Myford ML7 Saddle Gib

Greetings. Recently got an early Myford ML7 (K2560), and busy cleaning and getting to grips with it.

I have been reasonably successful with the gib adjustment for the top-slide and cross-slide.

The saddle is giving me some extra grey hairs

I've taken it apart, and disconnected it from the apron. With all the gib adjustment screws slacked off, it moves freely across the length of the bed. I have also used a vernier to get rough measurements of the ways, and it seems pretty consistent at 4.494.

When I start by adjusting the screws (outside ones first as per manual), the saddle runs ok closer to the headstock, but binds toward the tailstock end ? If I adjust it to run free at the tailstock end, there is a noticeable back and forth rocking motion at the headstock side. Any suggestions or tricks to get this sorted ?

Also, what is the function of the ecentric clamp C33 ?

Lastly, could someone pls try to explain to me the best way to re-install the apron w.r.t. minimizing leadscrew movement when the half-nut is engaged.

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

Eben,

John is quite correct the lathe bed is worn at the headstock end as most lathes are after a lot of use.

The eccentric clamp C33 is to temporarily lock the saddle to the bed to prevent it moving whilst certain operations are taking place such as facing or parting off. Make sure that after use it is immediately slackened off as it is easy to forget that it has been deployed and damage could be done to the half nuts, lead screw or gear train if the auto traverse is engaged with the clamp tightened up. I have fitted my clamp with a permanent bright red painted handle which is self-indicating whether the clamp is on or off.

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

If my memory serves me correctly Myford changed the saddle guide from the front way only to being guided across both ways. Way back in Model Engineer 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.

Peter

>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

Thanks for all the info guys, much appreciated.

Any way of checking/measuring if the saddle on my particular lathe is guided on the front way or on both ?

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

It is an ML7 so it will be guided by the front shear. As regards checking wear, on these the back of the rear shear does not get worn in use so all measurements should be taken from there. I.E. back to front overall measurements will show amount of wear on front face of front shear, once this is corected you can move on to check the front shear width. Unfortunately the top of the shears will also be worn.

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

Do make sure the gib strip is slightly bowed so that it contacts in the middle first. This obviously doesn't eliminate the wear, but allows the saddle to move from end to end of the bed whilst biasing the shears into close contact and removing play.

Martin

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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The Myford tailstock is guided by a clamped fixed square jib block that is set to fit the width between the shears. The tailstock clamp merely pulls the tailstock down onto the shears.

When Myford went to the "broad gude" arrangement the use of the inside face of the front shear was abandoned.

Myford beds were not generally hardened. In all cases the wear is predominately at the chuck end of both the top of the shears and the guide faces for obvious reasons, hence the tightening towards the tailstock end if the jibs are set at the chuck end.

No amount of adjustment will correct this unless and until the unworn parts are brought into alignment by grinding or scraping. This can be done my careful measurement but is not a quick fix.

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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The reasoning behind the 'narrow guide principle' is that it is less likely to jam under load. It is incredibly difficult to find any information on it on the web and I strongly suspect it was largely snake oil...

in practice, has anyone here ever experienced the saddle showing any tendency to jam under load, on any lathe?

Neil

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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

There is a book about on narrow guides. The principle is easy to grasp - just a round bar in a hole. Say there is 0.0005in clearance and the length of the hole carrying the bar is 1 diameter. It will waggle about by n degrees. Make the hole longer in relation to the diameter and it will waggle less.

Applied to a machine tool the mechanism used to move the saddle is usually mentioned. Ideally it should apply it's forces axially to the guide - not always possible but it's obviously better to have it as close as possible as this will result in a smoother action. Twisting forces and lubrication can be bought into the argument as well. Also on a lathe how cutting forces are applied to the bed but that is also related to the width of the bed not just the width of the guide.

The net result on a lathe nearly all lathes really is a prismatic bed.

John

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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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Martin,

I've just re-read you post, and; whilst I accept that this might "make the best of" an already worn lathe bed ... It looks like a recipe for introducing problems on a good machine.

May I just ask: Is this your own idea [an expedient solution to the problems caused by existing wear]? or is it an historic general recommendation? ... If the latter, then that might explain some of badly worn Myford beds; because it defeats the principle of the Narrow [Long] Guide.

MichaelG.

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N.B.: I mean no criticism of your suggestion, as a method of mitigating the effects of a worn bed.

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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]