There have been a few questions on setting up compound/transposing gears for cutting Metric threads on an Imperial Model A 9". I thought that I would put this post together to help people out as it can be a bit confusing when you start looking at the charts. This post is based on the original setup.

If you have the gears from AMH for the 9" then you need to follow that chart that Mal has attached on the photos on his website, It would be a good idea to save a copy of that image when you purchase that set of gears, The 260 Imperial to Metric chart will not work for that system and nothing in any of the Hercus literature will work for that system either. They have been generated through a gear calculation system to suit the 9" gearbox. These gears are definitely a nicer and more compact system to use than the giant gears from the original system.

Starting with the 100/127 gears if they are not connected by a keyed bush or there is not one in the set then this is the first thing that you need to make the system work.
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Next step is to set the gearbox and stud gear for the Metric thread that you are preparing to cut.
In this example I will use a 1.75mm Pitch.
For this you will need a 28 tooth stud gear and set the gearbox to 16TPI
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Next you need to fit the 127/100 compound gear, always remember to follow the chart with this setup, Stud gear connects to the 127, 127 and 100 are joined to form the compound and drive together , 100 drives the screw gear on the gearbox input shaft.
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Note that in the attached photo there is a small gear to space out the screw gear on the gearbox, you will need to place a small gear or a spacer if you have one

Next you fit the 56 tooth Screw gear, this gear remains the same for all of the threads on this chart, it is only the Stud gear that changes.
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This is also the view from the front of the lathe looking down on the set up.
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Attached Images




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