Thursday, January 7, 2016

39 Tooth Gear for my Emco Maximat V10 Metal Lathe

Make a 39 tooth gear for my lathe to allow me to cut 1mm metric threads on my imperial lathe

Difficulty Level (Easy, Medium, Hard, Insane):

After I built the Dividing Head and the Fly Cutter making the gear was actually one of the more exciting projects.

The way my lathe is set up is in the gear change box there is a 45 tooth gear made out of nylon that serves as a sort of "sacrificial" gear in case the carriage got stuck or jammed into the chuck or any other such catastrophic event so that way it would strip the teeth off of the nylon gear instead of breaking somewhere else. The nylon gear has a metal core with the main hole for the shaft plus two smaller holes for two roll pins that lock together with a larger metal gear behind it.

It also looks like there originally was a second nylon gear which must have broken over the last 43 years of use, but the metal core was still there so what I decided to do for this gear is to bore the center hole to about 10 thou smaller than the diameter of that extra steel core and press it in with my vise. That actually worked out quite well and I can now officially cut 1mm threads on my imperial lathe.

The theory behind it is that I can use different gears in place of the 45 tooth gear to create an approximation of a metric thread. On my lathe, I have the following imperial TPI (Threads Per Inch) settings: 8, 9, 9.5, 10, 11, 12, 13, 14, 16, 18, 19, 20, 22, 24, 26, 28, 32, 36, 38, 40, 44, 48, 52 and 56.

Now, taking the 22 TPI setting as an example and converting it to metric, with the regular 45 tooth gear it will cut a (25.4 / 22) = thread.

HOWEVER, if I use a 39 tooth gear INSTEAD of the 45 tooth gear it will change to a (25.4 / 22) * (39 / 45) = thread. As you can see, the error in my thread is 6 ten-thousandths of a mm for each thread. In other words, for a 4 foot threaded rod using my 39 tooth gear I will be off by less than one mm which for my applications is more than accurate enough.

I have also calculated a chart for most other metric threads and might cut me some gears just to have them on hand should I ever require other metric threads.

Math is awesome!!!

The dividing head set up with my gear blank
Cutting the first few teeth
Another view
The metric test thread
The 39 tooth gear installed at the place where the 45 tooth gear normally sits
Another view
A picture of the chart I printed out with the TPI settings, gear tooth numbers and tolerances
The finished 39 tooth gear
Another view
Metric threads by changing 45 tooth gear.pdf

Lathe and accessories
Dividing Head
Fly cutter

2" of 2" nylon




It works! So pumped about this!


Tony Kent said...

Hi Mate,
I like what you did here.
I am in the process of restoring a V10 and have next to nil lathe experience. My question is would you be interested in making another 39 tooth gear and ship to Australia - I will obviously pay you for it.

Chris Eigenheer said...

Tony, I'd be glad to help. Can you email me at eigenheerc at hot mail dot com?

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