# Having a problem with a gib strip



## kd5ahl (Dec 28, 2009)

:help:

I have a Micro Mark 7 x 14 lathe that I purchased over the summer.

I recently disassembled the cross slide from the saddle to lap the dovetails and noticed a funny thing about my gib strip.

See the illustration below







No matter what I try, I can't seem get the gib strip to engage any more than what is depicted.

I confess, I can't recall how the gib was engaged when I got the lathe, It has always been accurate enough for my needs until recently when it started chattering more than normal. I decided to try and remove as much play as possible - hence the lapping endeavour.

What would you recommend I do to correct the issue? I can't imagine the orientation of the gib is normal, it seems it would suffer excessive wear.

In fact I can see a wear line on the gib at the contact point, it seems to be very shallow.

Thanks in advance!


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## gadget_lover (Dec 28, 2009)

Good question. I've always assumed the gib was supposed to lie flat against the saddle's dovetail. 

If that's true, the screws are way too high, not hitting near the center of the gib.

I'll be interested in the answer. My first thought was that the gib was rotated 90 degrees.

Daniel


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## kd5ahl (Dec 28, 2009)

yeah, I thought they should lay flat too. that's why I'm like, "whoa, better get some opinion on this"

my drawing isn't perfect, I just whipped it up but it illustrates what's going on.
I imagine the little divots the screws are supposed to go in aren't in the right place. It just seems the screws are torquing the gib around out of parallel.


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## gadget_lover (Dec 28, 2009)

Is there any chance that it was put in upside down, so the divits are too high?

Daniel


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## KowShak (Dec 28, 2009)

Depending on how accurate (or inaccurate) your drawing is, it looks like the gib may just want taking out and swapping end to end. Is that something that could happen or did you put it back together the only way it would go together?


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## kd5ahl (Dec 28, 2009)

@ Gadget_Lover - Don't think so, I'll check.
@ KowShak - I'll check that too.

I _HAVE_ had the thing apart once before, and conceivably flipped it end for end.

Good points, I'll check when I get 'ome.

UPDATE - Gib is not upside down, and not rotated 18 degrees (front / back)

After looking closely, the actual amount of "racking" is darned close to the drawing I made. I've got some photos to upload to show you what's going on.

I'm at a loss with what to do, I fiddled with it for more than an hour it seems, and still have the same issue. If I try to force the gib to engage more, it's too tight to use.


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## precisionworks (Dec 28, 2009)

> I'm at a loss with what to do


It looks like making a new one is the best option. I'll grind one if you can provide exact angles & thickness dimensions, or you can grind one with a belt sander & some method of holding onto the square stock (that gets reshaped). It can also be done on a mill, starting with stock that is over length for clamping.


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## kd5ahl (Dec 28, 2009)

I have some other stuff I want to oreder from LMS and they have replacement gibs for like $4. i think I'll just grab one (or 2) and go from there.

I found the photo below on http://start-model-engineering.co.uk/begin-with-bogs/begin-with-bogs/preparing-your-mini-lathe/ and it shows a slightly different model lathe but with a gib strip that is installed how I expected mine to fit.






I'll keep you guys posted. Thanks for the responses!


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## 65535 (Dec 29, 2009)

You can drop screws in threaded holes in the top of the cross slide to set the gib flat against the saddle. 

My assumption is the gib is just undersized for the application.


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## kd5ahl (Dec 29, 2009)

Gib does look undersized based on my previous post's picture. I have a replacement gib in my LMS order on it's way.

If it exhibits the same problem, I'll probably ask if someone here can machine one that fits more closely.

Here's an actual photo of the gib situation:


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## gadget_lover (Dec 29, 2009)

It looks like the right side is bing forced to line up against a flat set screw end. Is the screw flat or pointed?

For some reason, I'd think that making the right side of the gib more perpendicular with relation to the base might fix your problem. A few strokes with a file might be enough to create flats where the screws hit.

Daniel


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## kd5ahl (Dec 29, 2009)

The screws are flat on the tips.

Here's the part page from LMS:

http://www.littlemachineshop.com/products/product_view.php?ProductID=1568&category=






Are you saying a rounded tip might allow the gib to pivot around the tip to line up better with the dovetail?

EDIT: Never mind, I see you are talking about modifying the gib, not the screw.

Personally, I'd like to get setscrews with a nylon patch so that I don't have to futz with the locknut, so if screw replacement is warranted, I'm game. With the amount of vibration on the lathe, would those "nylock setscrews" maintain their setting?


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## 65535 (Dec 29, 2009)

NyLock should keep it's grip, that's what they're designed for.

Milling a flat on the gib where the screw(s) meet it is probably the best fix. Realistically screws should meet the face perpendicularly not some weird gib angle.


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## kd5ahl (Dec 29, 2009)

Makes sense.

There is a divot in the gib which is where the screws touch. they aren't very deep, say, maybe 1/16 of an inch.

I might just try making a gib from delrin tomorrow. Movie night tonite!

I have access to a wood shop, and I'm pretty sure I can cut up a delrin gib on the table saw. I may try making a gib with a flat side for the screws to bear on.


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## gadget_lover (Dec 29, 2009)

I was under the impression that my screws were pointed. That lets the gib rotate to press fully against the dovetail. Now I have to go look. 

Daniel


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## StrikerDown (Dec 29, 2009)

Have you taken the gib out to see if it already has flats on it for the screws to bear on?


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## gadget_lover (Dec 30, 2009)

I looked at mine.

The screws are like the ones from LMS. Flat on the end.

The gib, however, fills the void between the saddle and cross-slide completely. 

Since I had the screws loose, I took the opportunity to readjust them. On a lark, I put an indicator on the tool post and indicated against the saddle. I was able to jiggle the indicator a full .001 by grasping the crossslide at both ends and pulling. An extra 1/8 turn on two of the screws and I get no measurable movement.

Thanks for making me check.

Daniel


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## kd5ahl (Dec 30, 2009)

were you pulling up on the slide? If so, you were replicating what I've got going on.

lots of chatter on facing cuts because the cross slide is tilting up on the side with the gib as the cutting force pushes the tool down.

Seems it would be a better design if the gib were on the left side of the cross slide.

I have to run for work, but I have some pictures of what I did last night to my gib that helped some. I'll upload them when I get to the orifice.


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## gadget_lover (Dec 30, 2009)

ooops. I was looking at the top-slide, and you are talking about the cross-slide. 

I did not pull out the gib on my cross-slide. I did find there was a lot of play when I lifted it. I simply did the same.. indicator between saddle and cross-slide, then tighten till there is very little (if any) movement. Then grease time again. 

Both of my gibs were too loose.

Daniel


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## kd5ahl (Dec 30, 2009)

ok, pix time.






Divot on Gib Strip






Slots filed into the gib for the screws to seat against






Depth of slot






The dastardly implement






The new fit

The gib is _*MUCH*_ more sensitive to adjustment now that more of the surface is bearing against the dovetail. However the right side of the cross slide still lifts up a bit if I have the cross slide cranked towards the centerline of the lathe. I haven't tried to do a final adjustment yet, since I still want to lap the cross slide dovetail surfaces using mothers polish.

One concern I have is that I can imagine under cutting loads the setscrew could slide in the slot allowing the right side of the cross slide to lift up.

I imagine an unmodified gib would tend to cause the setscrews to bind tighter into the gib under cutting loads.


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## tkelley (Jan 9, 2010)

I be been around lathes over 30 years and have never used one that had straight gibs like this. I'd have to think it is just a poor design to start with. 
They should be tapered (with gib pocket having matching taper) and actual tensioning adjustment be done by moving gib in the X axis to tighten the "fit". The gib (if it were tapered would need capture bolts at each end to lock the tapered gib in place. (these are also used to jack the gib in or out during adjustment. 

With what this lathe is fitted with..., the notches are probably the best solution...

You might get better, smoother performance by making a new gib that is as big as possible and still able to be inserted. The extra strength from the new thicker gib will probably spread out the tension over a wider area (other than just under the adjustment bolts).

Look at it this way..., if you can increase the thickness of the gib by 20%, you will have 20% more stiffness in the gib which would help spread out tensioning bolt pressure over (possibly) the entire gib length instead of just the tension bolt zones of the gib.

Depending on the performance..., This is just an option if the notches on the old gib didn't allow the gib tension to be set tight enough to hold but still not bind up. Another option might be to add more tensioning screws to help spread out the tension along the gib without getting any region too tight.


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## mdocod (Jan 10, 2010)

Looks like you already tried what I was going to suggest, which is cutting out some flats for those set screws to land on....

Seems odd that this would happen, only reason I can come up with is that the original placement of the tension setting set screws was a bit higher than ideal, with proper flats for the screws to engage, and the position correct, this style gib should work without much trouble.


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