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9th May 2021, 11:29 AM #1Senior Member
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Compound gear configurations on 9" model A lathes
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.
IMG_0774.jpgIMG_0775.jpg
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
IMG_0783.jpg IMG_0778.jpgIMG_0786.jpg
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.
IMG_0776.jpgIMG_0787.jpg
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.
IMG_0788.jpg
This is also the view from the front of the lathe looking down on the set up.
IMG_0789.jpgIMG_0791.jpg
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9th May 2021, 11:53 AM #2Senior Member
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- Aug 2015
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- Adelaide
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Cutting Imperial Threads on a Metric Model A 9"
For cutting Imperial threads on the Metric Model A 9" you need the 120/127 compound gears.
In this example I will use the setup to screw cut 12TPI.
With this setup the stud gear remains at 32 teeth and the screw gear is what gets changed for the different pitches.
When you set up the gearbox for this you use the top line of the gearbox for the Left hand lever and then set the Right hand to the required A,B,C or D positions.
For this example of 12TPI the gearbox is set to 5.0 on the left lever and C on the right lever and you need a 36 tooth screw gear.
bs968-500x500.jpgIMG_0794.jpg
Set up the Gears that you need for 12TPI noting that this setup it is the stud gear driving the 120 tooth gear and the 127 tooth driving the screw gear.
IMG_0792.jpgIMG_0793.jpgIMG_0796.jpg
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9th May 2021, 01:25 PM #3Senior Member
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- Aug 2015
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- Adelaide
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260 A and AM thread charts
Keeping the compound gears in one place, this is a quick explanation on the 260 setup for both the metric and imperial gearboxes.
For Imperial treads on a Metric gearbox using the AM chart with the 63/64 compound gear.
Example of cutting a 16TPI screw you will use the setup of 0.9 for the left hand lever and B for the right hand lever, you need to replace the Stud gear with a 25T gear and the Screw gear with a 48T gear.
The 25T Stud will be driving the 63T gear, the 64T tooth will be driving the 80T, the 80T drives the Screw gear on the gearbox, the 80T idler can be removed from the train if you do not have a spare bush and stud as long as the compound gears can connect between the stud and screw gears, the 80T is used as a spacer between the compound and screw gear.
260 AM Metric to Inch.jpg5H592-500x500.jpg
For screw cutting a Metric thread on an Imperial gearbox you will need the 60/63 compound gear.
In this example I will use a setup for cutting a 1.75MM pitch
The gearbox will be set up to cut 36TPI so left lever will be in the B position and right lever will be lined up under 36 (or 2nd hole).
You will need to change the stud gear over to 42 and the screw gear over to 40 so the gear train will be 42 stud gear driving the 60T, 63T driving the 80T, 80T driving the 40 Screw gear. Remembering that the 80 tooth idler can be removed if you do not have the spare stud and bush and the compound can connect between the stud and screw gears.
260 A Imperial to metric.jpg260 Imperial gearbox.jpg
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9th May 2021, 02:00 PM #4Senior Member
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- Aug 2015
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- Adelaide
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Standard Gear configurations
Please follow the link to see the standard gear configurations from Mal
Standard gear configuration for Hercus 9" and 260 lathes
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22nd Nov 2021, 08:37 PM #5Senior Member
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- Aug 2015
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- Adelaide
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Photos of the 260 set up
I had a bit of time on the lathe the other day so i decided to take a few photos of the 260 A Metric to Imperial gear set up to add to the post.
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18th Dec 2021, 10:53 PM #6.
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- Nov 2008
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- Perth WA
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Steve,
You have done an outstanding job ! Thank you,
Bob.
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