Mill Gibs

[Harold_V]

Drinking make little difference as we get older...unless you over do it

Chuckle!
I'd have to agree! I'm in a constant state of confusion whether I enjoy a margarita (or scotch and water) or not.

H

[seal killer]

Harold and All--

Yeah. Well I used to enjoy all of it many years ago. Now, I drink vicariously via my wife. She has a drink about once a month.

I think I need more vicarious in my life, but one wife is enough.

--Bill

[seal killer]

Pete--

Some pictures! Is this what you are looking for in order to help me? (I have reduced the table movement generated by the cross feed screw from about 0.002" - 0.003" down to about 0.0005" as indicated by a dial indicator marked in 0.001".)

Grizzly G3616 mill...

Front cross feed adjustment screw . . .

Rear cross feed adjustment screw . . .

G3616 mill manual p44 . . .

--Bill

[pete]

Yep thanks and those will work Bill. And yeah tapered gibs. That's roughly about the same size as my mill. By the looks of your second picture, that's your gibs fat end, so tighten the fat end of the gib screw and loosen the narrow end screw to decrease clearance. That moves the gib IN. Your knee locks are on the opposite side to mine. But your knee gib "should" be on that same side and under your knee locks between the slide and the fixed vertical way surface. And if it's the same as mine, it's fat end should be at the top of the slide. Your X axis gib should be on the front of that Y axis slide and again under the X axis table locks, no idea which would be it's fat end on yours, but now you know enough to identify which is which.Your gib adjustment screws on that gib are a bit odd and I've not really seen that design before. They look like a more standard screw head with a washer under that? Mine are one piece with a heavy flat head normally called a cheeze head screw. There dimensioned to closely fit the slot in the gib at each end. Other than those screw heads, it's all pretty much the usual design so easy enough to adjust. After making your final adjustments, tighten both screws to lock those adjustments from moving. Again tight so the screws can't back out on there own, but not tight like your putting hull plates on a ship. What are your back lash numbers on X,Y?

[seal killer]

pete--

I have located the remaining gibs. My gibs work via an offset that moves the gib towards the way when the screw is turned . . . I suppose they all work in that manner. When I successfully tightened the cross feed, I did it as you mentioned, by adjusting the rear screw and locking it down with the front screw.

I do not know the X,Y backlash numbers. I am used to removing the backlash on the fly when necessary. It is fairly significant. I will measure it and report back!

pete, thank you again.

--Bill
ps Completely off topic, but I wonder whatever happened to coalminer? I always enjoyed his comments on the forum.

[rmac]

I do not know the X,Y backlash numbers. I am used to removing the backlash on the fly when necessary. It is fairly significant.

Same here with me and my despicable mill drill. Aside from the annoyance factor, though, I never saw it as something to worry about. Am I missing something important? Pete?

-- Russell Mac

[John Evans]

You back off the small end a bit ,adjust the big end ,then lock the small end. Much as I hate to say it most of the import mills have the 2 adjusters. Bridgeport on the other hand only has the adjustment on the fat end!! So the gib always has a bit of movement from the clearance between the screw shoulder and the notch in the gib.

[NP317]

Backlash can often be decreased by adjusting the 2-piece nut on the screw. I know that at least some Bridgeports have those, as do other brands.
Mill-drills not so much.
Worth looking for, anyway.
RussN

[Bill Shields]

unless you have a ball screw (or the backlash is from axial travel of the screw itself for whatever reason), that is the only way to correct it.

some ball screw setups have dual nuts that are spring loaded between the two of them....

think about it...

[pete]

As John said, the REAR screw on the gibs thin end get's backed off and the FRONT and gib fat end to be moved in to reduce excess clearance. It's the fat end of the gib moving either in or out that reduces or increases clearance. The rear screw does or can make an adjustment by moving the gibs fat end back out of the tapered slot to increase the clearance a bit if your initial adjustment made the gib a bit too tight. Overall your mostly going in on the gib to reduce any wear. And after the adjustments are finalized, both screws are tightened to lock the gib in it's new adjustment position.

Back lash is easy to measure. Move the table in one direction only with the feed screw, creep up on let's say your dials zero mark as the table moves. Once it hits that zero mark then stop. The screw and nut are then loaded on that side of the thread flanks. That zero gives you your starting measurement. Now slowly turn the table handle in the opposite direction, it should turn real easy because it's not yet moving the table, STOP! as soon as you start to feel an increase in that resistance as the back lash is taken up and the screw/nut thread flanks start getting loaded in the opposite direction as they just begin to move the table in the opposite direction. Whatever that measurement number is will be your back lash amount. That can of course vary along the screw depending on where the the screw is most worn. And yes adjusting the nuts into the lowest back lash condition possible WITHOUT being tight is imo highly desirable. (That's surmising your mill does have adjustable nuts) If it wasn't important the manufacturer's sure wouldn't add them. First it's a whole lot easier to mentally work with a few thou back lash and add/subtract your compensation than larger numbers when using the dials. It's also much more satisfying to work with a tight but well adjusted machine. If the clutch in your car slipped every time you started off in first gear would you live with it or adjust it properly until it didn't? And light climb milling cuts of a few thou deep can still be done on non ball screw equipped mills to get a far better finish cut. Large amounts of back lash makes that a lot more error prone. And if you ever forget to set all the table locks on every axis your not using, the table is free to flop around like a dying fish within the amount of back lash on the nuts that's present. Your user manual should show how the nuts are adjusted if they are in fact the adjustable type. If my mill wasn't designed with them already, I sure would have been investigating how to either partially split the factory nut or redesign and machine until I could get some type of adjustable nut design in there.

Back lash checking, adjustments etc that are above are exactly the same for a lathe as well. In some cases it might even be more important on it. Nut, gib adjustments, and that cleaning and re-lube are just standard maintenance items no matter if your user manual mentions it or not. I have a home shop because I really enjoy it. Sloppy, poorly adjusted machine tools make everything tougher and to me far less enjoyable. I'm having to work around the machines defects instead of me making the machine do what I want. A few hrs work every year or two to do what's required gets instantly paid back the first time you use the machine afterwards. If you've never once done any of this and just let the machine degrade, how do you know what the differences and pay back are going to be if your willing to invest a few hrs into doing that imo non optional maintenance? I dunno, maybe it's the industrial experience I've had even with a non machine tool environment. That standard level of maintenance isn't even considered abnormal. It goes with anything mechanical and a minimum level of expecting it to work properly every time it's used. And these are just the simple operator adjustments that take very little skill other than a sense of touch. Most decent machine tools will have adjustments on there spindle bearings as well. Again it's more involved and a bit touchy to do, but at some point those expensive bearing adjustments are going to be non optional as well. If you own any machine tool, your simply going to have to learn to do what's required unless you can afford to treat them as semi disposable.

[rmac]

First it's a whole lot easier to mentally work with a few thou back lash and add/subtract your compensation than larger numbers when using the dials.

I've never bothered to try to measure the backlash. It's not good, though, on my (despicable) mill-drill--probably in the 0.020-0.030 range. To date I've dealt with the problem by always approaching the desired position from the same direction. In fact, I've never heard anyone suggest adding/subtracting a correction like you're talking about, but I have run into situations where doing that would have made things easier. So question: Assuming that the backlash is consistent along the length of the leadscrew, how close can I expect to get when turning the dial in the "wrong" direction and adding/subtracting a correction? Seems like that might be iffy.

And light climb milling cuts of a few thou deep can still be done on non ball screw equipped mills to get a far better finish cut. Large amounts of back lash makes that a lot more error prone. And if you ever forget to set all the table locks on every axis your not using, the table is free to flop around like a dying fish within the amount of back lash on the nuts that's present.

All good stuff that I hadn't thought about. Thanks!

-- Russell Mac

[Harold_V]

Seems like that might be iffy.

You are correct. I worked in the machining industry for 26 years as a machine operator. In all those years, I never encountered anyone who worked that way. If for no other reason, it's not reasonable to assume the backlash is consistent, and it generally is not. That's due to wear of the screw.

Learning to work (properly) with backlash is critical to success, even when a machine tool is equipped with a DRO. If one does not use proper practice, it's only a matter of time before poor procedure results in scrapped parts. That's fact and can't be avoided.

And light climb milling cuts of a few thou deep can still be done on non ball screw equipped mills to get a far better finish cut. Large amounts of back lash makes that a lot more error prone.

I disagree, and that's from years of application. Excessive backlash makes no difference in the results of finish climb cuts. What makes the difference is the depth of the finish cut. Depth beyond that which can move the slide results in irregular finish and can even scrap the part by propelling the slide unreasonably. So long as the depth of cut can't propel the slide, the degree of precision isn't altered.

And if you ever forget to set all the table locks on every axis your not using, the table is free to flop around like a dying fish within the amount of back lash on the nuts that's present.

I NEVER use the locks when taking finish cuts. They simply are not required, and they create problems that can be avoided by different work habits. That's particularly true if the dimension intended to be finished has a tight tolerance. Many machine tools lose position when locks are applied, due to the method of locking that is employed (usually bearing down on the gib). What works best is to take proper depth of cut for the finish passes by climb milling, with the slides in the relaxed (unlocked) state. By working in this method and knowing when to back off the slide, step (or notch) free corners when milling pockets can be easily created.

H