Metric thread on an ML7

This ought to be simple so I'm probably missing something. I'm trying to cut a 1.5mm thread on an ML7 with 8TPI lead screw.
I have a 127 tooth gear but no 21 tooth. Duncan Munro's Ml7 Gear calculator suggests 60 on the spindle and 127 on the lead screw with various idlers between. The is not enough space between spindle and lead screw to make that work. Via a Google search I found a suggestion taken from Martin Cleeve's book for a compound train using the 38 tooth and 65 tooth gears. Once again I can't make the train fit the space available.
My memory says that I have cut metric threads in the past but I probably shouldn't trust that.
What am I missing?
Cheers Henry
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On 8/15/2017 7:29 AM, Dragon wrote:

Go here and use "other lathes" and it will give you all the gear changes for your gear set and tell you the error if any. Also remember you have to leave the threading handle engaged and use reverse to back it back out for next cut... <http://littlemachineshop.com/reference/change_gears.php> Jim the yank
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On 15/08/2017 20:19, Jimmy Alpha GeD wrote:

Thanks for the suggestion Jim. I'd already taken a look at it but have not tried to use it. Once I make the effort to find the limits of what will fit on the banjo I'll give it a go. The Duncan Munro software does a similar job and is specific to the Myford ML7 so has the facility to use 6 gears as well as 4. Digging around a bit more I think I have found the answer to the basic problem. I either need special gears that will fit on the existing banjo or a bigger banjo to enable the 127 gear to be used. I've yet to check but suspect that previously I had cut a metric thread of less than 1.5mm and that needed a bigger reduction ratio that enabled the smaller gears to fit on the banjo.
Cheers Henry
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On 8/16/2017 3:33 PM, Dragon wrote:

In the LMS program you type in all of the gears you have and leave out the big 127 gear and see what they give for a solution, type in even doubles if you have any. Sometimes the error is so small you wont notice in perhaps .5mm or so?
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On 8/16/2017 3:33 PM, Dragon wrote:

>
In the LMS program you type in all of the gears you have and leave out the big 127 gear and see what they give for a solution, type in even doubles if you have any. Sometimes the error is so small you wont notice in perhaps 12mm or so?
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On 16/08/2017 22:33, Jimmy Alpha GeD wrote:

Thanks for encouraging me to give it a go Jim. I eventually gathered all the information and it did indeed come up with usable answers for several metric threads which I printed and now have on hand when needed.
Cheers Henry
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On 29/08/17 20:50, Dragon wrote:

My neighbour borrowed a ML7 metric cutting kit from another neighbour and it was a true conversion with the 127 wheel and IIRC it wouldn't fit within the standard cover so I doubt HSE would be impressed with the exposed gears but it did the job and IIRC did use a larger banjo or extension for it. All subsequent metric cutting has been done on my Harrison M300 which does both TPI and metric but I think it is pseudo metric, close enough for most things but not absolutely correct as the lead screw is inch.
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wrote:

The 127 tooth gear or equivalent should take care of that inch lead leadscrew. It has on every lathe I have run. Being in the USA metric leadscrews are not so common. As everywhere else. Eric
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On 8/29/2017 3:50 PM, Dragon wrote:


thumbs up!
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On Tuesday, August 15, 2017 at 12:29:38 PM UTC+1, Dragon wrote:

The 21 tooth gear is an option you can buy from Myford I found the best solution is to buy one of these.
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On 06/01/2019 16:25, snipped-for-privacy@gmail.com wrote:

Thanks to a reply to my 2017 message I was able to set up a compound train using the existing standard gears. There is a nice bit of software that does the calculations for a wide range of thread pitches. http://metal.duncanamps.com/software.php
Cheers Henry
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