Cross slide, uneven wear.

OK, I've solved (more or less) the cross-feed, it's now got about 2 thou' backlash in the middle and pretty much zero at the ends, which is doubtless
down to wear in the screw.
The next thing to receive attention will be the slide ways. It's a more or less conventional dovetail shape thing, with 2 gib strips in one side of the slide. They're a bugger to adjust, but the biggest problem seems to be uneven wear, which means that if you get it tight enough to have more or less no play in the most-used area (about 1/3 of the way along) it won't readily get to either end, so you end up with a compromise.
So. Any suggestions for how to skim the mating faces to get them back parallel? Obviously, there's some adjustment to be had in the gibs, or indeed they could be replaced; but there's not much point in that unless the main surfaces are parallel.
The cross-slide comes off easily, the saddle probably not so easy, although obviously it comes apart somehow, and I don't doubt both need attention.
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Austin Shackles. www.ddol-las.net my opinions are just that
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It is most likely that the gib strip is worn, as the main cross slide casting is probaby worn uniformly so no problem. check the gibs on a blued surface plate and scrape them flat ie take the bow out, should improve things.
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On Wed, 23 Jan 2008 18:53:36 +0000, Austin Shackles

Get yourself a copy of:- Machine tool reconditioning and applications of hand scraping by Edward F Connelly.
None on amazon.co.uk but a number available on amazon.com.
Read, mark, learn and inwardly digest it.
Then you'll know how.
regards Mark Rand
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On Wed, 23 Jan 2008 21:04:11 +0000, Mark Rand

I found that book fairly boring and not much use. Probably just me.
Charles
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Charles Ping wrote:

Not just you, Charles.
The book is a good, technical, reference material kind of book, that expects the reader to have a sound understanding of the principles and the physical act of scraping machine tools, as well as a great deal of experience already. It's a really good book to borrow from a public library for a preview, if you are considering doing any machine tool rebuilding.
There was a gent by the name of Michael Morgan, that put out a book and video on Scraping, that is a far better investment for someone that does not have experience or an experienced scraping hand, to fall back upon. I am certain that the likes of Camden would have similar titles as well.
http://www.machinerepair.com/video.html
Borrow Machine Tool Reconditioning first. Try to get Fundamentals of Dimensional Metrology, and Foundations of Mechanical Accuracy on the loan too. All great books, but of generally less use than their price would make you believe.
Any companies in your area with a surface grinder that can skim the surfaces? Some things are better aproached from a mercenary perspective. The money spent will save an awful lot of time for using it!
Cheers Trevor Jones
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wrote:

Glad I'm not alone.
I have Michael Morgan's book on scraping and as you say it's much more practical.
Regards
Charles
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wrote:

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Sorry about pressing the button too early. Will try to remove! Austin, you mentioned 2 gibs but failed to give us the clue to the lathe. Am I right in assuming that this is a Myford Super 7? If it is, the classic question is- 'is the thing warped?
Without 'connolising', there is a lot, lot on recons. Even little me!
Norm
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On Thu, 24 Jan 2008 04:24:32 -0800 (PST), ravensworth2674

Norm, I think Austin has a Colchester Student.
Peter
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On or around Thu, 24 Jan 2008 04:24:32 -0800 (PST), ravensworth2674

sorry, I didn't. Colchester Student Mk 1, 1960 vintage IIRC, so it's 6 years older than me.
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On Thu, 24 Jan 2008 07:46:10 +0000, Charles Ping

I have the Morgan book and the video, as well as Connelly. Whilst Morgan Is good for learning scraping, its coverage of alignment and reconditioning work is close to non-existent. Without understanding the importance of the alignment part of the job right from the start, you can end up with perfectly flat surfaces that are all cockeyed.
Of course, all of my tools are still within the manufacturers warranty and in perfect condition. :-)
Actually, the newest machine I own is actually the long bed ML7B, which cost Father 168 10/5 in January 1966, so reconditioning is of some interest to me...
Mark Rand RTFM
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Thanks, Richard, but there is a lot more- somwhere. There is also a reference to how he used green grade diamond paste to lap tungsten carbide inserts and also how he used a jig of sorts to achieve negative rake and the controlled curvature of the cutting edge.
I am wondering whether using scraping is what is needed for more. I did Johnoder and got details of another jig On Homeshop Machinist BBS where I write as Aviemoron has a series running about diamond use on DE grinders. OK, they are the wrong voltage and not in UK but that should not be impossible to make something up. I am looking at my Kennet which is gathering rosebuds or whatever under my bench. Humn, humn?
This is a huge subject over the Pond and Forrest has done scraping classes. I'm just a geezer with a memory. How long will it last? Not long!
Cheers
N
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On or around Thu, 24 Jan 2008 02:05:22 GMT, Trevor Jones

I'm not averse to getting the local engineering types to work on it, they have more equipment and knowledge. I might go and ask 'em.
As for wear and where it is, it seems unlikely to me that the wear is ONLY in the strips and none on the saddle itself, although that's possible. It would, of course, be simple to get the strips straight.
The problem, as I see it, is that unless you turn a wide variety of sizes, the most of the movement of the cross-slide is over about 3", which must lead to uneven wear on the saddle. In particular, the cross-slide is rarely pulled back all the way, so the end nearest the operator is hardly touched.
now, I could adjust it "tight" so that it works in the bit that's normally used, but is stiff at either end... if I make a special extra-short allen key to get at the adjusting screws. I'll try that first, might be possible to get it "good enough".
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how much difference is there between tight at the worn middle and tight at the ends 1/8 of a turn? 16th of a turn?
derek
message enlightened us thusly:

rarely
touched.
possible
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Derek, It doesn't work like that. You should be going to Schlesinger's limits which will explain lead screw testing- and a lot more tests on parts which make up final accuracy in machine tools.
I apologise but I am not trying to be rude or anything like that. It is the famous- or infamous- adding incorrect dimensions which don't even work in two dimensions or three.
Unquestionably, such concepts are far too detailed to be listed here.
Norman
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On or around Thu, 6 Mar 2008 05:36:44 -0800 (PST), ravensworth2674

For what I use the machine for, it's possible to work around most of the wear issues, anyway. Now that I've done the split nut mod on the leadscrew nut, it's a bit better behaved.
Currently, the cross-slide is a touch too slack (feed and ways) in the middle and a bit tight (again, feed and ways) at the extreme end towards the operator; if you like, it's optimised for turning small items 'cos that's what I mostly do. If I had a need to do significant amounts of work on a large diameter, I could re-adjust the gibs in the cross slide and get more freedom at that point, at the cost of having it a bit slack near the middle.
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Austin, I haven't seen your cross slide but I can understand wear in the screw in its middle but I would question wear in the middle of the cross slide itself. If this is so, you would have the rear bit unworn because the gib is the wearing/working face but the front edge bears against the male front apron edge. Logically, you should have original scrape marks at the front of your cross slide but wear in the middle.
Forgive me but I am being pedantic on your behalf.
With a decent ruler and a bit of blue, you should be able to offer the rule moving it, perhaps half an inch to find what you claim is a hollow. You haven't said that but it is implied. Well now?
Cheers
Norman
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On or around Sat, 8 Mar 2008 04:25:08 -0800 (PST), ravensworth2674

I dare say I could, but it's a lot of hassle to get it "right" and all the time it works "OK" I intend to live with it.
The facts are that if adjusted so that there's no play with the cross-slide where it would be to turn something (say) up to about 3" dia., then it gets increasingly stiffer as you move it further towards the operator. If you adjust it so that it's free to move but with no discernible play when wound most of the way out (i.e. turning something and more or less max. diameter) then it has play when moved to a position near the centre.
I've not invesigated which parts (slide, saddle, gibs(2), etc.) is actually worn, although logic says it should be the saddle to give that effect, since the gibs can be adjusted to take up wear.
despite that there are 2 gibs, I suspect the rear one doesn't do a lot unless using a rear toolpost.
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On Sun, 09 Mar 2008 15:59:48 +0000, Austin Shackles

Sounds just like my DSG <g>
The cross slide gib was worn unevenly, the slide clamping screw works on the centre of the gib & it's probably been run with the clamp nipped up instead of adjusting the gib properly. I've surface ground the gib and packed it, beyond that I intend to live with the wear for the time being.
Tim
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