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Making new gib strip for cross slide

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Rowan Sylvester-Bradley20/05/2020 12:33:34
30 forum posts

I have just discovered that the cross slide on my Portass PD5 lathe is missing its gib strip. What is the best way of making a replacement? It needs to be 3mm thick, 12mm wide and 230mm long. Do I make this from gauge plate? If so, do you know of anyone selling 3mm x 12mm gauge plate (I can only find 3mm x 10mm, which would at a pinch be OK but 12mm would be better)? What is the best way of making the conical recesses for the pointed grub screws (there are 5 of these) to locate into? Do I need to heat treat the gauge plate once I have got it to the right size and made the 5 recesses? If so, how?

Thanks - Rowan

SillyOldDuffer20/05/2020 12:46:53
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6194 forum posts
1345 photos

Gauge plate is for hardening and I see no advantage in hardened gib strips.

I'd go for brass because it's easy to work and polish, and there's a nearby standard size. Cast iron would be OK but maybe awkward to source in that size, or mild-steel for cheapness (but more difficult to shape.)

Dimples can be pretty crude as long as they're in the right place - a centre punch.  Posher to cone them out with the end of a drill, and best of all to cone them at the correct angle so the screws align nicely.  Not sure dimples make an enormous difference unless the gib tends to tilt, their main purpose is to stop the gib sliding out

Dave

Edited By SillyOldDuffer on 20/05/2020 12:52:18

Andrew Tinsley20/05/2020 12:54:47
1171 forum posts

I have used gauge plate for gibs without hardening. It is an easy way to get good dimensional accuracy stock without any fuss. What is more, they work exceedingly well in practice. The oldest one that I have made, has done around 35 years of service with no problems.

Andrew..

Peter G. Shaw20/05/2020 13:00:58
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1150 forum posts
44 photos

My very limited experience suggests that mild steel will be satisfactory, especially if the cross-slide is made of cast iron.

I had to make some new gib strips for my milling machine and used mild steel which I attempted to scrape flat, ie I don't know how good they were! In respect of the recesses, what I did was to make a suitably sized screwed tool to fit the existing adjustment screw holes (you only need one tool). This tool was screwcut in the lathe and had a hole drilled through it to take a suitable sized drill for the recesses (or dimples). The idea being that as both thread and hole were made without removing the tool from the lathe, then both thread and hole would be concentric. Now, with the tool inserted into screwed hole on the cross-slide, and the gib strip clamped up tight against the inside of the dovetail, then by gently inserting the appropriately sized drill into the tool, a conical recess can be carefully drilled, at an angle, into the gib strip. In other words, the tool acts as a guide to locate the drill which creates the recess.

Peter G. Shaw

Hopper20/05/2020 13:01:31
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4782 forum posts
105 photos

Plenty of 1/8 x 1/2" gauge plate on ebay. Would that do?

No need to heat treat. Comes ground flat. Wont crack like cast iron or embed swarf particles as easily as brass.

Divots for the screws are done with a drill poked down the screw hole while strip and cross slide are clamped in position. Round the ends of screws to a hemisphere to sit nicely in the divots.

Michael Gilligan20/05/2020 14:10:23
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16210 forum posts
707 photos

I agree with Andrew & Hopper

... and incidentally, this choice has been discussed quite recently.

MichaelG.

Edited By Michael Gilligan on 20/05/2020 14:11:22

John Baron20/05/2020 14:41:33
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309 forum posts
123 photos

Hi Guys,

In general I agree ! Brass would be my material of choice, and it comes in 3.2 mm thick by 12mm (actually 1/8" X 1/2" X 12" ) but mild steel would be good too.

 

Edited By John Baron on 20/05/2020 14:42:46

Edited By John Baron on 20/05/2020 14:43:10

Rowan Sylvester-Bradley20/05/2020 14:57:45
30 forum posts

Thanks for all the advice. I have ordered a piece of 1/8" x 1/2" gauge plate. Will this be too hard to make the dimples with an HSS drill or countersink bit? Thanks to Peter G. Shaw for the idea about the drill guide tool. I'm not sure that my screws are big enough to make this practical - it would be a very small drill. And drilling through the holes without such a tool sounds very difficult to do without damaging the threads. I think it may be a case of marking through the holes onto the strip of steel, then making the dimples on my pillar drill. But all that fun comes after the strip has arrived...

Thanks - Rowan

John Baron20/05/2020 15:03:49
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309 forum posts
123 photos

Hi Rowen,

Buy a length of silver steel rod and make a spotting tool. Its just a length of rod of the right diameter to pass down the hole with a point on the end turned in the lathe and the end hardened. A quick tap with a hammer and done. Dimple it on the drill press.

David Davies 820/05/2020 15:09:07
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121 forum posts
8 photos

Rowan

If you pin the gib strip to the cross slide using a piece of 1/8" silver steel, as described by George Thomas in his "Model Engineer's Workshop Manual" this will prevent movement of the gib. The dimples will not positively locate the gib to the screws.

I have carried out this mod to both Boxford and Myford lathes. This included making a new gib strip on one of the machines for which I used bright mild steel. I'm sure the method could be applied to the Portass.

HTH

Dave

HOWARDT20/05/2020 15:09:20
584 forum posts
15 photos

The gib strip material should be more wearable than the mating material. You have a long bedway, which is cast iron and may be hardened to a degree, a short gib which is short and harder than the way will wear a local length close to the chuck. The difference in hardness doesn't have to be much, they could be equal and still have damaging consequences. You can adjust the gib to take out its wear but you cannot adjust the way. On hard ways gibs were originally cast iron then later fitted with Turcite with the slides I used to design and work with, these were for high production machines were movement over a day could be measured in kilometres.

So my advice would be brass, cast iron or a soft steel.

Rowan Sylvester-Bradley20/05/2020 16:35:39
30 forum posts

Could someone copy the relevant pages of George Thomas "Model Engineer's Workshop Manual" for me, assuming that there are not too many? There seem to be no copies of this book at prices less than hundreds of pounds.

Thanks - Rowan

Rowan Sylvester-Bradley20/05/2020 16:40:45
30 forum posts

>The gib strip material should be more wearable than the mating material.

I read somewhere many year ago that actually the harder material wears more, because abrasive particles get embedded in the softer material, and these then wear the harder material. I can't say that I have ever observed this in practice.

Also the gib strips that I do have (on the saddle and on the combination slide) seem to be made of some hard grade of steel.

Any further thoughts on gauge plate vs brass?

Thanks - Rowan

Oldiron20/05/2020 16:45:09
484 forum posts
22 photos
Posted by Rowan Sylvester-Bradley on 20/05/2020 16:35:39:

Could someone copy the relevant pages of George Thomas "Model Engineer's Workshop Manual" for me, assuming that there are not too many? There seem to be no copies of this book at prices less than hundreds of pounds.

Thanks - Rowan

Still in print so presumably copyrighted. Available for less than £30 here

regards

Michael Gilligan20/05/2020 16:48:14
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16210 forum posts
707 photos
Posted by Rowan Sylvester-Bradley on 20/05/2020 16:40:45:

[…]

Also the gib strips that I do have (on the saddle and on the combination slide) seem to be made of some hard grade of steel.

Any further thoughts on gauge plate vs brass?

Thanks - Rowan

.

My further thought ... You have observed traditional and well-proven design.

MichaelG.

Andrew Tinsley20/05/2020 16:52:07
1171 forum posts

Never used brass, but gauge plate works for me. I have not had problems with bed wear either. Then I don't move the saddle kilometers a day. What is needed for high speed modern machinery is not very applicable to ME.

Andrew.

P.S. Correct and regular cleaning and lubrication is more important than gib material.

Rowan Sylvester-Bradley20/05/2020 17:17:04
30 forum posts

Posted by Oldiron on 20/05/2020 16:45:09:

Posted by Rowan Sylvester-Bradley on 20/05/2020 16:35:39:

Could someone copy the relevant pages of George Thomas "Model Engineer's Workshop Manual" for me, assuming that there are not too many? There seem to be no copies of this book at prices less than hundreds of pounds.

Thanks - Rowan

Still in print so presumably copyrighted. Available for less than £30 here

regards

Thanks for pointing this out. For some reason Google failed to find this, and I just assumed it was out of print so didn't try the original publisher. Unfortunately they seem to have shut up shop for coronavirus, and their web site is not allowing me to order anything. So I've still not been able to order it.

Thanks - Rowan

Neil Wyatt20/05/2020 18:37:06
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Moderator
18141 forum posts
713 photos
77 articles

A supplier of brass 'upgrade' gibs told me they felt they were just 'upgrade bling' but as people wanted them, they met the demand.

I've made gib strips out of steel and brass, hard (non-compo) brass was actually the worst stuff to machine a gib from, but they all worked OK in the end..

Neil

Clive Foster20/05/2020 18:52:54
2323 forum posts
76 photos

Rowan

Many years ago I did a write up of my version of the GHT improved gib with a bit more background information, but no pictures, for an American acquaintance. I'm inclined to think I actually stole the idea from Smart & Brown before seeing Georges write up.

Unfortunately the nice version disappeared into computer black hole space around the millennium but I still have a rougher, E-Mail format, version that might be good enough. PM me your E-Mail address if you'd like a copy. Might take a day or two to find it tho'!

I've done my full monty version to several small lathes in the Myford / Boxford et al class with excellent results making up for what often seems like far too much wear. When doing this sort of thing to an older machine its worth remembering that old oil varnish build up to embarrassing thickness over a decent fraction of a century. Especially if cheap automotive and similar lubricants have been used. Darn difficult to shift it but worth the effort. I swear its ahrder than the cast iron. My experience is that something like half the apparent "wear" on an old, shed living, machine is due to uneven oil varnish build up in the wrong places.

Clive

Jon Cameron20/05/2020 19:05:57
340 forum posts
104 photos

I've been watching this thread and replies with interest it was a question I was going to ask.

I intended to use black steel, and then Polish it on plate glass with fine abrasive paper. Working upto using simply some brasso or autosol, on the backing paper. The gib I have is too thick for the new saddle I have for my ML4. The old one had been previously machined and included a 10thou error when traversing the cross slide from front to back. (Ie was higher at the far end than when it started it's journey).

The whole bed needs grinding or scraping, but it isn't a skill I've practiced and will leave that for another day, also on the ML4 is not likely to see any return in any future sale/upgrade, despite the return of accuracy over the next few years of using it. But that's another story.

Edited By Jon Cameron on 20/05/2020 19:06:19

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