Evaluating & Correcting Wear in an ML7

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

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.

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

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.

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

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.

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

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

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.

Er, no not £50/m £3.17 +VAT & post for 20mm tape with a sticky back.
Turcite and similar products are rather more expensive.
I bought a metre of tape 100mm wide and cut a slice off, hence having some spare. That was £21 delivered in a couple of days from ordering.
I ordered the wide stuff as I wasn't sure if I need to build up the flat surfaces on the knee of my machine, but got away with just scraping it flat.
It needs a very thorough de-greasing of the cast iron for obvious reasons.
It might not be a permanent solution, but just an exploration of the method.

Also companies like Starrett make feeler strip in 12" lengths; I used some 25thou, but you might be able to get it thicker. Modern adhesives can be quite good.
My thoughts are that arranging for minimum clearance on the short sliding interface will obviate the need for major re-work on the leadscrew etc. At least in the short term anyway, whilst just exploring the suitability of the preferred final method.

Bill

Edited By peak4 on 28/10/2020 23:34:13

Sounds like a plan.

Slideway Services has been mentioned on here before for regrinding. I think they went out of business but someone found an alternative or someone took over the business, or something. A search of past threads on here containing "Slideway Services" should reveal more.

Quick update - I’ve gone back to my plan’A’ from page 1, and combined it with Bill’s suggestion of feeler gauge material. I’ve ordered some 0.75mm x 12.7mm x 300mm stuff from RS, which I will bond to the rear saddle face with retainer.

I’ll scrape or file any un-worn bits from the horizontal bearing surfaces.

I’ll fit the new gib strip, and see what happens.

When it all shakes out, the feeler gauge strip should give me a net 0.008” saddle movement, towards the back of the lathe. The half-nut should cope with that hopefully.

What are the easiest tests to do once rebuilt and adjusted? There’s the DTI over a face-plate to check for perpendicularity, and the dumbbell test for bed twist. How about a test for tailstock height and horizontal alignment?

I’ll report back with how it goes.

Thanks all.

A quick and dirty wide-guide test using the 0.75mm shim steel from RS just now seems to confirm that it makes no discernable improvement at all to the binding issue (as predicted by the figures). Still waiting for the new gib strip, but I doubt that will make any difference either.

Didn't get anywhere with Slideway Services (or their replacement) either, so all a bit disappointing. At least I tried!

Assuming that cutting forces are in general pulling the rear saddle face into contact, Would placing short, stiff compression springs between the gib strip screws and the strip itself improve matters, or would it just cause chatter? Im thinking they would compress to compensate for the 0.002" dip, but be stiff enough to resist cutting forces.

I wouldnt think so. Any spring weak enough to allow movement will also move under cutting forces. If there is only 2 thou of variation, you should be able to adjust the gib strip with the standard screws so its that 2 thou loose on the worn bit and just clearing the unworn bits without inducing chatter etc. With the wide guide surface giving added stability you might find this works ok.

You could try very carefully easing the high spots off the surface of the front bed surface with a fine flat file, say a 10-inch flat single-cut mill saw file. If the variation is only 2 thou, you might only need to ease one thou off it to get it moving ok.

Otherwise, contact details for Slideway Services are still on the net on their website, but no idea how current that is:

Contact us

Slideway Services Ltd
Unit 24
Hammond Business Centre
Hammond Close
Nuneaton
CV11 6RY

Tel/fax: 02476 327874
Mobile: 07775 683363
E-mail: [email protected]

Edited By Hopper on 30/10/2020 11:01:00

Some previous discussion on this thread **LINK**

Sounds like if you can get hold of the Slideways Services guy he will put you in touch with someone who can help.

Or there is mention of Birmingham Machine Tool Services also.

Otherwise, there is Myford themselves, but premium price. Not sure how much these days. Youd have to ask them.

Edited By Hopper on 30/10/2020 11:14:29

Thanks Hopper, yes I already read that thread. I called Slideway Services, but he just said he'd retired. Birmingham M/C Tool Serivces number fails, so no contact there.

I did wonder about flatting the front edge. That would cure it.

Can you file hardened surfaces, or would it be scraping? What would the best technique be?

What about a fine flap wheel, followed by some wet and dry/oil wrapped over a 6" long piece of ground rectangular bar?

I already know the distance from the end and the amount I need to remove, ie a pretty accurate profile of how much to remove and where. I could use calipers as a go/no-go gauge.

The bed is not hardened so files easily.

Don't you dare attack your lathe bed with an abrasive flap wheel. It will dig trenches all over the place. All you need to do is ease about one thou off the highspots. Large flat file will do that if used carefully with restraint. Its a bit of a bodge but better than regrinding cost wise and in theory this is a clearance surface under load so ...

Understood.