Evaluating & Correcting Wear in an ML7

[Dr_GMJNParticipant @dr_gmjn]

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 1Participant @derekhall1]

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_GMJNParticipant @dr_gmjn]

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.

[HopperParticipant @hopper]

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_GMJNParticipant @dr_gmjn]

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

[HopperParticipant @hopper]

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_GMJNParticipant @dr_gmjn]

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

[HopperParticipant @hopper]

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_GMJNParticipant @dr_gmjn]

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_GMJNParticipant @dr_gmjn]

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.

[HopperParticipant @hopper]

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.

[HopperParticipant @hopper]

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_GMJNParticipant @dr_gmjn]

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 1Participant @derekhall1]

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_GMJNParticipant @dr_gmjn]

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.

[peak4Participant @peak4]

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

[Dr_GMJNParticipant @dr_gmjn]

Posted by peak4 on 28/10/2020 13:45:15:

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

Thanks Bill, will do. I had a look at Garsides, but as you say no mention of them doing re-grinds.

[Dr_GMJNParticipant @dr_gmjn]

So the results are in. Again.

I inspected the rear face of the back bed, and to my eyes it's pretty much perfect. There's no "R" designation on the number, so it's not been re-ground by Myford:

No measurable wavyness with a straight edge and 0.002" feeler gauge either.

So I used the direct measurement method, using the rear face as a the datum, front and rear faces of the front bed:

I guess there will be an error due to the positioning of the lever, but the needle doesn't lie: About twice as much wear on the front face than the rear, approx. 6" from the chuck end. Tallies with the micrometer readings and the spreadsheet. Actual readings on the dial were approximately -0.0015" on the front, 0, -0.0005" on the back, slightly offset from each other.

Looking at the saddle, the short bearing seems to have a slight step at the tailstock end, pretty flat at the chuck end:

Haven't been able to get the retainer strip off the front yet, but there's nothing much wrong underneath as far as I can see:

What's the advice then – mill the short face away; if so, would it be best to get a new gib strip?

Anything to lose if it all goes wrong; presumably if it's a disaster I just have it re-ground and re-assmeble as wide bed?

I'm a bit surprised it binds as badly as it does given the apparent 0.002" (or less) wear. I wonder if I should get a new gib strip anyway and try re-adjusting. I honestly don't know which way to go now…I can only think that eliminating the slight wear on the inner front face and short saddle bearing will improve things at least a bit, and combined with a new gib strip might gain me another bit of bind-free saddle travel.

[peak4Participant @peak4]

When the saddle is in place, with the short face in contact with the back of the front shear, how much clearance do you have between the unworn back of the rear shear, and the unworn rear vertical of the saddle top?

If it's not much, you could try an experiment with either ground stock, or a long feeler gauge, or maybe a length of Tribo Tape, which is what I used to pack out a gib strip 's bearing surface on the knee of my grinder. (I used the B160, which claims to be 0.71mm if you buy it with the self adhesive tape.

Different circumstances I agree; in my case it was a tapered gib, which I re-scraped after bonding a 0.030" feeler gauge to one side of it. I then made up the difference that I'd scraped off with a length of Tribo Tape on the main casting.
Might be worth it as an experiment, before committing to machining the top of the saddle.

This is the plan for my S7, but I've not got around to it yet, I'm hoping that adding the tape to the back of the saddle will give just enough clearance for the short front face.

Bill

[HopperParticipant @hopper]

Yes. I would try the wide guide conversion and new gib strip before regrinding. If you end up regrinding the bed get the saddle done too.

[Dr_GMJNParticipant @dr_gmjn]

Bill,

It's a consistent 0.022" gap at the back of the saddle.

Hopper,

I know this isn't your preferred method, but for someone with my current experience/ability, it's probably a case of it being the best compromise. The current plan is to:

1) Mill the short guide back by 0.030", and undercut the adjacent horizontal face very slightly.

2) Mill or file away the unworn step in the rear horizontal bit of the saddle (next to the currently unused bearing face), and undercut very slightly as per 1). Obviously being very careful to avoid the face.

3) Drill the saddle face and fit new wide-bed felt and retainer.

4) Fit a new front gib strip and hope the gib screws will take up another 0.022" (I think they will)

5) Make and fit a pair of 0.025" shims behind the leadscrew bearing castings to maintain the apron/leadscrew alignment.

6) Refit and adjust – Maybe do the dumbell test bar test.

I wouldn't touch the inner faces of the beds (the tailstock bearing faces) at the moment.

I'm going to trust my metrology here, and predict it won't make a lot of difference, however, there seems little to lose by doing it. The only chance of improvement I can see is it will at least eliminate the lesser of the two wear/bind points (rear of front web). So even if that gives me only another 2 or 3 inches of bind-free travel, the feel of the lathe would be vastly improved, and I could move the tool out of range of my hand when messing about with the workpiece – I have several scars to prove this isn't currently possible!

If I do end up having a re-grind, presumably I wouldn't need the saddle doing if I use this method?

If anyone can see something daft in any of that then, please let me know – plan is to do the deed this weekend.

And again, any recommendations for re-grinders would be appreciated. I assume a Myford job will be the most expensive option.

Cheers!

Edited By Dr_GMJN on 28/10/2020 22:00:37

[Dr_GMJNParticipant @dr_gmjn]

Just for information, I removed the saddle gib strip, but some felt tip ink over the face and put it on the surface plate. it is worn at the ends (ink removed from the middle area when I moved it around). In fact, I could rock it slightly, like a see-saw, on the surface plate.

[peak4Participant @peak4]

Just a thought, If you've got a 22 thou gap at the back, then that's just less than a layer of the Tribo Tape I mentioned. (0.71mm)
It should move the saddle back just enough for the short part to clear the front shear by about 5 thou (ish), so effectively you might be able to try a wide bed conversion without needing to alter anything at all.
I think mine is a bit less than 22 thou.
A few thou shouldn't really affect the leadscrew, since it's probably already worn a bit.

I'll be over in Sheffield Monday, so could possibly drop off a suitable length
(I'm going to NGH, depending what sort of Dr your user name implies)

Bill

[peak4Participant @peak4]

Posted by Dr_GMJN on 28/10/2020 22:30:04:

Just for information, I removed the saddle gib strip, but some felt tip ink over the face and put it on the surface plate. it is worn at the ends (ink removed from the middle area when I moved it around). In fact, I could rock it slightly, like a see-saw, on the surface plate.

That's probably not surprising if the saddle has been rocking.
I had to scrape one back to flat on the grinder I was re-assembling.
Are you sure it's actually worn at the ends, rather than being bowed?
If the latter, the adjusting screws will probably straighten it up a wee bit.

Bill

[Dr_GMJNParticipant @dr_gmjn]

Posted by peak4 on 28/10/2020 22:38:31:

Just a thought, If you've got a 22 thou gap at the back, then that's just less than a layer of the Tribo Tape I mentioned. (0.71mm)
It should move the saddle back just enough for the short part to clear the front shear by about 5 thou (ish), so effectively you might be able to try a wide bed conversion without needing to alter anything at all.
I think mine is a bit less than 22 thou.
A few thou shouldn't really affect the leadscrew, since it's probably already worn a bit.

I'll be over in Sheffield Monday, so could possibly drop off a suitable length
(I'm going to NGH, depending what sort of Dr your user name implies)

Bill

Bill,

Hmmm tape. This is very similar to the method in Hopper's M.E. Articles, but of course he uses pinned steel instead of tape. The leadscrew would be aquestion mark. I think Hopper suggests machining the brackets back.

Is it worth a try? Probably. £50/metre though….wow.

I'd still need to remove the raised, un-worn portions of bed, but the other side.

Unfortunately no, I'm not a medical doctor – I've got a Ph.D though. I live about 2 miles from the NGH, but at present I'm working from home, and have remote meetings, so I'm not sure if/when I'd be free. I can PM you though.

Thanks very much for the offer.

Anyone else have any opinions on using the IGUS tape? I've used IGUS components for work projects in the past, and its all pretty good industry standard stuff.

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