Play in cross feed and compound

Any machine will have some backlash. That is a given. Mine is old and "loose" meaning in this case around .030. I often see more on other's. The best I've ever seen is .003. The best suggestion is that when it's fairly low, compensate for it and go on about business.

Gibs: They should be tight and evenly adjusted. As in all should have the same snugness. They should be so tight but not so much as to give trouble moving the whatever by hand. Pushing by hand, it should not be so loose that it moves when you bump it. But you don't want it so tight that it takes a pry bar or "come along". Tight and snug are very personal concepts. What you consider snug, I might consider tight. And a real machinist might consider loose. My machine (Craftsman 12") has wear in the center of the gibs. They are adjusted so they are snug on each end. But things are too loose in the middle. I found some knobs that fit hex capscrews. No link, this was way back BC. I have three gib screws down the side of the cross slide. I removed the center one, replacing it with a cap screw and one of the knobs. When I adjust for a cut, the screw is loosened, the slide moved, then the screw tightened finger tight. Just how tight depends on how I feel that day.

Leadscrew/Nut: When the machine is(was) new(or freshly ground), there was little or no play in the nut. This is in part from the gibs. The tighter the gibs, the faster the nut wears. That's why the nut is a softer metal. It wears rather than the screw. Up front, unless you have replaced the nut yourself, assume it to be worn. It will need replacing someday. When is a matter that you must decide. I have a couple of "zero backlash" devices in my mind. But they are far too large for a machine slide. The best one was for a plasma torch "X-Y" table I built for a friend. At 5 inches high and 4 wide, it would be a little too big for a lathe, even a shipyard lathe. A double nut with a spring in the middle would work. But how strong a spring? Best bet is to adjust in only one direction. For an inward adjustment, back out 100 thou and take it back in only 098.

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ARC-170 said:
The gibs are new and adjusted a bit on the tighter side. Everything else is snug, like it's supposed to be. I just find it hard to believe there is no way to lock these down.
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What do you mean by "lock these down"? The gib screws should already have lock nuts.
 
I think that he means to have a screw of some sort to lock the compound and cross slide in place like you can lock the carriage in place.
 
OK. As I have written several times in the past, the simple solution is to replace one of the three or four gib screw/nut combos with a T-handle locking screw such as the Atlas 9-508 Gib Lock as found on the 500A Milling Attachment. I did that on my 3996 more years ago than I like to think of.
 
That's what I would do. And I might do that. Especially on the compound. I only use the compound for threading and to cut short tapers. The rest of the time I have it locked in place by tightening down the gibs. I have even thought of removing the compound and making a tool post to fit in its place.
 
There are two sources for backlash in the cross feed and compound feed on an Atlas lathe. One is running clearance between the cross feed or compound feed screw and nut. This is not adjustable and can never be zero as there must be some clearance or you would not be able to turn the crank & screw. The other is cross feed or compound feed screw end float. This is adjustable and by careful differential adjustment of the two nuts that retain either crank, can be reduced to about 0.001" to 0.003" before the crank begins to feel as though it were binding. This adjustment should only be made while the cross feed nut is run completely off of the end of the cross feed screw.

Beyond that, you should from the beginning get into the habit of always approaching the setting for making a cutting or threading pass only in the direction to increase Depth Of Cut (DOC). If you go too far, back up half a turn or more and start over.
 
Thanks to all. I think replacing a gib screw with a bolt or t-handle locking screw is the way to go. I just wasn't sure it would affect the gib adjustment, but from what you're all telling me, it will be just fine.

This is the Atlas 9-508 Gib Lock as found on the 500A Milling Attachment:
gib lock.JPG
Maybe I'll make one.

Seems like a socket head bolt would work as well. I'd have to keep the Allen key handy, though. Maybe I could turn down the head of a hex bolt? Just musing aloud here. Let me know what's best.
 
If you use any common screw, you will still have to put a dog point on it. And if you use a common screw, you will need to modify the head, or use a wrench to tighten it because otherwise you will not be able to apply enough torque to tighten it enough to properly lock the slide. That is why the factory made the locking screw the way that they did. And the only standard screw head that might be tall enough to drill for the solid pin or roll pin is the Fillister head. If you try to cross-drill a socket head, which otherwise would probably be tall enough, you will probably break the drill tip of the bit when part of it breaks out into the socket.
 
It seems others have "smoothed" my comments for me. I had to leave in a hurry when something personal came up.

I would suggest a way to fabricate a larger head screw if I may. A knurled knob, threaded in the center, will give the grip you need. LocTite and crimping will hold the knob. Crimping is easily done with a center punch and a 3 pound drilling hammer. A small setscrew would look nicer, even a pin through the edge of the thread. The concerns would be clearing the rounded top of the slide. And not so long as to foul the tail stock. The knob can be quite large so long as these points are considered.

For what it's worth a socket head setscrew is not so hard it can't be cut. I have cut down several diametricly to use as socket wrenches. And making the rounded nose on the gib end, of course. Conceded, I was using carbide cutters at the time. Granted, most of my work is small, but a Nr8-32 setscrew does fits that description.

I avoid any specialty tools lying around. Things should be set up to do by hand whenever possible. In theory, all you should need at hand is the square headed wrench and the chuck wrenches. And whatever measuring tools are needed for the job at hand, of course. With several chucks at hand, even that gets busy. I have done the (Atlas) shaper and the (Atlas) horizontal mill the same way. The 7/16 clamp screws are now 3/8, same as the feed screws. The mill has two wrenches that fit every operational fastener. Maintenance is a different matter, but needs specialty tools there anyway. Set-up should be simple as possible.

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