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Myford super7 saddle / tight toward tailstock

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Jak2g16/12/2021 20:05:14
36 forum posts
10 photos

I've got a super7 of late 1960s vintage, so it adopts the narrow guide saddle.

The saddle operates smoothly and there is no play when toward the headstock end and in the middle of the ways, but when I move it further than half way toward the tailstock it gets stiff, very stiff to the point that you don't want to crank it when it nears the tailstock.

Its a new machine to me, so I did some research and anticipated that the inner edge of the front way would be worn toward the HS, and that the tightness could be compounded by the narrow guide having been worn, mostly toward the tailstock.

Today, I stripped it down and to the naked eye the narrow guide looked near perfect. Unfortunately I do not have an appropriate micrometer to measure between the front edge of the saddle and the narrow guide, but I used a mitutoyo digital caliper on the gap at both ends and the middle (the readings will not be perfect, but they are averaged and I think fairly indicative of the gap). Toward the headstock I have 50.44mm and toward the tailstock 50.21mm. at the middle I have 50.3mm. according to these readings, the inner guide is actually less warn toward the tailstock, which surprised me but also reassured me that my eyes were working pretty well.

I then looked at the gap between the ways. Scraping marks from factory are present on inner edge of the rear way all along. Scraping marks are present on the inner edge of the front way from the tailstock to midway along toward the headstock, and then fade. I tried to get some representative readings from my digital caliper but it was no use. In any event, there was definitely some ware on the inner edge of the front way, but not a 'lot' - visually they look in good condition as well.

Latly, I used the tailstock to provide an indication of ware toward the headstock by adjusting the Gibs with the TS at its proper end - no play evident - and slid it all the way to the headstock -at that point, there was some play evident but a ' fairly' small amount, nothing drastic.

Ayways, my primary goal is to get this thing operating smooth allt he way to the tailstock end, and I was considering to alter the saddle to operate off the wide guide, i.e. the inside face of the rear way - but seeing that the saddle is not very worn, and the ways are also seemingly not 'that' worn, I wanted to make sure I wasn't overlooking anything first.

I'm relatively new to model engineering, so whilst I have a head scrrwed on (I think?!) I am not a machinist by trade, so apologies before hand if what I've said above doesn't make sense.

If anyone could point me in the right direct / share their thoughts on this situation and what I want to achieve in the end, I'd be very appreciative.

 

Cheers

Edit: 

 

Two other things. Even with the saddle gib loosened off completely, there is a noticeable difference in effort required to wind the saddle toward the tailstock (from about 2/3 of the way along), and the gib strip looks brand new to me - it is approximately 4.58mm wide the entire length.

 

Edited By Jak2g on 16/12/2021 20:16:30

Jak2g16/12/2021 20:07:48
36 forum posts
10 photos

Here's a photo of the saddle, if that helps. 20211216_185830.jpg

Martin of Wick16/12/2021 20:36:45
249 forum posts
5 photos

Don't think you have missed anything, the shears are worn at the headstock end, most of the wear will be on the front shear. The narrow guide myford is a poor design which is why the later models  use the outer edges of bed shears as the saddle bearing surfaces.

The front shear is mainly used on the narrow guide design and this is subject to most of the wear, not helped by the short bearing surface of the middle of the saddle which allows the saddle to rock. As most of the work is usually done close to the headstock, the front shear inner and outer edges wear most in that area over time. This is confirmed by your visual -Scraping marks are present on the inner edge of the front way from the tailstock to midway along toward the headstock, and then fade

Unfortunately, your lathe exhibits the most common problem with that class of machine. Not a lot of wear visually observed is more than enough to cause this problem. Effectively your front shear tapers down towards the headstock.

If you cant live with the problem and adjust the saddle fit to suit the job you are doing, then you options are

  • You can get the bed and saddle reground if you can find anyone still capable of doing it and you have deep pockets
  • You can do the standard documented wide guide modification which uses the outside of the back shear
  • Some people have claimed that they have scaped/filed/ground the shear edges, but I wouldn't recommend it

Should also add, that if the bed is significantly worn, the shears can also be thinned on the z axis towards the chuck, so you will need to check the thickness of  front and back of each shear chuck to tail every 30mm along the bed. If this is the case, the wide guide mod may not solve the problem.

 

 

Edited By Martin of Wick on 16/12/2021 20:40:47

Edited By Martin of Wick on 16/12/2021 20:48:09

Edited By Martin of Wick on 16/12/2021 20:56:24

Martin of Wick16/12/2021 21:14:12
249 forum posts
5 photos

BTW the saddle design suggests your lathe is an ML7 not a Super7

Jak2g16/12/2021 21:22:52
36 forum posts
10 photos
Posted by Martin of Wick on 16/12/2021 21:14:12:

BTW the saddle design suggests your lathe is an ML7 not a Super7

Cheers for all the information, I think I'll look into the wide guide conversion.

What about the saddle suggests it's not a super7? Says super7 on the machine and serial number of the bed matches?

Martin of Wick16/12/2021 21:36:49
249 forum posts
5 photos

Sorry you are quite right, if it says S7 then it is. The early S7 apparently had the same poor saddle design as the ML7. Change to the rear shear bearing on the S7 was only implemented in 1972 (I thought it was earlier for some reason, but just checked on lathes.co).

Jak2g16/12/2021 21:59:18
36 forum posts
10 photos

Have to admit you had me concerned for a second!

Prhaps a silly question, but would a saddle from a later model post 1972 work on an earlier pre 72 super 7?

Martin of Wick17/12/2021 10:43:05
249 forum posts
5 photos

Couldn't say for sure.

In theory it should, assuming your early model has the 3/4 inch leadscrew (my opinions not to be trusted on early S7s as you have discovered!). I have a late PXF version of the S7 and the saddle looks quite different (although the fitting dimensions to the bed must be the same, albeit with the middle bearing surface cut back for clearance).

Not quite sure what you would gain unless the current saddle is in poor condition, (or you don't have access to a mill or second lathe to trim back inner bearing surface, which is usually the problem for most of us!).

Perhaps somebody can chip in if they have gone down the saddle replacement route?

I would suggest that you acquire a micrometer(s) a piece of paper and a pencil and take some defined and detailed measurements of shear width and depth over the bed ( tablet and spreadsheet will do if you are a young whipper-snapper). This will accurately map the location and amount of wear and give you a good idea if the wide guide fix will work. You could also measure the gap between the back of the rear shear and rear saddle bearing surface with the saddle set up in the usual arrangement towards the back of the lathe. Feeler gauges may help here.

You may then be able to find / fabricate a suitable piece of steel to that thickness plus about 0.020 thou and epoxy it to the saddle back bearing surface. This will pull the middle bearing surface away from the front shear enough to avoid binding. This particular kludge depends on there being enough slop, flop and fitting clearance on the apron fitting and leadscrew clasps. clearly if you go too thick on the stick on plate, you may lose leadscrew/clasp nut clearance. This method avoids having to cut back the middle bearing on the saddle.

Disclaimer - I have only read about those claiming to use this approach second hand, so cant guarantee success.

Phil Whitley17/12/2021 11:05:26
avatar
1437 forum posts
147 photos

I had this problem on my Colchester student, and eventually found it was the saddle lock that needed an extra half turn towards "loose" because of course there is less wear on the underside of the bed at the tailstock end!

Phil

KWIL17/12/2021 11:41:23
3549 forum posts
70 photos

Jak2g, your public profile does not give any indication of your location.A general location might enable someone better equipped to offer help with mesurements.

Neil Lickfold17/12/2021 11:48:51
835 forum posts
166 photos

On mine I scraped the bed back to being parallel and used a micrometer to measure my progress. The saddle looked fine and made no changes to it. The tailstock needed to be adjusted due to the now wider slot and of course needed its centre line position to be corrected. It took a long time to hand work the bed and probably needs redoing again at some point as well. It was around 1997 when it was fixed. I have since added a gravity oil feed system to the lathe to keep oil between the saddle and the bed to compensate for the bed wear towards the headstock. Since doing that, it has been much easier to get very consistent results. I have been thinking about building up one side with thin turcite strip, but that stuff is very expensive and from what i have seen the thinnest available may still be too thick. Mine was not as badly worn as your one. The bed was about 0.1mm of metal removed from the thickest part. And it seems that the thinnest turcite is 0.8mm thick. So have to give it alot more thought. I just don't recall the amount of adjustment that is in there. I do wish that I had taken notes or pictures of what I did at the time, but didn't because I just needed it back together to be making some model engine parts. Funny how you think that you will remember at the time though. Micrometers are not that expensive either these days, and as it is more of a comparator than an exact measurement that is needed, any micrometer will make the measuring easier than No micrometer. Mine is about the same vintage as your one by the sounds of it.

Good luck with the restoration, and will be nice to hear what you decide on doing to repair it.

Peter Sansom17/12/2021 12:02:21
107 forum posts
2 photos

Your lathe appears to be suffering a common problem with old lathes. Most of the wear in the lathes occur close to the head stock. If you measure the thickness of the shears you will find the front shear has more wear than the back.

The best way it to put the bed upside down on a surface plate, but this is not usually practical. A camelback can be used , if you can find one the length of the bed. I found a 900mm straight edge and with feeler gauges could determine the wear, worst spot was about 0.010". Wear is on the top of the bed.

If you look around you may find a shop with a suitable surface grinder. It needs to be able to grind the full lend of the bed, travel needs to be longer than the bed including the head stock. I ground the bed on my 1958 Super 7 this way and it solved a lot of issues. Also did the wide bed conversion at the same time.

Peter

DiogenesII17/12/2021 18:24:58
516 forum posts
202 photos

On my ML7 I found that a shim could be inserted between the back of the rear shear and the rear guide of the saddle to give sufficient clearance for the former 'narrow' guide to easily clear it's mating surface on the front shear and transfer the guiding to the rear one - in effect, a kind of expedient wide-guide conversion, tho' of course, not a repair..

As the old 'narrow' shear is out of the way under the saddle, there doesn't seem to be any problem with the ingress of debris - I've never felt anything in the ?3 years it's been thus modified.

As Martin suggested, the shim is bonded in place - 638 compound applied to the clean back surface, the saddle replaced and the gib screws used to apply some tension and 'clamp' it overnight.

I'll measure up in the morning, I can't remember how thick it was off the top of my head.

Whilst this doesn't negate wear on all the bearing surfaces, it did result in a restored ability to traverse the saddle smoothly from one end of the bed to the other, prevented the saddle 'cocking' on the shears when traversed or putting on a cut, and made for a much smoother and more positive feel to the action all round.

I think prior to fitting I removed (with an end-scraper) a slight wear-ridge present in the the inner 'back' corner of the rear saddle guide, a result of the chamfer present on the far upper corner of the back shear..

As this is the only 'metal-off' required, it makes for an easy and reversible bodge-up 'work-around' for a worn narrow guide - although the shears (and much else) are 'on-the-limits', at least the action and cutting performance of the lathe is more-or-less pleasant, and some operations that were previously 'fraught' are at least now 'okay'..

Werner Habbel18/12/2021 09:39:32
12 forum posts

My name is Werne and I am from Germany.
I own a Myford S7 MKI from 1955 with an already reground bed but again worn from the pre-owner. After long thinking I decided to let the bed regrind again in the Netherlands from Frans van der Meeren from myfordsolutions.com
https://myfordsolutions.com/

For me it was important to get to know Frans and see his workshop. Frans is a lovely gentleman with a well equiped workshop and a large grindning machine. I live in South Germany so it was a 1000km trip to bring him the bed and saddle.
My bed was too much worn for a regrind so Frans took another bed and saddle from his srock of used parts.
With the regind he did an excellent job and he knows exactly what and how to do which I think is very important.
I could have send the bed in a wooden box, but that was not what I wanted to do.
So Frans is highly recommended by me.

Frans plans to do regrinds still the next year and then wants to sell the grinding machine but will keep on selling spare parts.

Werner

Jak2g19/12/2021 12:17:45
36 forum posts
10 photos

Hello everyone

Firstly, thank you all for your input.

I got my hands on a 25-50mm micrometer and taken some careful measurements along the bed at 30mm intervals, as suggested by Martin. Here's what I found:

The width of the front shear at the very start of the bed (toward the HS) is 44.43mm. This is exactly the same as at the very end of the bed (at the TS). This makes sense because both extremes are not used often.

The width begins to narrow at 60mm from the headstock to 44.42mm, and at 90mm from the headstock it is at 44.41mm. It remains as 44.41mm until 330mm from the headstock, where widens back to 44.42mm. It remains 44.42mm wide until 540mm from the headstock, where it becomes (and remains from there forth) to be 44.43mm.

From the above, it is clear that there is a .02mm difference between the most used portion of the bed, and the tailstock. That's just under a thou in old money.

I'm fairly surprised that this level of wear would cause the issues I was experiencing, but I imagine that any issues are compounded by wear to the inner guide on the bottom of the saddle.

With the apron removed and the saddle free to slide up and down along the bed, I carefully tightened the gibs (middle screws first, followed by the one nearest the HS, and then the last one toward the TS). My measurements are 'verified' in action, because the saddle moves freely nearish to the headstock, but then tightens at around 540mm from the headstock. It also tightens if you move the saddle forward to as close as you can get to the HS, right at the very beginning.

To see whether the wide guide mod would help, I took a .4mm shim of phosphor bronze and put it between the saddle and the rear face of the rear shear. The effect of this is that when the gib is tightened, the saddle inner guide rail does not contact the rear fact of the front shear. This worked, and the bed slid freely from one end of the bed to the other.

What I've learnt from this is that the difference between 'tight' and 'loose' when dealing with gibs and ways, etc, is VERY small. it seems that a mere thou' of wear can cause problems (when compounded with slight wear on the saddle inner guide).

Now, to remedy the issue I will be doing the wide-guide mod, but am just deciding the best material to use to line the saddle (on the rear inside face). Do you guys think gauge plate would be suitable? That seems the way some have went, but most suggest that rulon or turcite B would be better (if they had it to hand). I can't find any of this stuff easily in the UK - does anyone know where I could get a small amount (enough to fix to the saddle)?

DiogenesII19/12/2021 13:44:08
516 forum posts
202 photos

Gauge plate will be fine, it works well with CI - I do wonder how many manufacturers used GFS for gib strips, just because they could buy it in already ground..

..should add, the 'shim' in mine is a piece of polished carbon (?spring) steel..

Edited By DiogenesII on 19/12/2021 13:44:38

Edited By DiogenesII on 19/12/2021 13:47:20

SillyOldDuffer19/12/2021 14:16:52
Moderator
8469 forum posts
1885 photos

Posted by Jak2g on 19/12/2021 12:17:45:

...

From the above, it is clear that there is a .02mm difference between the most used portion of the bed, and the tailstock. That's just under a thou in old money.

I'm fairly surprised that this level of wear would cause the issues I was experiencing, but I imagine that any issues are compounded by wear to the inner guide on the bottom of the saddle.

With the apron removed and the saddle free to slide up and down along the bed, I carefully tightened the gibs...

What I've learnt from this is that the difference between 'tight' and 'loose' when dealing with gibs and ways, etc, is VERY small. it seems that a mere thou' of wear can cause problems (when compounded with slight wear on the saddle inner guide).

Now, to remedy the issue I will be doing the wide-guide mod, ...

Although reasonable to assume the cause is wear because of the lathe's age, maybe not: a measured difference of 0.02mm isn't much. Before rushing to modify the machine I suggest experimenting more with the gib adjustments.

My advice is to trust nothing! It's quite easy to lead oneself up the garden path. One possibility is the wear is worse than 0.02mm because of faulty measuring - achieving this level of precision needs care and practice. Another is that the problem is simply that the gibs aren't adjusted properly yet.

Although gibs aren't exactly rocket science, they can be tricky.

  • Gib inserted upside-down or wrong way round.
  • Locating indents on the gib not aligned with the points of the adjusting screws
  • Adjusting is harder than it looks. (My theory is that tightening up in one position tends to wedge the gib slightly, causing trouble when the slide moves. Obtain best fit by tweaking repeatedly over the full sliding range until the sweet spot is found.  )

On a bad day several attempts have been necessary for me to get the gibs right on an unworn machine.

So I suggest before diving in at the deep end, it's worth trying persistently to find a combination of adjuster settings that work acceptably over the range of travel needed in practice. Even if the lathe is worn, it may not matter if the slide is tight at the extreme tailstock end provided it's OK over the useful part of the bed.

Nothing lost by comprehensive tweaking apart from a few hours labour - if a setting can't be found, Plan A is still available.

Dave

Edited By SillyOldDuffer on 19/12/2021 14:17:47

Martin of Wick19/12/2021 14:26:58
249 forum posts
5 photos

Ordinary MS will be fine, gauge plate OK, no need to harden. Probably best to avoid the copper based alloys. I have even read of someone that claimed to have used some of the blue steel banding strip from large packing cases!

I had (still have) a 1947 ML7 that had much worse wear issues. In the end I had to admit defeat and used Slideway Services to regrind. I asked them also to grind out the saddle to allow a wide guide conversion using turcite. They did a superb job but the proprietor cautioned me that the turcite must be kept fully lubricated at all times to avoid rapid wear, that could in theory impact the angle of the saddle over time.

One thing you could usefully do is check play in Z axis of saddle at the unworn part of the bed and again in the wear zone. Set Y gib to give smooth play free movement over the bed. Set the saddle retainer strips to give you nil/minimum vertical play at the RH end of the bed (shimming/de shimming as required. Move saddle to wear zone and check vertical play again. If acceptable to you, then you are good to go. I could probably tolerate a thou or so movement.

Jak2g19/12/2021 17:07:08
36 forum posts
10 photos

Martin: I could be misunderstanding you, but the issue is as soon as I tighten the saddle gib the saddle fouls as it moves toward the TS end of the bed. I don't have any noticeable vertical (z) play in the saddle.. are you suggesting that the saddle retainer strips are tightened at the TS end so that these assist to restrict y movement / slack at the saddle with the saddle gib loosened off? I could be way off, apologies if that is the case.

 

Edit: went out and checked - it's not threaded, but the gib screw inserts into it and acts as a locator. Just looked up some photos of late model super 7 saddle Gibs, and this seems standard. Got excited there for a second and thought the gib strip might have been incorrect.. 

 

Dave: my measurements could be off here or there, but not by much. I'm, let's say 80% confident that my measurements of the front shear width are accurate, at least for the purposes of comparing measurements along the shear. BUT..

you've got me wondering about the gib strip. It looked brand spanking new to me upon removal. The gib strip is rectangular, and only has one hole about two thirds of the way to the 'right' side (TS end) of the gib strip. That hole is threaded, and the third adjustment screw threads into it. It does not have any dimples or anything for the other adjustment screws. I've never seen a myford saddle gib strip before, does this sound correct or has someone just jammed some gauge plate in there to be used - the threaded hole seems odd, because surely the third gib screw would go through and actually meet the bed (I'd need to check this, possible that the end of the thread has been fouled so that doesn't occur.. but still).

Edited By Jak2g on 19/12/2021 17:17:05

Martin of Wick19/12/2021 20:18:42
249 forum posts
5 photos

Can't honestly remember what the gib looked like on my S7, I dont recall any threaded holes in it though.

Wear will occur on the sides of the shears, but also on the top and bottom. Don't tighten the saddle gib for this test, Set it sufficiently loose to all full and free saddle movement up and down the bed.

Then check to ensure the saddle clamp plates are in place and all bolts are all fully tightened (just in case, cos I am prone to finger tightening then forgetting to nip up fully!). When fully tightened, these should not significantly affect movement in the Y axix (or the X!)

Can you still move the saddle nice and easily up and down the full length of the bed -

Yes? great, now move the saddle so its LH side is at the location you measured the greatest lateral wear on the shears. Then seize the front of the saddle in both hands, one each side, fingers on the plates, thumbs on top of the saddle but also contacting the bed and attempt to lift and or rock the saddle vertically up and down to detect any looseness in this location. You are only concerned with detecting vertical movement in this test. If there is no vertical movement that you can detect you can try the same test with a DTI.

If there is still no, or virtually no movement up and down, then consider yourself more fortunate than most as there is insignificant wear to top and bottom of the shears.

Edited By Martin of Wick on 19/12/2021 20:21:53

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