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Myford S7 Cutting Barrel Shaped Cylinders

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JasonB29/05/2020 18:15:59
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Posted by Graham Meek on 29/05/2020 17:30:31:

Hi Mike,

I am a little confused by the XXX "mm" readings which in some instances are larger by a factor of 10, from what I would want to see, taking the 0.068 mm on the Headstock Alignment-Vertical as an example.

If as the opening post suggests then it is like ft that the carrage and dti are going down as they are moved away from the headstock due to the 5thou wear in the bed, any of these readings that involve moving the carrage along the bed surely can't read zero.

Graham Meek29/05/2020 20:57:09
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Posted by JasonB on 29/05/2020 18:15:59:
Posted by Graham Meek on 29/05/2020 17:30:31:

Hi Mike,

I am a little confused by the XXX "mm" readings which in some instances are larger by a factor of 10, from what I would want to see, taking the 0.068 mm on the Headstock Alignment-Vertical as an example.

If as the opening post suggests then it is like ft ?? that the carrage and dti are going down as they are moved away from the headstock due to the 5thou wear in the bed, any of these readings that involve moving the carrage along the bed surely can't read zero.

Hi Jason,

Now I am even more confused, where do "ft" come from.

The point I was asking was where does the "0,068 mm" come from when there is another entry written below on the Vertical Alignment Test which is more in keeping with the required dimension which Myford stipulate.

As regards the "5 thou", I take this to be wear across the bedways and as such will have very little effect on the vertical alignment. Yes there is a measured 0.0025" wear on the bed surface but as this wear only affects the tool height it will not give the effect to the barrel shape that has been found. It might have some effect on the Vertical Alignment if the saddle was under a loading similar to that imposed by a turning tool. In the free state I think the error will not be worth worrying about.

The wear to the vertical face will not extend completely down the bedway, otherwise the lathe would be turning parallel. Thus by using the setting bar technique and running a clock along the side there should be an error which replicates the wear. However there should come a point along the setting bar when the clock reads a fairly constant reading.

Further if a clock is mounted such that the carriage is only working on the less worn portion of the bedway then, the clock should read pretty well zero along its length, provided there is no twist.

My concern at the moment is that there is a twist in the bed, coupled with a semi floating spindle, combined with too long a test piece. Unless the problem is approached in a logical manner then Mike might as well role a dice and pick just any of the replies.

Regards

Gray,

blowlamp29/05/2020 22:26:47
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I'm wondering how worn or loose spindle bearings could move to allow both the near & the far end of a test-piece to be cut narrower than the middle portion. indecision

Martin.

Hopper30/05/2020 05:54:29
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Posted by Mike Donnerstag on 29/05/2020 15:51:56:

...

As such, I don't think I can trust the accuracy of my spindle taper.

Do you have think the bearings may be worn, or need adjusting?

Mike

Yes most definitely. You must. Given the wear on the bed, the bearings are probably similarly sloppy. The bearings should be adjusted as posted by Martin Kyte above before any attempt is made at bed alignment. Otherwise you are trying to align to a moving object. Impossible.

All readings and test results so far are invalid if the headstock bearings have excess play in them. When you said in your OP that you were overhauling your lathe and were now doing the bed alignment I assumed you meant you had already set the headstock bearings to tolerance, as this is the normal sequence of events in lathe overhaul.

There have been whole threads on this forum on adjusting these rather unusual Super 7 bearings so have a bit of a read before you proceed.

Before you adjust, measure your current spindle movement by holding a 12" long piece of 1" bar in the chuck and yank the end of it up and down, and side to side. Have your dial indicator measuring movement of the spindle (not the chuck) right behind the chuck. Record the amount of movement horizontally and vertically. (And let us know what you find.)

Give it a try. You might luck out and be pleasantly surprised.

 

Edited By Hopper on 30/05/2020 06:05:42

JasonB30/05/2020 07:09:24
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Grey Don't know what I was typing there

The two readings on all tests are simply Metric with Imperial below 0.068mm and 0.0027", ones with more are as readings are taken at two places along the bar.

As the DTI is mounted on the carriage or may be held in the toolpost and the wear is likely to be in the 6" nearest the chuck I can't see how it can be moved in a perfectly parallel plane to whats in the spindle, even if wear is side ways unless an elephants foot is being used the dti may not stay on the crest of the test bar

Sketch below shows an exagerated bed with wear and the test bar. As the dti is moved along the bar by the carriage it will dip down as the carriage follows the worn bed and give a +ve reading as the resulting 0.068mm shows. which at 0.0027" is very close to the quoted 0.0025" bed wear, if I were to revolve that red line about the lathe axis you would actually get a barrel shape

dti path.jpg

Edited By JasonB on 30/05/2020 07:33:04

Graham Meek30/05/2020 09:32:29
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Hi Jason,

Thanks for explaining the dimensions, I would have liked to have heard from the OP.

I was aware the DTI will not stay on the crest of the bar, due to the wear across the bed ways. The amount of "drop off" on the Clock will depend on two things. The diameter of the test bar and the distance moved off centre, let us assume it to be the full 0.005". Simple Pythagoras shows that for a 5/8" test bar the clock will drop 0.00004", too small for me to worry about and a mere fraction of the error found. (It would be less again with a larger diameter test bar.)

What we are not told, and which would be extremely helpful is how this wear progresses down the bedways. The 0.005" could be over just the last 2" of the bed nearest the headstock. It could however be over 10", we are not told this.

This is why the bar test method mentioned initially would show up this wear. Plus as I said earlier, If the the clock is so arranged that the carriage is operating on a less worn part of the bedways then the OP would be avoiding the severity of the wear and proving that there is, or is not, any twist present.

This is also why I initially mentioned the use of the Engineers Level as my first choice. As this method does not involve any machine movements and wear can be very simply compensated for.

Once twist is ruled out then we can move on to the other checks. An un-twisted bed should give 0.010" taper during the turning test, if the 0.005" wear is progressive down the bed. If it is isolated as I suspect, then there might be a very different answer.

Regards

Gray,

Generally,

Like Martin I think the spindle needs looking at, but lets sort one thing out at a time. Otherwise should the lathe miraculously start turning parallel after altering several things we will be none the wiser as to which was the culprit.

When Myford's started building this lathe it was with a flat bed plane. From this everything else is added. It was not assembled and then checked by turning a test piece. Tweaking this and that, to get it to turn parallel and round. The Test Sheets show they went about in a systematic way. This is the fundamental way all machine tools are built.

Regards

Gray,

Hopper30/05/2020 09:42:45
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Posted by blowlamp on 29/05/2020 22:26:47:

I'm wondering how worn or loose spindle bearings could move to allow both the near & the far end of a test-piece to be cut narrower than the middle portion. indecision

 

 

Martin.

My Myford had almost 15 thou of spindle movement when I got it. The previous owner had been using it like that. Any kind of weirdness can happen as the belt pulls the spindle one way, cutting forces another, the job climbs up over the tool, the job gets pulled into the tool, etc etc. Then add in bed wear moving the tool in another weird direction, both vertically and horizontally, plus wear on the carriage allowing carriage to pivot. Leadscrew alignment and halfnut adjustment can then get involved. And we havent even mentioned gib adjustment. It gets complicated, and weird. Anything can happen.

You can't align a bed to a spindle that is flopping about all over the place like mine was. It's something that needs to be checked.

Edited By Hopper on 30/05/2020 09:48:29

Edited By Hopper on 30/05/2020 09:49:28

Mike Donnerstag30/05/2020 09:53:06
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Many thanks for all your posts and sorry for the confusion with the readings - I only have metric indicators, hence the conversion.

Gray: the test bar has been ground to 0.671", though I will double check its accuracy later

I set up the headstock bearings to the best of my ability a few months ago, having made a peg spanner as a little lathe project. However, as I'm no expert and I'm learning as I go (and doubt many things I do!), I'll do the bearing setup again, following the instructions to the letter and take further measurements after.

Mike

Hopper30/05/2020 10:12:02
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Take some spindle movement measurements before you adjust so you know if they have influenced the tests done so far.

SillyOldDuffer30/05/2020 10:22:52
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Posted by Hopper on 30/05/2020 09:42:45:
Posted by blowlamp on 29/05/2020 22:26:47:

I'm wondering how worn or loose spindle bearings could move to allow both the near & the far end of a test-piece to be cut narrower than the middle portion. indecision

Martin.

My Myford had almost 15 thou of spindle movement when I got it.

... Then add in bed wear moving the tool in another weird direction, both vertically and horizontally, plus wear on the carriage allowing carriage to pivot. Leadscrew alignment and halfnut adjustment can then get involved. And we havent even mentioned gib adjustment. It gets complicated, and weird. Anything can happen.

You can't align a bed to a spindle that is flopping about all over the place like mine was. It's something that needs to be checked.

...

Hopper makes a really good point when he says 'anything can happen'. Been up the garden path myself many a time due to misleading measurements.

Struck me often since joining the forum that much lathe adjustment advice assumes the machine is in generally good order, for example levelling a lathe to remove bed twist assumes the ways are flat.

Unfortunately a pre-loved machine might well have multiple problems : worn bed, floppy spindle bearings, loose gibs, wonky head and tailstocks etc. And in addition to wear and tear, the machine might have been bodged in the past by CoCo the Clown.

I've never seen a comprehensive assessment guide explaining how to check an untrustworthy lathe for several faults. Faced with a well-used lathe in unknown condition where everything is suspect, how would the team go about making the machine fit for use again, and in what order should tests be made?

Dave

Hopper30/05/2020 10:27:34
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See my recent articles in MEW on doing just that with the Myford.

Pete Barker

Mike Donnerstag30/05/2020 10:43:39
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Apologies all - I'm struggling to keep up with all of the information, but I'm formulating a plan for today:

  • Check the spindle bearing play
  • Adjust the bearings
  • Take spindle nose measurements again, this time without belt tension (last time measured under tension)
  • Try turning between centres to eliminate the possibility of headstock misalignment
  • Test the concentricity of the test bar
  • Lay in the sun to recover and contemplate findings

Gray: below is a photo of the measurements showing the difference from the unworn end of the bed in thousands of an inch. This only shows the thickness difference. Somewhere I have a photo showing the width difference. I know there is an unexplained very worn area on the front of the front shear that I've posted about before, but I'm fairly convinced this is not influencing anything.

img_0522.jpg

Mike

Edited By Mike Donnerstag on 30/05/2020 10:48:21

blowlamp30/05/2020 10:44:41
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There are too many variables with using a test bar in the spindle of a generally worn lathe to reach a reliable conclusion, in my opinion. If it's not concentric, not coaxial with the spindle axis, and there's some play in the spindle, then it's hard to find a true reference plane - couple this with wear in the bed and it becomes almost impossible to obtain readings which can be trusted.

I'd be inclined to take wear measurements of the faces of the vertical shears by comparing against a known straight edge. It could be clamped to the top of the bed and aligned parallel to a less worn part of the vertical shear being tested. Then run a DTI along this straight edge whilst noting variations in the reading along the shear. Other methods could be used as well.

 

Martin.

Edited By blowlamp on 30/05/2020 10:44:53

Mike Donnerstag30/05/2020 10:49:45
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Posted by Hopper on 30/05/2020 10:27:34:

See my recent articles in MEW on doing just that with the Myford.

Pete Barker

Hi Hopper, can you tell me which articles you are referring to, and I'll look them up.

Many thanks,

Mike

Hopper30/05/2020 10:58:36
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Posted by Mike Donnerstag on 30/05/2020 10:43:39:

Apologies all - I'm struggling to keep up with all of the information, but I'm formulating a plan for today:

  • Check the spindle bearing play
  • Adjust the bearings
  • Take spindle nose measurements again, this time without belt tension (last time measured under tension)
  • Try turning between centres to eliminate the possibility of headstock misalignment
  • Test the concentricity of the test bar
  • Lay in the sun to recover and contemplate findings

Gray: below is a photo of the measurements showing the difference from the unworn end of the bed in thousands of an inch. This only shows the thickness difference. Somewhere I have a photo showing the width difference. I know there is an unexplained very worn area on the front of the front shear that I've posted about before, but I'm fairly convinced this is not influencing anything.

img_0522.jpg

Mike

Edited By Mike Donnerstag on 30/05/2020 10:48:21

Wow look at the wear on the front corner of the bed there at the left. She's been rode hard and put away wet. Looks like long and repeated use of a die stock or tap wrench on largish threads with the steel handle of the wrench/stock resting straight on the bed there. Was this lathe used commercially or for production work of some kind before your stewardship?

But yes, that scarring will not unduly change carriage travel overall. Provided you have run a flat file over it to knock off any raised burrs and bumps that could well be there. Especially on the front vertical surface. A 10" single cut mill file is perfect for this job. It does look in the photo as if there could be some raised bruising around the edges of the scar. Hard to tell from pics though.

More than the thickness of the shears shown here, it is the width across the outside (in your case of wide guide bed) that is critical. The wear on the rear vertical surface that guides the wide guide saddle is critical, allowed only 3 thou wear before a regrind according to Myford literature. You can also measure the width of the rear shear itself to ascertain the amount of wear on the rear surface. Wear on the inner vertical surface that far up the bed should be negligible as the tailstock does not go that far. Tailstock does wear those inner vertical surfaces where it runs bak and forth.

Pete Barker

 

Edited By Hopper on 30/05/2020 11:00:47

Hopper30/05/2020 11:16:11
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Posted by Mike Donnerstag on 30/05/2020 10:49:45:
Posted by Hopper on 30/05/2020 10:27:34:

See my recent articles in MEW on doing just that with the Myford.

Pete Barker

Hi Hopper, can you tell me which articles you are referring to, and I'll look them up.

Many thanks,

Mike

If you can search an up to date index for Pete Barker you should find them. But digging through my pile by the armchair it seems like issues:

285 -- Measuring bed wear and saddle wear on the Myford

287 -- My simplified wide guide conversion requiring no milling machine to perform. (No use to you though with factory wide model) This includes setting up leadscrew alignment and half nut adjustment.

289 -- Using a vertical slide on the carriage to machine the bed's inner shears that guide the tailstock. (After the wide guide conversion so the carriage is now running true on the new unworn surface at the back.)

290 -- Setting tailstock alignment to turn parallel between centres.

292 -- Spindle bearing measurement, scraping, shimming and installing. ML7 bearings, not Super 7. (Which is actually the first step in the overall process despite being last in series as it was not a formal series per se.)

Pete

 

Edited By Hopper on 30/05/2020 11:17:46

Martin Kyte30/05/2020 11:16:29
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Correct me if I'm wrong but you cannot assume that wear on the top surface of the bed only affects tool hight. If the front surface wears more then the back the toolpost will drop away from the work as well as down.

Just to simplify the argument and to make my case, assume a right angled triangle with side lengths 3.5" (ABC where abc is a right angle) the base A B representing two points on each top way and the apex C The tool tip. If B drops by 5 thou and A is unworn then point C moves out by 5 thou.

Agreed if the wear is even on both top faces anly the tool hight changes and this has little effect on diameter.

regards Martin

Hopper30/05/2020 11:42:10
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Posted by Martin Kyte on 30/05/2020 11:16:29:

Correct me if I'm wrong but you cannot assume that wear on the top surface of the bed only affects tool hight. If the front surface wears more then the back the toolpost will drop away from the work as well as down.

Just to simplify the argument and to make my case, assume a right angled triangle with side lengths 3.5" (ABC where abc is a right angle) the base A B representing two points on each top way and the apex C The tool tip. If B drops by 5 thou and A is unworn then point C moves out by 5 thou.

Agreed if the wear is even on both top faces anly the tool hight changes and this has little effect on diameter.

regards Martin

Yes it sure will add to the mix. In reality, there is usually some wear on the back shear as well though. But Myford literature does specify a max wear of 5 thou on the top faces and only 3 thou on the vertical faces before a regrind is recommended. So they seem to see the vertical surfaces as almost (about) double the importance of the top flat surface.

On my ML7 I had from memory about 4 thou wear on the top flat surface so left it as is. But there was about 3 thou wear on the vertical shear. So I did the wide guide conversion. Now with the wide guide vertical surface but still running on the 4 thou worn top flat surface, the lathe turns parallel to well less than 2 tenths of a thou over six inches.

Setting it up to do that when I moved it to a new bench recently was a matter of putting a 3 thou shim under the front tailstock end foot of the lathe after a turning test.

I didn't use a level. Just followed the Myford manual's instructions of bolting it down with a dial indicator bearing on the far end of a 12" length of 1" bar in the chuck and making sure the needle did not move during bolting down. If it does move, a shim is needed under that foot to fill the tiny gap there. That way, the lathe is sitting totally unstressed and if it has not developed a twist of its own over the years, should be sitting straight.

The turning test was then done and the extra 3 thou shim added to remove the 1 thou taper it was turning over a six inch length. Not bad for a bed with a 4 thou dip in the front bed way on top. I think if I added another 1 thou of shim I could eliminate the last  tenth per six inches of taper but sometimes you have to quit while you are ahead. Besides, that's what emery cloth is for. laugh

 

 

 

 

 

Edited By Hopper on 30/05/2020 11:53:32

Edited By Hopper on 30/05/2020 11:56:32

Mike Donnerstag30/05/2020 13:21:45
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Hopper: I don’t know much about the use the machine had been put to prior to my owning it, but I think your suggestion of a previous owner threading using a die-holder would account for that bed wear.

Measuring again, apart from the last 2 inches of the bed, the bed width across both shears shows no more than 1thou of wear (not bad at all!), according to my digital calipers (the only micrometer I have is 0-1&rdquo. This includes the visibly worn area on the top of the front shear. The final 2” measures 1.5-2thou above that, which accounts for my initial wear measurement of 3.5thou.

Slightly off-topic, but where did you get your small red magnetic indicator stand?

Or, is it an expensive Noga? My magnetic stand is quite large and the dial gauge on top is even larger. For that reason I tend to use a sensitive dial test indicator in the toolpost whenever possible, but I do need to buy a more compact magnetic stand to make setting up easier. My Batty in the magnetic stand is pictured below. I don't use it much as it's just too bulky and a pain to set up.

magnetic stand and large clock.jpg

Edited By Neil Wyatt on 30/05/2020 22:02:03

Graham Meek30/05/2020 13:27:47
213 forum posts
148 photos

Mike,

Thanks for the info on the Bed, it does show she has had a hard life. I would hazard at a guess that the Universal Parting Tool has been used quite a bit on this lathe. There are slight nicks showing in the rear bedway which makes me think this is all Hacksaw damage. Having previously owned such an example. Luckily for me mine was not so bad and at the time I had access to the necessary equipment. An hour on the Snow Surface grinder soon had the bed back to new. The question then has to be asked why was the Hacksaw used in the first place, Inexperience perhaps? or Chatter due to a sloppy or worn bearing?

Looking at the wear across the bedways then on average you have roughly 1 thou more wear on the front edge when compared to the back edge at that station. This does not concern me as the tool height will only be effected by this.

A sloping tool path should produce a Hyperboloid of Rotation, that is the opposite to what you are getting.

(For those wanting more information on this then Page 88 Part Two, of Workshop Technology, by W.A.J. Chapman, Third Edition. The chapter also covers machine tool accuracy and alignments)

The wear pattern across the ways is more important to me at the moment, and can you tell me if you have a wide bedway bearing saddle.

Regards

Gray,

Generally,

Installing a complete workshop during a move of premises for one employer proved to be a good learning curve in installing used and abused machine tools. My training means I never take anything for granted, but check everything at least twice.

Regards

Gray,

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