Gear cutting calculation - 73 teeth

Some interesting comments coming up. Just to hark back to the start the reason for the original gear being made would be because the the early Myfords used the 46/73 combination on the brass thread plate. the fact that you could do it other ways is not relevant to that. Early Drummonds used a 63. I think a slightly later Myford plate shows the use of 127 but obviously the accountant wasn't on the ball giving away extra teeth like that.

Anyway 73 is a nice easy one to make with differential indexing as the ratio is just 7:12 (from memory) so you can use common change gears. I feel a bit sad for the ebayer as he probably made one for himself at the same time.

Having the ability to cut metric even if you never do is like getting a boxed set of drills half of which never get used - just nice to know you can. It derives from the instinct to collect things which evolution found was kind of useful, albeit mostly in relation to food sources.

Bazyle I am about to cut my first thread in over 35yrs it will be 30x3.5. It was also first time setting up the Myford for gear cutting since I bought it. I jumped onto this thread to follow the gear making for future ref.

My boxford came with the ultimate example of that - a brand new metric leadscrew. As the previous owner said - gets things much closer to being able to cut metric threads even with an imperial gearbox.

I'm as bad. I needed a metric left hand tap. Found a decent quality set that cost little more than one off some suppliers so bought the set. I've worried about not having any dies since. So last time I bought something of a suitable supplier I ordered 2 just for if. Then more recently saw a 3 tap set plus die in one of the other sizes at a silly price so bought that too.

Screw on chucks and metric threads in my view don't really mix well. I have used the conversions I posted a few times - never the 100/127 even though it will fit but there is always the chance of the chuck unscrewing. Not happened on the boxford but did on another. Then the time it takes for a metric indicator to line up - if there is one. And screw cutting to a shoulder - much helped even with an imperial indicator. Imperial is so much quicker/easier.

John

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