Restore Or Not To Restore...

I wonder if a person could reverse the leadscrew end for end and reduce leadscrew backlash? It might take some adjusting or extending or drilling/tapping for modified ends or such. Not suggesting it would work, but seems like 99% of my use on the leadscrew is in right/left direction. Maybe less wear on the other side of the thread? Curious if anybody has tried it and how it worked out.
 
It would not make any difference if you turned it around.
the backlash is created by the width of the Valleys that have been worn between the threads.

Acme Threads Start out with a Flat Top almost like an inverted "U". but Flat on Top.
All wear occurs on the sides of the thread and the FLAT Top of the Acme Thread is reduced as the sides wear and create wider valleys.
Eventually the Valleys are worn to the point the top of the thread becomes pointed like an inverted "V".

By that time the Valleys have become wider and there lies the backlash. To get from one side of a thread to the next you end up turning the lead screw with nothing happening until the other side of the thread finally comes in contact with the Half Nuts.
 
My leadscrew has been reversed. The previous owner/abuser before my grandfather bought it in 1955 apparently used it for grinding, and the headstock end threads were round and gouged. My GF took the leadscrew off and in to the plant machine shop and had it remachined to swap it end for end. It works. It looks strange because the long unthreaded portion normally at the headstock is at the tail end, but it works and it got the 'fresh' threads to the headstock end where they will get used.

So yes, it can be done, and it works, but I'm not convinced it is better than buying a section of ACME blank and machining a new one.
 
If one end has considerably less wear on the threads then yes it makes sense that it would work. Because you now have FULL Threads where you will use them. But for many of us the lead screws are worn along the entire length. When that happens it makes no difference.
 
It also doesn't help with backlash from half nut wear, but it MAY help in some cases...IMO backlash wear is annoying, but quite managable. Bed wear is killing me...
 
Another problem with flipping it is that 2-1/2" of the right end is 1/2" dia. When you flip it, you have to cut that off as the left end of all Atlas 10" and 12" lathe lead screws are either 5/8" or 3/4" dia. So you will have to relocate the right bearing about 2-1/2" to the left.
 
is the bead wear that much of a killer? in other words, do you turn stuff that's long enough to produce a measurable taper? not criticising or anything, but most of what I've read about bad wear says that it has to be truly shagged out before you start getting measurable taper. if it's 2 thou low at the headstock that'll drop the cutter by that much which = tiny difference on the diameter (which is way beyond my mathematical abilities to work out, just that statement was hard enough). sounds like a NOS lead screw, half nuts and this bearings fixes most of it, the rest you can fix with some scrap and ingenuity :)
 
For an analysis of the diameter errors caused by 10 thou vertical error between headstock and tailstock or by that amount of wear if you are running the carriage from an unworn bed area into the area with the wear, see Downloads in Machine Manuals, Catalogs & Drawings\Atlas/Craftsman/AA\A/C Lathes\A/C Charts, Tables & Misc Docs\Tailstock Height & Bed Wear Errors.txt. Note, however, that this only addresses diameter errors caused by vertical errors. Differential wear on the back of the bed is another matter. 10 thou wear on the back of the rear way would result in 0.020" diameter error if you started the pass all the way down at the unworn tailstock end. But of course, that seldom happens (and is the reason why there is usually no wear at the tailstock end).
 
Cleaned everything since it was all apart, got both races and the right bearing today so they are installed, just waiting on the left bearing. Spindle is reassembled and loose in the headstock.
 
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