Gib adjustment tragedy

[zephyr9900]

A while back on the Yahoo group Greg wrote:

>There’s a [gib adjustment] technique mentioned in section 9.5.5 of
>the latest version of the manual

After crashing a toolholder against the vise (boneheaded move, don't ask) I decided it would be prudent to check the machine's tram.

I also decided this would be the time to adjust the gibs first per the new procedure, not having checked or adjusted X or Y previously.

My gibs must be on the small side (machine #128) because I was able to turn the left-hand X screw over 4 turns before it tightened up, and I then backed it off the specified 2 turns and locked the adjustment with the right-hand screw. X still rapids fine, so the adjustment must be good.

Y, on the other hand, just kept tightening. I was able to turn the front screw over 6 turns after backing off the rear screw. Unfortunately I can't adjust either screw without first moving the Y axis toward the other end of the motion (in hindsight it would have been better to totally remove the Y-axis waycovers instead of just unscrewing them from the saddle as specified...) and while moving Y away from the machine column, the gib slipped off the rear screw's washer (since it was only screwed in about two threads at this point) and the gib wedged in solid.

I cannot move the Y axis--the stepper doesn't have enough torque. I've backed off the front screw and removed the rear entirely for clearance, placed two aluminum blocks to protect the gib end and saddle and tried using a crowbar to lever the gib loose with no success. It is in there really tight.

The saddle is way toward the rear of the Y travel so there isn't a lot of room to work. The end of the gib is projecting a good 3/8" past the rear face of the saddle (the X gib is just about flush with the right face of the saddle).

Has anyone else experienced this? How did you recover?

In my previous adjustments of the Z-axis gib to minimize the head drop, its top end is also recessed way below the Z axis slide.

Thanks for any help (the mill's not going anywhere fast),

Randy

[pete from TN]

I almost was where you are right now the other day. I was reassembling my Lathemaster machine and was trying to get the ballnut thru the motor mount and had the gib in there loose to get it lined up right and not realizing what I was doing managed to get the screw thru and put the nut on it and proceeded to spin it with the cordless drill. The Y traveled maybe an inch and locked up pretty tight. Since the adjusting screw was not in there I managed to tap it out with a brass drift and hammer and it was fine. Perhaps you can temporarily remove the stepper mount and the way covers and try something similar. I would be careful with the crowbar as it is really easy to break something important that way. Can you remove either of the adjusting screws? Which way do you think the axes must travel to loosen the gib? I would make sure that tormach can provide you with another gib strip and adjustment screw if necessary and then if you manage to destroy either in getting it out you will be fine. The gib certainly can tighten things up with surprisingly little travel and I would think that the same amount of travel the other way against a fixed object would get it loose for you. How much travel is left until you hit the stop? I will try to think of something with you but maybe you can get it done this way. It is difficult to tell from the pics what is what....Good luck man...peace

[zephyr9900]

Pete, thanks for the reply. It's stuck really tight, just in front of the rear limit switch. I can't budge the Y axis in either direction using the stepper--it just cogs. I tried moving the axis rearward (the direction that would loosen the gib) while levering on the gib with the "aluminum-padded" crowbar--no dice either. There is no room to get a hammer and drift behind the gib--the rear face of the table/saddle is 5" from the column.

"y_gib" is looking down the rear edge of the table and saddle to the Y dovetail. The bit with the parallel grooves sticking out in the base of the dovetail is the end of the Y gib. The black anodized aluminum plate on top of the waycover is the "fulcrum" piece that I placed against the column for my levering attempt. You can see the dent in it...

"z_gib" is looking down at the top of the Z axis slide. The piece in the base of the dovetail down below the surface with the lube line plumbed into it is the top of the Z gib, and the round thing with the screwdriver slot, also down below the surface, is its top retention screw.

I do have both y-gib retention screws backed out completely. It's only being held in by (a whole lot of) friction at this point.

I'm going to try to reconfigure my aluminum levering plates to see if I can get a little more leverage from the crowbar. I'll also try giving the lube pump another pull and see if I can get a little more oil in there too (the Tormach has a central oiling system).

Randy

[zephyr9900]

Originally Posted by zephyr9900 After crashing a toolholder against the vise (boneheaded move, don't ask)

Actually, that's wrong. I should provide a root cause analysis report.

I had completed running a gcode program, but didn't unload it from the interface. The program was a drilling program that I had generated with a macro from my CAD program. It didn't have any toolchange callout, just preliminary setup (G17 G90 etc.) and start the spindle and coolant and run.

I changed tools to a 1/4" endmill, put another workpiece in the vise and set up to square its left-hand edge that was extending from the vise about half an inch.

The boneheaded part was that I hit cycle start rather than spindle start. The still-loaded program started running and crashed the tool first into the part (which, fortunately, was acrylic) and then stalled against the side of the vise.

I could have avoided this with any of the following:

1. Always unload a program when finished (allowing for repeat runs if I'm doing multiples of a thing).

2. Modify my drilling macro to put an "M6 T0" line at the beginning so the machine will wait for a second cycle start press. (I always type 0 in the tool window before I zero Z when drilling when I haven't mounted a drillbit as part of a multi-tool program.)

3. Pay more attention to what I press on the interface!

Randy

[pete from TN]

I was out there looking at my machine and trying to figure out how you might fix yours and the only thing I can think of to do is to remove the Y axis motor and mount allowing the ballscrew to just hang there supported by the ballnut. Then take some sort of steel square piece and kinda wedge it between the end of the gib strip sticking out the back of the Y slide and the column or a piece of aluminum in front of the column. Then take a 2x4 or some soft wood and place it across the front of the apron as close to the base as you can and carefully hit it with a mallet hopefully pushing the slide back and keeping the gib stirip where it is and loosening that axis so you can then slide it where you need it to repair the gib. Does that make any sense? Another option is if you have any woodworking pipe clamps use one on each side of the apron and from the back of the machine with some sort of wood block for protection you could do the same thing as the mallet only more controlled and allowing even pressure based on how you tighten each clamp as you go . It should only take less than an inch to get it loose I would think.... There is no way that I can think of to get the hammer and drift in there as you said so you gotta go about it from the front of the machine somehow. Overlubing the setup is also a good idea to hopefully help free it easier. Sorry you got into this mess man, hope you can get it freed without damage.... peace

[zephyr9900]

Originally Posted by pete from TN Then take a 2x4 or some soft wood and place it across the front of the apron as close to the base as you can and carefully hit it with a mallet...

*sigh* I think you're right, Pete. I'll need to disassemble the enclosure and remove the drip trays from the stand to be able to do that. I'll save that for a last resort. I'm going to see what tapping on the crowbar to hopefully set up some vibrations into the gib while I'm levering will do first. I'm still in the think twice, bang once frame of mind.

Thank you for taking the time for the analysis, and the good suggestion!

EDIT: I think moving the gib by 1/4" or so will free up the slide. That's what's giving me hope at this point.

Randy

[justgary]

Randy -

If you take the way cover off you might have enough room to use a bolt and nut as a jack to push the gib back into place. Cut a bolt just long enough to fit between the gib and the column, then thread a nut onto it and lay it into the dovetail. By unscrewing the nut with a wrench, you can jack the gib back under the saddle. If it still doesn't move, bump the stepper motor with the gib still under pressure from the jack.

Like you said, once you get it to move at all, you are home free. It's worth a try before you do something more drastic, and you don't have to take everything apart to try it.

Good luck!

- Just Gary

[Superman]

HI guys,
a little bogged down ?

Can I suggest something ?
say 1" thick piece of plate , tapped thru in the corner , hex head bolt, and either use it like a mini-jack on each gib or as a deadstop to stop the gib sliding back any more while giving the table little taps ( after leadscrew is disconnected )

You have to stop 1 of them moving as the other is moved
Hope it works for ya

Steve
OOOPS
Serves me right , should read all the posts ---ditto- as justgary said

[zephyr9900]

Just Gary and Steve, thank you for your suggestions.

The gib is free. After I removed the rear waycover completely (thanks for the nudge, Just Gary) I was able to get a better angle with the trusty crowbar. I found a big (1"-8) nut that I was able to use as a fulcrum on the "knuckle" of the crowbar, and was able to lever, through an aluminum spacer, the gib almost flush against the saddle.

Almost flush. I reinstalled the rear fixing screw, jogged the table towards me (+Y) and the gib promptly fell off the collar of the fixing screw and jammed again. But this time I knew what to do, and levered the gib until it was just under-flush in the saddle, and re-installed the fixing screw.

It is obvious to me now, that the gib adjustment system depends on both ends of the gib being below the surface of the saddle, so the collar on the fixing screw at each end sits in its circular bore in the saddle and prevents the screw from deflecting and letting the gib slide past it.

My gibs--at least the Y and likely the Z--I haven't gotten to that one yet, seem to be thin enough that to adjust them to spec causes the "thin" end to project past the saddle. That is a recipe for a repeat of this disaster! Since there seems to be enough travel on the front-side Y gib fixing screw, I might just take that gib out and shorten it by 5/8" or so to allow proper adjustments with both screw collars properly trapped in their bores.

But I'll probably wait until Monday and talk to one of the guys at Tormach. I've seen a picture of the newer gib design, and it has a notch to help trap the collar on the adjusting screws. It might be worth my while to buy new gibs.

I did first try the screw-and-nut you suggested, Just Gary, but the nut tended to twist sideways against the bearing plate that I had protecting the column, and wouldn't let me give a direct push to the gib. Steve, I'm sorry but I didnt' see your post until I was already back up from the shop having freed the gib.

The machine is powered down now and I'm ready for bed.

Randy

[Scott_M]

Hi Randy

Sorry I'm late to the party.

Another way that may have worked would have been to get a longer screw that fits the "fixing" screw hole and just turn it back in. It may have need a washer under the head. Doing it this way would also require blocking the saddle so it cannot move back any further so when you start turning in the screw the only thing that can happen is the gibb goes back in. ( Without the saddle blocked the gibb could stick to the machine and actually pull the saddle )


Scott

[justgary]

Originally Posted by Scott_M Another way that may have worked would have been to get a longer screw that fits the "fixing" screw hole and just turn it back in.

Woooooooh, I really like that idea. The simplicity...

Originally Posted by Scott_M Without the saddle blocked the gibb could stick to the machine and actually pull the saddle

I doubt that the gib could stick harder than the normal force of milling operations on the ballscrew, provided that you are pushing on the gib directly with the longer fixing screw. I don't think I'd block the saddle at all, but to be sure and not wreck something, it wouldn't hurt.

I'm glad you got it done, Randy. And you only stayed up until most hours, not all hours. Good luck with Z.

Regards,

- Just Gary

P.S. Drilling your bearing plate and grinding the end of the bolt (so that it fit into the hole in the bearing plate) would have kept the nut from walking. Sorry I didn't mention it.

[zephyr9900]

Originally Posted by Scott_M Another way that may have worked would have been to get a longer screw that fits the "fixing" screw hole and just turn it back in.

Thank you for the suggestion, Scott, but I don't think this would have worked. As it is, as soon as the collar on the stock fixing screw isn't seated in the bore in the saddle any more, it deflects and the gib pushes past it with normal machine motion. That's how I got into the mess in the first place.

The 1/2-20 screw I had tried didn't budge the gib so I'm doubtful that the small fixing screw would have had enough strength anyway.

Originally Posted by justgary Drilling your bearing plate and grinding the end of the bolt (so that it fit into the hole in the bearing plate) would have kept the nut from walking.

Just Gary, the next time I need to jack something with a bolt and nut I'll remember your suggestion. At 2 in the morning I just wanted to "git 'er done" and was probably not thinking the clearest, and probably should have waited until this morning to continue.

Randy