Myford ml7 21 tooth change gears

[John Stevenson 1Participant @johnstevenson1]

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.

[BazyleParticipant @bazyle]

"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.

[Michael GilliganParticipant @michaelgilligan61133]

Vintage Computer enthusiasts may like this

Wang PCS-II as used by Prof. Cane.

MichaelG.

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by John Stevenson on 28/12/2015 22:02:37:

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.

(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

[egaParticipant @ega]

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.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by ega on 29/12/2015 09:57:23:

My understanding is that a 127T gear would have to be involved to achieve theoretical exactness.

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Quite so …

**LINK**

MichaelG.

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by ega on 29/12/2015 09:57:23:

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?

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

[Neil WyattModerator @neilwyatt]

Posted by Roderick Jenkins on 29/12/2015 08:13:18:

Posted by John Stevenson on 28/12/2015 22:02:37:

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.

(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

Do they?

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

[egaParticipant @ega]

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!

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 29/12/2015 11:06:00:

And talking of not being exact.

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

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

MichaelG.

[egaParticipant @ega]

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.

[egaParticipant @ega]

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.

[CotswoldsPhilParticipant @cotswoldsphil]

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

[John Stevenson 1Participant @johnstevenson1]

Posted by CotswoldsPhil on 29/12/2015 11:31:23:

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

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

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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.

[Roderick JenkinsParticipant @roderickjenkins93242]

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

[egaParticipant @ega]

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.

[Michael GilliganParticipant @michaelgilligan61133]

This 21 tooth Timing Pulley may be of interest.

I bought 'the last one' today, but presumably there will more availale sometime.

MichaelG.

[John Stevenson 1Participant @johnstevenson1]

Michael,

Think you are going to have problems running that alongside a 20 DP Myford change wheel

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Stevenson on 29/12/2015 21:09:47:

Michael,

Think you are going to have problems running that alongside a 20 DP Myford change wheel

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John,

Running alongside shouldn't be a problem … meshing-with would, of course

MichaelG.

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P.S. … it may, or may not, end-up on the Myford.

[John Stevenson 1Participant @johnstevenson1]

Something like this ?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Stevenson on 29/12/2015 22:17:20:

Something like this ?

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Yes, very much like that [except mixed with the changewheel set], which is why I was rather surprised that you [of all people] didn't immediately guess what I had in mind.

MichaelG.

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P.S. …. Martin Cleeve's use of a reduced pitch 127 tooth, mixed in the Myford train, is maybe my source of  'inspiration'. 

 

Edited By Michael Gilligan on 29/12/2015 22:44:52

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by Roderick Jenkins on 29/12/2015 16:33:35:

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:

… 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 .

Apologies to John . The gearbox metric conversion set does use a 60/63 pair together with a 50/45 pair permanently on the banjo for metric threads. To get all the threads shown in the table you only have to change the tumbler stud gear and the gearbox input gear. But you still get a very close approximations to the true metric pitches so, presumably, the 50/45 pair refines the translation. I blame the (self inflicted) jet lag. Anyway, sorry – that will teach me not to be sarcastic (maybe)

Rod

[John Stevenson 1Participant @johnstevenson1]

Posted by Roderick Jenkins on 01/01/2016 12:28:33:

. I blame the (self inflicted) jet lag. Anyway, sorry – that will teach me not to be sarcastic (maybe)

Rod

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Never, ever leave the sarcasm out. It makes life far,far more interesting

And no need at all for the apology.

[Rufus RoughcutParticipant @rufusroughcut]

Hi All

Pleased to see I created a bit of fuss of exactness, has anyone tried jacking up a Myford 7 and extending the quadrant (non gearbox version) and fitting a 256T to the lead screw?

Pleased to see that even the professors and computers are rounded to best guesses exactness.

Ed, Did you achieve the thread and was it significantly cheaper than the use of the correct Tap/Die

Happy new year

Rufus

[John Stevenson 1Participant @johnstevenson1]

Why would you want to use a 256T ?

Think you mean 254 ? and as it's not a prime 127 is exactly the same.

[Author]

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