Metric Screwcutting on imperial ML7

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Metric Screwcutting on imperial ML7

This topic has 8 replies, 6 voices, and was last updated 10 May 2020 at 15:24 by Howard Lewis.

Viewing 9 posts - 1 through 9 (of 9 total)

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9 May 2020 at 17:34 #470402
metalfettler
Participant
@metalfettler
Last November I received an email from <<noreply@model engineer. co uk>> referring me to a thread on metric screwcutting on an imperial Myford Super 7 with gearbox. Link to << **LINK**

I am eternally grateful to whoever sent me this link. I have read it probably 30 times and have bought Brian Wood's book "Gearing of Lathes for Screwcutting"

I am bemused by mention of 16-1/2 tooth gear wheels etc and am on the point of buying some bits once I can find the serial nos. of the lathe and gearbox – mine has the power bulge i.d.ing it as an early gearbox. The lathe is a mid 50's unit in quite good condition.

btw I know where the serial nos. are supposed to be but so far cannot find them.

The reason for this post is to query the availability lifetime of the thread archive (I would be zapped without it) and aslo to ask how to get a printout of the metric threads tables included in the various postings.

Hope I have posted this in the correct topic?

Regards, Les Rix
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9 May 2020 at 17:34 #27348
metalfettler
Participant
@metalfettler
life of archive
9 May 2020 at 17:53 #470407
Neil Wyatt
Moderator
@neilwyatt
Hi Les,

There's no definite lifetime for the forum, but it is third-party backed up to web.archive.org which has 347 snapshots…

To print images, right click and 'view' to see as large as possible., then right click and save as to save them as a jpeg on your computer which you can print.

Neil
9 May 2020 at 18:07 #470411
Simon Williams 3
Participant
@simonwilliams3
That "16-1/2" tooth gear was perpetrated by me, with active encouragement from the late John Stevenson.

If you want to pursue the matter further let me know what suits.

Rgds Simon
9 May 2020 at 18:38 #470422
Enough!
Participant
@enough
Posted by Leslie Rix on 09/05/2020 17:34:03:

The reason for this post is to query the availability lifetime of the thread archive (I would be zapped without it) and aslo to ask how to get a printout of the metric threads tables included in the various postings.

You could try printing each page of the thread to a pdf file to keep as a record. Or indeed print each page to your printer and store the hard-copy.
9 May 2020 at 19:33 #470443
Howard Lewis
Participant
@howardlewis46836
The ideal for a 7 Series Myford is a 127T gear, for a supposedly perfect translation Imperial / Metric or vice versa, .although it is large (6.45 " O)D ) I had one!

"Supposedly" because even the Leadscrew may have slight errors!

Others use a 63T gear (popular with mini lathe users ) It is not absolutely accurate, but the error is small, as Brian Wood's book shows, and for most purposes can be ignored.

Howard
9 May 2020 at 19:34 #470444
Howard Lewis
Participant
@howardlewis46836
The ideal for a 7 Series Myford is a 127T gear, for a supposedly perfect translation Imperial / Metric or vice versa, .although it is large (6.45 " O)D ) I had one!

"Supposedly" because even the Leadscrew may have slight errors!

Others use a 63T gear (popular with mini lathe users ) It is not absolutely accurate, but the error is small, as Brian Wood's book shows, and for most purposes can be ignored.

Howard
9 May 2020 at 19:41 #470446
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Howard Lewis on 09/05/2020 19:33:53:

The ideal for a 7 Series Myford is a 127T gear, for a supposedly perfect translation Imperial / Metric or vice versa, .although it is large (6.45 " O)D ) I had one!

"Supposedly" because even the Leadscrew may have slight errors!

[…]

.

< Pedant Alert > … but I feel obliged to say it:

The translation is perfect … but remember GIGO

MichaelG.
10 May 2020 at 15:24 #470651
Howard Lewis
Participant
@howardlewis46836
Quite right Michael.

But we are all in thrall to any error in the leadscrews or graduations on our machines

According to the DROs on my mini lathe, the Cross and Top slides are 10 tpi. The leadcsrew is 1.5 mm pitch!

Ok as long as you know the error and can compensate for it.

May not matter if you are cutting the male and female threads on the same machine, since a 9.99 tpi pitch will mate quite nicely with another!

Don't want to start a hare running about traceabilty back to NPL standards!

Howard
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