Steel for cross slide feed screw

TheArkBuilder said:
I don't have a picture right now. I have about 2thou of play, The main issue is the thread. This is a very old lathe, and originally it was square thread and an odd size and tpi as well so I am going to make a new one of standard size and pitch using acme threads
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2 thou, that's nothing.. I would love 2 thou.

edit: you always want to go in one direction.. I always feed in... If I need to come out, I come out further, and then go back in to the spot I want to go to. That prevents you from losing your values. I have a lot more play than 2 thou if I push the cross slide either way. I have a lot of backlash as well, and can still do some fairly accurate work.
 
TheArkBuilder said:
I don't have a picture right now. I have about 2thou of play, The main issue is the thread. This is a very old lathe, and originally it was square thread and an odd size and tpi as well so I am going to make a new one of standard size and pitch using acme threads
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.002?! A new lathe has more than that.

How much is one rotation of the dial?


TheArkBuilder said:
I understand this is a difficult job but I'm trying to learn and I would like to attempt to make part from start to finish. More so as a personal challenge if nothing else
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That's the best reason.
 
woodchucker said:
you always want to go in one direction.. I always feed in... If I need to come out, I come out further, and then go back in to the spot I want to go to.
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Great tip thank you
woodchucker said:
I have a lot more play than 2 thou if I push the cross slide either way.
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This was really just a guess, I haven't truly measured back lash and it is most likely more than this
 
TheArkBuilder said:
I'm looking at options to try the technique sdelivery suggested, but cannot find 7/16ths acme rod. Would 3/8s be enough or should I try to go up to 1/2. Or stick with the original design?
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Either way , going up to 1/2 inch would be a good choice but going down to a 3/8 if necessary would work as well . Acme threads are strong and will provide the needed leverage.
I would post a picture of the screw and nut.
Let's get some more information on the lathe as well.
More than likely the screw will be usable and the nut worn.
Some machines are designed so the back lash can be adjusted partway out, acme screws need clearance to operate.
 
TheArkBuilder said:
That is a good Idea, although I was just looking and I need 7/16ths and they don't have it I may look around at other suppliers
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That is the way I would go for a precision screw.

You can actually get a class of precision ground acme screw just for this application.
 
TheArkBuilder said:
Yeah this was, I'm sure a highly inaccurate guess, I haven't measure back lash. I'm sure it's much more than this. I will measure it when I'm home and get a more accurate number
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Good thing, .002 it too tight and would indicate some sort of problem IMO.
 
I am from the school of : roughing pass, measure; semi-finish pass, measure and calculate amount of spring; adjust for and take finish pass.
 
Thomson Linear is another choice. SS or 4140 are standard options for commercial screws. There are several classes of precision ranging from about .01/ft to .003/ft. There is also rolled vs ground but ground are more rare in standard sizes and LH isn't as standard as RH Some companies also have choices in nut designs that you can modify to fit. Is the nut adjustable in any way ( split nut ) or must it fit the screw exactly? Dave
 
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