Gib screws

[Feeop]

On a bench mill or small lathe, should the ends of the Gib screws be flat, pointed or dome shaped? Mine are currently a little flat and this causes the axis to creep when they are tightened.

Thx

 

[PeterT]

I have seen a few variations on hobby class Asian machines (like mine). They can be flat bottom screws which is not optimal for exactly the reason you mention. The outer edge of the screw makes tangent contact with the 60-deg gib strip & has a tendency to laterally displace or 'walk' the gib. Its not an optimal design. I've also seen cone end set screws which reduces this effect, but they don't have a lot of surface area so tend to dig into the strip & you lose some sensitivity. The cone usually does not match the gib angle BTW. A simple fix is to get a ball ended set screws which will make tangent contact on the gib but minimal displacement effect. Hopefully you have a metric machine where this hardware is abundant & cheap. Depending on size you can get them steel/brass/nylon tipped.

There is a variation to this theme where the gib has divots in them intending to match the set screw position. My tool cutter grinder has this, I suppose because the gib is so short this was their means of keeping it into position so it doesn't drift when the dovetail block was being displaced a longer distance. I guess the idea is OK, but in my case the hole pattern did not match so it was a PITA to remedy.

 

[PeterT]

Forgot to say you can make your own by center drilling or ball end milling a divot & insert a bearing ball retained by Loctite or whatever. its a bit fiddly but I made my own this way,
Some of the commercial ball ended ones you see are sprung (different animal) so be aware of that.

 

[Mcgyver]

It should match match what is in the gib - there should be counterbores, either round or flat bottom, that either a round or flat ended screw mates with. I replaced a gib once and put the counterbores in with a drill ground to cut flat on the end.... you could try that or use a ball end mill both using the machine part as drilling jig. if using an ball end mill take care that it doesn't deflect sideways into the threads (super slow feed, maybe use carbide so it flexes less)

 

[PeterT]

It should match match what is in the gib - there should be counterbores, either round or flat bottom, that either a round or flat ended screw mates with

I suspect that that's how its SUPPOSED to be done. But my Taiwan mill & lathe just have flat sided gib faces (other than the pecker marks made by the set screws LOL). No matching surfaces or CB's like you mention. Actually where this issue came up on my lathe was not the gib adjustment, that was dealt with by the 2 axial screws that displace gib fore or aft for fit. It was the table lock screw that basically acts on the gib strip. Trouble was, you can displace the table or cross slide or whatever some unwanted amount just by tightening/locking. Set your DRO to 1.000", lock the table, oh look at that, DRO now says 1.002". So I ended up making a bearing ball ended lock screw & that reduced the effect to nill.

 

[Susquatch]

Wouldn't it be a good idea to make small cylinders out of brass that go into the screw holes before the screws? They would have a flat the same angle as the gib, and a recess or flat to match the screw.

My Deckle S0 Clone even uses these to replace the gib. It bears directly on the dovetail. I think it would work great on a gib. Unless the screws are long, it would prolly need to be shorter than this.

 

[PeterT]

That's exactly what I did on my lathe. Depending on the depth of the thread passage, they may not be as fun to remove. I bonded the ball to the brass foot IIR, not the set screw end. Then a magnet just zips them out. Unless the ball is stainless :/

 

[Ishmael]

Wouldn't it be a good idea to make small cylinders out of brass that go into the screw holes before the screws? They would have a flat the same angle as the gib, and a recess or flat to match the screw.

That's what I did with my Busy Bee lathe/mill combination machine (please don't laugh too hard; it does what I want for cheap with extremely light cuts.and a digital caliper adapted as a depth indicator).

 

[DPittman]

please don't laugh too hard; it does what I want for cheap with extremely light cuts.and a digital caliper adapted as a depth indicator).

Nothing to laugh at, many of us make do with what works for us despite fancier, bigger machines being all around us it seems sometimes. I think it's admirable.

 

[Susquatch]

That's what I did with my Busy Bee lathe/mill combination machine (please don't laugh too hard; it does what I want for cheap with extremely light cuts.and a digital caliper adapted as a depth indicator).

I ain't laughing. Two of my close friends have even smaller combos. Both are Smithys. Nice machines that do a lot of good work.

 

[Ishmael]

Thanks, @DPittman and @Susquatch, for the kind thoughts, though "good work" is not something in which I excel.