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# Need Help calculating change gears on Clausing Colchester model 600 vs12 lathe.

##### Plastic
I have the Service and Part manual which has formula to calculate gear change. I must be loosing gray matter because it just doesn't click. My machine has the English pitch leadscrew. I'm trying to figure if I can cut metric threads on it. I have a bunch of gears, both phenolic and metal. machine currently set up in L configuration.

#### Attachments

• Clausing 600 VS12.jpg
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#### johnoder

##### Diamond
I have the Service and Part manual which has formula to calculate gear change. I must be loosing gray matter because it just doesn't click. My machine has the English pitch leadscrew. I'm trying to figure if I can cut metric threads on it. I have a bunch of gears, both phenolic and metal. machine currently set up in L configuration.
Here is some thinkng on the subject. Say your lead screw is 8 TPI. Say also your QC gear box lists 8 TPI. I can theoretically stick in exactly two gears together as a two gear compound and imedtialely cut a 2.5mm thread. Those two gears would be 127 and 100 teeth - and they would have a ratio of 1.27 to 1. 1.27 divided into the .125 (8 TPI lead) will equal 0.098425197 - which just happens to be a 2.5mm metric thread. The practical problem is get such a pair of gears in a position where they can do some good

#### john.k

##### Diamond
The Colchester books are generally written for the UK delivery models,the US and some Canadian delivery models (Clausing?) often have a different feed gearbox ratio set......In general the UK and world delivery models have a metric /imperial change lever in the gear,generally the last gear train onto the leadscrew..............However ,if you have a 127 /120 ,or 127/100 gear combination ,you can translate metric pitches with a 8tpi lead .........there are other ratios ...80/63 etc ,etc.

##### Plastic
Thanks for the replies. My machine has a 4 TPI leadscrew. I know the gears are 14-1/2 P.A. and 5 D.P. I have all the US version gears, now I just need to find some 127/100's and EDM the ID. I start at Boston Gear!

#### Attachments

• Clausing gear panel.jpg
3.7 MB · Views: 2

#### john.k

##### Diamond
There is no way your gears are 5DP......this is truck gearbox size teeth......as well as being a rather odd size.......I d suggest more likely 12DP ,14DP or 16DP......with 16 DP being a common Colchester change gear size on the smaller lathes .......my big old Swift has 10DP change gears .

#### johnoder

##### Diamond
There is no way your gears are 5DP......this is truck gearbox size teeth......as well as being a rather odd size.......I d suggest more likely 12DP ,14DP or 16DP......with 16 DP being a common Colchester change gear size on the smaller lathes .......my big old Swift has 10DP change gears .
A way to look at that is to visualize how many 5DP teeth fit on a 1" diameter circle - the answer is 5

##### Plastic
Thanks John, I calculated wrong! it is 16 dp.

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