Myford ml7 21 tooth change gears

It's probably due to the design of the shop software - users will always find tricky ways around features.

Phil

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Thanks for the information, ega,

No I did not know that. ... So far as I recall, I have never read the original article, or the subsequent correspondence.

My sole reason for mentioning it was to reduce risk of modern readers relying upon the statement as 'fact'.

What does surprise me [in the context of engineering/computing] is that he works to four decimals of mm, but only two decimals of inches. ... Please forgive my ignorance of the article: Does he explain that oddity?

MichaelG.

Nice to see they were counting 'Angels on Pins' in 1960 as well.

A very good letter in the same postbag as Shackell's commenting that 'we were all beginners once'.

Neil

Neil Wyatt:

I sometimes think Postbag should have been called Punchbag!

Michael Gilligan:

Please see my PM.

And talking of not being exact.

The factory supplied Metric conversion set for a Myford isn't either. [ Shudder, falls flat on the alter of Microns and cast two Hail Mary's a Mitutoyo's and two Moore and Wright's ]

Because it uses 60 /63 as transposition gears instead of 120 /127 but don't think I have seen this mentioned before.

"Does he explain that oddity?""

I think it is more a case of starting with showing a level of accuracy at the top of the table ie 0.2000 not 0.20 then maintaining the number of decimal places for the remainder of that table for neatness.

Vintage Computer enthusiasts may like this

Wang PCS-II as used by Prof. Cane.

MichaelG.

(Deep sigh) The whole point of this thread is that Myford use a 21 tooth gear as a driver, not a 63 tooth. Do try and keep up

How accurate do you want to be?:

The above is the table taken from the S7 handbook. The 1:1 changewheels are just a convenient way of introducing the idlers into the Excel spreadsheet. I'm not really worried by the odd tenth of a micron.

Cheers,

Rod

Roderick Jenkins:

Thanks for the table. The presence of the "Actual" column surprised me as my recollection was that Myfords did not include this (hence, perhaps, the uncertainty as to exactness). Having checked my edition of the manual (No. S.723N), it seems either that you have a different edition or have helpfully included a column of your own derived from Excel.

Can you please clarify?

Incidentally, I believe I mentioned the "not exact" point some time ago and it's certainly not new. My understanding is that a 127T gear would have to be involved to achieve theoretical exactness. The inconvenient size of the 127T gear has led to continuing attempts to find closer approximations but, as you imply, this has more to do with mathematics than engineering.

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Quite so ...

**LINK**

MichaelG.

Sorry, I should have made it clearer. I've taken the table of changewheels supplied by Myford and then used Excel to calculate what the actual pitch is using those changewheels for each metric pitch. The Myford table introduces idler wheels for some of the pitches so I have replaced the idlers by a 1:1 ratio, just so that I can use the same calculation for every row - it's just an easy way to use Excel by copying the calculation cell down the column.

HTH

Rod

Do they?

www.myford.co.uk/acatalog/METRIC-CONVERSION-SET-1481-1-503.html

Standard change wheel machines use two 21T gears. The metric conversion set does use a 21 driver but I think only for BA pitches.

Of course, one is free to use gears in any way that one chooses!

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What a pity they didn't reduce the VAT inclusive price by 40p.

MichaelG.

PS Has anyone calculated the corresponding "actual" column for the metric conversion set? It would be ironic if the (cheaper) standard machine is capable of greater accuracy.

As has been pointed out before, the alternative to the metric conversion set for gearbox machines is to use different spindle gears instead of the standard 24T.

Michael Gilligan:

"What a pity they didn't reduce the VAT inclusive price by 40p"

Well-spotted! You would almost think someone is having a laugh. Better yet if the price were £127.

Thanks for the NPL link which is a pleasing example of international compromise.

Ye gads, I can think of better uses for £254.40 (inc vat) of beer tokens!

I once purchased a piece of electronic test equipment in an earlier life - price £888.88, true as I sit here. I can still remember the smile on the my bosses face when I was trying to justify the purchase.

I've used 21 tooth set up's to make 2 ER collet chucks with great success. The 21 tooth gears came from RDG when they were not £900 and some odd pounds.

Phil

Edited By CotswoldsPhil on 29/12/2015 11:42:08

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Some years ago when I had a couple of Myfords I lusted after a quick change gearbox and Doris at the corner shop but we will leave Doris out of this for now and every time I had to swap gears over for different pitches I thought if I hadn't wasted my money on Doris I could have bought a new gearbox.

Eventually I found a S/H unit in VGC and fitted it. Went down to Myfords and bought the bits for the Metric conversion set.

We have a winner !!

No such luck.

To do a gear change on the non gearbox model used to take me 3 - 4 minutes at most, with the gearbox this turned into a 10 - 15 minute chore having to swap the banjo etc and then have to swap it all back again after.

I know it's horses for courses but much of my work is specials and not the standard range of imperial's that are in the box.

With hindsight if I had known of the trick of using 33 / 34 gears instead of the 24 driver I would have gone this route.

Roderick.

I did say Metric conversion SET.

Confusion reigns. The metric conversion set is for the the gearbox version, which is why it includes a new banjo to replace the fixed geared version on the imperial gearbox. We are talking about cutting metric threads using the changewheels, aren't we? For this, you just need to get an extra 40T and 2 x 21T gears to add to the standard set to cut all the threads shown in my table above.

In response to ega, the actual threads cut using the gearbox conversion set are:

Column 4 is the gearbox setting. Still very good in my view and no use of the 63t gear, which is only used for DP and BA pitches. You can't wriggle out of it that easily John .  But, as I've mentioned before, I much prefer the 33/34 trick which I learnt from you.  However the ability to use all the various gear options has come in dead useful for setting up leads for helical gears.

Cheers,

Rod

Edited By Roderick Jenkins on 29/12/2015 16:38:17

Roderick Jenkins:

Thank you for the gearbox table; at a quick glance the gearbox actuals seem to correspond pretty closely with the change wheel results.