# Cutting a M39 x 4 Thread



## 96cb750 (May 25, 2014)

Hi all i am new to this fantastic site .I know a bit about turning so i am not a novice but i am no expert.I have a 9 x 20 asian lathe and i have done a good few mods to it and have made a couple of extras for it .I want to make a Er collet chuck for it .My spindle has a M39 x 4 thread and the lathe only seems to cut a 2mm pitch thread. Is there any way i can cut the thread i need on my lathe ?
Thanks Jimmy.


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## Terrywerm (May 25, 2014)

There is a way, but how it can be done will depend a bit on how your lathe is equipped.

If your lathe has a quick change gear box, and is capable of doing a 2mm pitch, then you will need to make or obtain some custom gears to double your QCGB input speed, then use the 2mm setting.  This is just one method, there may be others.

If your lathe has change gears that you must manually change, then you will need a set of transposing gears to allow you to do a metric thread. A set of transposing gears usually is composed of two gears, one with 100 teeth and one with 127 teeth which will allow you to cut accurate metric threads.  Optionally, you could use a set of transposing gears consisting of one with 37 teeth and one with 47 teeth, but this setup allows a 1/10 of 1% error, thus long metric threads will have problems. 

A fellow named Conrad Hoffman has an excellent writeup on the process on his website, which you can visit here: http://conradhoffman.com/metricthreading.htm


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## savarin (May 25, 2014)

assuming you have the 9x20 with the 9 position gear box and change gears then the following setups will give a 4mm thread
gear lever position 1, A=80, (stacked 127, 120), B=30
The following combinations require sized gears that didnt come with the lathe.
gear lever position 2, A=90 (stacked 127, 120), B=30
gear lever position 4, A=120, (stacked 127, 120), B=36
gear lever position 5, A=110, (stacked 127, 120), B=30
gear lever position 7, A=80, (stacked 127, 120), B=20
gear lever position 7, A=120, (stacked 127, 120), B=30
gear lever position 9, A=140, (stacked 127, 120), 30=20 from.
HTH
There is a spreadsheet available somewhere that gives all these threads in both metric and imperial but I cant remember where I obtained it
found it, its in the files section of the 9x20 lathe group
https://groups.yahoo.com/neo/groups/9x20Lathe/files


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## 96cb750 (May 31, 2014)

Thanks all for your help 
my lathe is a metric lathe so will the same gearing give me the same results
        thank you Jimmy


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## Ozwelder (Jun 4, 2014)

This 39 x 4 thread caught my eye.

I have a 12 x 36 Chinese lathe  and was wondering about the gear stack combination. 

Are the gear trains the same in their set up?

By using the same stacking/number combination would I be able to reproduce a similar thread pitch.

The outboard spindle is 39 x 2 from memory.Its an internal thread with a flat crown( butchered at the factory).

I am hoping to machine an outboard spindle spider and for that I need the 39 x 2 thread.I know i have to change something in the train to get a 2mm instead of a 4mm

I would grateful if I can be pointed in the right direction.

Thanks
Oz


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## ddmunroe (Jun 5, 2014)

terrywerm said:


> There is a way, but how it can be done will depend a bit on how your lathe is equipped.
> 
> A fellow named Conrad Hoffman has an excellent writeup on the process on his website, which you can visit here: http://conradhoffman.com/metricthreading.htm


Terry that's a good article, quite in depth has all the answers
Cheers
dd


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