Proper Gib Adjustment

[Scra99tch]

As I understand making gibs too loose results in too much play, too tight and bind and wear occur.

How would I go about getting just the right feel out of the gibs that are set with several set screws.

My table gib on the Van Norman is a wedge style where it has one setscrew to advance the gib. Do I advance the table outside to limit and put an indicator on the end for side to side play. Do I tighten until I get <.001 play, then advance the table back feeling for unnecessary drag?

The knee gib is a bit more daunting as it had the several set screws here it seems like I would tighten maybe even torque them down to a few oz-ins then back them all off 1/8-1/4 of a turn. Where would I put an indicator to show me pitch and roll of the knee?

Thanks

 

[sdelivery]

Using a .0005 indicator( linear travel) will help guide you But worn ways and necessary clearance will prevent you from ever reaching a no movement reading.
With multiple set screws, I like tightening until lightly seated and backed off to start the adjusting process.
With the screw driving the wedge, I like adjusting in the worn area then trying to reach the end travels(un worn) areas without forcing or hard cranking.
It will be a compromise but almost everything is.
If you have no experience in gib adjustment then only tighten a little at a time and try it.
To tight and being forced to move can break a cast iron gib.
Can you post a picture?

 

[Scra99tch]

Sure when I get home I can post some. I did not tighten them too tight just until a firm stop then backed them off, but there was some surface rust on the top part of the dove tail that bound it up. I'll have to scotch brite it off then lightly stone.

 

[sdelivery]

I would encourage you to clean and stone all faces and use light oil then make your adjustments.

 

[Rex Walters]

If everything is freshly scraped and unworn, it's mostly a matter of personal preference, I think. The difficulty comes with wear. I think most machines tend to be used most heavily along just a small portion of the travel, so adjusting the gibs for minimal movement in that area usually makes it too tight elsewhere (or vice versa).

I'd second the comment about cleaning, stoning, and oiling before making adjustments. Especially since you mentioned surface rust.

You can also check that the gib is straight and not bent when it's removed from the machine (wear can sometimes cause a gib to become significantly bent). It pays to be methodical about bending it back straight using an indicator if it is bent: support the gib by the ends (on 123 blocks or whatever) and measure the bend with an indicator (convex side up). Use a clamp to bend it in the opposite direction too far (it will spring back a bit) then measure the improvement. It's not perfectly linear, but if your first bend was, say, 1" but it only got, say 33% improvement after springing back, try bending it farther on the next cycle (measuring the improvement and adjusting the bend amount accordingly each cycle).

There's a LOT of mechanical advantage with a leadscrew, so I tend to adjust my gibs pretty tight, FWIW.

 

[Scra99tch]

Thank you.

I'll try that out. I won't be scrapping this time around as I have not attempted it before and the machine itself has very little wear. I'll double check with an indicator anyways.