# Tapered Gib Adjustment Pm935



## Smudgemo (Oct 1, 2015)

Hey you guys, does anyone have instruction or advice on adjusting the X and Y gibs on my 935?  I tried a couple of times and it seems like they are either too tight where the feel is wrong, or too loose where the table will jump on a climb-cut.   

I'm sure I'm not approaching this correctly, so any help would be very appreciated.  This is probably a somewhat generic adjustment, but based on a quick google search, it sounds as if there are various flavors of tapered gibs. 
Thanks,
Ryan


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## BrentParker (Oct 1, 2015)

Most of my gib adjustment knowledge comes from bullards and various CNC equipment. Back the small end of the gib adjustment bolt out a ways, if you are sure everything is clean tighten the large side of the gib adjustment bolt till it is fairly snug, then back the large side adjustment bolt out 1/4 to1/2 a turn. Now tighten the small side bolt up. You will feel the gib move then tighten up as it contacts the bolt on the large side of the gib. Now tighten the large side bolt to verify everything is tight. There is a learning curve to it but it not that difficult. Movement should be smooth and fluent. After stopping or changing directions you shouldn't feel any catch or jump. If so its to tight. If you took them out make sure they have a good coat of the recommended lube on them before installing, and everything is clean.


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## Kernbigo (Oct 1, 2015)

sounds like back lash in the screws,like the previous reply it is not had to set gibs


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## coolidge (Oct 2, 2015)

Deleted


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## Smudgemo (Oct 2, 2015)

Okay, makes sense.  Can you clue me in on how to adjust backlash?  I recall playing around with the nut on my G0704, but I haven't had this one that far apart yet and I'd prefer to not relive the "spindle nut has reverse threads" learning experience.  

It worked very well when it was new, so something loosened or went out of whack.  Of course, the manual is more specific about not wearing jewelry or long hair...


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## Rich V (Oct 2, 2015)

Ryan
Download this Jet manual for their mill:
http://content.jettools.com/assets/manuals/690008_man_EN.pdf
It is very similar to the PM 935 and has much better details on operating and adjusting the mill.


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## Smudgemo (Oct 2, 2015)

Now I see what's going on - thanks for the link to the manual.  I took a quick look underneath and the nut matches the Jet manual, so I think I'll be all set.  It looks like I either need to make a pin spanner with long pins or get my hands in there, unless I'm missing something.  I'll let you know what happens.

Thanks,
Ryan


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## Smudgemo (Oct 2, 2015)

So I ran out to the garage to give this a try, but maybe I'm doing something wrong.  I loosened the locking bolts and tapped the adjusting nut clockwise just a bit.  The results seem to be the handles are much harder to turn, but barely any reduction in backlash.  I set up an indicator, ran the table to 0, zeroed out the leadscrew dial and found the indicator doesn't move until .080".  That number improves to maybe .075" when I tighten the adjusting nut, but the screw is way too hard to turn at that point.  The table will also still move noticeably when I push/pull it.  

In contrast, the cross travel is smooth and seems perfect.  Backlash measures just over .005" and there isn't any perceptible movement when I try to push/pull the table in that direction.  Some noise, but I can't feel the table move.  This suggests to me that I've got an issue with the nut.

Thoughts?


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## JimDawson (Oct 2, 2015)

Check your endplay in the bearings.  This sounds like there is no preload on the leadscrew support bearings.


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## Smudgemo (Oct 2, 2015)

I took another look at it, and I could see deflection at the feed nut bracket when I ran the Y so I determined the feed nut bracket had become loose and was the source of my trouble.  I pulled the screw out and moved the table far enough to get at the bolts.  All four were loose, so I snugged them up and did the reassembly.  I haven't had a chance to really dial in the nut or the gibs, but now the table moves nicely and I'm easily under .005" of backlash.  The table also won't move when I try to slide it in either direction.  Well, at least I didn't have to completely remove the table (supported it w/ a sawhorse) and I learned more about my machine.  Unfortunately I learned one of the three bearing retaining screws on the left end is stripped, but I suppose it's not a critical fix right now.  Any suggestions on that?  Female stripped threads, of course.

Thanks for the help.  It got me off my rear to figure out what was going on.

-Ryan


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## coolidge (Oct 2, 2015)

Wow I would be more than aggravated that's the kind of quality issues I have seen on the made in CHINA machines. .080 no wonder it was jumping when climb cutting. I wouldn't try to fix that stripped bracket, I'd have them replace it under warranty.


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## JimDawson (Oct 2, 2015)

Smudgemo said:


> Unfortunately I learned one of the three bearing retaining screws on the left end is stripped, but I suppose it's not a critical fix right now. Any suggestions on that? Female stripped threads, of course.




Heli-coil maybe?
.
.


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## Smudgemo (Oct 2, 2015)

I don't have any heli-coil stuff on hand, but I've got the power feed and Matt shipped the removed bearing bracket with the mill.  Any chance left and right are the same part?  Seems odd they'd look the same but not be, so maybe that's my solution.

The table was also binding as it went far-left so I loosened the gib and the nut, and it seems much better.  I'll have to play with it more to get things dialed.  I did take some cuts on a project I was working on last weekend, and holee-cow what a difference.  I think the problem snuck up on me and I assumed gibs plus lack of practice was to blame.


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## JimDawson (Oct 2, 2015)

Not sure if the bearing brackets are the same, I guess I would just try it.  Happy to hear you have things under control!


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## coolidge (Oct 2, 2015)

Jim here's a pic of the back side.


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