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Repair a gib?

David

David

Scrap maker
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Last night after I removed the cross slide gib to measure it for @grease monkey I took the liberty of removing the compound gib because the compound has always been very tight to move.

With the gib removed I discovered the reason was that the dial was tightened too much so there was too much friction.
But I also discovered that the end of the gib that is supposed to rest against the stop screw (no idea if that's what it's called) is slightly rounded off so the gib just pushes past the head of the screw.
This allows the gib to move too far into the dovetail causing binding.

I think I have two options to fix this:
1) Make/buy a new gib. Making one is obviously a non-trivial task. No idea if I can buy one.
2) Trim off the damaged portion. This could affect the adjustment range. The adjusting screws have about .75" of range so I may be able to get away with this.

I'm 100% certain the gib is cast iron otherwise I'd think about making a tiny MIG bead on the end and filing it to shape.
Are there options I'm not considering?
 
Just trim it, and maybe make a better fitting screw that doesn't deflect so much. That seems to me to be the path of least resistance
 
Mike R said:
Just trim it, and maybe make a better fitting screw that doesn't deflect so much. That seems to me to be the path of least resistance
Click to expand...
The major diameter of the screw is definitely on the small side and the head could be a smidge larger.
This could be an easy fix.
 
Wouldn’t weld a gib. Brazing an extension is legit, but may cause stress relief and warp your gib requiring rescraping. Not a JB weld fan for this job. Not the end of the world if the gib gets warped or ruined- they are not that hard to make. Agree with some comments above. Trim end of gib to a good fit with new adjustment screw (maybe you mean captive screw?) Make new screw to be a slightly tight fit in threaded hole and good running fit on gib with minimal clearance.

If it had been binding, I’d suggest bluing up both sides of gib to check. Also blue up topslide against its base without gib in place to ensure when you scrape your gib to match you have a parallelogram not a quadrilateral gib in section.

Hint: photos are helpful ;-)

Edited to add checks on gib
 
Last edited:
Sorry, I used wrong description in my note. Delete ref to quadrilateral. I meant trapezoid or trapezium as the undesirable form gibs can take and have binding, when you want a parallelogram.

Had to look it up. Apparently too long out from school, or never learned it correctly.
 
If its what I think it is, the screws on either end are glorified adjustable stops to position the tapered gib relative to cross slide. Loosen one, tighten the other, it gets displaced a bit & stays in position. Screen grab of my 14x40. Some gibs have notches for the screws, I think so they can push or pull the strip from that end? Anyway, there should not be a lot of axial force on the gib. just snug enough so it doesn't drift. I can't see where tightening hard would accomplish anything other than a cracked gib.

JB Weld might work if it was just building up a plain end, but probably not so well if we are talking about a restoring a notch end. A picture would be helpful!
Failing that I'd agree with the suggestion If there is any way to modify or make a new the screw/head in conjunction with minimally dressing the end of the gib might be next best path. As long as you get achieve the required action & setting.
 

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PeterT said:
If its what I think it is, the screws on either end are glorified adjustable stops to position the tapered gib relative to cross slide. Loosen one, tighten the other, it gets displaced a bit & stays in position. Screen grab of my 14x40. Some gibs have notches for the screws, I think so they can push or pull the strip from that end? Anyway, there should not be a lot of axial force on the gib. just snug enough so it doesn't drift. I can't see where tightening hard would accomplish anything other than a cracked gib.

JB Weld might work if it was just building up a plain end, but probably not so well if we are talking about a restoring a notch end. A picture would be helpful!
Failing that I'd agree with the suggestion If there is any way to modify or make a new the screw/head in conjunction with minimally dressing the end of the gib might be next best path. As long as you get achieve the required action & setting.
Click to expand...
Your diagram is spot on Peter. Fortunately it's the plain end that's slightly messed up.
I think the screw head is slightly undersized so it managed to sneak under the edge of the gib.
 
David said:
Your diagram is spot on Peter. Fortunately it's the plain end that's slightly messed up.
I think the screw head is slightly undersized so it managed to sneak under the edge of the gib.
Click to expand...

Ya, sounds like a lathe job to make a custom screw.

I think you should model it in CAD and then make a triple scale 3D prototype and then build a destructive test fixture so you can analyse the performance. Might give the rest of us some time to finish something before you do for a change.
 
Usually its something like this so the screw head has intersecting area over the end of gib & the threaded portion can clear of course
If the screw is more difficult to replace or just wont cooperat, maybe you could make a simple spacer in the shape of gib end to provide the gap distance. Its not like the gib fit relies on this tiny segment of the whole length to do its job fitting the length of dovetail. I made some 3DP gib strip testers for my TCG just to validate, you could print some samples.

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Thanks Peter, after some fussing last night I managed to get the screw to engage the edge of the gib.
First thing I'm going to try is swapping the screws.
 
What would actually be overkill but smarter is a thrust washer. The screw head engages one side of the bearing but transmits only axial force to the gib end on the other side. As opposed to current mode where friction imparts some unwanted torque action on the gib. If the gib/dovetail parts are well fitting this shouldn't be a problem but I've seen some offshore installations where this aspect was not well thought out or sloppier fits.

Actually I wanted something like this thrust washer principle on my cross slide lock because the screw acting perpendicular to gib can displace the cross slide it a couple thou as evidenced by DRO. Not cool if you are trying to maintain a set position. But there isn't room for thrust bearing so I used a bearing ball on the end of lock screw & footpad angled 60-deg combination. There's a picture deep in the website somewhere.
 
PeterT said:
What would actually be overkill but smarter is a thrust washer. The screw head engages one side of the bearing but transmits only axial force to the gib end on the other side. As opposed to current mode where friction imparts some unwanted torque action on the gib. If the gib/dovetail parts are well fitting this shouldn't be a problem but I've seen some offshore installations where this aspect was not well thought out or sloppier fits.

Actually I wanted something like this thrust washer principle on my cross slide lock because the screw acting perpendicular to gib can displace the cross slide it a couple thou as evidenced by DRO. Not cool if you are trying to maintain a set position. But there isn't room for thrust bearing so I used a bearing ball on the end of lock screw & footpad angled 60-deg combination. There's a picture deep in the website somewhere.
Click to expand...
You've just given me an idea. I'm going to make a washer and see if that will work.
 
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