SC3 gib strips

[Martin Shaw 1Participant @martinshaw1]

I recently purchased an SC3 from Arc which I've had a few problems with. To be wholly fair to Arc they have been most helpful and accommodating in overcoming the issues and I have absolutely no complaint about them. Despite following their recent advice I'm still having difficulty with the cross slide gib strip, and I'm lost as to where I go now.

If the cross slide is sitting with it's left hand dovetail hard against the saddle dovetail, and the brass gib strip is also hard against the saddle gib strip, how much clearance would you expect between the gib strip and the cross slide dovetail? On mine it's about 1.0mm, maybe a tad more, this maybe right but I'm struggling to get the whole assembly tight enough to make the tool rigid whilst retaining sensible movement of the cross slide fed screw. Any thoughts?

Regards

martin

[Martin Shaw 1Participant @martinshaw1]

[Nick_GParticipant @nick_g]

Posted by Martin Shaw 1 on 29/07/2017 22:24:03:

On mine it's about 1.0mm, maybe a tad more, this maybe right but I'm struggling to get the whole assembly tight enough to make the tool rigid whilst retaining sensible movement of the cross slide fed screw. Any thoughts?

Regards

martin

.

Hi Martin,

Can you please take a photo and post it of the area that has this 1mm ish gap.

Nick

[Martin Shaw 1Participant @martinshaw1]

Nick

When I can work out how to do that I will.

Martin

[Martin Shaw 1Participant @martinshaw1]

Here we go

[LathejackParticipant @lathejack]

The gap down the side of the gib strip bearing against the gib adjusting screws shouldn't cause any problems, as long as the bearing surface of the gib strip fits snuggly against the cross slide dovetail.

But on your first photo, gib bottom left hand corner, the bottom edge of the gib strip appears to be fouling the root of the crosslide dovetail. The relief groove in the bottom of your crosslide dovetail seems a bit shallow, this together with the sharp bottom edge of the gib strip maybe preventing the gib from seating correctly on the bearing surface of the dovetail.

If you remove the sharp edge from along the gib and leave a slight flat there to give some clearence between it and the root of the dovetail it might improve things.

Edited By Lathejack on 29/07/2017 23:36:05

Edited By Lathejack on 29/07/2017 23:38:48

[Neil WyattModerator @neilwyatt]

In short, the size of the gap doesn't matter within reason, but about 1mm (or a bit more) would be normal on any lathe. It's how well you adjust the gibs that matters. I find doing up each screw until the slide virtually locks, then backing off a little works for me, but it is matter of developing a 'feel' for what is right. Don't forget to lubricate the slide, if you haven't, loosen it, wind it right out to one end and then the other. Get plenty of machine oil of the moving surfaces (confession I use my neat cutting oil to lube the slides and in 18 years I haven't had significant wear).

<edit> difficulty in adjusting often means that ONE of the screws is too tight, not enough to lock the slide when the others are loose, but too much when the others are nipped up. Also, use an allen key to stop the screws rotating when you tighten the lock nuts. Always tighten the lock nuts before deciding whether a screw is properly adjusted. Take time and all will be OK.

Neil

Edited By Neil Wyatt on 30/07/2017 08:14:55

[Michael HornerParticipant @michaelhorner54327]

Hi Martin

I fitted the ARC after market gib strips to my 20 year Chester mini lathe. They improved the feel of the cross slide but I was still getting problems which I put down to the gib strips rotating (original ones did to). I do hammer my lathe. To try an improve things I shimmed up the gib strip to try and prevent this and to a point it has worked. If I get a dig in I can still see the tool post move. I just used some shim strip I had around. My thoughts on this are because the adjustment screws now touch lower on the gib stip it is harder for it to try and rotate.

HTH

Michael.

[HOWARDTParticipant @howardt]

I have the same problem and it is on my todo list. Under cutting were the tool point is further from the cross slide, such as a boring bar, the slide seems to rotate bringing the tool tip down. I have stripped the slide and added locking screws to the gib but like you feel there is too much clearance between the gib and slide this relying on the adjusting screws to prevent the slide from lifting.

Some months ago I changed the keep strips to taper gibs under the main slide. These stiffened that up, I found the keep strips were bent when I removed them. I still have further improvements to make in that area but needed to use the lathe to prove that the change was worthwhile.

Perhaps today I will look further. Will keep you informed of my changes.

[SillyOldDufferModerator @sillyoldduffer]

My mini-lathe gib strips had three small pits on one face. They engage with the tips of the gib screws to stop the gib sliding and rotating. Is it possible your slide has been re-assembled without the screws locating into these holes correctly? Don't ask how I know about getting this wrong. Blush.

It took me a while to get a feel for gib adjustment. There's a fine line between too tight and too loose, and of course, all the gib screws have to be adjusted to keep the gib straight in the dovetail with equal pressure along the slide.

If you've had the lathe apart and not spotted anything wrong with the internals (bent, burred, gib size wrong etc), it's probably an assembly/adjustment issue.

Dave

[HOWARDTParticipant @howardt]

I managed to get the gib on the head slide on my SX2 the wrong way round and it slid down every time I unlocked it.

[Martin Shaw 1Participant @martinshaw1]

Gents

Thanks for all the thoughts, it seems I'm not the only one who has this problem. Interestingly the 35 year old Cowells ME90 I also have works as sweetly and as solidly as you might wish. I appreciate it's unfair to draw the comparison, but never the less I have.

Lathejack's suggestion about the lack of clearance in the root of the dovetail is an interesting one and fairly easily checked and altered.

I found that I was also having a problem with the gib rotating and at Arc's suggestion repositioned the holes for the adjustment screws closer to the edge. Apparently they did this in the days when they prepared machines, and despite entreaties to Sieg, the Chinese didn't want to change their manufacturing process. It certainly improved things, but obviously not enough.

Neil

I can probably take the saddle assembly and compound slide apart with my eyes shut, it's been on and off that often, and I have your book on the subject, which by the way I found invaluable before committing serious money, but this is I think more than just a 'feel', or lubrication, there is something not right, or am I expecting too much for the cost of the machine.

Regards

Martin

[Neil WyattModerator @neilwyatt]

When I made my own brass gib for a t-slotted cross slide, I had rotation problems, until I made the locating 'holes/dimples' deeper (I actually machined out u-shaped recesses). This totally solved my problem. I can say I haven't had this issue with the original fit steel gib on the supplied cross slide.

Your lathe has the brass gibs fitted and should be smooth as the Cowells – at least pretty much so.

Looking closely at your picture, the gib may be rotating, perhaps you need to deepen your dimples as well?

Neil

[Martin Shaw 1Participant @martinshaw1]

Neil

Since my last post I have taken the top slide off, and holding the gib into the dovetail I can rotate it on its corner in the root of the dovetail, and not just a bawhair either. Unless I totally misunderstand the relationship between the gib and the dovetail it should be nearly a close fit on both sides, should it not? The gib screws have been changed to cone point and into brass form a pocket, whether this is deep enough I don't know. Tomorrow I'll strip the cross slide and see if that's the same.

Regards

Martin

[Neil WyattModerator @neilwyatt]

Posted by Martin Shaw 1 on 30/07/2017 18:18:41:

Neil

Since my last post I have taken the top slide off, and holding the gib into the dovetail I can rotate it on its corner in the root of the dovetail, and not just a bawhair either. Unless I totally misunderstand the relationship between the gib and the dovetail it should be nearly a close fit on both sides, should it not? The gib screws have been changed to cone point and into brass form a pocket, whether this is deep enough I don't know. Tomorrow I'll strip the cross slide and see if that's the same.

Regards

Martin

It sounds like you have swapped out the original gibs for the brass ones which come with cone point screws? If so, compare the new and old gibs.

If you think about it, once the screws are pressing on the gib, the outside of the gib won't be touching the metal of the slide, so the size of the gap is effectively immaterial, as even a tiny amount of rotation is enough to upset adjustment.

The gap on my original cross slide is about 1mm, but the TOP of the gib contacts the underside of the slide, which stops it rotating.

The gap on my home made slide with a brass gib is about 1.5mm. The gib does not touch the underside of the slide, and this may be why I had to deepen the pockets so they go past half the depth of the gib. I have a theory about ideal depth, but the key point was that once I went past a certain point the gib worked 100%.

If you don't want to drill the dimples any deeper, you could try fitting a shim along the top of the gib.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Martin Shaw 1 on 30/07/2017 18:18:41:

…

The gib screws have been changed to cone point and into brass form a pocket, whether this is deep enough I don't know.

…

Martin

Apologies if I'm misreading your sentence Martin, but do you mean that the gib didn't have pre-drilled pockets, and that the cone points made their own by being tightened up?

That could cause the problem. Without existing holes, the gib may have been tilted out of position as the screws bit into it, also leaving the dimples so formed misaligned. The gib screws are meant to push the gib flat against the side of the dovetail, not free to twist it or push it into the notch.

If that is the problem then drilling the holes deeper and straighter should fix it. Fingers crossed it's that easy!

Dave

[Martin Shaw 1Participant @martinshaw1]

Neil

I think we might be slightly at cross purposes. Looking from the front the two adjacent surfaces of the gib strip, left and bottom, should be in close contact with the inside of the dovetail and the top surface of the saddle. The right hand side obviously will be at a distance form the cross slide by virtue of the adjustment screws and the top doesn't want to contact the underside of the slide so it doesn't try to lift it. It is therefore I feel axiomatic that the fit of the gib strip into the dovetail is as close as needed without binding and cannot possibly be achieved if the corner of the strip bottoms out. This does assume that the angle of both the gib strip and dovetail are the same, are they?

You have pointed out other things I can look at as well so thank you for that.

Regards

Martin

[Douglas JohnstonParticipant @douglasjohnston98463]

I had a problem with the gib strip on my Speed 10 lathe where the strip tended to move vertically under adjustment, despite the screws fitting into a dimple on the strip. I then found a source (can't remember where I saw it now ) which explained how to avoid this problem.

​ The solution was to very carefully drill and ream two holes through the slide and gib (with the slide removed from the lathe and the gib clamped in place ), one hole near each end of the gib. A close, but not binding, pin was then fitted through slide and gib so that the gib was perfectly located while being adjusted.

After doing this on a number of slides on lathe and mill I have never had a repeat of the dodgy gib problem and adjustment is very smooth.

Doug

[Neil WyattModerator @neilwyatt]

The screws should hold the gib strip in its vertical position, it doesn't need to be right into the corner, although that shouldn't do any harm if the corner of the strip is rounded/bevelled off so it doesn't bind.

Not many images of real end-on gib strips on the web! Those I found seem to be held by their screws and not forced into the corner.

This example (on an Emco by the look of it), doesn't touch at top or bottom.

Looks like this one has had turcite strips fitted, but the gib (which might be a taper type) doesn't contact them.

But this one does!

I found THIS where someone cured this problem by putting better points on their screws. There are two photos and you can see that in the 'after' one the gib is not contacting at top or bottom.

If I recall correctly, George Thomas fitted pins to the gibs on his Myford S7 and reported a significant improvement.

Interestingly, it seems some other mini-lathe owners have had the issue and solved it with deeper holes for the screws. Also, its clear that there are lots of different detail arrangements for the machining of the dovetails, although not everyone means the same machine when they say 'mini lathe'.

Neil

Edited By Neil Wyatt on 30/07/2017 20:53:04

[John OlsenParticipant @johnolsen79199]

If you look at Martins original pictures, the gibb has definitely got an angular gap between itself and the dovetail, so I think Lathejacks suggestion is right, the tip is fouling in the corner.

Reading some of the rest of the posts, it is not desirable for the gibb strip to bear against the surface below. The downwards pressure from the contact between the dovetail and the gibb should be transferred out to the actual slide through the screws. If the gibb is bearing against the surface below, then the slide may not be. The George Thomas modification was intended to prevent this happening.

I think that gibb strip would work better if it was thinner, which could be effected by deepening the dimples that the points of the screws work in so that their action is much closer to the other side of the gibb. But the first thing to do is to make sure the point on the left side is not fouling.

Kohn

[HopperParticipant @hopper]

Posted by Martin Shaw 1 on 29/07/2017 22:48:25:

Here we go

That's the thickest gib strip I have ever seen. It appears to be wider than it is tall. No wonder some users referred to above have found the strips tend to rotate. Really bad geometry there. I think Neil's suggestion above about drilling the holes for the screws in the gib strip deeper might be the answer. I would drill them through to within about 3mm of breaking out the other side. It looks like the gib screws are long enough to accommodate this.

This would put the pressure point in close to the bearing surface and cut the tendency to rotate. If you look at most lathes of reasonable to good quality, (eg Myford, Drummond, South Bend, Boxford etc etc etc) the gib strips are a flat profile, say 3/16" thick by 1/2" wide and so forth. They don't have these kinds of problems so you might be well to copy them. If you Google gib strip images for the above lathes you will see what I mean.

The below sketch from an old thread on similar matters shows the more usual proportions of a traditional gib strip and how to set it up.

Edited By Hopper on 31/07/2017 06:22:25

[Martin Shaw 1Participant @martinshaw1]

After all the useful posts I have been playing around. I managed to mill a fraction off the tip of the gib which made it fit snugly into the dovetail, but somewhat surprisingly if I reversed the gib it fitted perfectly which suggest it isn't a parallelogram in section. Either way nipping up the cone point screws did what was needed, the gib sat exactly where you would expect it to.

However I still couldn't get a satisfactory compromise where rigidity was maintained but ease of operation enabled, so I tried deepening the points in the gib, bad mistake, now the adjustment tipped the gib out of alignment. I think that this a partly due to drilling into a surface at an angle and on reflection it is the pointed dimple surrounding the cone point that maintains the correct angle to the dovetail. The brass gib now had so many wrong holes in it that the scrap bin beckoned. I reverted to the original steel gib but the other way around. This worked as described above so I thought maybe a centre punch would be adequate to maintain alignment of the gib, it does but by no means ideally and I have come to the conclusion that you should do no more than screw the adjusters tight to form a dimple and then adjust for operation.

The net outcome of this is that I will obtain a replacement brass gib from Arc, BTW you do have to polish out the machining marks to have a chance, mean while the steel one will do, but the optimum is not really satisfactory, rigidity is compromised by operability. I think the truth of the matter is that the manufacturing tolerances are sufficiently lax for the odd rogue to slip through, maybe I really am expecting too much. Thanks though for all the help.

Regards

Martin

[Danny M2ZParticipant @dannym2z]

One tip that I learned from the Minilathe user group many years ago was to slip a small ball bearing (about 2mm) into the dimples on the gibs and use cup point grub screws as the adjusters.

Along with gently lapping the bearing surfaces with a fine diamond file and dressing the (warped) gibs flat this really improved the cross slide/ top slide smoothness and rigidity. Also the brittle iron saddle gibs only lasted a few months before they cracked but the brass replacements have lasted ten years.

* Danny M *

[SillyOldDufferModerator @sillyoldduffer]

It's interesting that not all mini-lathe owners encounter this problem, at least not in the severe form Martin and others describe. I didn't for one. It's true that finding the sweet spot took time, but I managed despite being cack-handed. My gibs show no signs of trying to rotate, and the action was smooth. I got a slight improvement by polishing the steel gib but I don't think it was worth the effort, and I never bothered trying brass.

I wonder if the shape of the gib screw end, and the shape, position, angle and depth of the dimples, and the shape of the gib all interact. Perhaps slight differences between these explain why users report good, acceptable, and bad performance. I suppose it confirms what we already know, which is that mini-lathes are an inconsistent breed. As such, it would be instructive to compare a 'good' mini-lathe side by side with a 'bad' example to see what the causes are. I'm out of the game unfortunately: my mini-lathe had to go when I upgraded.

Dave

 

typos!

Edited By SillyOldDuffer on 03/08/2017 11:20:58

Edited By SillyOldDuffer on 03/08/2017 11:21:18

[Martin Shaw 1Participant @martinshaw1]

I though you might appreciate an update. Having stripped the complete saddle assembly it was obvious that both the dovetail of the cross slide and the surface of the gib strip were somewhat rough so the brasso came out and much rather mundane to and fro has polished up the rubbing surfaces nicely. They felt quite sweet when dry so with lubrication they are much improved. This was all done by hand without the leadscrew in place, and what remains is a slight tight spot which suggest a machining problem that I haven't quite polished out.

Having put the leadscrew back in and adjuted the nut properly it is much improved with almost complete lack of movement of the crosslide, except of course where it's meant to. I am much heartened by this, and if I can get the top slide as good it will at least make the lathe reasonably usable. At some point I am going to make a new gib strip that fits accurately into the space, whereby the adjustment screws will just be to snug it up and the strip won't then be able to rotate at all..

Regards

Martin

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