Author Topic: Metric Transposition gears  (Read 14883 times)

Offline steamer

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Metric Transposition gears
« on: September 05, 2012, 01:58:34 AM »
While I was working on my early 1900's Waltham machine works lathe, I realized that it needed a new drawbar.   This is no small job!.....

Additionally, the thread is wierd!   The toolmakers at Waltham decided they were going to scare the (*#&$@ out of their customers and specify a 20mm x 1.6667 mm pitch, 45 x 5 degree buttress thread for the collets!    YIKES....
This lathe was made for export to the Swiss watchmakers....which in 1914 or so...it was far from guaranteed that the lathe would end up in Switzerland...and not with the opposite side during WW1.   At the time a precision lathe was a dangerous thing to give up to a foe...so ...
Waltham stopped making this lathe in 1914.....Well those wiley Swiss decided to make on of their own using the same tooling....and in about 1915...started Schaublin....with a W20 collet.....which is 19.7mm x 1.6667 mm pitch 45 x 5 buttress thread!

The Waltham collets were made of cast iron and left soft.....says so in their brochure!   I still have  one !....but it's very worn out...
Guess what fits right in!    Schaublin collets!.....but the thread is ever so slightly smaller.

HEY! says I ....I bet I can cut that thread!   How about brazing in a new piece of steel in the drawbar and rethread the bore to Schaublin and use a nifty set of metric W20 collets I got off the bay!

Problem.....how the hell am I going to cut metric threads on my English lathe.....and how am I going to cut 1.6667 mm pitch!

I started noodling....playing with gear ratio's and such...I figuired if I could add some gears in train ahead of the QC on my Logan, I could maybe make it cut 1.6667mm.    But how?

It dawned on me that if I add a metric transposition set to my lathe , it was like multiplying by a conversion coefficient.   Take the number on the QC box....multiply by 1.27 and get the metric equivalent threads per inch.   Multiply by .03934"/mm and take the reciprocal and I end up with the metric pitch of the thread.

For instance.     12 threads per inch X 1.27 = 15.24 threads per inch.     1  / 15.24 threads/inch x .03934 inches/mm = 1.6679 mm pitch....

Cool!   OK lets find some transposition gears for my Logan......GASP!....they don't give them away!...I'll make some!

OK ...next problem...my Logan has a fixed gear case cover that I can't fit 127/100 gears into...what else could I use?

47/37 = 1.27027 as compared to 1.2700.......I'll live with that!

I cut some gears for this and I made extra.   I still have the extra!
They're 16DP and I think 20 degree pressure angle

I added a quadrant to my lathe banjo and clustered the gears together with a grease fitting

Cutting the gear blanks



Making the dividing head tailstock match the dividing head....a mixed set from an auction..


Cutting the gears on the VanNorman #12.






Here's the bar before I bored the old threads out

And with the insert fitted and ready to be silver soldered in.

Bored to size for threading


And complete with the threading tool in the picture....like a glove!


Dave


« Last Edit: August 24, 2013, 12:27:32 PM by steamer »
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Offline steamer

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Re: Metric Transposition gears
« Reply #1 on: September 05, 2012, 02:14:11 AM »
And again.....here we are making tools to make tools.....namely the gear blank arbor, the milling arbor, were made up from scratch by me while the dividing head tailstock was modified to fit the dividing head., and I needed to make a spindle gear twice as wide as the original so I could fit in the transposition set..... ::)


There is a 12 step program for this hobby.....right?

Dave
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Offline Don1966

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Re: Metric Transposition gears
« Reply #2 on: September 05, 2012, 02:20:41 AM »
Dave I can see I have to way to go to understand all these gear ratios and I am working on it. I have a banjo gear on my Myford that sets the inch per spindle rotation of .139 to .002" this is my second stud gear of 19/57 teeth cluster gear. But the 712V manual on the gear box show a lot of gears to change plus the quadrant bracket. If there was a way to change the banjo gear ratio and do it, I would give it a try. One thing I don't under stand is, the book also shows a chart with different DP for different gear setup. What does this mean? I know DP is diamentral pitch, but what is the chart doing?

Don

Offline steamer

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Re: Metric Transposition gears
« Reply #3 on: September 05, 2012, 02:52:03 AM »
Hi Don,

I'm not sure. but I'd guess they have a limited space to put gears in under the guard....and therefor change the DP to limit the physical size of the gears under the cover......I'd need to read the manual to be sure.

Dave
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Offline steamer

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Re: Metric Transposition gears
« Reply #4 on: September 05, 2012, 03:08:19 AM »
Hey Don,

See if this helps....
My lathe before I added the transposition gears



Droping the banjo


Adding the gear and banjo extension



Dave



« Last Edit: September 05, 2012, 03:14:47 AM by steamer »
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Offline Don1966

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Re: Metric Transposition gears
« Reply #5 on: September 05, 2012, 03:20:40 AM »
Dave I finally had a chance to read the gearbox manual. The DP chart is for cutting worm screw so you can match the worm gear DP. I still need to research the Banjo gear and see where this leads me. Once I have had a chance to figure out all these ratio with the addition of the gear box, maybe I can figure  it out. Thanks for the info. I will be out of town on work for a few days and will do more reading.

Don

Offline Stuart

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Re: Metric Transposition gears
« Reply #6 on: September 05, 2012, 08:28:05 AM »
Don

you only need to change one gear in the gear train to convert to very very near metric on a Myford with a norton gear box


John Stevenson sold the gear( there are two in the set but only one is used at a time )

you change the first gear from the banjo for a 31 tooth gear and you have metric threading and slow speed as normal

PM if you want more details

Stuart
My aim is for a accurate part with a good finish

Offline steamer

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Re: Metric Transposition gears
« Reply #7 on: September 05, 2012, 10:20:23 AM »

Hi Stuart!
Yes   I just set my QC to 12 in my case and added the gear cluster.   If you pair up a set of gears to make a transposition set...your doing the same thing... and it could very well be done with 1 gear.

Dave
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Offline steamer

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Re: Metric Transposition gears
« Reply #8 on: September 05, 2012, 11:02:48 AM »
Don,

OK, now I understand what your talking about.   It's basically the same thing as the transposition set, except instead of 1.27  you converting for PI/2 or 1.57 and in that case...I suspect a 8 , 9 , and 10 thread will cut a worm with 16, 18, or 20 dp pitch.

Would be good for making gear hobs....

Dave
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Offline Stuart

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Re: Metric Transposition gears
« Reply #9 on: September 05, 2012, 12:52:14 PM »
yes thats it
there are two gears supplied one 31 and a 34 they go one one at a time to give a spread of metric threads and BA to boot
its not quite to NASA standard but hey its simple and give Myford owners with the QC gearbox metric and fine feed in the normal way


I have the chart but as John  S. sold them on his site I am reluctant to put it in the public domain  ( note JS does not list them any more )


Stuart

My aim is for a accurate part with a good finish

Offline gbritnell

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Re: Metric Transposition gears
« Reply #10 on: September 05, 2012, 08:51:34 PM »
Nice work Dave. I run into situations just like you, make a tool to make a tool.
gbritnell
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Offline steamer

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Re: Metric Transposition gears
« Reply #11 on: September 07, 2012, 10:20:52 AM »
Thanks George!    :NotWorthy: :NotWorthy: :NotWorthy:
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Offline Don1966

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Re: Metric Transposition gears
« Reply #12 on: September 08, 2012, 03:39:38 AM »
Dave and Stuart many thanks for the help. I have ordered a 20dp involute cutter to make my gears with. Hey I want to give it a try, I haven't made a gear yet. What better way to learn. My 5C indexer should be in at about the same time. Will post the process when I do.

Don

Offline steamer

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Re: Metric Transposition gears
« Reply #13 on: September 08, 2012, 11:01:25 AM »
Hi Don,

Is it a standard 5C indexer with the division pin?   What tooth count are you trying to cut?

The standard 5C indexer I'm thinking of will only cut a minium of 1 degree increments.......it may not give you the division your looking for

Or do I have that confused with something else?

Dave
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Offline Don1966

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Re: Metric Transposition gears
« Reply #14 on: September 08, 2012, 02:37:50 PM »
You are  right Dave I had not thought of that. I will have to use my RT.

Thanks Don