Worn Myford

[Brian AbbottParticipant @brianabbott67793]

[Brian AbbottParticipant @brianabbott67793]

Afternoon all.

After some advice, have just faced a 3” diameter piece of aluminium on my Myford super 7.

Seems to be facing a dome, approx. 0.1 from outer edge to inner.

Hunted around and would seem like the saddle has worn and needs a regrind to correct,

Would anyone know of somewhere I could get this done in the Midlands ?

Not a major problem at the moment but would like the machine to be right.

Thanks

[David Clark 13Participant @davidclark13]

You probably don't need a regrind. You could set it up on a mill and skim the faulty area. As long as you set the sadle correctly you won't have to take much off and then only off one face.

[ianjParticipant @ians]

Brian.

You could try Brian Caddy of Slide way services at Nuneaton

**LINK**

Ian

[CotswoldsPhilParticipant @cotswoldsphil]

Hi Brian,

Is your machine/saddle narrow guide? <1973 or later wide guide?

There is a potential solution if it's narrow guide.

Regards

Phil H

[KWILParticipant @kwil]

Remember if you do grind/machine away the reference face of the saddle to slideway, you may need to adjust the alignment of the main leadscrew. There is limited freedom in the clamp screws which hold the apron in place. All possible with care.

[John CParticipant @johnc47954]

I have had Brian Caddy regrind a Myford S7 bed and saddle. His work is first class. No connection etc.

[Brian AbbottParticipant @brianabbott67793]

Thanks for the reply's.

Its the narrow type guide, as David points out i could possible take a very light cut on the mill to correct but think i would like to entrust this to someone else.

The bed seems to be in good order for such an old machine, I will contact Brian Caddy and ask him his advice,

Thanks,

[Neil WyattModerator @neilwyatt]

Wait for Phil's suggestion, which I think will point you at JA Radford – and conversion to wide guide and using unworn rear shears.

Neil

[CotswoldsPhilParticipant @cotswoldsphil]

Hi Brian,

And thank you Neil – yes Mr Radford's mod with a slight twist…

As your S7 is narrow guide, then measure the gaps (left and right) with feeler gauges between the back of the saddle and the vertical faces of the rear shear. On mine the gaps were <> 19 thou. They should be equal, most likely not – the fixed narrow guide which bears on the rear of the front shear is worn and the gib is unable to be set correctly causing the saddle to rock. Or the gib has been set incorrectly causing uneven wear on the fixed guide.

The bed on my S7 shows very little or even wear but I still converted it by removing the saddle to clean out any debris at the rear the saddle and inserting a 1/2 inch wide shim just a tad thicker than the measured gaps at the rear – no machining required. This effectively converts the saddle to wide-guide principle (after <> 1973) making use of the unworn rear shear. The shim (brass) must be just thick enough to move the saddle back to the unworn position (on mine the shim is 20 thou) creating a small gap between the rear of the front shear and the worn fixed guide on the saddle.

Readjust the saddle gib-strip, taking care to have equal pressure on all screws – my S7 now faces as good as flat, over 5" and I can move the saddle to the tailstock end without any binding, showing that the bed is not unduly worn. It took less than a couple of hours to carry out and has restored the accuracy of the S7. If you now measure the very small gaps which have been created at the rear of the front shear they will most likely NOT be equal, proving that this is the wear point.

The shim has stayed in place with stiction, but it does need the later "bridge" shaped wiper on the front of the saddle to replace the older "rifle" type. There is a small chance that swarf will enter the small gap that has been created, but I fitted a swarf tray anyway to minimise swarf on the bed in front of the saddle.

This mod. is completely reversible – just pull out the shim and readjust the saddle – no harm done.

I've obtained a spare saddle to carry out a more drastic machining operation to fit a 1mm thick Turcite strip in place of the shim but that has gone onto the to-do pile for now.

As a point of interest, does anyone know what the factory clearance was at the rear of the saddle? Having this measurement would help me restore the saddle to it's designed position and reduce any misalignment of the lead-screw and half nuts.

Regards

Phil

Edited By CotswoldsPhil on 16/09/2015 15:32:19

[AjohnwParticipant @ajohnw51620]

I don't know if (may have the name a little incorrect) David Piddlington that used to work at Reeves when they were in marston green is still around but I seem to remember that he would do this for people. He also used to design things for them. Age wise he probably is still about.

These people are in B'ham and it seems it is possible to park outside of their premisses.

**LINK**

One thing I would mention is that you want to turn very very slightly concave, thou's. All of these people can be a bit extreme.

I'd wonder how bad your bed wear is and if you have tried locking it at various angles – they will rock when worn as most of it is usually in the saddle and some on the bed as well even when they are hardened.

John

–

[Brian AbbottParticipant @brianabbott67793]

Thanks all.

Phil, sound very simple, whats the catch ?

[CotswoldsPhilParticipant @cotswoldsphil]

Hi Brian,

 – – Phil, sound very simple, whats the catch ?

None that I have found in the 10 months since I carried out the mod on the S7 machine I bought to replace an ML7 I had owned for 40 years.

Other members may have different opinions especially as it is so simple – just a matter of working out the shim thickness required and some dismantling, cleaning and reassembly.

It's possible of course that the unused machined face at the rear of the saddle that is being brought into use is not true on ALL machines but I'm happy with facing flat over 5 inches and I mean checked with blue.

At least measure the gaps as suggested and post your results, we might be able to work out the factory gap eventually.

Worst you can do is confirm that the saddle is skewed across the bed.

Regards

Phil

Edited By CotswoldsPhil on 16/09/2015 17:09:47

[Brian AbbottParticipant @brianabbott67793]

Thanks Phil, sound like it may be do the trick, will have a look tonight,

Do you know why Myford used the narrow section in the first plate ?

Edited By Brian Abbott on 16/09/2015 17:49:46

[CotswoldsPhilParticipant @cotswoldsphil]

Hi Brian

— Do you know why Myford used the narrow section in the first plate ?

Your guess would be as good as mine…

It is rather odd as the saddle casting could have been much simpler.

Regards

Phil H

[Roderick JenkinsParticipant @roderickjenkins93242]

I believe the narrow guide was perceived as being better at resisting twisting. I seem to recall that when Tubal Cain got a new Super 7 he converted it from wide guide back to narrow guide It's in the ME archive somewhere!

And David Piddington has articles currently in MEW

Rod

[KWILParticipant @kwil]

The back (unused) face of the rear shear was I believe the reference starting point in the factory for the whole bed, having machined the feet pads and then that rear face, the whole bed was flipped over and worked from there.

Moderator JS may know more about it.

Front shear only is a classical narrow guide as indeed is the more modern " flat wedge" used on Colchesters and Harrison lathes etc.

[AjohnwParticipant @ajohnw51620]

The prismatic beds generally have huge width to length ratios. The faces of the vertical V can also provide large areas to resist wear.

The myford way with the front guide attempts to put the lead screw and rack central and beneath the guide as they all do which should lead to a lack of twisting forces as the saddle is moved. My ML7 which had hardened rails showed around 0.0005" wear on the rear edge of the front rail. In practice it could have been more because the only way I could measure it was with a straight edge – to remove any wear from the front which appeared to be ok.

I'd be very surprised if Myford didn't do all of the rail grinding in one setting but they may have ground the underside of the rails as a separate setting. i'd expect them to have a machine that would do all of it at one setting though. Perhaps they couldn't afford a slide way grinder.

Chis Heapy's, hope I have spelled that correctly, idea of improving the narrow guide on a myford was to add a gib strip to the rear of the front rail. I can't see that this would help other than making it easily replaceable and allowing the lead screw to be correctly aligned. I assume he got this idea from some one maybe Tubal Cane. He never gave any details, just mentioned it.

I can remember talking to David P and am pretty sure he was the one with a form grinder but it could have been some one else that worked there. I had a Raglan at the time. It's odd that the similar bed arrangement on those does wear better than a Myford – it causes less trouble just as prismatic V do.

There was a slideway grinder in Worcester as well. Brand new around 12 – 15 years ago. They offered to see if they could convert my ML7 to a prismatic bed or even fit it with wear strips. I wasn't happy about the amount of material they wanted to remove. I can understand their problem – set up time. They can grind the grinders table to make sure that is aligned – not keen to do that – then stand the bed on parallels upside down and grind the feet true and then turn it over, set up and do the grinding – all in one go. Actually in this case the saddle was carried on a sub table behind the bed with the V matched by off setting it so that was done too by the same diamond wheels.

John

–

[Brian AbbottParticipant @brianabbott67793]

Been and had a quick measure with the feeler gauges,

the left hand side measures 0.039 the right hand side is 0.030 approx

so either the back shear is machined incorrectly or hopefully it shows it's on an angle,

the front guide measures 0.753 at the tailstock and 0.752 at the business end.

anyway, strip down clean and do as suggested,

Thanks all.

 

Edited By Brian Abbott on 16/09/2015 21:40:35

[CotswoldsPhilParticipant @cotswoldsphil]

Hi Brian,

That's as expected – being that the machine is facing convex. I would expect the wear on the bed to be on the rear face of the front shear where the narrower fixed guide runs. What's the dimension across both shears?

Regards

Phil

[Brian AbbottParticipant @brianabbott67793]

Hello Phil,

Measures 4.505" maybe 4.506" if you really try, thickness again seems good, 0.500 – 0.501"

Surprises me, I think the bed seems very good, so why is the saddle so worn ?

[CotswoldsPhilParticipant @cotswoldsphil]

Morning Mark,

I'm just about to go out…

When I get back I'll measure my bed and both saddles – the one on the lathe and the spare I picked up.

Based on your's and a previous set of measurements provided by another member in an earlier post I am getting the feeling that the saddle on my machine has been re-ground to correct the narrow guide face, ie I need only 20 thou for the shim, your machine will need 35 ish. to do the same job. Unless of course Myford did not bother about this dimension which I doubt. The leadscrew on my machine appears to be aligned quite well meaning that the saddle is not too far forward.

IMHO I think that the narrow guide design makes it very easy to set the tailstock end of the gib too tight (it's not pulling directly against anything) increasing the wear and skewing the saddle.

John's explanation of having the leadscrew as near the centre of the guided ways makes a lot of sense to reduce twist induced friction.

Go to go

Phil H

 

Edited By CotswoldsPhil on 17/09/2015 08:57:29

[David Clark 13Participant @davidclark13]

Myford used to gang mill the bed so they are probably all the same within a thou or two.

[KWILParticipant @kwil]

Brian, You ask why the saddle is so worn?

It is very easy to adjust the front gib strip screws so that they actually force the saddle to "twist" meaning that the pressure on that short face running on the rear of the front shear is pressing harder at one end that the other.

Because the front gib strip is longer than the under saddle rib you cannot easily feel that is the situation. IE, if it is tight and wrong it still does not rock to tell you it is not correctly aligned.

On one of my Super 7's I spent a considerable time measuring and correcting the wear, replacing the material taken off with a steel shim strip bonded to the short rib. Since then the facing performance has been well inside specification.

[CotswoldsPhilParticipant @cotswoldsphil]

Hi Brian,

As promised I put the spare saddle on the bed in it's running position and got the following results:

Rear gaps .032 and .031 so encouragingly little wear on the spare (but scruffy) narrow guide saddle.

Front bed to saddle where the gib sits is 0.225, as near as, on both saddles.

My bed 4.5015 sharp end and 4.502 at tailstock.

I now don't think my saddle or bed has been reground but why is the rear gap only 0.018 inch compared to 0.030+ on two other saddles. David C explained about gang milling the bed; if the same process was used for the saddle you would think the setting up would have been pretty consistent – or do you know otherwise?

Regards

Phil

 

Edited By CotswoldsPhil on 17/09/2015 15:40:45

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