Cut the Gib?

D

DMS

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I spent a little time today adjusting the gibs on my new Monarch. It didn't take very long to figure out why the cross slide was so loose. The gib adjustment screw was binding in it's hole (slightly bent...); it felt tight, but there was about 1/4" of play between it and the gib. Once I rectified that, I got the gib adjusted so that cross slide is firm, but not tight, the problem is that the gib is sticking out the back of the cross slide by about 1/4". What's the protocol here? Do I just pull the gib out, cut off the excess, debur, and replace? Is there something I'm missing? I figured I would post this before I just started hacking away at things...

DMS
 
DMS said:
I spent a little time today adjusting the gibs on my new Monarch. It didn't take very long to figure out why the cross slide was so loose. The gib adjustment screw was binding in it's hole (slightly bent...); it felt tight, but there was about 1/4" of play between it and the gib. Once I rectified that, I got the gib adjusted so that cross slide is firm, but not tight, the problem is that the gib is sticking out the back of the cross slide by about 1/4". What's the protocol here? Do I just pull the gib out, cut off the excess, debur, and replace? Is there something I'm missing? I figured I would post this before I just started hacking away at things...

DMS
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There should be a screw on each end of the gib. They go down into counterbores on either end. Here's what the screw on the back looks like:

IMG_3456.jpg

This is a round-dial, but it's the same on a square-dial. Without the rear screw there's nothing to keep the gib from tightening as the cross-slide is moved.

My machine had a very rough life and it still has plenty of adjustment left on the gib. I can't imagine how yours could have that much wear. The gib was probably deliberately bent to try to compensate, but this probably caused more wear to the mating dovetail.

A proper repair is to put a shim behind the gib.

Cal

IMG_3456.jpg
 
I hadn't thought of shimming the back side. I'll give that a try.

I also agree, seems like an awful lot of wear. The previous owner had the machine 10 years, and did not use it much (was mostly restoring it during that time). I don't know what kind of history it had before that.
 
I just checked with a feeler gauge to see what kind of shimstock I would need. Looks like about 7thou would be just about right. I also noticed that the adjustment screw and the lock screw cannot both be set flush. Seems like the gib strip is a bit too long? If I adjust the larger screw (the one in front) so that it is flush, the rear screw is proud of the cross slide surface by about 1/8". I'm wondering if this was a replacement gib :think:

In any case, I'll try to get some shim stock cut and see where that takes me.
 
It's probably a replacement gib.

The screw in the back loosens the gib, the one in the front tightens it. I would cut it off a bit more than the 1/8" by which the screw protrudes. Note the depths of the counterbores and size it accordingly. I don't believe that both screws are supposed to be flush with a factory gib.

You can glue the shim to the gib with Lock-Tite to keep it from creeping around.

Cal
 
That worked pretty darn well. I had some 5 thou brass shimstock handy, so I used that. The screw in the rear is a little proud, but at least it's partially in the counterbore. I may trim some off the end in the near future. I also adjusted the gibs on the compound (also waaay loose), and had no problems. As a test I tried to turn down the end of a piece of ball screw. Little bit of chatter till I got to the chewy center. I could see the carriage vibrating during the interrupted cut. I think the carriage is the next thing to adjust.
 
Loose gibs can cause a lot of problems with chatter and poor surface finish. It's a common mistake to adjust them too loose. Put a test indicator on the tool post with the tip on something in the chuck, then grab the toolpost, twist/push/pull with all your might; there should be very little deflection of the indicator. If there's anything close to a thou, thighten the gibs.

Cal
 
I tightened until I could still move the carriage handle easily, but I felt some resistance if I tried to move the carriage back and forth by hand. Got much improves surface finish after that. I'll try a dti later tonight. I'm assuming you mean push perpendicular to the gibs..
 
Play is currently 0 to the accuracy of my ability to measure (0.0005 thou DTI). Not bad for an old girl.

I adjusted the carriage rollers (I gotta say, this is one part of the lathe I don't really like). Looks like I am missing the "clamp rings" (not sure what else to call them) on the back 2 bearings. Guess I should make a couple of those up.
 
If they're what I am thinking, Holokrome makes a good quality collar in a 1 piece or a two piece design if you don't want to bother making them. I think they call them "clamptite" collars.
 
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