Adjusting Gibs.

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AllenH59
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Adjusting Gibs.

Post by AllenH59 » Sun Feb 21, 2021 10:26 pm

Could one of you guys who made a living running manual machines, please give a good explanation of your preferred technique for gib adjustment? I want to do this on my mill and my lathe, and of course I want them as good as I can do. Thanks.

Harold_V
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Re: Adjusting Gibs.

Post by Harold_V » Mon Feb 22, 2021 2:35 am

My opinion only, not to be taken as the way it should be done.
Most slides have uneven wear, being tight at the ends of travel and sloppy in the center. In order for the machine to not lose travel, my policy is to set the gib so it's snug at the extremes of travel. That means that you feel distinct drag when you're at the ends of travel, but the handle can still be turned without too much energy.

It should not require one to use more than one hand to turn any handle. If that's required, the gib is too tight. It should also not be so free that the handle spins effortlessly. If the gib is too loose, you'll experience shifting of the slide when it is reversed.

One critical setting is the knee. It should never be loose, and is highly unlikely to have severe wear, although I suspect if the machine is old enough and had poor maintenance it could be possible. For the knee, the gib should not be so snug as to suspend the knee. It should always settle of its own weight, but not be sloppy. A loose gib on the knee offers the risk of knee sag, which is not good. When I adjust a knee, I usually tighten the gib until the knee must be powered down, then back off the gib until it will settle of its own weight.

Don't know that this will help.

H
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tornitore45
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Re: Adjusting Gibs.

Post by tornitore45 » Mon Feb 22, 2021 8:42 am

Talking about movement after reversal.
My lathe has that problem on the carriage, not the cross-slide. After a cut toward the HS it will recut a couple of thousands on the way back.
The carriage has no gib in front since it sits on the V way
The back way is flat. It used to have a fixed, non adjustable plate underneath to prevent lifting but it was soo loose that after installing the rear tool post there was objectionable lift so I modified it by adding a tapered gib adjustable in the usual manner with a longitudinal screw.

Never correlated the tool movement with the gib and can not see any mechanism for the carriage to move on the Y axes while reversing the X axis motion, but will experiment.

One observation is that the carriage movement seems to depends on the previous depth of cut and the king of material. Less noticeable on harder stock and deeper cuts. Does not compute at all.
Mauro Gaetano
in Austin TX

Harold_V
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Re: Adjusting Gibs.

Post by Harold_V » Mon Feb 22, 2021 3:40 pm

tornitore45 wrote:
Mon Feb 22, 2021 8:42 am
Does not compute at all.
Actually it does. The condition you report is most likely due to tool pressure and deflection. Very common on light duty machines, not so much on large machines. I do not recall what lathe you have, but I suspect it's not an industrial rated machine. Makes little difference if it's Chinese or domestic. Light duty lathes all suffer that condition, it's just a matter of degree.

This condition is the reason one should follow a strict regime when attempting to achieve size when turning. My practice is to take three successive equal depth cuts, so loading of the tool is consistent. The first cut is to establish tool load, with a measurement taken after the cut. The second cut is half the remaining material. Final cut is taken after measurement of the second cut. By then, the tool loading should be consistent, so the last cut dialed should be the equal of the previous cut, but minor corrections are taken if necessary. Make sense?

In regards to the condition you report, you may notice a difference when using ultra sharp tools and light cuts as opposed to less sharp and large contact area tools. If so, it should confirm my hunch.

H

Edit:
Place an indicator against the carriage of your lathe, then reverse direction a time or two. If the carriage is shifting, the movement should be reflected by the indicator. It is possible that it is shifting, by the way. The pressure on the carriage from the rack and gear may be the cause. The carriage may be riding up on the V way. Place an indicator on the face of the apron as well as the top.
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tornitore45
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Re: Adjusting Gibs.

Post by tornitore45 » Mon Feb 22, 2021 5:08 pm

Thanks for the tips.
I will try to diagnose the cause with the Indicator. Possibly move the carriage manually, under power feed or with the half nut to see if the point of application of the moving force has an impact. So far I have limited myself to observe and complain without taking the time to diagnose the problem.

I use the 3 equal cuts method and have success in hitting the size. My 290 pound Chinese 9 x 10 will never be a tool room quality but strangely enough it has increased accuracy and reduced scrap as it ages, or may be is the operator, who knows.
Mauro Gaetano
in Austin TX

AllenH59
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Re: Adjusting Gibs.

Post by AllenH59 » Mon Feb 22, 2021 11:05 pm

tornitore45 wrote:
Mon Feb 22, 2021 5:08 pm
Thanks for the tips.
I will try to diagnose the cause with the Indicator. Possibly move the carriage manually, under power feed or with the half nut to see if the point of application of the moving force has an impact. So far I have limited myself to observe and complain without taking the time to diagnose the problem.

I use the 3 equal cuts method and have success in hitting the size. My 290 pound Chinese 9 x 10 will never be a tool room quality but strangely enough it has increased accuracy and reduced scrap as it ages, or may be is the operator, who knows.
I bought a lathe 20 years ago, after not have played with one since grade 10, about 24 years before that. It is a cheapish Indian made lathe, but it is 16x48, and I bought it new. I am still learning. The first problem was to get it to hit a size. I wanted to sneak up on a size, making smaller and smaller cuts. That did not work, I got to a point where I had .005 left, and too much spring in the lathe to take a cut that small. Right now my compound slide on the lathe, and cross slide, both of which have gibs, are in need of being adjusted. I have played with , and got them somewhat better but not to my satisfaction. The compound wiggles a bit if I try to cut a taper with it, leaving a crooked surface. I watched in awe the other day as a guy on youtube who wanted a #3 morse taper, and just cut it, and on the first try it was tight in his tail stock. Both of these gibs have 4 Allen Head screws for adjustment. One of these days I will get serious, and put some time in trying to get that correct. I just hoped there was a miracle cure. I have turned a lot of stuff on it, and lately have been making a little money at it. I bought a much better chuck, that made things better also.

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Rich_Carlstedt
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Re: Adjusting Gibs.

Post by Rich_Carlstedt » Tue Feb 23, 2021 12:03 am

Harold's comments are +1
Let me add a few more
There are generally two methods to adjust Gibs.
Set Screw clamping ( right angle to the flat Gib Surface ) and Tapered Gib screw adjustment ( Parallel to the Gib)
Both methods have a potential issue with lateral movement ...so always use your finger or a indicator on the gib when you move the slide,
You never want any movement because if the gib moves, it changes clearance values .
Set Screw Gibs
On some Set Screw Gibs, the "Pocket" for the screw are C'Bored too wide and the screws slide in the pocket . They should match the Screws OD . To prevent movement , some Gibs will have a slot milled vertically on the jib and a dog point Setscrew used there , Or , one setscrew will have a "V" point and the gib have a small matching "V" in it , so the screw both adjusts clearances and retains lateral movement.
Taper Gibs
These are very sensitive to linear movement and good ones have a stop screw at the far end so both ends have counter-moving screws. If your Tapered Gib does not have a stop screw and uses just a slot in the gib for the adjusting screw, make sure the head of the screw fits very snugly in the slot. ***
Hope this helps
Rich

** For example, you may want to put silver solder on the head and file it to thickness of the Gib slot

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tornitore45
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Re: Adjusting Gibs.

Post by tornitore45 » Tue Feb 23, 2021 7:18 am

Good info on gibs stabilization, fairly easy to add.
Mauro Gaetano
in Austin TX

curtis cutter
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Re: Adjusting Gibs.

Post by curtis cutter » Tue Feb 23, 2021 8:47 am

Before making adjustments would it be wise to disassemble and clean on older machine?
Gregg
Just let go of it, it will eventually unplug itself.

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tornitore45
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Re: Adjusting Gibs.

Post by tornitore45 » Tue Feb 23, 2021 10:27 am

Cleaning is always a good thing but I never found anything but oil around the gibs. They are usually in a place where crud does not accumulate leaving no more than a oil film gap.
Mauro Gaetano
in Austin TX

Harold_V
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Re: Adjusting Gibs.

Post by Harold_V » Tue Feb 23, 2021 3:29 pm

What Mauro said, although if the machine has not been wiped and oiled on a regular basis, the film may be what results in a black lapping compound, thanks to the accumulated worn metal. In such a case, a good cleaning would certainly be in order. Alternately, repeated wiping and oiling will eventually expel the crud.

H
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FKreider
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Re: Adjusting Gibs.

Post by FKreider » Tue Feb 23, 2021 10:27 pm

Harold_V wrote:
Mon Feb 22, 2021 3:40 pm

This condition is the reason one should follow a strict regime when attempting to achieve size when turning. My practice is to take three successive equal depth cuts, so loading of the tool is consistent. The first cut is to establish tool load, with a measurement taken after the cut. The second cut is half the remaining material. Final cut is taken after measurement of the second cut. By then, the tool loading should be consistent, so the last cut dialed should be the equal of the previous cut, but minor corrections are taken if necessary. Make sense?
This is basically the exact method that I use and it produces extremely repeatable and precise of results.
-Frank K.

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