New Chuck won’t screw on

It seems Myford were not alone in picking odd increments for the Spindle Nose thread.

Schaublin did one lathe with an M37.6 x 3 thread, and another with M47.6 x 3.

Regards

Gray,

Obviously, many years ago, a lot of manufacturers thought that it was 39 x 1, including E Leitz!

None of my photographic books, dating back to the 60s mention 26 tpi,

As an aside from this thread and in the hope of ending this particular argument, I have used my Starrett No 158 thread gauges to check:

The f/2.8 lens from a Fed 2 camera (The Fed and the Zorki were Russian copies of the Leica camera )

A f/2.8 Corfield Retro Lumax lens (A wide angle lens for the Leica fitting Corfield Periflex camera which used a small periscope to focus instead of the coupled rangefinder of the Leica, Reid, Canon and Contax cameras of that time )

A set of BDB Extension tubes, with a box marked "39 x 1 for Leica".

A Kopil "Bellowscope for Leica"

All the male threads checked out as 1 mm pitch.

An odd ball size or fitting will hold aftermarket sales, for a while, until it gets copied, or someone makes a tool to fit it.

(Use UNEF instead of UNF, or Metric Fine instead of Metric Coarse, because "Most people won't have them. Buy from us!" is the motto ).

So for Myford to use a non standard size or pitch of thread is nothing new. The early ML series soon went from the standard 7/8 x 9 BSW thread to 7/8 x 12 tpi, and the 1947 launch of the ML7 introduced what we now regard as a the Myford "standard" of 1.125 x 12 tpi.

In the same way, Boxford use a non standard pitch thread ( 1.5 x 8 tpi )for their Mandrel, as does my BL12-24 with its 2.250 x 8 tpi Whit form thread.

It is difficult, but not impossible, to get a 4 jaw independent chuck for the flange on the Clarke CL500M, without paying a high price to machine mart.

Standardisation is the name of the game unless there is a special technical reason, or you want your product to be exclusive, to retain aftermarket sales of spares and accessories.

Howard

Many thanks for the email, we can only offer it in standard UNF which we sell all the time for the Myford backplate, it should really be a whit form thread but over the years we must have sold hundreds and we always let people know and we've never had anyone say it didn’t work, so I think your be fine with it. 
I could quote to have a whit form tap manufactured but the cost would be around the £150 mark which doesn’t always seem worth it.

Thanks Brian, today I put a piece of silver steel 10mm in the Chuck and used dial indicator to find a 2 thou run out. I have seen some people loosen backplate bolts and tap the Chuck to try and reduce the error. I found I could move the Chuck on the backplate register by just over 2.5 thou, is that fit tight enough?. If not I will get another backplate and have a go at machining, will a steel one do or is cast iron best?. After putting Chuck on and off a few times it goes on easy now.

Thanks Richard

Just wondering …Have you checked any actual Leitz parts, Howard ?

MichaelG.

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For interest: https://www.l-camera-forum.com/topic/293651-why-did-leica-use-a-british-thread-pitch-and-profile-for-the-l39-mount/page/3/

Edited By Michael Gilligan on 30/07/2021 20:22:59

Richard, just leave it as it is. .0025" slop is plenty good enough for a 3 jaw chuck & will give you a bit of leeway if you want to get a part dead on for concentricity. My brand new Warco supplied 3 jaw chuck had a .010" run out from new, in the end I had to reduce the register diameter to get it to run true, obligatory inspection report said run out was within .001"

Tony

Must have given you a copy of the report my my Warco chuck after rounding it up to 3 decimal places

Edited By JasonB on 30/07/2021 20:27:38

Sadly, Michael, no longer any Leitz lenses to check, may have an enlarging lens (An El Nikkor ) though.

Unfortnately, gave my Leica book to my grandson, who has just had to isolate, so cannot check it.

It would seem odd if Japanese, Russian and British camera (as well as the other independent lens manufacturers ) ALL made the same mistake, particularly since Reid and Sigrist were given the Leica drawings as part of war reparations.

It can now be said, that as a homework job, I did get a 42 x 1 female to 39 x 1 male adaptor made, which I still have, to adapt a Pentax /Edixa fitting lens to to be used on either of my two Periflex cameras, and fitted the Corfield Periflex focussing screen for use with extension tubes..

I was given a genuine Leitz rear lens cap, and that screwed perfectly onto my 39 x 1 fittings.

So I rest my case, based on a lot of first hand practical experience.

Have read the camera forum previously and am still convinced that the topic is wrong, possibly the result of using the wrong form gauge to check the pitch.

Unfortunately, neither the Reid, Corfield nor Canon Rangefinder sites can throw any light on the pitch. And Google has never heard of the Tower copy of the Leica!

So, I remain the only one in the regiment in step, and after nearly 70 years interest in photograhy!

Howard

35 years ago I had a Myford Ml10 and from Myford I bought a 4 jaw chuck.This would not go on and Myford sent out a man in a suit to sort my problem.He used hand chasers to sort the problem.That sort of service is unheard of today.Perhaps buying the correct hand chaser would be an option to fitting of poor threads.

Using a 12 tpi tap to clean the thread is effectively using it as a chaser, to round the peaks of the thread, and provide the last bit of clearance to produce the desired fit.

Howard

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I am sorry to disillusion you, Howard, but:

I removed the lens mount from a Leica and have photographed it for you this morning.

Although the surface finish is rougher than I expected, the thread form is quite clearly intended to be Whitworth ... and I have checked the pitch against a 1/4"BSF tap [which, at 26tpi, fits very nicely indeed].

It was difficult to photograph, but I am sure you will agree this cannot be a Metric thread form:

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MichaelG.

Clearly it would be impractical to accurately measure the thread-form on the lens mount without sectioning it [!] ... so I took a wax mould and sectioned that instead:

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MichaelG.

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Ref. https://en.wikipedia.org/wiki/File:Whitworth_Thread.svg

Edited By Michael Gilligan on 31/07/2021 15:02:07

Hi Michael,

AMAZING!

So hordes of people have been screwing 1 mm pitch 60 degree threads threads into 26 tpi whit form threads for all these years, or kidding us with what they claim to be making.

Must be a lot of slack metric threads about in the camera world, probably due to the Russians and the Japanese, when they made their copies.

Thank You

Howard

You're welcome, Howard

It’s been bugging me for a while, so I thought I really must settle it to my satisfaction.

MichaelG.

Michael, do we know if your image is of an early L39 thread or a possibly M39 thread on a later item?

Are you able to scale the image and measure distance between the current triangle and another?

I suppose it's a bit like screwing new 1/4" UNC mounts into old 1/4" whit ones, they will go. I made 10 long spikes for a Gitzo tripod a couple of weeks ago, screw cut the 3/8" thread with a metric insert and chased it with a 3/8" whit die to finish, fitted the tripod fine.

Edited By JasonB on 31/07/2021 18:09:18

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Jason,

As stated, I removed the ring from a Leica body [actually a microscopy version, which has no rangefinder] … so, by definition, it’s obviously L39.

I’m not really happy scaling the pitch from a photo of the wax … but [again as already stated] I checked the actual ring with a 26tpi tap, and it feels right. … The same tap does not nestle sweetly in an M42 thread.

The matter under discussion was whether Leitz actually used 26tpi Whitworth form, and I’m convinced that I know the answer.

MichaelG.

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Indeed !

The standards specify a class of UNC fit which is loose enough to achieve that.

Tripod thread DIN 4503-1 / ISO 1222

https://shop.bsigroup.com/ProductDetail?pid=000000000030215707

MichaelG.

Edited By Michael Gilligan on 31/07/2021 18:47:50

Hopefully BSI will permit one very short quotation from the standard ... as a 'teaser'

NOTE Deviations and tolerances basically refer to USC 1A and 1B (with minor changes for deviations d and d2 to permit international interchangeability with existing apparatus).

MichaelG.

Returning to chuck back plates, would a 2mm pitch internal thread chaser be of any use in getting a back plate on to a Myford M42.5 x 2 thread?

I have never used a chaser having tidied up cut threads with a die (my internal cut threads have been microscope threads cut to a mating plug gauge).

JA

A matching pitch thread chaser would be of great service with a slightly tight thread, and excellent for removing that difficult pressed in swarf that defies wire brushes.

Returning all the way back to the original ‘Myford Series 7’ …

KWIL posted a dimensioned and toleranced drawing of of the mandrel [spindle] nose, here: **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=122670

Unfortunately it is not directly credited to Beeston, and some of the tolerances look ill-stated, but it may be the best available to us.
​​​​

MichaelG.

Edited By Michael Gilligan on 01/08/2021 07:26:21