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cutting imperial threads on a metric Sheraton Defiance lathe

Straydog01

Plastic
Joined
Apr 4, 2021
Can anyone please provide some guidance on cutting imperial threads on a metric Sheraton Defiance lathe?
The end of the lathe has a chart showing the gears that need to be changed as well as the position of the lever on the head and the position of the lever on the box. Setting this up is straightforward but there is no mention of what setting to put the feed/pitch selector in on the front of the machine. Above the pitch selector there is a nameplate that gives the metric pitch but no mention of what to use for imperial.
Today I needed to cut a 12TPI thread so I followed the setup but then had to find the correct pitch on the front selector by trial and error. It turned out to be the middle one, but its unclear if this varies for different imperial threads or if its always the middle one. I can't understand why there is no mention of this anywhere on the machine. Can someone please provide some guidance?
I've attached some pictures for reference. I'm aware when cutting the threads the half nut will need to stay engaged and the spindle reversed for each cut.
 

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If you found 12 TPI it sounds like you have a good start. I would use a travel indicator and measure each position and make m own chart.
 
The layout of the imperial conversion threading plate is exactly the same as the metric one. So the grid in the middle shows the position of the feed / pitch lever for each thread. Most positions being blank because the pitch produced doesn't correspond to valid thread.

Reading the top row of the metric plate looks like 4.5, 4, 5, and 3 mm pitches are the only positions of the box selector lever producing valid imperial threads.

Either make yourself up an aide memoir table to stick on the machine, usually such things go under the change wheel cover, or print off a picture same size as the machine plate and arrange things so you can hook it on to cover the metric one when cutting imperial threads. Paper print-out laminate into a plastic cover using one of the cheap machines is durable.

Clive
 
"... It turned out to be the middle one..."

The chart on the lathe indicates the 12 TPI position is not the middle selector on the box, but the 4th from the left. I had no problem understanding the instructions on the chart. I suspect that middle position cuts something a fraction off from 12 TPI.

Larry
 
"... It turned out to be the middle one..."

The chart on the lathe indicates the 12 TPI position is not the middle selector on the box, but the 4th from the left. I had no problem understanding the instructions on the chart. I suspect that middle position cuts something a fraction off from 12 TPI.

Larry

I'm starting to understand what you are saying however in practice that doesn't match up. At least not for 12TPI which only cut a correct thread in the middle position. Btw the middle position was with the gear selector 4th from the left (and 4th from the right )
I know this was a correct 12TPI because my piece screwed in nicely on the factory nut.
Perhaps I will try some of the other pitches and measure the travel with a dial indicator to see if they match.
 
Thanks everyone for the replies. I've realised I made an error when I changed over the compound gear to the 120/127 gear and I put it on backwards. My bad. Hence the feed rates didn't match up but I obtained the correct feed rate by selecting the next higher feed gear. I see it makes sense now looking at the table.
 








 
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