Flat way repair

I need to correct a mistake here.

You only need a 12" straight edge to measure a hobby lathe. they can be had for under 30 bucks. I don't know where Craig is coming from but it is simply not true. On a lathe you will find that the only discernible wear will be within 10-18" of the headstock. Even on 100 year old lathes, the way seem to not be worn right against the heaststock and can serve as part of the reference surface. I chose 12" to be safe, but I personally use a 10" reference surface with very good effect.

This is something you will eventually need for good quality control on your machining, if you care to do close tolerance work, eventually. For a long time I used a 6" parallel and borrowed a straight edge for the 3 or so times a year I needed it. I then graduated to a 10" Moore and Wright engineers' level, used as a straight edge (It was ground to be within 2 tenths, but the reality was closer to 4 tenths).

I now have a 10" straight edge from Starret that I use in place of the level. If I had been smarter, I'd have bought a 12" which is why I'm recommending it to you. You can measure an entire lathe bed - even a 60" one in 12" increments and learn a lot. All you need is a straight edge and a bright flashlight.
 
I did say "ideally". The Veritas 36" straightedge is USD $92.50 and guaranteed to be within 1.5 thous over its length. They also offer an aluminum straightedge that is half the price but only guaranteed to be within 3 thous. For an old lathe bed that was on the junk heap, a 3 thou measurement error is probably not be a big deal. If the bed only showed, say max 6 thous out, I would be done!

A 12" straightedge seems a bit short to me. OTOH, if the OP can beg or borrow any straightedge, that would be a start. If there is a serious valley (like 50 thous) in front of the chuck, the cost of correcting that likely exceeds any reasonable value for the machine. OTOH, if no light shows...

Craig
 
If a smaller straight edge can be used, then I'm back in the game. I did spend an hour going over the ways with a micrometer. I'm now wondering about the accuracy of my micrometer. I was unable to come up with a variance of greater than .0005" from one end to the other...anywhere. I did not plot these measurements, as I should have. But I can always do it again later. I'm unable to get into spots that are obviously lower, due to the rack being in the way. It's been pinned in at some point, and I haven't thought much on how to remove it. I'm always thinking it's a taper pin, and remembering horror stories of driving a taper pin from the wrong end in cast iron.

While using a 6" parallel and a light, I could see blue light or no light, in all the areas of obvious wear. I tried my feeler gauge anywhere it looked like "more" light, but it still wouldn't fit. The areas of wear are not as wide as a feeler gauge evidently. I'd say less than 8 inches from the headstock, there's no more light. I did just realize I was using the wrong light source, so I'll make the test again.

Thank you gentlemen.
 
A 12" straight edge will give you a better reading... a 24" better still, but with diminished returns, the longer the better, but you'll find 12" is more than sufficient.
 
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