Adjusting gibs on lathe carriage

I have been cleaning and re-assembling my 12 inch Craftsman lathe (I know it's only a toy to most of you guys, but it fits my needs). I can't seem to get the carriage gib adjusted just right- there must be a procedure that I need to follow. The carriage uses a square edge (not tapered) gib with 4 recesses that the adjusting screws seat into. I've tried several times to adjust the gib and no luck so far. Is there a sequence that I need to follow when adjusting the 4 screws? Tighten inner screws first then outer ones? Start tightening on one end and then go successively to the other?

I'll have the same problem with adjusting the gib on the cross slide too. It is tapered on both edges. Will it adjust the same way?

Thanks for any help or advice you can offer (other than getting rid of the *toy*).

Mike

I'll be betting that you find its loose some places and tight others.

That is from wear, I have some of the same problem.

If so, you gotta live with it or re-scrape/grind the machine until it doesn't happen.

Is it possible that the gib can be put in upside down? You said it isn't tapered- maybe it has a set where the adjusting screws have seated. Just a thought. Otherwise, I would run the carriage to the right, and start by adjusting the third from left screw, then the second from left. Leave the other two loose. Run the carriage back and forth, see if things bind. Loosen whichever screw is tight. Then take the carriage to full right again, adjust the rightmost screw, then the leftmost. Run the carriage back and forth, loosening whichever screw is tight, just enough to not bind. As you traverse the ways, there will be loose spots, and you'll have to live with this. I'm assuming that normal wear is going to give you this situation.

My rationale for this procedure is this- you want to make the gib contact with as much area as possible, thus adjust one of the inner screws first. The third from left will likely not need readjustment once set, so start there. Balance the pressure from the gib by going to the second from left. The tightest spot for the far right screw would likely be at the far right of the ways, so that screw would be next, and may not require readjusting once set there. The far left screw may bind at the far left carriage position, so that's where it's critical adjustment might be.

If need be to tighten the gib at any particular position of the carriage, try to use just one of the inner screws, and that's the one you loosen when you need the longer range of motion from the carriage.

What, exactly, isn't working in the adjustment? I've got one and have never had a problem in adjusting - move the carriage to the tailstock end of the bed, loosen the locknuts then tighted the screw inside until you feel it tighten up a little bit. Then, while holding the screw tighten the locknut. You'll usually want to back the screw off just a little bit before tightening the locknut as the nut with drag the screw in just a little bit.

After things are tight at the tailstock end move the carriage back to under the headstock where it'll likely be a little bit loose from wear. If it's too loose then repeat the tightening where you're going to use it and don't try to get to the tailstock without loosening things again.

I usually adjust gibs by wiping off and lightly oiling them. Then I snug all grub screws down until the slide cannot move. I then back out each one a fraction of a turn to give maybe 5 ten-thousandths or so of allowance for lube.

If the ways are worn, you would need to adjust them either at the least worn end, or, if you want a tighter fit, somewhere between the most worn and least worn areas.

Den

The lathe doesn't have a lot of wear, and it's not that it's tight in just one spot. I can't seem to find the correct amount of tightness for the screws. I either get it so it won't move easily or where it's so loose that I can feel play in the carriage. I haven't been able to find a happy medium.

I think darryl might have the sequence I'm looking for. I know I read somewhere about a *gib tightening sequence* for machine tools, but I can't remember where.

I appreciate all the suggestions so far- I'll try to adjust the carriage again in a few days when I get another off-day.

Thanks, Mike

One of the fellows in the Yahoo Maximat Super 11 group was an old pro at this stuff. He strongly advocated using a small torque driver to consistently adjust the screws.

IMHO, this is not a sequencing deal like torquing down an engine head. What you're doing with gibs is setting the final clearance for a sliding mechanism. If it were precisely fitted, lapped, etc. without gibs, the goal would be a slight clearance to allow for an oil film. It seems like the goal is the same here. But ... I'm still learning

First off check to see that somebody
did not put a lock screw in on top of
the adjusting screw.

Second, dismantle and clean the gib, and
the screws. Check for burrs and other
defects.

Third, install longer ones so you can
locknut them.

Fourth, lubricate the ways and gib. You
will get poor results trying to adjust
dry ways.

What I do is run the travel to one extreme,
and snug down the screws that are on that
side, with the others fairly loose.

Then do the other extreme of travel.

Individual screw adjust gibs are always
a compromise. You will find you have
to set them too loose in some areas to
allow free motion in the snug regions.

Jim