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Myford Metric Conversion

Use with Imperial threads

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Don Eggleton12/01/2016 20:12:27
2 forum posts

When a Myford Metric conversion is added to a Myford Super 7 lathe wth an 8 TPI imperial Lead, Can Imperal threads be cut or do you have to remove the conversion and replace the original quadrent, ?

Brian Wood13/01/2016 16:48:31
2317 forum posts
37 photos

Hello Don,

I'm surprised no one else has answered your question. The short answer is 'Yes' you need to change the quadrants You also lose the fine feed gearing when the metric quadrant is fitted.

Regards

Brian

Neil Wyatt13/01/2016 18:57:56
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Moderator
18409 forum posts
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Welcome to the forum Don.

Neil

Chuck Taper02/12/2020 11:32:04
15 forum posts
5 photos

Reanimating/hijacking this topic to bear witness to the fact that I searched (at least a little bit)

Myford offered two versions of the Metric Conversion Set (to supplement quick change gear box)

1481 had 13 change wheels whilst 1481/1 had 12 change wheels.

Can anyone enlighten me as to the specifics of the difference.

I'm in training to be a pedant.

Thank you for your time.

Frank C.

Tony Pratt 102/12/2020 13:47:18
1346 forum posts
5 photos

Frank C, I don't know the answer but you do not have to buy a metric conversion set at great expense to cut metric threads on an imperial Myford.

Tony

Chuck Taper02/12/2020 14:38:49
15 forum posts
5 photos

Tony

I appreciate what you are saying and I suppose I should have made myself a little more clear ( rather than being a bit flippant )

Having just acquired said 1481/1 (in original packaging nerd) I am wondering what the "missing" gear wheel could be.

I'm actually interested for reasons other than thread cutting. I'm collecting accumulating various add-ons & accessories & original documentation for ML7's as I can afford/acquire.

I hesitate to describe myself as a collector, rather a curator or historian - but not actually that either.

Thank you for your time.

Frank C.

ega02/12/2020 15:17:50
1937 forum posts
159 photos

Chuck Taper:

The gearbox manual refers to:

"THE METRIC CONVERSION SET (No. 1481/1 not 1481)

I have Myford literature going back to the 1980s but can only see listings for the 1481/1 in the more recent price lists.

Where does your information about the 12/13 change wheels come from?

Is the answer something to do with the North American version of the gearbox?

Edited By ega on 02/12/2020 15:21:58

ega02/12/2020 15:32:25
1937 forum posts
159 photos

Chuck Taper:

PS The only occasion that I recall using my (shop-made) metric quadrant was for turning a worm for GHT's HDA. He does mention the conversion set in his book but confusingly calls it the "1401/1". I could not see any reference to your 1481.

It may be that you need the answer to your question more than you need the 1481/1!

Chuck Taper02/12/2020 16:47:01
15 forum posts
5 photos

Picture below should speak 1k word.

I was going by the first paragraph.


"ega said:

It may be that you need the answer to your question more than you need the 1481/1!"

That's it exactly.

Was it simply one gear wheel dropped or was the overall mix of the gear set altered?

Regards

Frank C.

data sheet.jpg

Michael Briggs02/12/2020 17:17:31
203 forum posts
9 photos

If the 1481/1 is the same mix as the 1481 but less one gear, you would be able to use either set with the above chart.

Michael

ega02/12/2020 17:19:47
1937 forum posts
159 photos

Chuck Taper:

I speculate that Myfords decided that they could get the job done with fewer change wheels.

As is well-known, any given ratio can be achieved in a variety of ways and to varying degrees of accuracy.

The last paragraph is intriguing, the inference perhaps being that 1481 was for an earlier gearbox. There are far more knowledgeable members than I here and maybe they will be able to comment.

I take it that there is no date on your paperwork which I suspect is relatively old.

In the meantime, I shall be comparing your chart with the one in my own machine.

Brian Wood03/12/2020 17:07:03
2317 forum posts
37 photos

Chuck Taper and ega,

This metric conversion thread is interesting in more ways than one. I made a thorough study of the gearbox for my book on screw cutting and am for ever grateful to the late John Stevenson for pointing out there had been a North American export version made presumably to compete with the Southbend lathes.

Myford made the change to accommodate the use of 23 tpi pipe threads as opposed to the UK choice of 19 tpi and to do this they sacrificed the 19 tpi gearing within the box, shuffled up the cone shaft gearing to install a 23 tooth gear in the E selector position. The export lathe now read 8, 9, 10, 11, 11.5, 12, 13 and 14 tpi as the base for the other ratios. It looked identical but for a new plate with the gear selections printed in blue rather than the more familiar red for the UK gearbox.

The effect this change would make on a table for metric ratios would be profound as the selector position C is used for metric results of 0.20, 0.25, 0.30, 0.35, 0.45 and 0.55 mm pitches and without any correction to allow for the ratio change within the gearbox from 0.8421 to 0.8000 the errors would be gross.

I am not minded to work out what Myford may have quoted in a new metric table or which gear they chose to make the necessary correction but I am sure they would have printed due warnings about getting the appropriate correction gear set to suit the altered gearbox. They were quite thorough over such things

Regards Brian

Howard Lewis04/12/2020 10:19:42
4143 forum posts
3 photos

If it can fit inside the gear cover, (unless you are prepared to run without it ), a 127T gear will allow Metric threads to be cut on a machine with an Imperial Leadscrew. being 20 DP, it is large, 6.45" diameter.

I had one which was sold along with the ML7.

Mini lathe users seem to use a 63T gear to convert Metric to Imperial or vice versa. It gives inaccuracies, but most are small enough not to matter in most cases.

HTH

Howard

Brian Wood04/12/2020 10:59:01
2317 forum posts
37 photos

Hello Howard,

Chuck Taper restarted this thread with a question about the metric conversion sets that Myford sold having in some cases 13 gears as opposed to 12 gears and why that was the case it was not actually about achieving the ultimate precision in metric conversion which of course comes from the use of a wheel with 127 teeth in the gear train.

As you point out, sensibly close metric values can be obtained on a lathe with an English leadscrew using a 63 tooth gear instead but that isn't what the thread was investigating.

Regards Brian

Simon Williams 304/12/2020 14:11:17
561 forum posts
80 photos

Brian - good afternoon.

Is it as simple as the 1480 kit suited the old Mk 1 gearbox, and the 1481/1 superseded it when the later (double speed) gearbox was marketed? Or is that too simplistic?

I'm trying to think if I've got enough information to follow this through and check the arithmetic works out right.

I believe that this is the diagram for the 1481 kit:

dsc_0530-1.jpg

And the label issued for the 1481/1 kit looked like this:

dsc_0531-1.jpg

I'm fairly sure (but haven't dusted off my notes from the last time we visited this) that the newer kit needed one less changewheel to achieve the same result. Which could, of course, have been the reason Myford decided to update the kit.

Best regards Simon

Chuck Taper04/12/2020 16:26:56
15 forum posts
5 photos

All

Just to add a (possibly pointless) update. The attached image shows 1481/1 as delivered. All else being equal I assume the void socket was where the 13th gear lived when the set masqueraded as 1481. Having just visited the shed to check, a 60 tooth gear fits precisely (allowing for temperature and humidity!!)

Not quite QED but it will do.

Regards.

Frank C.

img_3172.jpeg

Brian Wood04/12/2020 16:46:21
2317 forum posts
37 photos

Hello Simon and Frank C

I think between you both this has cleared things up.

For Frank's benefit as the information may be new to him, the early gearbox had an outrigger housing on the saddle side containing two 18T gears and an idler linking them [to correct rotation on the leadscrew] The necessary reduction of 1:2 to make the gearbox work was provided by a 12 tooth gear driving the outside gear train.

The later gearbox has instead a 26/52 reduction built into the left hand side of the gearbox, the 52 gear is coupled to the leadscrew which is brought right through the gearbox. All this is largely hidden behind the plate that the cover is hinged from and the outer gearing driver tooth count is now 24. That gear is case hardened..

The later gearbox also sports hardened gears and engagement dog clutches, altogether a more robust piece of equipment.

Regards to both

Brian

ega04/12/2020 18:22:05
1937 forum posts
159 photos

Chuck Taper:

I take it that your 1481/1 includes the two 60T gears which are necessary for use with the later gear box.

I confess I had forgotten about the earlier gear box with its "power bulge" on the leadscrew side.

"(allowing for temperature and humidity!!)", I hope your set is well-protected against rust; that MDF or whatever it is looks as though it might absorb moisture.

Edited By ega on 04/12/2020 18:22:29

Ady104/12/2020 19:16:22
avatar
4138 forum posts
576 photos

At the end of the day everything is TPI

Our stuff

Their stuff

Stuff on the planet zog

Once you can do the math it's the best system of the lot

Michael Gilligan04/12/2020 19:56:15
avatar
17037 forum posts
756 photos
Posted by ega on 04/12/2020 18:22:05:

[...]

"(allowing for temperature and humidity!!)", I hope your set is well-protected against rust; that MDF or whatever it is looks as though it might absorb moisture.

.

I'm fully prepared to be wrong, but ... I think 'whatever' is multi-layer corrugated cardboard.

MichaelG.

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