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Adjusting gibs on a milling machine or others

Richard King

Diamond
Joined
Jul 12, 2005
Location
Cottage Grove, MN 55016
I was telling a member of another forum how to check gib clearance today and wanted to show a You-Tube show my friend Adam Booth made of how I showed him how to check and adjust gib clearance. You can scroll to minutes 9, 14 and 22. When adjusting gib clearance you need to take in account the wear in the ways and non wear area's and make a happy medium. Most cast on cast machines need a minimum of .0005" clearance per side or a total of .001" clearance. To tight and there is no space for way oil. If it has Turcite then you can slowly tighten the gib to zero clearance or .0002" per side. When measuring ...push and release, pull and release and only measure the "lost motion" or gap. You can push and pull to hard and bend things. Also on large machines with heavy parts, chuck up (vise) a long 4 x 4 and push and pull it to increase the leverage. Checking Gibs For Wear & Needed Adjustments - YouTube

The same way could be done on other machines like a lathe cross-slide or a VMC head-stock
 
Hi Richard,

On my Deckel FP2, I got advice about this from Franz Singer, who is the German expert on all things Deckel. Franz told me to tighten a gib until it just locked, then back off one turn. Easy advice to remember, and seems to work well for that machine. Edit: these are tapered gibs.

Cheers,
Bruce
 
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I used to get someone to carefully and slowly wind whatever it was I fitting the gib in to. They’d wind the element in the direction of away from the gib and I’d follow up by pushing the gib in to place lightly with my thumb. Once the gib wouldn’t go any further it was time to stop. Do not use excessive force.

Larger elements like Hor Bore saddles etc usually had two gibs, one at either end of the saddle. In that case I’d always put a DTI on the saddle to the table. I’d wind the table one way, zero up, and wind back in the opposite direction. I’d expect to see the DTI needle move 0.001”. If it didn’t I’d re adjust the gibs until It did.

Regards Tyrone.
 
Hi Richard,

On my Deckel FP2, I got advice about this from Franz Singer, who is the German expert on all things Deckel. Franz told me to tighten a gib until it just locked, then back off one turn. Easy advice to remember, and seems to work well for that machine. Edit: these are tapered gibs.

Cheers,
Bruce


That would seem to make good sense. With 100:1 tapered gibs and a screw with 1mm of 1.25mm pitch you would gain 0.01-0.0125mm (0.0004"-0.0005") clearance. I think that's OK for a fine small machine if you've got plenty of oil pockets I think I will adopt that for my current rebuild.
 
I once worked on a medium sized ( 12ft bc ) lathe made by a British company called “ Churchill- Redman “. It was a typical flat bed lathe. The saddle gib was at the front of the saddle and it was attached to a lever on the right hand side that was fastened to the saddle by a screw that had something like a four start thread. When you raised the lever it propelled the gib inwards. It doubled as a gib and as a saddle lock. When you raised the lever and locked the saddle it was locked better than any lathe I ever worked on. I’ve never seen that idea on any other lathe.

Regards Tyrone.
 
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I am sure most of you are familiar with the Bridgeport mill knee to column gib notch breaking off and sliding in deeper and sticking the knee. That locks it up tight. If I remember right a Bridgeport is .008 per 12" of taper. My dad taught me to indicate the gib "shake" so you know the amount as all machine taper gibs are different. I have seen one mill with a lock like Tyrone describes but can't recall the brand. It had a rack on the side of the gib and you lifted a lever and a rack pinion slide in the gib to lock it. You can start with a .002" feeler gage to get it close and then indicate it to fine tune it.

In Taiwan some of the factories made a bar they fit into the tee slots to check the shake on X tables. I've read about how some use ammeters to check the power draw as the gib gets tightened. I still use the indicator method so I know their is and how much clearance, no hoping or guessing.

Peter makes a good point about scrap marks wearing off and no oil pockets. That's why one has to keep in mind where the wear is and set the gib to a happy medium. You can as a preventative maintenance, pull the gib, clean it and scrape some new or 1/2 moon flake the gib. I had a Ukraine immigrant work for me years ago who had worked in a factory who said during holidays the maintenance crews would pull slides apart, 1/2 moon the ways, no bluing to give the machines extra life without rebuilding. Isn't this fun to have a real conversation on here!
 
Pushing the gib in by hand will work good for a small machine where the act of doing so can move the table to take up the slack, but not so good for a machine with very heavy parts. You're stuck with the indicator there. I generally like to use the indicator regardless. And as Richard noted, if the machine isn't in great shape, better watch how tight you set the gib. Wear in the ways will bite you if you set the gib for the most worn area then run the machine to the unworn area. That can cause galling, excess wear on nuts and ways and all sorts of trouble.
 
It obviously wouldn't work on more industrial sized machine tools where the sizes, weights or design complexity prevents it or takes too long to do. For the smaller and more simple machine designs like his Myford, George Thomas advocated in one of his books of pulling the cross and top slide feed screws and adjusting the gib until the slide can be smoothly pushed by hand from end to end without a trace of going tight or slack. That's also not going to work with a whole lot of wear if that's present. But this is a machine tool rebuilding forum.:D To me doing it that way is a lot more sensitive. But also double checking for any excessive side to side clearance with an indicator as eKretz mentioned is my method as well.

To me those tapered gibs are imo the first sign of being a decently designed machine and it's what my BP clone has. A whole lot of older/smaller machines had or have the much poorer set screw adjusted non tapered gibs. So fwiw maybe I can add something here because oddly I've never once seen it mentioned in any forum post yet that this type of gib design has a major and built in fault. G. Thomas explained and illustrated the problem extremely well and how to properly fix it. As he said, the general adjustment method would be just fine if the slide didn't ever have to move, since it does and the instant the slide is moved, then due to friction between the parts, it then tries to drag the gib in whichever direction the slide is moving. And those pointed in most cases gib screws and the divots they seat into on the gib work exactly like miniature wedges that then help to tighten and ruin even the best set adjustments. Once that gib rides up enough on the slope of the screw tips it over rides that frictional drag and it's then held in place but still tightens up those carefully set adjustment clearances. Because of that, the gib adjustments need to be run a bit looser than ideal. No it's not much movement, maybe less than a thou, but it can and does affect how much feed screw pressure it takes to move the slide as well as giving the slide a certain amount of stick/slip and logically a bit more part wear.

How he solved the problem was with a simple cross pin and a hole drilled through the side of the slide and just through the gibs depth while the parts were fully assembled and in there working position. Then he disassembled and re-drilled the hole in the side of the slide to be a close slip fit on the pin. The hole in the gib was left as a light press fit. Then he drove the properly measured for length pin into but not past the other side of the gibs face. That pins the gib in place and prevents it from trying to move with the slide at all. Yet the few 10ths or so of clearance allows removing the parts during any future disassembly. Yes I've done it and it does exactly what he says it will. On larger machines than his Myford, reaming the two different sizes instead of only drilling them might be the better method though. Those tapered gibs also solves the same problem if it has the two opposing screws to lock the gib from moving.
 
I am sure most of you are familiar with the Bridgeport mill knee to column gib notch breaking off and sliding in deeper and sticking the knee. That locks it up tight. If I remember right a Bridgeport is .008 per 12" of taper. My dad taught me to indicate the gib "shake" so you know the amount as all machine taper gibs are different. I have seen one mill with a lock like Tyrone describes but can't recall the brand. It had a rack on the side of the gib and you lifted a lever and a rack pinion slide in the gib to lock it. You can start with a .002" feeler gage to get it close and then indicate it to fine tune it.

In Taiwan some of the factories made a bar they fit into the tee slots to check the shake on X tables. I've read about how some use ammeters to check the power draw as the gib gets tightened. I still use the indicator method so I know their is and how much clearance, no hoping or guessing.

Peter makes a good point about scrap marks wearing off and no oil pockets. That's why one has to keep in mind where the wear is and set the gib to a happy medium. You can as a preventative maintenance, pull the gib, clean it and scrape some new or 1/2 moon flake the gib. I had a Ukraine immigrant work for me years ago who had worked in a factory who said during holidays the maintenance crews would pull slides apart, 1/2 moon the ways, no bluing to give the machines extra life without rebuilding. Isn't this fun to have a real conversation on here!

The only drawback with the locking gib I described was that it wasn’t interlocked with the rest of the machine. It was possible for a careless operator to engage the power longitudinal feed or the screw cutting with the lock still in place. Obviously that could lead to fire ups on the ways. This particular lathe must have been 25 to 30 years old when I repaired it but the ways were still in good condition. Maybe it had a good operator ? Having said that most machines made in that era had manual locks that weren’t interlocked.

Regards Tyrone.
 
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That is a problem Ive sen in many factories. They have a machine several operators use. Many never unlock the clamps. I rebuilt a 54" Bullard VTL and the rail had lock on both sides of the vertical column and both sides in the back of the ways where the clamp blocks were, the ways were galled up because some lazy or was never taught to unclamp the column before raising or lowering the rail. It was a on the floor rebuild and all I could do was to file off the burrs, scrape the back parallel to the front faces and leave the deep scores. I did have the electrician add a limit switch to the clamp lever that would not allow the rail move unless the lever was moved off. When I found issues I changed or fixed the issue above and beyond the original design.

Bridgeport's gib design with the one end notched gib screw was a poor design. Most other machine builders used a screw on both ends. I am not sure if the new Bridgeport's have changed the lousy design.
 
Which oil you use is also important for the lifespan of gibs IMO. Last week in my scraping I had the opportunity to put this to the test when I mated the top slide of my TOS mill to the casting by scraping the flat ways and dovetails. Initially I used a light oil to float the top slide on because I didn't really want way oil on the bare filler on the casting which I'd stripped the paint off previously. I found that I could 'feel' the scrapes when pushing it with your hand. I also found that if I left it parked in one spot for a short while I had to shove it off to get it sliding on the oil film again.

So I used a heavier oil ISO45 hydraulic oil coz I happened to have big pot of it to go in the gearboxes of this machine. It did slide a bit better but you could still feel the ways scraping when you got a significant overhang plus it was still stick-slipping just that it would take longer being parked before you had to shove it off to get it sliding.

In the end I put ISO68 way oil on it. It slides smooth as silk as you can see in my video, you can't feel the scrapes and you can run it out to at least 50% overhang and it is still sliding nicely on the heavy oil film. It doesn't stick down when parked and even with 50% overhang I put the dial on it and lifted as hard as I could and got only 0.0002" lift.

Here's the video of me moving the top slide easily and smoothly just by hand, yet wth yery little clearance in the gib.

Dropbox - y slide moving.mp4 - Simplify your life
 
George Thomas, sounds like he had a lot of time on his hands. I have used the indicator clearance test on 8" boring bar machines that have 3 - 12" wide ways and the saddle and column weighed tons. One was to use long pinch bars, porta-powers or long 4 x 4's. One can also engage the feed in opposite directions and the movement on some machines can be seen. A machine maintenance man is not going to loosen the feed screw nuts or brackets to adjust the gibs. He wrote about it, but did he actually do it? I have done it and it works. I have taught classes at new machine builders and that is the way they do it. On those bigger machines we used Vactra 4 oil too.
 
Yeah G. Thomas was a pretty well known English author in his time. Maybe 1950's - early 80's but I'm unsure of exactly when he passed away. But I know he was a very talented professional level designer/machinist and wrote from that perspective. And yes your right, the method isn't going to ever work in a production setting for maintenance. It's just another method that may or may not be useful depending on your circumstances.
 
That is a problem Ive sen in many factories. They have a machine several operators use. Many never unlock the clamps. I rebuilt a 54" Bullard VTL and the rail had lock on both sides of the vertical column and both sides in the back of the ways where the clamp blocks were, the ways were galled up because some lazy or was never taught to unclamp the column before raising or lowering the rail. It was a on the floor rebuild and all I could do was to file off the burrs, scrape the back parallel to the front faces and leave the deep scores. I did have the electrician add a limit switch to the clamp lever that would not allow the rail move unless the lever was moved off. When I found issues I changed or fixed the issue above and beyond the original design.

Bridgeport's gib design with the one end notched gib screw was a poor design. Most other machine builders used a screw on both ends. I am not sure if the new Bridgeport's have changed the lousy design.

Clamps that the operator forgot to release have caused me plenty of trouble over the years. When they’ve dragged on the back face of the column of a big planer for instance it’s not easy to put right. As you say you’ve just got to make the best of a bad job.

Regards Tyrone.
 
Bridgeport's gib design with the one end notched gib screw was a poor design. Most other machine builders used a screw on both ends. I am not sure if the new Bridgeport's have changed the lousy design.

Yup. Noticed friend’s import turret mills don’t have this on at least x axis. When I had mine apart for re-scrape I added a screw at right side as well. Also drilled and tapped the bottom of the knee so I can push out the vertical gib if it ever gets stuck.

Really, I should have just bought a new mill….

Regards,
L7
 








 
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