A variable Lead threading attachment. Author Ted McDuffie

[Brian WoodParticipant @brianwood45127]

Some help please with Mr McDuffies article which was published in MEW in the Autumn edition 1990, before the time I started taking the magazine.

My interest stems from Theodore Clarke's artic;le in MEW 204 [ the current issue] which refers to Mc Duffies work as a reference; it would make useful background reading on what seems to be an interesting method of altering thread pitch.

Can any of you help please with a back copy or similar?

Thank you

Brian

[Brian WoodParticipant @brianwood45127]

Article in MEW ??? published Autumn 1990

[Robin KingParticipant @robinking15611]

If you've managed to log in to post this message presumably you can also access the digital edition, issue 2 on the last page of the digital listing – would that help?

Robin

[Brian WoodParticipant @brianwood45127]

Hello Robin,

Thanks for the suggestion but don't I have buy into the digital issues first? And in any event I am missing the actual issue number to look for as well.

I'm not being deliberately mean, I already pay for my copies at subscription rate

Brian

[JasonBModerator @jasonb]

If you have a paper subscription to MEW then you can view MEW back issues on line, if you get it from newsagent etc you can't.

Its issue No2.

[Brian WoodParticipant @brianwood45127]

That's very helpful Jason, thank you.

Brian

[Sub MandrelParticipant @submandrel]

Brian,

You need to enter your subscriber number on your profile page before you can access your digital issues.

Neil

[RobboParticipant @robbo]

Brian,

If you're not a subscriber but an "over the counter" reader of MEW, I can send you a digital copy of the article.

Phil

[Brian WoodParticipant @brianwood45127]

Gentlemen,

Thank you one and all for the sage advise. I do pay for postal subscriptions but I usually dump the wrapper which has the Sub. number on it; this time I need it!! Ah well, there's no rush, I now have the information I needed to retrieve that particular article

Phil. Thank you very much for your generous offer, it is greatly appreciated but I hope I can work the digital method satisfactorily. My suitably aged grandson lives in the USA so I shall have to muddle through; it doesn't come as easily to me as making swarf and failures.

If all fails I will knock on your door.

Thanks again to everyone

Brian

[RobboParticipant @robbo]

Brian,

Forgot to say in previous post that I have all the paper copies of MEW, so can just scan several pages into one file.

As my wife would say "silly old fool" I wish she wouldn't call me old!

Phil

[Brian WoodParticipant @brianwood45127]

Hello Phil,

I get the same sort of disrespectful comment, it depends on the crime of course but "daft old bu**er" gets used for serious offences!.The 'old' bit does grate doesn't it.

Thanks again for your support if I need it.

Best wishes Brian

[jacques maurelParticipant @jacquesmaurel42310]

I've published a "universal threading attachment" almost completely contained on a toolholder, based on Thales theorema, point E being fixed and BC being adjustable:

[jacques maurelParticipant @jacquesmaurel42310]

This was in ME issue 4270 (march april 2006) general view:

[jacques maurelParticipant @jacquesmaurel42310]

There are numbers stamped on the lever and charts are given so it's easy to cut any lead. On the photo (metric lead screw) one side of the groove is graduated for imperial leads, the other for module leads (for cutting single start worms). No change gear is needed, all cutting is from the standard gear box but the thread must be short (50 mm) read the article for details.

[Gary WoodingParticipant @garywooding25363]

I don't take ME, so could you make details available on this forum, or maybe email to interested parties?

[jacques maurelParticipant @jacquesmaurel42310]

The calculation is BC = 30/(p'/p-1) mm, p' being the lead to obtain and p the standard one.
Ex for p' = 20 TPI (1.27mm) and p = 1mm, BC = 111 mm (position 2).
The charts and graduations are here to help when setting the lathe for standard leads (imperial and module for a metric lead screw, metric and diametral pitch of an imperial one).
Almost any lead can be obtained within the range of the lathe gear box.

My attachment is quickly set up (contained on a toolhoder). Because for me the time for removing and resetting the top slide, is the same as the time for setting and resetting the banjo arm.

Ex : chart for machining module leads from a metric lead screw:

[Brian WoodParticipant @brianwood45127]

Hello Jacques,

I have been busy elsewhere since my posting on 5th June, you have added helpful information and some detail to flesh out the story and extend the understanding a trifle. Thank you

Gary Wooding

If you want a copy of the Mc Duffie article that I started this thread with, send me a PM with your email address, I can now copy one to you.

Regards

Brian

[jacques maurelParticipant @jacquesmaurel42310]

With the universal threading attachment (and the others variable lead attachments) it’s possible to use the “Thread dial indicator”, so it’s possible to open and close the “Half nuts”,(as you are using a standard thread from the gear box). This makes thread machining far easier!
It’s possible to work against a shoulder from left to right as described in this video:

**LINK**

[jacques maurelParticipant @jacquesmaurel42310]

This link will work :**LINK**

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Just a few simple thoughts :

? Increasing geometric error as linkage goes away from the all square condition .

? Correcting link , correcting slide or correcting cam .

? Analysis same as for pantograph and parallel motion mechanisms .

MikeW

[Sub MandrelParticipant @submandrel]

But are the errors ever big enough to need this level of correction? Only for leadscrews or similar.

A 1% error in an M6 thread would amount to about 0.05mm over the thickness of an M6 nut. Smaller than the production tolerance, and as good as a die-cut thread.

Neil

[jacques maurelParticipant @jacquesmaurel42310]

The purpose of this attachment is not to correct the lead but to use the standard gear boc leads for machining any odd lead, so no change gear is needed (only the standard gear box is used).

Of course there is some geometric error as the linkage goes away, but for about 50mm long (short thread) this is negligeable (less than the lead screw error).

[Ady1Participant @ady1]

Will it do metric threads on an imperial lathe? Will the dial indicator work?

Edited By Ady1 on 16/06/2013 02:33:47

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Jaques and Neil ,

With representative proportions of device as in drawing positional error of tool is of order 0,4 mm when top of combining lever is offset 25 mm .

Whether this level of error matters depends on the kind of work that is being done and the fineness of thread being cut .

Regards ,

MikeW

[BazyleParticipant @bazyle]

Jaques, Thanks for the dual language titles on your video. I am learning some new French words.

I somehow missed the ME article in 2006 so am glad this came up. It looks very useful for old lathes where most of the change wheels have gone missing and there never were metric combinations anyway. The error shouldn't matter since I find most threads are at most only 2 nuts long.

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