped holes in the carriage for 8

10-32 brass-tip setscrews to locate the carriage in perfect alignment to the spindle, and set the clearance between carriage and bed. There's 4 screws straight down in the corners, two horizontal in front and two in back. I loosened the front screws a hair to remove, and then snugged them back when the Moglice-coated carriage was placed back on the bed. The screws are then used to pop the carriage free from the bed. It still takes significant force to pop the bond, even with their recommended mold release agent.

Jon