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Evaluating & Correcting Wear in an ML7

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Dr_GMJN29/09/2020 12:45:36
612 forum posts
Posted by Hopper on 29/09/2020 12:32:31:

I suppose you could glue a piece of 25 thou shim on there but it would be kind of flimsy. And the very small gap on the old narrow guide could jam up with swarf. I'd prefer some 1/16 gauge plate or maybe at least 1/32 myself. But you could give it a try and see how it goes.

If you were to use 1/32" gauge plate or ground stock you might get away with just enlarging the apron mounting bolt holes to get apron alignment back in spec.

OK great, I'll think about it some more.

I was just thinking that in your article, you Loctited your 1/32" strip (and of course dowelled it). I know that good bonded joint design means putting the joint primarily in shear, which of course this would be exclusively. Quite a large surface area too, and it's always clamped. I'd say it ticks all the boxes for a purely bonded joint. Even so, "glue" just seems a bit of a short cut, even though that's not necessarily true.

Milling the short bearing isn't an issue for me if it needed some more clearance, it was avoiding machining the leadscrew bearing housings if at all possible that I wanted.

Cheers.

Hopper29/09/2020 13:02:35
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I used 1/16 gauge plate. My gap was larger than yours though.

Machining the lead screw mounts was dead easy.

Or if you use the Ganderton method and machine away the narrow guide and use no strip , you could just put shims behind the leadscrew mounts.

Dr_GMJN29/09/2020 13:06:11
612 forum posts
Posted by Hopper on 29/09/2020 13:02:35:

I used 1/16 gauge plate. My gap was larger than yours though.

Machining the lead screw mounts was dead easy.

Or if you use the Ganderton method and machine away the narrow guide and use no strip , you could just put shims behind the leadscrew mounts.

Yep, so many options I forgot that one. Use the 0.022" shim steel to make shims for the bearing blocks I guess.

Dr_GMJN27/10/2020 23:10:43
612 forum posts

All, I finally got around to measuring the ML7 beds today, using some borrowed micrometers.

I noted the measurements as per Pete's article instructions.

Disclaimer: this is the first time I've done this, so I may have made incorrect assumptions!

So the first assumption is that the rear vertical face of the rear bed is totally unworn, ie straight left-to-right. This is my "reference" surface for overall widths and calculating other stuff.

The second assumption is that "wear" is the difference between the largest and smallest measurements of a particular area. Seems valid w.r.t. Myford's dimensions, compared with the least used bits of the beds.

Anyway, on the evidence of just the raw data, all the wear is within the stated limits for re-grinding, and - I'd hoped - for the wide-bed conversion...

I then put the data into a spreadsheet, and plotted graphs of the measurements at the 1" spaced 24 points along each bed. The individual graphs are here:






The scatter here is probably due to the tiny differences in width





I then calculated the gap width between the two beds. Seemed reasonable - more wear at the tailstock end from moving it backwards and forwards, but nothing massive:



I then plotted graphs that represent a plan view of the rear and front beds, with their actual width variations exaggerated, and this is what I got:



So, unless I've made an error somewhere, my lathe seems to be an anomaly according to Pete's article, becasue it seems to be the front of my front shear that's worn, not its rear. This appears to be confirmed because the overall bed width and front bed width graphs are pretty much the same shape. Anyway, it is what it is.

So the question is: in view of the fact that my lathe appears to have a uncommonly worn front vertical shear (no idea why, as far as I know it was only ever used for model engineering), is it even worth considering converting it to wide bed? I can't see it will make any difference if I've understood the method correctly?

So is the only option a re-grind, since it seems to be within limits for that?

Thanks all.

Dr_GMJN28/10/2020 08:29:48
612 forum posts

Than again 0.002” removed from just the right side the front vertical slide would sort it...is there a method? I guess it could even be a bit wavy so long as the gib strip spanned any low bits...

derek hall 128/10/2020 08:32:17
109 forum posts

Very interesting results, and great use of a spreadsheet to show what is happening with the wear on your lathe bed.

I have a myford super 7 circa 1962/3 and I will check mine in the same way as you did.

I will leave it to others with more knowledge than me regarding wear on machine tools but it does seem to agree with your conclusions that much of the wear is on the front of the front shear which suggests that conversion to wide guide will not have much affect...

The middle two graphs at the tailstock end do seem to confirm this is due to the tailstock as it uses the middle two shears for guidance.

Not sure what the myford tolerances are but since we are looking at 1 or 2 thou over 24 inches in the worse case is this acceptable for a myford?....I am not sure...

Over to the other boys and girls of the forum....

Regards

Derek

Dr_GMJN28/10/2020 08:38:42
612 forum posts

Thanks Derek. IIRC the Myford limit is 0.004” for thickness and 0.003” for width. I don’t know if there are limits that if you go over it can’t be ground, or when it should be ground.

I can’t for the life of me think why the front bed should be worn; surely cutting forces make it more likely the back edge would wear, especially with the smaller bearing width.
Cheers.

Hopper28/10/2020 10:39:18
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Hi Doc, That's interesting and certainly seems to fly in the face of 50+ years of experience by Myford owners doing the wide guide conversion. Plus a host of Drummond owners doing the equivalent mod with success. I cant imagine why wear would be on the gib side of the front vertical surface rather than the load bearing rear face of the front way. Maybe if the gib strip was run over tight? Or left so loose the whole carriage pivoted so it would bear on one corner of the carriage and it wore badly, Or cast iron swarf etc embedded in the steel gib strip abraded the bed? Seems very odd.

Not quite sure if you have some accumulative error in calculating rather than measuring the gap between inner vertical faces perhaps?

But, what you need to do is first double check your measurements and then try to confirm them by a second method. So far you have assumed the rear face is perfectly flat, straight and unworn. I would run a 10" fine flat file over it to make sure it is clear of burrs and the gummed up oil of ages. Then carefully inspect it for any signs of wear. Original curved machining marks should be visible all along it. Then I would double check it with a straight edge and feeler gauge. Even a simple steel rule would suffice if used carefully and of good quality. The thicker rule out of a combination square set works well for this.

Then ditto for the front vertical surface. Run a fine file over it. If its worn like you have measured thus far, you should be able to test it with the steel rule and thin feeler gauge, say the 1.5 thou that most sets go down to.

And ditto for the rear vertical surface of the front way. A straight edge and feelers should show up any wear here.

Then recheck all your micrometer readings again.

If your mike readings and straight edge and feeler gauge readings confirm there is 2 thou wear on the front vertical surface and none on the rear, it is still within Myfords 3 thou recommended limit before a regrind. So its up to you if you want to spend the time and effort on a regrind. And money. It depends on how the lathe is in use.

A lot can be done by following the ML7 owners manual and adjusting or shimming the mounting feet on the tailstock end of the bed to get the lathe to turn parallel over a 4" length of 1" diameter bar held in a GOOD chuck with no tailstock centre in place. If you can get it within say half a thou or so, that might do for most home hobby work.

And you can always use the time honoured method of a touch up with emery paper to knock the last half thou off a job and get a nice finish at the same time.

That said, it would be good if you could really confirm there is no wear on that rear surface of the front way. Straight edge and feelers would be the easiest way. But the way machine tool fitters often do such things is to make up a "sled" that slides along the bed, with two pins that locate on that unworn rear vertical surface of the back way and then a dial indicator is mounted on the sled and takes a reading off the vertical rear surface of the front way. Sometimes you can use an old time marking gauge for this. They had two small dowel pins that could be tapped down to protrude from the flat bottom surface of the guage for this purpose. Or if you fit the wide guide strip to the saddle, the saddle itself can be used as the sled, with the strip bearing on the rear surface and a dial guage mounted to the saddle bearing on the front vertical surface. I may have a pic of how I did that somewhere if I can find it and post it later.

PS. If you have copies of the Measuring Bed Wear ariticle there are pics there of using the marking gauge base and a DTI to measure variation between the rear unworn surface and the worn front vertical surfaces. This would be a really good thing for you to do before spending money on a regrind.

Edited By Hopper on 28/10/2020 10:47:50

Dr_GMJN28/10/2020 10:45:07
612 forum posts

Thanks Hopper. I'll digest your points and reply in more detail later, but unfortunately I have to return the micrometers now! I can probably borrow them again though. As I said, I may have made a mistake somewhere, but I can't see how - an overall distance front to back is easy enough to do, and that's the only one that really matters here. Thanks.

By the way - did you always measure overall width before committing to the wide bed conversion, or just assume the front bed measured wear was on the rear face? Your article does say measure it overall as a check. Just wondered.

Edited By Dr_GMJN on 28/10/2020 10:46:54

Hopper28/10/2020 10:49:56
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4887 forum posts
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See the PS I just added to my post above re pics.

As the pics in the Measuring Bed Wear article shows, I used the marking gauge base and DTI to check the variation between the unworn rear surface and both front vertical surfaces. On mine, the very front surface was parallel to the very rear surface with little or no wear measureable. The wear was all on the rear vertical surface of the front way, as measured by micrometer and confirmed by the DTI on the marking gauge "sled".

Edited By Hopper on 28/10/2020 10:52:58

Dr_GMJN28/10/2020 10:55:31
612 forum posts

Thanks Hopper, I'll have another poke around with it later this afternoon.

Hopper28/10/2020 10:58:27
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4887 forum posts
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PPS

As far as how much wear makes a regrind impossible and how much makes is a necessity: You pretty much cant wear it out beyond regrinding. You could grind 50 thou off there and still make the carriage fit by suitable spacers etc. 50 thou would be about 10 lifetimes of wear.

As to necessitating a regrind, that depends on how good you want it to be. If the machine is accurate enough for your needs after the adjustments described above, all good. But if you have problems with the carriage being tight at each end of its movements and sloppy in the middle, and you absolutely can't live with that and you absolutely cant do a wide guide conversion, then its regrind time I guess. Very much a matter of personal choice.

Mine was pretty close to Myfords stated wear limits of 3 and 4 thou or so in the horizontal and vertical planes but with the wide guide conversion now turns close to perfectly parallel as near as I can measure with a standard micrometer -- within 2 tenths of a thou anyway. Plenty good enough for an old bodger like me. Any better would be waxing a dirt floor in my case.

 

Edited By Hopper on 28/10/2020 10:59:51

Edited By Hopper on 28/10/2020 11:03:29

Dr_GMJN28/10/2020 11:05:27
612 forum posts

It's really not a question af absolutes - for me using the lathe is for a hobby, and it's just good to have things that are nice to use. If it's simple and/or inexpensive to do, then why not? If it's complicated and expensive then I'd put up with it and make allowances/adjustments.

At the end of the day I just finished my first steam engine (and first ME project) - a simple thing that took 5 months. I'm now planning a more complicated one, so wanted to get my house in order to the best of my ability and budget before starting it.

That's about the long and short of it!

Dr_GMJN28/10/2020 11:35:55
612 forum posts

Excuse the possibly daft question, but so far I've measured the beds by moving the saddle out of the way to do measurements.

What's the quickest way to completely remove the saddle, and be able to replace it again with the minimum fuss?

I'm still using the lathe for odd jobs, so don't want to disable it long term, just to make measurement easier.

Thanks.

Hopper28/10/2020 11:37:52
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4887 forum posts
106 photos

You probably should just do the wide guide conversion anyway. It's pretty simple, cheap and not time consuming and brings the lathe up to post-1972 spec with the longer bearing surface that gives greater carriage stability.

Hopper28/10/2020 11:41:59
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4887 forum posts
106 photos
Posted by Dr_GMJN on 28/10/2020 11:35:55:

Excuse the possibly daft question, but so far I've measured the beds by moving the saddle out of the way to do measurements.

What's the quickest way to completely remove the saddle, and be able to replace it again with the minimum fuss?

I'm still using the lathe for odd jobs, so don't want to disable it long term, just to make measurement easier.

Thanks.

Remove cross slide by screwing handle all the way out. Undo the three or so allen head bolts that hold the apron on to the saddle. Undo the bolts that hold the catch plates on to the saddle, the ones that run underneath the ways to stop the saddle from lifting upwards. Lift the saddle off, leaving the apron and leadscrew etc intact. As you say, no need to remove it for measuring. Just park it down the far end after sliding the tailstock off the end of the bed.

Dr_GMJN28/10/2020 11:42:24
612 forum posts
Posted by Hopper on 28/10/2020 11:37:52:

You probably should just do the wide guide conversion anyway. It's pretty simple, cheap and not time consuming and brings the lathe up to post-1972 spec with the longer bearing surface that gives greater carriage stability.

...and I already bought a new felt, so yeah.

derek hall 128/10/2020 12:19:00
109 forum posts

I am sure the late great Tubal Cain aka T D Walshaw, made a case described in the ME years ago of converting his wide guide Myford to narrow guide...

Cannot recall the rational for this, but I will try and find the article

Regards to all

Derek

PS "waxing a dirt floor"......I like that!!!

Dr_GMJN28/10/2020 13:14:09
612 forum posts

Just thinking - at the end of the day, how much is a re-grind? I'm in Sheffield; does anyone know of anywhere local to me that might do it? I've stripped the head/gearbox/leadscrew off before and it's not a big job. Presumably once its ground you just plonk everything back on it and re-adjust the gibs, levelling and tailstock?

I'll re-check using different methods later, but I'm not sure I understand the Myford wear limits. If they're saying that 0.002" on width doesn't need a re-grind, how come I can't adjust the gib to get a decent action for more than about 1/2 - 2/3 the bed length? Surely that limit implies that there might be slight variation in feel, rather than it locking up?

Something's not right here.

peak428/10/2020 13:45:15
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1256 forum posts
146 photos
Posted by Dr_GMJN on 28/10/2020 13:14:09:

Just thinking - at the end of the day, how much is a re-grind? I'm in Sheffield; does anyone know of anywhere local to me that might do it? I've stripped the head/gearbox/leadscrew off before and it's not a big job. Presumably once its ground you just plonk everything back on it and re-adjust the gibs, levelling and tailstock?

I'll re-check using different methods later, but I'm not sure I understand the Myford wear limits. If they're saying that 0.002" on width doesn't need a re-grind, how come I can't adjust the gib to get a decent action for more than about 1/2 - 2/3 the bed length? Surely that limit implies that there might be slight variation in feel, rather than it locking up?

Something's not right here.

I hadn't realised you were that close. I recently moved from Crookes to Buxton when I retired from BT.
If you're ever over our way, drop in for a brew when we are allowed to socialise again.

Re. lathe bed re-grinding; I came across this firm a while ago, On Facebook, but in the private Myford Group rather than on their own page; I've never used them myself, nor do I know the cost.
James Garside & Son, Their website only refers to them being machinery movers, but I'm almost certain that they were the ones who posted about regrinding Myford beds.
Large machinery, I seem to recall they had three or four set up to machine at the same time.

Cheers
Bill

Edited By peak4 on 28/10/2020 13:46:20

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