Sounds like the bed is worn near the headstock I'm afraid, not surprising on an old lathe.

There are 2 plates that hold the apron down on the bed strips. If there is a lot of wear, usually is, one can be turned over, the other has to be reground. The back one is probably more important. The problem then is that these have to be shimmed up to suit the bed. Not an easy job but it can be done however bed wear might show it's nasty head again.

It is possible to lap out bed wear but it can be difficult to tell where it is. If a sensitive dti and a suitable stand can be used the best reference is probably the inside edge of the rear rail. Some scribing blocks have pins that can be pushed down to use against an edges that can be used for this sort of thing.

If there are any shims left under the bearing caps on the head stock these can be adjusted and scraped back in.l.

It's been a while but my recollection is that Myford saddles run along the front bed strip, their idea of a narrow guide so over all bed width measurements don't have much influence. Fractions of a thou wear will cause jamming. The inside of the saddle that runs on the inside edge of the front rail can wear into an odd shape as can the gib strip that is adjusted to maintain that contact.

John

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Edited By John W1 on 18/06/2015 10:57:08

>some enterprising soul worked out how an older Myford could be converted to the current system and thus eliminate a bed regrind although the saddle would need a possible grind.

J.A. Radford 'Improvements and Accessories for your Lathe'.

GHT travelled to New Zealand to visit his workshop, 'nuff said.

Neil

I think the manual is wrong! The screw at the right hand end is pushing against nothing, as the inner guide face is shorter than the outer. I used to do the LH screw and the one(s) which is are against the inner shear first, then the others (can't remember how many there are now). If you do it Myfords way you get just what you describe

You also mention that the lead-screw moves when engaged. If you think about what's happening, the narrow-guide and rear vertical face of the front shear of the bed are worn (the saddle gets tight as it moves towards the tailstock) This means that the saddle has been pulled forward when adjusting the saddle so the half-nuts are now out of line from where they were when the machine was new.

You can adjust the apron position a bit to overcome this provided that the bed/saddle is not too worn. Adjust the saddle gib strip as described above – not too much tension on the tailstock-end of the saddle. You can check saddle skew by inserting feeler gauges between the unused back of the rear shear and the back (vertical unused face) of the saddle. It was 0.019 thou at both ends of the saddle on my machine. Do let us know what gaps you find.

Move the saddle towards the tailstock. Loosen the apron fixing screws a little, engage the leadscrew, notice that the apron will move a little to align itself and then tighten the screws. Check by engaging the leadscrew a couple of times at different positions on the bed.

Phil H

The wear on top of the rails is usually rather low if it's a hardened bed but it can still be sufficient to prevent a perfect fit when the strips that hold the saddle down are shimmed to suit. This aspect touches on why prismatic beds are a lot better – also the length to width ratio of the guide. It can be a lot higher on a prismatic bed.

As I said it's been a long time but does the tail stock clamp tend to push it up against the inside edge of the rear rail? I might be confusing it with another lathe. I'd hope so as this would tend to maintain tailstock alignment as the bed wears.

While Myford might change the arrangement so that the rear edge of the rear rail also guides it would be rather tricky to use the rear rail in the same way as the front one is at the same time – both sides are used to guide. It would be possible to add a gib strip that runs along the rear edge of the rear rail but this wont really help counteract wear in the saddle and front rail area.

I took lead screw movement to be axial ?

John

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My ML7 bed was hardened but the wear was still significant. Too much so for me. I fitted it with a super 7 head stock at one stage a found the complications associated with that part.

The switch to a wide guide – a crazy idea really explains something I read on Chris Heapey's web pages some time ago. That concerned obtaining a narrow guide on the front rail as I read it by grinding and adding a gib strip. This didn't make much sense to me at the time. I looked at one of the archives of his pages but couldn't find any signs of the comment. It was just a comment. No details.

John

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Just the tiniest snippet of 'timeline' here

Adds nothing to the understanding though.

MichaelG.

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Edit: Bedtime reading for those interested in the theory, here

Edited By Michael Gilligan on 20/06/2015 23:51:48

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John,

A reference to aforementioned book would be useful, if you have it … thanks

The argument in favour of Narrow Guide is, as you suggest, quite simple. [and might have been more popularly understood if they had said Long rather than Narrow].

What I have yet to see, is a good explanation of why Myford moved to a Wide Guide, circa 1972 … This appears to coincide with the introduction of Power Cross Feed, but I struggle to see the logic.

MichaelG.

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It may be worth mentioning that Mr Radford's exemplary work on the saddle [Chap.19 of the book] was a repair job on a worn-out lathe. He is not promoting the use of Wide Guides, although he is critical of Myford's implementation of the Narrow Guide.

I suspect that Myford may have changed the guiding arrangement simply to make room for some structural feature of the new Saddle for the 'Power Cross Slide' … but I have not seen the workings of this device; so I look forward to some education on the matter.

MichaelG.

[Meanwhile: Off to the Car Boot sale]

I'm away from home Michael but I will dig it out when I get back. Like most books on something basically simple I wouldn't describe it as money well spent. I found mine in a 2nd hand book shop.

I'm very critical of Myfords bed design. The aim with mine after many many hours trying to improve it was to send it back to Myford for a saddle and bed regrind along with a saddle refit. The later is an incredibly fiddly job. The Boxford came up so sold it to a friend for very little and told him what to do. He didn't and Myford went bust. I'm not at all sure that conventional regrind services are a good idea on a Myford. They wont set the lathe up accurately so take heavy cuts and then use stick on materials to make the sizes back up. My father had an answer to that but people who work for large companies and put a lot of work out can waive a big stick.

There is one reason I can think of for Myford changing. When the saddle's reference edge is the inside of the front rail that part of the saddle can't go past the tailstock or headstock. This limit's it's length and also has the problem that cutting forces are applied largely to the corner of the saddle guide nearest the headstock. That wont promote even wear. By using the outside of the rails the guides can pass the headstock and tailstock and cutting forces mean that the rear edge of the rear rail will become the main guide. Cutting forces could also be taken up within it's length rather than at one end. This might also help the lathe work more normally, pass. When moderately loose bearings and slides spoil the finish the usual answer on most lathes is to take a heavier cuts. The force from the cut takes up play so if the feed is constant finish improves. That didn't apply to my ML7 and I put it down to bed width – too much force down and not enough out so everything needed to be tight.

John

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It's not something I personally thought of, it's what Myford did from new at their factory.

The procedure was to adjust the saddle centre gib screws first, working outwards, leaving the tailstock 'unsupported' end screw until last, which was then merely nipped to provide contact.

Martin.