Gib clearance setting question, and auto oiling of ways.

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Flynth

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I know this subject has been beaten to death, but still after reading (and watching) everything I can find few questions remain for me.

I have no problem setting gibs by feel for tables and cross feeds, but I have a large-ish (just under 2 tons - 4000 pounds) knee type rectangular/box way milling machine I'm having difficulty setting gib clearance on. The machine is not a popular type (an east German Heckert FW250) so I'm making my question generic.

The questions are:
1. what is the correct clearance (the manual doesn't specify it, it only says how to increase /decrease it).
2. what method is used to determine it in detail.
3. Should there be knots/pieces of string in ways oiling holes under gibs?


I found a bunch of answers to 1 with the consensus being somewhere in the region of 1 thou, but methods of measuring it vary. The wear of the ways on this machine is a bit under a thou.

Someone said they just put a dial indicator on the column and reversing hand cranked movement direction shows them the clearance. This doesn't work on my machine. The dial indicator stays still (I'm using a 1um indicator, similar to tenths in English units).

Then there is the rocking method, essentially you grab a hold of it and you push-pull with all your strength. This indeed shows movement and I thought I was doing it correctly until I saw a youtube video where it was mentioned at the correct gib setting when you release your pulling/pushing the indicator should settle in the middle.

That's not how it works for me.

Finally the oiling. The machine has an oiling system where when a valve is pushed oil is sent to all way oiling holes connected to each other so it will go the path of least resistance(which is usually the column as the oiling hole is located the lowest). If the valve is held long enough oil eventually reaches the table, but upon release it slowly drains all the way down again. Perhaps if there was felt or string in those holes it woukd prevent it? On the other hand I don't want any material being pushed into the space between the gib and the casting. This sounds like a recipe for a jammed way. Again the manual is useless in this regard :-(
 
They make inline adjustable check valves you need for the oil system. No idea on the gibs if they seem to be good enough I would leave them as is. Practical Machinist might have an answer.
 
Gib setting is usually a compromise on used machines, as they will have more play in the middle and less at the extremes.
I usually tighten them so I can still get into the extremes, with some additional drag.
 
This how I show students how to set gibs. You need some clearance for oil On a worn machine you have to have a happy medium and adjust it where it isn't worn or if you tighten a gib where it is worn, it will bind up where it isn't worn. One should have way oil in the machine when setting the gibs. I say .0002" to .0005" per side clearance or "lost motion" Use an indicator to see the clearance. On Keiths demo I would shorten the indicator rob so you don't get multiplication of the error.

On many old machines they put wicks (like oil lamp wicks or pipe cleaners) inside the lube holes so the oil would slowly feed out or they used white felt. With modern lube systems like Lube USA, BiJur or Willy Vogel they have metering units that let small amounts of oil out at different rates to a bearing or a way. If I were you pump it until it comes out the furthest location. Better to have to much oil then no oil. In the old days we would also squirt oil on our hand and spread it out.
https://lube-global.com/english/product.php?ItemID=97
 
Richard King 2 said:
This how I show students how to set gibs. You need some clearance for oil On a worn machine you have to have a happy medium and adjust it where it isn't worn or if you tighten a gib where it is worn, it will bind up where it isn't worn. One should have way oil in the machine when setting the gibs. I say .0002" to .0005" per side clearance or "lost motion" Use an indicator to see the clearance. On Keiths demo I would shorten the indicator rob so you don't get multiplication of the error.

On many old machines they put wicks (like oil lamp wicks or pipe cleaners) inside the lube holes so the oil would slowly feed out or they used white felt. With modern lube systems like Lube USA, BiJur or Willy Vogel they have metering units that let small amounts of oil out at different rates to a bearing or a way. If I were you pump it until it comes out the furthest location. Better to have to much oil then no oil. In the old days we would also squirt oil on our hand and spread it out.
https://lube-global.com/english/product.php?ItemID=97
Click to expand...
Thank you for the answer. When you say 0.0002'' to 0.0005'' per side that's a total of 0.0004'' to 0.001'' for both sides. I assume that when measuring by rocking (like in the video) we measure the total. Please let me know if this is wrong.

I have one more question, when you set it too tight on a large-ish machine that has a fair bit of strength required to crank the handle, do you feel before it binds and you can back it off, or does it bind stuck and you now have a big problem to "unstuck it"? The fear to not get it stuck permanently stops me from testing the limits.

Edit: I rewatched Keith Rucker's video and he says there when you rock the table(or other axes I assume) it should snap back to zero. Is this just for angled ways? My Z axes which uses a rectangular way doesn't snap back. When I rock it it moves a little, but it stays as I leave it.
 
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If a person s mechanically inclined like 99% of the people who read on here the answers are easy. Over the years some people who wrote on theses forums made it sound like rocket science and it is not. The total clearance is what you need to avoid stick slip and stick slip means no oil on the ways and the oil gap is to small and the ways wear because of lack of lubrication. You are correct about leaving the gib loose and check the clearance or gap the entire length of the ways. If you tighten it to much and there is no gap, when it hits a tight area the gib will jam and then you will have a mess. This is very common on the Bridgeport knee gib. The taper gib sucks deepeer into the tapered positive side of the gib , breaks off the gib screw groove and jams so tight one has to lay thee column on it's back and cut a hole in the base so you can hammer the gib out.

This is more prone on a tapered gib then on a straight gib. On old machines that don't have hardened ways, most of the old iron American machines were hand scraped and hand 1/2 mooned once the scraping and flaking was worn down and only you saw or see it on the ends the machines started to get stick slip - meaning then high and low scraping spots were completely worn off. No place for oil to adhere to, no oil on ways and the ways or slides start to sick to each other because of friction. It's like rubbing inspection gage blocks together, they ring or stick together. Scraping averages .0004" deep and 1/2 moon flaking averages .002" deep. I teach you flake the non air side or hidden side, but many people flake the open to aid or exposed side because it looks good. Like Bridgeport. Way wipers wear and a hole .002" can allow crud to lay in the .002" flake spot or hole and crud gets under the ways.

Once a machine gets this condition you have to make sure to keep them lubricated with way oil or the iron low level welds together and you get scores. So you are correct and leave the gib loose because it is worn in most cases in the center and nothing on the ends. Move the table 12" and shake the table in and out and see what the gap is. write it with a marker or make a sketch and make a game plan. So if you set it up with .0002" per side you have a total of .0004" and a max of .001 total. In some old worn out machine you may get .010" or more. Once you get that much you have to use it that way or get it rebuilt.

Many machine shops starts to see the scraping wear off they take apart the machines and 1/2 moon the oil pockets back in to make sure the ways don't low level weld together. Oil needs places to lay in or it gets squeezed out.

Rich

PS: Another student of my scraping classes Adam Booth also has a You Tube show on how to check gib clearance I have many students who have made you tube shows on scraping: Keith Rucker, Adam Booth, Tom Lipton, Jon Brooks, Stefan Gottswinter (who lives in Germany), Jan Sverre Haugford who lives in Norway, John Saunders of NYC CNC and a few others.
 
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Also I've written about this before that as a machine like a knee mill with a long table, like a Bridgeport the table bends high in the middle and that makes the ends get stuck. Some Popeye strong guy tightens the vise on the mill using a pipe on an Allen wrench and that stretches the iron of the T-Slots and the table bows up in the center. One has to leave the oil gap bigger or it really binds up on the ends.
 
Thank you for detailed answers. I do consider myself mechanically inclined :)

Based on all I read I think I've got it right where it should be on the knee (z axis). The last thing I need is to have it stuck. My machine has no scraping marks visible anywhere, even on the very ends. So I suspect the ways were ground. They're one piece with castings so I don't think they're hardened. It seems a bit unusual to me, but it's the only East German machine I have. All Polish machines from the same time period are scraped (a lathe and a surface grinder).
 
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