Screw Cutting Gears!

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Pmma-Granville

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hello!
My first problem to put to you lot!
Basically my old Granville lathe has some of its gears missing, sourcing them is not as problem as the myford gears fit. My problem is which ones do I need?
Iv attached 2 pictures, 1 is a list of gears which I have, the other is the screw cutting table on the machine.
IMG_0624.JPG IMG_0625.JPG hello!
My first problem to put to you lot!
Basically my old Granville lathe has some of its gears missing, sourcing them is not as problem as the myford gears fit. My problem is which ones do I need?
Iv attached 2 pictures, 1 is a list of gears which I have, the other is the screw cutting table on the machine. Can anyone confirm which ones I need to get?
Also, the table shows for the 1st and second stud just " can't work out what that's telling me!
This is the first time iv had any experience on a lathe without a quick change gear box so any help is much appreciated!

Thanks!!
Jack
 
Please take post a picture of the gear train.


Sent from somwhere in east Texas by Jake!
 
The only one that I see missing is a 25t, a lot of gear sets have a extra 60t also.
 
Would I need an extra 20t? It's listed twice for some threads.
And what about the " marks for 1st and 2nd studs? Says idle wheel for the first thread, what do they mean by that?

Thanks for the replies!
 
Jack
Its hard to read the chart, but If you are going to cut 114?tpi then you will need the extra 20t gear.
The tern change wheel is another word/term for the gears, it is used to complete the gear train when you are using small gears. An example if you are cutting 14tpi you will install a 20t on the mandrel and a 35t, on the leadscrew there will be a large space between the mandrel 20t and the leadscrew 35t that's when you install any gear that will take up the space between them. The number of teeth on the idler wheel/gear will not matter its just connecting the two gears to complete the gear train.
I hope this not to confusing,:boxed in: its hard to explain unless you are in person to show how its done. South bend lathe has a book on line how to run a lathe that has a good explanation. :encourage:
 
Thanks a lot tom makes perfect sense!
I didn't think it would be as simple as slapping on any gear that makes the space up.
I'll look into the southbend lathe book.

Looking at myfords parts, the small gears are ok to make out of SRBP (tufnol), a material iv got plenty of.
What do you reckon my chance are of CNC cutting the gears? Got access to CNC routers and mills at work, could try to scale a picture of the gear and turn that into a dxf for the CAM software?
 
I think the bottom two lines on the chart are for finish machining, not cutting threads. Offhand, I'd say you're missing the 25 and the 40, and the second 20, for 25 to 40 tpi.
 
Thanks for your reply!
40t is a reasonably sized gear, do you think I'd be better off buying that gear?
They're not expensive to buy, I'd just like to make them myself! Would have to be SRBP though!
 
You will also need a 120 x 127 gear if you ever want to make any metric threads.
 
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