Gib Strip Fettling

[Dr_GMJNParticipant @dr_gmjn]

All,

Having re-started working with my SX2P again after winter hibernation, and been reminded of how bad it feels to operate, I’ve decided to try and improve it. Medium/long term plan is to replace it with something better, but in the meantime…

Despite my best efforts at adjusting gibs and backlash on the handwheels, all axes are sticky and difficult to move smoothly without having excessive rocking about the axes. I fitted the x/y wheels with roller/thrust bearings soon after I got the mill, which improved them a lot. However, the issue seems to be with the gibs.

As noted in several other posts in the past, I’ve always had issues with poor machining in the Y-axis. Tools digging-in and poor surface quality.

This is what they look like:

X-axis

This screw appears to be bent at the end:

Y-Axis:

 

There is no cover on the rear of the Y-Axis, so swarf is free to fall into the gib-dovetail gap, and presumably get compacted until it moves the gib outwards:

The X-axis gib is covered by the table.

For some reason the ends of the Y-axis screws are flat, the X-axis are hemispherical.

In all cases, the indents in the strips are not machined very well.

Is there anything I can do to improve these gibs? I assume the difficulty in adjusting them is something to do with how the screws locate into the strip indents?

Thanks in advance.

 

 

[noel shelleyParticipant @noelshelley55608]

Just a thought, shorten the jib by an 1/8″ and silver solder an 1/8″ or 3mm ball bearing in having drilled the end to give a location. Noel

[Dr_GMJNParticipant @dr_gmjn]

Sorry,  why?

The way I read that, I’d end up with a slightly shorter gib with a ball bearing stuck on the end, in fresh air?

Is a jib the screw, and you mean solder a ball on the end?

 

[Dr_GMJN]

On 17 June 2024 at 19:46 Dr_GMJN Said:

…

For some reason the ends of the Y-axis screws are flat, the X-axis are hemispherical.

In all cases, the indents in the strips are not machined very well.

Is there anything I can do to improve these gibs? I assume the difficulty in adjusting them is something to do with how the screws locate into the strip indents?

…

Good assumption!

Unfortunately, this is an example of incompetent design and execution. OK, millions of machines work well with this type of gib strip and adjuster screws bearing on its back – but a lot don’t, and it’s not well thought-out. If the screw tip can engage what is effectively a ramp – the rounded, conical or graunched recess in the strip – then, as the strip tries to move because of drag, it’s forced into harder contact, creating more drag, and so on. Exactly this happens on the cross-slide of my Cowells 90ME – just one of its many design deficiencies.

The answer is to prevent the strip from moving relative to the member with the adjusting screws. This may not be easy to do without re-making the strip. The best solution is probably to do what GH Thomas advocated for Myford top-slides, and add one or two dowels, parallel to the adjustment screws. Second best, in this application, probably, is to make the contact face of the gib strip flat and at right angles to the screw, with a flat-ended screw. This means a cylindrical pocket in the gib. At least one pocket should fit the screw end as a dowel, to prevent the strip from moving lengthways.

Just a thought – are you setting up the gib adjustment with the feedscrew disengaged? You should be… If things get worse when the screw is replaced, it could be misaligned or bent.

Having said all that, there are still many other possible explanations for your problems. Is the gib straight and flat? Have all other possible sources of backlash been investigated? Is the problem with head location or machine geometry, etc., etc….?

 

 

 

[HopperParticipant @hopper]

Wow. Appallingly bad assembly by the factory. Absolutely woeful. It looks like some of the gib screws are sitting right on the edge of the strip, instead of the middle. One even appears to be only half on the strip. And the divots, which usually are a nice 118-degree drill point hole look like they were made by their trained rats. Cancel that. Untrained rats.

You need to have a real good look at how those gib strips and sitting and make sure they are contacting the dovetails only on the flat sides, not the narrow edges, and that the gib strip is not being forced up into the dovetail in such a way that it jacks the flat bearing surface up away from its intended partner. Also make sure there is clearance on the non-bearing flat surfaces next to the dovetails so the load is not bearing on them.

There is a good video on YouTube about doing this for an equally shoddy Chinese lathe. If I can find it again I will post you a link.

Back to the divots. You need to carefully set the gib strips in position and re-drill those divots, carefully without boogering the threads in the screw holes. They need to be drilled in situ with the gib strips clamped in position with the other existing adjuster screws. The divots need to go in far enough that you have the full diameter of the drill cut into the gib strip.

Then you need to spin the adjuster screws in the lathe and file a nice half-round dome on the end of each one. This helps locate the strip. The balled end sits in the angle of the drilled divots and hold things reasonably fast.

As KiwiBloke has said, you can follow GH Thomas and go one step further and put in little dowel pins. I did that on my Myford but did not notice any improvement over doing the above steps. And its easier to put a Myford top or cross slide in the drill press to do this than a milling table etc. But could be done with a pistol drill with care.

Also I would smooth down the bearing surface of your gib strip with a hand-held rubbing stone (slip stone). It looks like the usual rough ground Chinese machine tool finish, suspiciously like they used a belt sander to do it.

A bit of careful fettling and you should be able to get it working to an acceptable level.

[HopperParticipant @hopper]

This is the good video I referred to. Good run though on what to look for on Chinese machine tool dovetails and gibs and their common problems. Same principles whether a lathe cross slide or milling machine table.

 

 

And a bit of a write up HERE about adding dowel pin to a Myford gib. Again, general principles apply.

[Clive FosterParticipant @clivefoster55965]

I’d say you aren’t going to sort things properly without going the whole nine GHT yards.

Although the work involved may seem daunting at first sight always remember that it’s invariably faster and easier to roll up your sleeves, say “I’m gonna do a proper job.” and get stuck in than it is to fiddle and futz about trying a number of things. Usually with similar results to Jerome K Jerome’s riverine adventurers at tea time.

One day I’ll learn to take my own advice!

Which means :-

1) Clean out the casting where the gib goes ensuring that the top and side meet in a clean sharp angle. With no itty bitty divots that will prevent proper seating of the gib. In the days when I did slide re-furbs I undercut the corner slightly with a hacksaw blade to ensure the gib seated cleanly.

2) Verify that the gib is naturally straight. If necessary de-burr edges.

3) Check the clearance between gib, casting and slide. If you have more than about 20 thou / 0.5 mm, less than 10 thou / 0.2  mm would be better, ideal is sliding fit bin the gib and get something that fits. It’s never er going to work as well as it should with excess clearance. If you re going to thais much trouble you want it right, don’t you. for our purposes the material isn’t critical beyond being reasonably hard, straight and of true thickness. Gauge plate is teh gold standard but brass or decent sheet steel will work fine. Last slide I did got a bit of zintec steel for the gib because it was a sweet fit with a bout a thou of clearance.

4) Now for the important bit. You must get this right. Clamp the gib firmly and accurately in place with the top fully home in the junction between side and top of the casting. This may take some creativity. Using the slide and clamping it sideways is effective, it’s the way I did top slides, but your parts may be too large.

5) Use a centre drill through the adjuster screw holes to create clean conical holes in the gib, don’t worry about the point going right through.

6) Drill close to one end for a dowel to locate the gib. I saved the rollers out of a couple of dead needle bearings for this sort of thing.

7) Obtain some new adjuster screws. Best would be ball ended type but I’m not up to speed on any supplier today but a loose ball bearing pushed by an ordinary cup ended grub screw will be fine.

The screw pressure transmitted to the gib from the ball ends or balls acting in the conical holes tends to push it upwards onto the bottom of the dovetail slot in the main casting. Obviously a vastly more stable set-up than simply resting on the adjuster screw points as per standard. But clearly the vertical movement possible without geometric upset is very small so its most important that the gib be well seated when drilling the holes.

8) Open up the dowel hole in the gib to make a nice, shake free sliding fit.

9) Ensure everything is clean, apply plenty of way lube and re-assemble without the screw fitted.

10) Slide things backwards and forwards numerous times as you carefully adjust the screws to find the best settings. Things will settle a touch but it’s worth taking the trouble now to get things right as then they won’t need touching for ages. If ever. I never counted but I’d be unsurprised if I did approaching 60 reciprocations when doing a re-furb.

11) Re-fit screw and job done.

The one total show stopper is if the male and female dovetails are not parallel. Never seen such but it is possible on an inexpensive machine where making it at a price the customer can afford seriously limits the amount of checking that can be done so not quite right parts that still fit can make it through assembly.

Clive

[Martin ConnellyParticipant @martinconnelly55370]

I’m glad my mill has well made taper gibs. I did have some float as the adjuster was in a somewhat slack notch in the gib but a careful tickle with a file and a suitable washer added to the adjuster fixed that.

Martin C

[Michael GilliganParticipant @michaelgilligan61133]

Hopper

Thanks for finding the video, but … for the sake of those who are STILL suffering the Bug that hides embedded YouTube stuff [thanks for nothing, Mortons] … could you please add the link.

Many thanks

MichaelG.

.

”unfortunate” screenshot, by way of explanation ^^^

[JasonBModerator @jasonb]

The divot that is right on the edge of the strip appears to be for the clamp screw and not the gib screws so should not be affecting your stiff movement. Clive’s ctr drill would probably not cure this or the position of any of the other divots. Also note ctr drill should not be a loose fit in the threaded hole if you want the position right

Regarding the uncovered Y axis, mine is like that on the X3 and I have not found that a problem in 17yrs of constant use .

Can’t add much more as I’ve never had need to remove any of the gibs on the 3 mills and one lathe I have, just the occasional adjustment is all they have ever needed and I’m happy with the work that comes off them.

[Michael Gilligan]

On Michael Gilligan Said:

Hopper

Thanks for finding the video, but … for the sake of those who are STILL suffering the Bug that hides embedded YouTube stuff [thanks for nothing, Mortons] … could you please add the link.

Many thanks

MichaelG.

.

”unfortunate” screenshot, by way of explanation ^^^

Hmm. I didn’t know about that. The LINK is https://www.youtube.com/watch?v=3GFTYegrHzY

Hope that works one way or the other.

 

Pete

[Michael GilliganParticipant @michaelgilligan61133]

That link works a treat … Thanks

MichaelG.

[Dr_GMJNParticipant @dr_gmjn]

Still not sure how to proceed with this. I don’t want it to turn into a minor project because I want to get on with the steam engine I’m building.

I doubt I can get access for a hand drill to do any work that requires direct drilling through the existing holes.

So it’ll be a case of marking with a punch and drilling on the pillar drill.

That’s not going to be easy without a jig to hold the strips at an angle.

Is it essential they’re angled? I imagine it will be a difficult drilling job either way.

Assuming I end up with 4 accurately drilled countersinks, then replace all screws with ball ended and assume they will take up free play once assembled?

Happy with any improvement – it’s doubtful it’ll end up worse whatever I end up doing.

 

[Tony Pratt 1Participant @tonypratt1]

You need to use the existing parts to get the correct position on the new gib strip, yes the holes do need to be angled.

Tony

[Michael GilliganParticipant @michaelgilligan61133]

Quote:

Happy with any improvement – it’s doubtful it’ll end up worse whatever I end up doing.

 

I haven’t drawn this,  but just mentally juggled with the idea

… I’m pretty sure that your ‘best value’ approach would be to have simple countersinks in the strips and good ball-ends on the adjusting screws.

Quite happy for anyone to demonstrate that I am bonkers !

MichaelG.

[JasonBModerator @jasonb]

But would you drill your CSKs into the flat side of the gib or hold it at 60deg?

This is where two angle plates come in handy for holding things at an angle, failing that one angle plate held at an angle in the vice can work with work clamped to that.

Anyone for dimples done will a ball ended milling cutter? would seem to be a bit more forgiving of the angle as screw would find its way to the bottom if a bit off.

[JasonB]

On JasonB Said:

But would you drill your CSKs into the flat side of the gib or hold it at 60deg?

[…]

I really wouldn’t worry about that much finesse, Jason

I would concentrate on getting the correct [probably uneven] hole spacing.

… a good ball-ended screw would bed-into the surface a countersink quite quickly, so might need frequent adjustment in the early stages … but it will get better all the time.

This I consider “good value” for the effort involved.

MichaelG.

[Kiwi BlokeParticipant @kiwibloke62605]

The comments and criticisms I made in my earlier post (#736609) about the shape of ‘dimples’ in the gib strip seem to have been missed or ignored by several recent posters. Dimples with a sloping bottom are a BAD IDEA, because the interface between screw end and dimple bottom can act as a wedge, forcing the strip into harder contact with its mating dovetail, when the strip is dragged sideways. It happens!

Dowels are the answer, but a dog-ended adjustment screw, entering a cylindrical recess in the strip, is effectively a dowel, although the thinness of the strip may not allow this approach. If the dog end properly engages with the side wall of its recess in the strip, it doesn’t matter what shape its tip is, although I advocated a flat end because that will still be immune to ramp effects, even if the recess in the strip is shallower than ideal. Also, a flat end allows the most side-wall engagement.

In summary, any sideways (lengthways) force upon the strip should be reacted by an interface at right angles to the force, without inducing an ‘inwards’ force upon the strip. Conical or part-spherical dimples don’t do this! (Sorry, too early for me, and before coffee – hope this is clear enough).

Edit… Just re-read Jason’s last. If it’s not obvious, the suggested cylindrical recess in the strip should be drilled along the axis of the adjustment screw.

[Dr_GMJNParticipant @dr_gmjn]

So…the way I see it after reading the comments:

I’ve no way of machining an extra hole per axis in the machine (in order to add a dowel).

So if I understand correctly, I could possibly:

1) Use one of the existing holes per axis for a close-fitting cylindrical gib screw.

or

2) Perhaps somehow add a retaining plate to each end of the gib slots. I could do this by drilling and tapping the m/c bed on the X-axis and making a pair of plates that hold the gib axially. On the Y-axis, I could d&t the front of the machine bed to attach a retainer, but at the rear, where there’s no access for drilling, I could JB weld a fixed retainer in place.

I’d then have to drill countersunk or spherical recesses in the gibs for the screws.

I’d imagine a ball-ended mill would be the easier option, considering they’d have to be machined at an angle. The spherical sockets would look like this (3mm diameter ball-end mill, and a 2.4mm screw end radius):

 

I think the machining of the original gib strips would be pretty much impossible to

a) Mark out accurately

and

b) Machine precisely

So, realistically, I’m looking at making new gib strips. I wonder if brass would be a good choice?

Procedure I’m thinking of is:

1) Obtain gib material or correct thickness.

2) Machine edges to angles.

3) Machine to precise length of each axis slot.

4) Add retainer plates to each end of each axis as previously outlined.

5) Mark gib indent positions using a screw machined to a point.

6) Machine indents using spherical mill, with gibs held at an angle in 3D printed jig.

I have to somehow do all this without use of the mill.

It seems like a monumental pain in the ar*e, but I seem to have little choice at this point.

 

 

 

 

 

 

[HopperParticipant @hopper]

Can you get in there with a right-angle attachment on your pistol drill? Available cheap at hardware stores. Or online you can get one with a flexible drive shaft that will get in almost anywhere. And maybe a short stub drill bit?

Or can you dismantle the mill to get better access?

Your chances of machining a new gib strip to align all divots and screws perfectly are pretty slim, but you might get close enough if you are lucky. Or not.

I would not use brass. Brass and cast iron are not a great bearing combination. Cast iron and steel are. Gauge plate or similar would work.

Or just use the existing gib strips and drill some decent divots in them where the screws have already marked them. Or flip the gib strips over and drill the other side?

One possible issue with half-round divots is unless the screw is perfectly matched, you will get only point contact and once that point wears, movement. The standard conical divots at least have line contact, sort of.

I would really explore the simpler options first.

Your idea of a retaining plate or button at each end of the gib is good. I have seen that done with just a round button with a screw in the middle affixed to the end of the dovetail in a drilled and tapped hole. Stops lateral movement.

[Dr_GMJNParticipant @dr_gmjn]

Thanks Hopper.

Re getting the divots in the right place – surely it’s easier to drill new metal, than into an existing ragged one?

Id clamp the new strip in place and mark it using a modified screw.

[HopperParticipant @hopper]

If you could get a drill bit into the existing holes onto the existing gibs, that would be the quickest, easiest fix. (Not necessarily the best, but quickest to get you going without it turning into a major project, which you said you want to avoid!)

But your idea of marking a new strip with modified screw points could work too. You would need, I think, some kind of drill jig to then hold the strips at the correct angle and to guide the drill bit at the same angle as the original holes would do in situ.

Without a jig that includes a stout drill guide bushing to stop the bit wandering, the hole could easily end up in the wrong place and or at the wrong angle. But should be easy enough to make something up in the mill and then use the dots from the modified screws to get exact location via a pointed pin the same diameter as the drill.

Jig could be something as simple as a block of mild steel with a slot milled in it at the angle and correct width to hold the gib strip, plus a hole drilled down from the top surface that then acts to guide the drill bit when putting the divot into the new gib strip. Probably need a couple of clamping screws in there too somewhere.

Or maybe, you could get away with clamping the gib strip on the table at the required angle and setting the point mark directly under the mill spindle, then drop a slot drill down on it to make a flat surface before then using a centre drill and then drill bit to make the final divot. (Or ball nose cutter if you so prefer. But that would still need to start on a flat to avoid sideways deflection if milling straight into a sloped surface.)

But the more steps involved, the more likely the divot will end up not quite in the exact right place, whereas spotting through the screw holes in situ will do a pretty good job location-wise.

Up to you. Horses for courses!

[Dr_GMJNParticipant @dr_gmjn]

If I was using a ball mill, the issue with wandering would be reduced?

Also I guess if I could mark a centre dot somewhere in the mangled original holes, then aligned the mill axis with it firmly clamped at an angle, that may work with a ball mill? (In conjunction with the gib end stops).

[HopperParticipant @hopper]

I think you would need to use a regular slot drill to make a flat surface first, then use your ball end mill or stub drill to make the actual divot on a nice flat surface that is not trying to bend the cutter sideways.  That would reduce wandering.

If you can get the divots sorted, and the screw ends, you may not need the keeper plates either end of the gib strip. But they may take it that one step further. Hard to be sure until you try it!

[Dr_GMJNParticipant @dr_gmjn]

From what others have said, the spherical or tapered divots can act as ramps for the screws, and cause binding. Hence the requirement for lateral constraints.

 

Having said that, when I tackled the gibs on my ML7, I don’t recall them having lateral constraint, and they work fine.

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