Top slide problem

[dave greenhamParticipant @davegreenham19379]

[dave greenhamParticipant @davegreenham19379]

Hi guys.

I have a problem that I hope one you you may know the answer to.

The lathe is a 7 x 14. Real bull lathe. what's happening is the top slide is loose on its slide. It's Not the Gibs , they will not go any thighter than they are. The play is in the dovetail. When parting off or straight cutting for that matter. The top slide ducks as soon as it hits a hard piece then jams the m/c. In the case of parting off the cutter dives under the steel. Short of replacing the whole lot or having it machined does anyone know of a cure. ? I've tried everything I can think of. So it's over to you. I'm sure I can't be the only one that's got / had this problem. But with my luck perhaps I am.

[Les Jones 1Participant @lesjones1]

Hi Dave,
When you say it is not the gibs do you mean that there is still play when the adjusting screws are tight enough to make the slide tight ? Or do you mean that with the screws tight you can still move the slide. Are the adjusting screws grub screws or do they have lock nuts ?
If they are grub screws could there be two grub screws in the hole ? The second one acting as a locking screw. Sorry to just ask questions without giving any possible solutions.

Les.

Edited By Les Jones 1 on 26/04/2013 18:16:29

[AndyfParticipant @andyf]

It may be that the dimples for the gib adjusters are misplaced, so the gib is pushing on the flat surface next to the male dovetail and forcing that side of the slide upwards. Indeed, if you have removed/replaced the gib, could it be that it is the wrong way up, so all the dimples are at the wrong height?

Have a look at this sketch. The caption should conclude: ".. it contacts the green base at X", but it would be a chore to redo the sketch and post the corrected version on Photobucket.

Of course, it could be something else entirely, but you shouldn't be able to get a feeler gauge in along either of the A-A surfaces, whereas you should be able to slide one in along B-B, and (though it would need a narrow feeler) under the gib at X. .

Andy

Edited By Andyf on 26/04/2013 18:25:58

[dave greenhamParticipant @davegreenham19379]

Hi Andy / les

Gib screws lave lock nuts , will recheck the dimples, re aa – x. When it jams up , I can get a feeler gauge under the tail stock end. ( 3th ) but nothing at the head stock end . I must admit the taking parts out and cut them with a hacksaw is getting to be a pain. Lol

Thanks for the info. as I say I'll strip it down again clean again and put it back together and see what happens

[dave greenhamParticipant @davegreenham19379]

Re AA And X. Feeler goes in on the X side

Dave

[AndyfParticipant @andyf]

Dave, do you mean that you can get a 3 thou feeler in along A-A on the side with the gib adjusters in it? The only gap along A-A (on either side) should be that caused by a thin film of oil.

Andy

[dave greenhamParticipant @davegreenham19379]

Hi Andy

have sent you a PM

regards

dave

[AndyfParticipant @andyf]

A post-script:

I find the best way of adjusting gibs is to remove the feedscrew and push the slide to and fro by hand. That way, you get a more sensitive feel for when each adjuster is just beginning to create a bit of drag.

Of course, as soon as you tighten up the lock nut, it pulls the screw back ever so slightly, even though you are using an Allen key to stop it turning. Sometimes, a few repetitions are needed.

Andy

[dave greenhamParticipant @davegreenham19379]

Thanks Andy I'll give ttry davetry dave

[dave greenhamParticipant @davegreenham19379]

Not sure what happened then lol. I'm give it a trtry .

Dave

[Clive FosterParticipant @clivefoster55965]

Be worth taking a close look at clearances at the points of the dovetail and recess. When I've refurbished slides I've always made a point of adding small flats and undercuts to the points to ensure there is clearance. Usually its wear that brings the points into contact with results similar to what you describe but have seen 50 or more year old machines which were obviously never really right from day 1! Make sure that the gib can seat cleanly and flat up into the top of the recess too. Have seen a DIY replacement gib attempt which didn't go in true settling at an angle which again gave similar symptoms.

Best thing you can do for conventional screw pushed gibs is to replace the adjusting screws with ball ended ones working in conical seats in the gib. Geo. H.Thomas has described the process for Myford machines but its worked a treat on everything I've tried it on, including a big milling vice. Basically you set things up so the gib is pushed really tightly up into the top corner of the dovetail and clamped hard against the side then use a centre drill to create a suitable size conical dimple to suit the ball end diameter of the replacement adjusters. The action of the ball in the angled conical seat tends to push the gib hard up into the dovetail corner. Clearly more solid than the conventional point in dimple approach where everything sort of floats. Whilst things are set-up fit a dowel pin ( rollers from a defunct small needle roller bearing are excellent as such dowels) to ensure that the gib can't try to slide back and forth when the direction of slide movement changes too. Been told that a loose ball and cup ended adjuster screw works fine if you cannot find ball ended screws.

I'd take the opportunity to fit an extra tapped hole for a thumb lever operated lock screw. 2BA or 5 mm works fine as the screw thread giving around 1/5 th turn from slack to real tight. Another ex needle bearing roller does nice for the thumb lever. Only tricky part is filing an angled brass pusher to go between screw and gib.

Clive

[Clive FosterParticipant @clivefoster55965]

Hi Graham

Interesting to know that a ball bearing will do instead of a proper pressure pad for a lock screw. As the contact between ball and gib is essentially point I'd have expected the action to be more bending the gib rather than pushing it so the effective "brake" area would be very small. I guess that it works because the actual gib movement involved is, probably, around a tenth of a thou or less so there is pretty much no room for the gib to bend or distort. Not sure if I've got the bottle to try it tho'!

Clive

[dave greenhamParticipant @davegreenham19379]

Hello guysI

Thanks for all the help.. I think that I have now sorted it out, at least I can now part off at last lol ( no more hacksawing. might save some blades now. Lol. ). The handles for winding in and out are almost at the point of being locked requiring two hands but until I can think of something else or get more advice, I can live with it.

Re your comment Gray about ball bearings, like Clive I don't think I have the bottle either.

I'm no engineer by any stretch of the meaning of the word. But I. TRY and sometimes I DO

Until I become more skilled thats all I can do

Thanks again for all the help and suggestions from you all

Best regards

Dave

[AndyfParticipant @andyf]

Another five points to add to those already made:

The parting tool should be at right angles to the work, so its sides don't rub as you go in, and it's overhang from the toolholder should be no more than required to get you to the middle of the job.

Nor should the topslide overhang its base; overhang = loss of rigidity.

The tool should be on centre height; if above, any tendency for it to rock down under cutting pressure will cause it to dig in. OK, with experience you might set it a smidgeon above centre, so it dips to centre height.

It helps a lot to have a saddle lock, so the saddle is clamped to the bed. There are designs around on the Web, but a small C cramp can be pressed into service.

Again, it can help to lock up the topslide, on the basis that it is best to lock all slides except the one you are using, which is the cross slide when parting off. My lathe is of similar size to yours, and has four gib adjusters on the top slide. I added a fifth in the middle, with no lock nut, a little lever and a bit of protective brass as per one of Gray's suggestions.

Sixth bonus point: If you are using a brazed carbide parting tool from a set with brightly painted shanks which the vendor of the lathe thought you might find useful, it would probably be best discarded. The cutting edge on those is usually rather broad for a small lathe, and the carbide may be to the special Chinese easy-chip recipe. I had one, and the tip fell off the first time I tried it, because the brazing failed. It was part of a set my brother gave me as a birthday present (came from Machine Mart, I think), so I couldn't complain, though I've had better presents.

Andy

Edited By Andyf on 27/04/2013 18:46:58

[AndyfParticipant @andyf]

Hi Gray,

The first thing I noticed about my useless brightly coloured set was the way they seemed to have been dipped in paint and left to dry the right way up, with the result that big uneven blobs of paint were present on the underside. That wasn't going to help mount them securely, or with any rigidity. And the tips all needed a regrind, which is difficult for a beginner. Even if he has a grinder, he probably hasn't got a green grit wheel.

Andy

[Sub MandrelParticipant @submandrel]

Some of my brightly coloured set needed to be milled underneath to give them reasonable angles!

I use them for intractable materials and nothing else.

Neil

[dave greenhamParticipant @davegreenham19379]

I agree about the painted tools, they are a bit crap

I tend to use 3/8" square HSS

Dave

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Clive Foster on 26/04/2013 23:14:05:

Best thing you can do for conventional screw pushed gibs is to replace the adjusting screws with ball ended ones working in conical seats in the gib. Geo. H.Thomas has described the process for Myford machines but its worked a treat on everything I've tried it on, including a big milling vice.

G.H.T. also goes on to say that the best solutiopn is to fit a dowel to prevent side to side movement of the gib relative to the slide.

Russell.

[dave greenhamParticipant @davegreenham19379]

Hi Guys. Here's an update to my problem.

having tried a lot of the things suggested with only a little improvement, and still convinced it was down to the Gibs. A member of the forum contacted me to offer advice, this entailed pinning the gib, still no better. So I sent a picture to him. He then very kindly offered to have a look at the lathe for me..

the lathe was taken down to him for inspection. Later I was told it would never work as it was. Leave it with me, I'll sort it for you, it's no good as it is. So it was left. Well. When the lathe was stripped down just about everything had to be machined . The bed was out, the saddle, had machined on the slant both ways as was the cross slide. Plus new Gibs had to be made as the new ones I'd taken down were the wrong angle and not thick enough.

I can't thank this member enough as the lathe is now great. Sorry I've not given his name, but he knows who he is and I don't think he wants to be loaded with machines to repair. Without members like this, where would we be. Very many thanks G.

best regards

Dave.

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