Myford S7 Spindle Nose / Chuck fitting.

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Myford S7 Spindle Nose / Chuck fitting.

This topic has 34 replies, 15 voices, and was last updated 27 December 2012 at 17:49 by Bazyle.

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30 August 2011 at 11:39 #74199

Steve Talbot 1

Participant

@stevetalbot1

Clarification needed !

As I understand it the ground axial portion of the spindle nose is the register which accurately locates the chuck.

However I have tried a number of chucks, supplied by Myfords (even on their new lathes that have recently been in the sale) and the chucks seem to be a ‘loose’ fit on the register when being screwed on.

Surely the fit should a slight interference fit to maintain the chucks accuracy, especially when work is removed with the chuck for secondary work and then returned to the lathe.

Having also measured this ‘register’ on two lathes there seems to be a 0.0005″ taper towards the threaded portion.

Any comments gratefully received.

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30 August 2011 at 11:39 #11810

Steve Talbot 1

Participant

@stevetalbot1

30 August 2011 at 12:09 #74205

blowlamp

Participant

@blowlamp

Myford were always very fussy about the faces of the register of the spindle and I doubt they would have let anything out that wasn’t close to being bang on to size.

I wonder if the 0.0005″ taper is due to wear from fitting and removing chucks over the years, perhaps without a spot of oil?

Martin.

30 August 2011 at 12:11 #74206

ady

Participant

@ady

The register ensures both axial and radial concentricity and should be a nice fit.

30 August 2011 at 14:40 #74213

Clive Hartland

Participant

@clivehartland94829

I am intrigued by the term, ‘Slight Intereference fit’. Any thing that interferes with the fit of the thread on the nose and inside the chuck will be an interference!

The chuck is registered nominally by the parallel portion and then the face and rear of the chuck.

No interference is involved slight or otherwise or the system will not work.

Manufacture of the shafts may well induce a slight taper which to me is of no consequence and should be ignored, here the cleanliness of the threads internal and external is of paramount importance because the build up of crud and particles will eventually after a long time cause wear and strain. Here, I am talking a couple of decades in modelling cicumstances.

Thinking about how chucks are mounted, Myfords are simple and efficient for the size of chucks involved but bigger machines and chucks are best served by the cam lock system.

Myford machines as modelling machines have to have their chucks transferred quite often to other mounts for further operations and then back to the register on the lathe so that the job is not disturbed from its settings.

Clive

30 August 2011 at 17:18 #74225

Tony Pratt 1

Participant

@tonypratt1

This is the weakness of this simple system, you have to have a slight clearance between nose and register to allow it to work. A taper to taper register will take up any wear.

Tony

30 August 2011 at 19:07 #74235

Bogstandard

Participant

@bogstandard

I have no idea about actual Myford lathe spindles, but in my efforts to have totally interchangeable tooling between my D1-4 mounting lathe and milling machine, I actually used the ‘Myford’ nose thread as a standard, directly fitted into my MT5 spindle bore. I made many of my own fittings, as well as using commercially available pieces.

During my journey, I had to measure many commercial items that were supposedly made to fit a Myford nose, mainly backplates.

I made my noses to exactly 1.125″ diameter with a 12tpi 55 degree thread. Some commercial items were too tight to fit the thread and had to be ‘cleaned’ out with a tap, but most had a good thread fit, but their registers were anything up to 0.004″ larger than optimum.

That reads to me that commercial suppliers rely more on a good thread and the rear face register than actually making them to fit the outer register on the spindle.

When I needed to make my own nose fittings, I always single point cut the thread for a perfect fit and opened up the outside register to 1.126″, and they all aligned and fitted perfectly.

Read into this information what you will, but what it looks like to me, the thread and rear register are the important bits.

John

30 August 2011 at 22:07 #74248

blowlamp

Participant

@blowlamp

My advice to anyone making their own nose fittings such as backplates and collet chucks for lathes with Myford style spindles, is to make the bore and abutment faces that are near the threaded section, as clean and accurate as they can, because they are the designated alignment surfaces for location of such equipment.

The diametric accuracy of the thread is of secondary importance and should be made with a little slack, to allow the register to do its job of pulling the chuck into alignment with the spindle.

Martin.

27 December 2012 at 08:41 #107216

geoff

Participant

@geoff

re bogstandards post august 2011 on myford spindle threads i have recently purchased an er collet chuck which is rather tight fit on the lathKke spindle thread i would like to know where i could borrow or buy the tap to try to rectify this

sidetrack

27 December 2012 at 09:45 #107217

Ady1

Participant

@ady1

Surely the fit should a slight interference fit to maintain the chucks accuracy, especially when work is removed with the chuck for secondary work and then returned to the lathe.

—

That's my understanding

I was always impressed by the accuracy of the nose on the wee Unimat SL, and how well original parts fitted onto it

The flat part parallel with the thread and the enlarged rear flat part are the all important register which is responsible for radial and axial concentricity

The thread is only responsible for tensioning everything up

27 December 2012 at 10:16 #107223

Michael Gilligan

Participant

@michaelgilligan61133

Posted by Steve Talbot 1 on 30/08/2011 11:39:09:

Clarification needed !

As I understand it the ground axial portion of the spindle nose is the register which accurately locates the chuck.

However I have tried a number of chucks, supplied by Myfords (even on their new lathes that have recently been in the sale) and the chucks seem to be a 'loose' fit on the register when being screwed on.

Surely the fit should a slight interference fit to maintain the chucks accuracy, especially when work is removed with the chuck for secondary work and then returned to the lathe.

Having also measured this 'register' on two lathes there seems to be a 0.0005" taper towards the threaded portion.

Any comments gratefully received.

Steve,

I agree with your understanding of the design; and I would venture to suggest that "a 0.0005" taper towards the threaded portion" was Myford's way of ensuring that the register would be effective.

… It would, of course, be a disaster if the taper ran the other way.

Without access to the design drawings; we can only guess, but I would expect to see that taper expressed as something like +0.0000/-0.0005 at the minor diameter.

With a suitably bored backplate [!] that would allow the chuck to screw on freely, with reducing radial clearance, to the point where the rear-face register takes effect.

Thus making the best of a theoretically imperfect design.

MichaelG.

27 December 2012 at 12:11 #107229

Chris Trice

Participant

@christrice43267

As has been mentioned before on a previous thread a short while ago, the thread constitutes a conical seating and as such, contributes to centralising the chuck combined with the rear face. It is theoretically possible for the register not to be in contact at any point when the chuck is screwed on tight. The register is there to limit how far off axis the chuck could be rather than a taper which would actively centralises the chuck. In practice, the system does work well enough for repeatability and accuracy for the sort of work our lathes are intended for. For the best results, you should always machine backplates on the lathe they’re intended to be used on for maximum cocentricity.

27 December 2012 at 12:31 #107231

MICHAEL WILLIAMS

Participant

@michaelwilliams41215

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From:	MICHAEL WILLIAMS
Subject:	Myford spindle
Date Sent:	20/10/2012 12:23:19
To:	joegib

Hello , The Myford spindle nose and Myfords own new backplates are made to a consistent matching set of tolerances These tolerances apply differently to the two zones – registers and threads . The registers are the the controlling features for aligning the backplate . The spindle register and chuck register are toleranced for a transition fit . This means that the spindle register is toleranced to be nominal size to oversize and the backplate register nominal size to undersize . Typically ( it varied a bit over the years ) : !.250 + 0.0002 – 0.0000 for spindle register . !.250 + 0.0000 – 0.0002 for chuck register . This means thate : (a) Any new backplate will fit any new spindle register with slight scraping in if needed . (b) Any new backplate will fit most spindles with worn down register on old equipment . The thread plays no part in the critical alignment and is basically just an ordinary medium precision nut and bolt thread . In general Myford made the backplate thread nominal size so that it could be finished with an ordinary commercial grade tap and made the spindle thread slightly undersize . Some references say 0.001 undersize but I can't confirm that . As important as the register diameter tolerance is the flatness and true running of the back radial part . There is no specific tolerance on this – Myford just made it as true as possible . If you have any questions I would be happy to answer them . Regards , Michael Williams .

27 December 2012 at 12:37 #107232

blowlamp

Participant

@blowlamp

Michael Williams has the correct understanding here.

Martin.

27 December 2012 at 12:45 #107233

Andyf

Participant

@andyf

To my mind, 3-jaw chucks tend by their nature to hold stock slightly eccentrically, often by an amount which varies with the diameter of the stock, and which might well swamp the effect of a very small amount of looseness in the register diameter. Slight eccentricity in the body of an independent chuck is immaterial, because the work itself has to be centered up.

However, an ER collet chuck needs to run true. Geoff, you might try a bit of emery paper (followed by a good clean-up) on the crests of the thread inside yours, in case the crests are poorly finished. And are you sure that it's the threads that are tight, rather than the register diameter?

Andy

27 December 2012 at 12:46 #107234

Tony Pratt 1

Participant

@tonypratt1

I agree Michael Williams is correct. I always undestood and practiced that screw threads are not an accurate form of location or register but only a means of fastening parts together.

Tony

27 December 2012 at 13:02 #107237

John Stevenson 1

Participant

@johnstevenson1

Tell me something then.

I have an ML7 clunker here with worn spindle nose, it's that worn you can see it.

The thread looks like a pipe thread and the register is about 3 thou under and also visibly tapered.

When the chuck is screwed on it flops about until it reaches the end of the register but when checked it has less than a thou run out.

A brand new backplate has the same runout.

An earlier lathe I have has just a thread, no register at all but still has a decent and REPEATABLE run out.

John S.

27 December 2012 at 13:37 #107245

Tony Pratt 1

Participant

@tonypratt1

In the first case perhaps the register diameter is not undersize right up to the shoulder. In the second case without a register, it's obviously pulling up on the thread, but I would still suggest it isn't the best way of locating a chuck to ensure concentricity?

Tony

27 December 2012 at 13:53 #107247

Chris Trice

Participant

@christrice43267

The thread does play a part in centralising the chuck as JS points out or if it's that poorly made then the thread is only pulling the chuck up tight on one side. I would imagine that after a while, some deformation of the materials involved will make a larger area of thread become in contact but that too only reinforces the idea that the thread is playing a part in positioning the chuck. A parallel register can only limit the amount of eccentricity, maybe to extremely fine and very acceptable tolerances but there must be a clearance in order to be able to get the thing on.

27 December 2012 at 14:02 #107248

John Stevenson 1

Participant

@johnstevenson1

OK, just as a test been out in the shop, put a bit of 3 thou shim [ only small bit I could find ] between the chuck and the back of the register on one side, screwed the chuck on, went on OK so proving the register must be well undersize but now got that much of a wobble on it's a joke to try and measure it.

Remove the shim and back to acceptable limits.

[EDIT] Unfortunately this machine has no motor or countershaft fitted, as I say it's a clunker and used for trying thing to fit but if I get time next week I'll get power to it and turn the register off.

Spindle is worn out anyway so it's not sacrilage.

Edited By John Stevenson on 27/12/2012 14:04:51

27 December 2012 at 14:03 #107249

Chris Trice

Participant

@christrice43267

Once the rear face of the backplate comes into contact with the spindle, it establishes the final angles between the thread faces in the backplate and the thread faces on the spindle and as the chuck is drawn on further, the two will settle into a centralised position where the radial forces are equal in all directions. Hopefully that position should lie where the backplate shoulder isn't in contact with any part of parallel register. In practice, it probably will be in contact with one side of the register but that means the register is then providing a sideways force to limit the eccentricity. Come on guys, this is basic mechanics.

27 December 2012 at 14:03 #107250

Chris Trice

Participant

@christrice43267

It's the same principle as a centre in a tailstock except the conical surface is a spiral rather than a straight cone.

Edited By Chris Trice on 27/12/2012 14:10:15

27 December 2012 at 14:12 #107252

Bazyle

Participant

@bazyle

I suggest that just because a thread isn't meant to be used to ensure the fit doesn't mean to say that on millions of lathes made some won't turn out to work ok on the thread.

After all if the register and thread were cut at the same time wouldn't the flanks and other dimensions of the thread end up just as concentiric and in effect are a taper that mostly would inadvertently result in alignment unless thrown out by some crud. with age of course the thin bits of the threads could wear unevenly and degrade the fit but it isn't per se a deliberate misalignment.

27 December 2012 at 14:15 #107255

John Stevenson 1

Participant

@johnstevenson1

What about the literally 1,000's of lathes that were mde with no register, early Myford, drummond, Winfiled, pooles, gamages etc.??

27 December 2012 at 14:28 #107257

Chris Trice

Participant

@christrice43267

Exactly.