Gib Screws Loose? Fix Them "Nyloc" Style!!

There have been previous discussions on gib screws working their way loose and ways to improve the situation from lock nuts, to Loctite, to Teflon tape, to monofilament fishing line. I'd been using Teflon tape on mine since reading that thread, and it works fine until you have to take the screws out:



After cleaning out all the old Teflon, I decided to fix the problem once and for all with a different approach. I cross-drilled all of my gib set-screws and inserted plastic vibration resistant plugs. Here's one of the finished products before screwing it into place:



Here's what I did. First, I made a little brass fixture to hold the setscrews for cross-drilling:





After drilling the set-screws, I turned down some Delrin that I had laying around to fit snug into the cross drilled hole:



Here's a close-up of the setscrew and the Delrin insert:



I did all the setscrews, both for the cross slide AND the compound, and it works GREAT!!! No Teflon or Loctite mess. Looks stock and no external lock nuts for chips to hang up on. I've had the screws in and out at least twice so far and they're still snug. I wish I'd done this years ago!!

What did I learn and what would I do differently?

a) The set-screws are of varying degrees of hardness. About half of them were no problem... Drilled easy and deburred with a file. Some of them, however, were very hard and I had to sharpen my drill bit a couple times just to get through it. One of them was SO hard that a file wouldn't even touch it for deburr and on that one, I had to resort to a Dremel with a cut-off wheel that I'd "dressed" into a thread profile V. If I were doing this job again, I would probably spring for a carbide drill bit. I don't know if a carbide bit would survive the interrupted cut, but I'd be willing to spend the money to find out.

b) Trying to force my way through the hardest of the screws put a lot of side load on the drill bit and started to oblong the drill guide hole. If I were doing this again, I would make the holding fixture out of steel instead of brass.

c) The drill bit guide hole ended up being right on top of a thread crest and if I were doing this again, I'd be less concerned with the absolute distance from the end of the setscrew and more concerned that the hole were in a thread valley instead of a crest. I believe trying to drill straight into the top of a thread made the side load on the drill bit worse than if it would be naturally guided into a thread valley.

I may still have a screw loose, but at least it's not on my gib!!

Another approach to pesky gib setscrews that won't stay put: make longer ones and
put on locknuts.



Jim

jim rozen said:

Another approach to pesky gib setscrews that won't stay put: make longer ones and put on locknuts.

Click to expand...

Yup. Lock nuts would work great on my cross slide... But not the compound.

As a matter of fact, I was all geared up to make some lock nuts until I saw how little meat there was between the moving part of the compound and the base that it slides on.



You can see that in Jim Bs picture above... There's very little meat there. The cross slide isn't so bad, but the screws in the compound are very close to the edge. You'd have a heck of a time trying to fit a lock nut in there without hitting the stationary part because of the proximity to the edge and the way the protractor flange extends way past the face where the lock nuts would go.

It depends on the application. I was doing this on my South Bend 9" workshop lathe. Other applications that don't put the gib screw on an internal corner wouldn't have this problem.

I figured if I was going to tighten my screws, I may as well do ALL of them. HAHA!! If I didn't do that, then I'd still have a screw loose!

Bruce

Bruce: Now that gold is worth North of $1,000 an ounce I think you would be well advised to sell that gold cube in your photo and make a new one out of AL. The problem is finding anyone with enough cash to buy it. Gary P. Hansen

Silly me, I thought that was iridium.



I specifically recall putting locknuts on the crossfeed
gib screws on my old 9" machine. I had to find new
screws and point them IIRC. I also recall having to
tap at least one of them up to a larger size as it was
well and proper stripped out.

If anyone ever finds a 9" model A out there with one
number 12 gib screw, that was mine.

Good point about the compound rest! No way that locknuts
would work there.

Jim

Bruce:
The compound screws on the 405 are 10-32 not the 12's of the later 9's.
There are "Nylock"10-32 set screws available at MSC if not ENCO, already made for put lathes.

I switched to a later compound to get the larger dial or I would have them in mine.

Jim B.

It looks to me like the modified screw would work great, nice and clean. Good job FTF.

Yeah, I'm not sure what they were thinking with the 12-28 screws on the gibs. There's been some discussion in the past that South Bend really loved the oddball hardware. Some kind of conspiracy theory? I didn't know that the earlier ones used 10-32. Seems really silly that they would have switched away from 10-32 to such a less common size.

I didn't start out to do this improvement this way... As I mentioned earlier, I was all ready to start cutting some lock nuts and I was studying the cross slide to see how small I needed to turn the nut diameter down in order to clear the edge of the casting. Then I looked at the compound and realized it would be impossible.

My next "plan" was to make (from scratch) a whole set of Delrin screws that would be slightly larger than the original set screws and have some small amount of natural friction when inserted into the threaded gib holes. That's what those various threaded Delrin and iridium stubs are in my one pic. After a couple of attempts I gave up on that idea for two reasons. First being that threading even that short length of Delrin was like trying to machine spaghetti. Even with a center supporting it at the tailstock end it would still bow away from the tool in the middle. The second reason is I discovered that the difference between a screw that will not thread into a hole AT ALL and one that threads in with no resistance is some small fraction of a thousandth. I tried four or five different times and just couldn't hit that magic sweet spot. They either wouldn't go at all or were no tighter than the original screws.

Then I hit on the concept of the plastic friction insert and went from there. I did look around a little for commercially available screws, but didn't find anything in that 12-28 size. I did consider drilling and retapping to 1/4-28 but I'm not sure the compound could have handled that. I think the holes are just too close to the edge.

Since we're on the gib improvement subject... In that other thread, the concept of pinning the gib to prevent lateral motion was discussed a little:

Winfield said:

Another trick is with this sort of gib arrangement is to drill and pin the gib so there is no lateral motion of the gib relative to the setscrews.

Click to expand...

Limy Sami said:

Pinning the gibstrip as already mentioned makes all the difference.

Click to expand...

Now that I've got my anti-vibration gib screws in there and my gibs are all nice and tight, I've notice that it seems a little tighter in one direction than the other. Most noticeable on the cross slide where it's definitely a little easier to screw it in than to back it out. My assumption is that the gib is squirming around a little in there and changing position a little based on the direction of travel. Anyone else notice this? Has anyone pinned the gibs on their 9" South Bend?

-Bruce

Do you think that Nylon might work good for the gib? Other, than it might wear out quickly it seems like a nylon gib just might work well. Gary P. Hansen

Or, maybe teflon-loaded delrin?

Jim

I'm not at home to try it out, but this looks like a wonderful idea, and I'm wondering if, lacking a piece of material to turn down, it would work to use string-trimmer cord for the inserts. If so, it would be a little easier than turning down material to size. The cord comes in numerous different gauges already.

bruto, I don't think the property of the plastic material matters too much in this application, and with that said, I don't see anything wrong with using string trimmer cord. I'm no plastics expert, but all it's got to do is resist oils and provide a little bit of interference. I drilled my hole at 1/16 because I figured I was going to donate a drill bit to the cause and that's the smallest bit that you can find on the shelf just about anywhere. Can you get string trimmer cord in .062 or something close?

Gary, You're talking about replacing the entire gib with a hunk of plastic? Seems it would work OK, but out of curiosity... Why would you want to do that? Is there some reason plastic would be better than the metal original?

One point about trying something like this though... It was clear from looking at the "business side" of my original metal gib that the pressure from the screws does warp the gib a little. You can tell from the wear patterns that there's more pressure directly under where the set screws contact the gib. Makes complete sense, but I would worry that plastic wouldn't be able to provide even pressure without using some sort of back-up metal plate.

-Bruce

Bruce: I just though that maybe the same properties that make Nylon work for your screws might cause it to be a good gib. Maybe or maybe not. I might try it. Gary P. Hansen

I don't know for sure, but I'd expect between monofilament fishing line and string trimmer cord, you should be able to find just about any diameter you need. No resources where I am right now so I can't rummage in the barn, or I'd find out sooner.

Gary:
I think you are looking for a more slippery Gibb.
Perhaps you could try UHMW stickey tape on one side of the metal gibb
For instance
http://www.coleparmer.com/catalog/product_view.asp?sku=0827726
Its also available in 0.005 thickness.
Note:
UHMW tape is almost as slippery as teflon but has much higher wear resistance.

Here is a woodworing source but its 1/32 thick
http://www.hartvilletool.com/product/10871

I use it in for some wood working Jigs.

Jim B

Serendipity

Thanks to FTF and others for the how to fix loose gib screw tutorial. I was about to go into the workshop to start on the same job using locknuts when I chanced on the thread, but I'm now going to try his way. I *had* thought of commercial self-locking grub/set screws but decided I'd never buy them in the size I need. I have two types in stock in another size; one features a "keyway" with plastics insert, the other just has a dab of red goo.
I was interested to see in one of the pics that the screw apparently bears on a ball and wonder whether the gib has a hemispherical recess to match. Also, to be sound a locknut needs to bear on a true machined surface.
Which way is best theoretically? The locknut when tightened just has to alter the setting but the self-locking screw is perhaps less sensitive.

ega said:

Thanks to FTF and others for the how to fix loose gib screw tutorial. I was about to go into the workshop to start on the same job using locknuts when I chanced on the thread, but I'm now going to try his way. I *had* thought of commercial self-locking grub/set screws but decided I'd never buy them in the size I need. I have two types in stock in another size; one features a "keyway" with plastics insert, the other just has a dab of red goo.
I was interested to see in one of the pics that the screw apparently bears on a ball and wonder whether the gib has a hemispherical recess to match. Also, to be sound a locknut needs to bear on a true machined surface.
Which way is best theoretically? The locknut when tightened just has to alter the setting but the self-locking screw is perhaps less sensitive.

Click to expand...

I'm inclined to think that the self-locking screw would be easier to get right quickly. If there's play in the threads, a nut will tend to pull the screw out a little, and you'll have to compensate by overtightening it a little first, by an amount that may vary from screw to screw.

ega:
The balls are my addition. They are not SB standard. The SB screws had cone shapped points.
In a thread that appeared on the Yahoo SB lathe site several years ago it was suggested that a better approach was cupped point screws and balls.
I made the adaption.

If you are using locking nuts then you need longer screws and cupped points are more readially available.

Jim B.

Jim B:
Thanks for the additional info. On reflection, the recesses need only be conical and the ball will seat on a diameter. I may well incorporate the idea on my own lathe (not an SB, as it happens). Incidentally, I believe Myfords went from cones to round-ended screws.

bruto:
Thank you for that. As it happens, there is hardly room for locknuts on my slide and it may be a case of making a virtue of necessity but I thought it worth raising the point. Locknuts have been a fruitful source of controversy here over the years.