Help me crunch some numbers

[AndyStobbs]

I'm good at maths, and am pretty certain I'm not missing something obvious here but two heads are better than one, so a forum's worth has to count for something.

I have an old flywheel here, I looked at and saw the basis of a rotary table. I was thinking I could turn a worm screw on the lathe to drive it. So...

Its 135T, 11.250" PCD and I reckon that works out to 12DP - actually its probably metric and using the module gear system but that doesn't matter for now.

Right so 360 degrees / 135T = 2.66666667 degrees per tooth.
For simplicity I thought it would be nice to have one turn of handle (at this point I envisaged the handle direct onto the worm) generating 1 degree of rotation. But the numbers got scatty, the angular movement of the 'table' at the OD was 0.098......" for a 1 degree movement, so it'll be impossible to cut a screw that'll create that amount of rotation in one turn - on an L5A at least.

However I got thinking the other way around and 0.375T = 1 degree, thats a nicer number, so I started thinking about how I could index 3/8 of a tooth, and at this point I got to the handle being indirectly connected to the worm,through gearing instead. So a gear system that can generate a reduction such that 1 turn in = 3/8ths of a turn out with a multiple of 8 teeth should work. Depending on worm pitch, which has to be quite a small number due to the sheer size of a starter ring gear.
Am I mad or am I crunching correctly?

 

[Agroshield]

It's 135T, 11.250" PCD and I reckon that works out to 12DP - actually its probably metric and using the module gear system but that doesn't matter for now... ...Right so 360 degrees / 135T = 2.66666667 degrees per tooth.

For it to mate correctly, you do not have any choice over the pitch of the worm. It has to match the circular pitch of the gear and the ratio you will get will be 135:1

You will need to mount the worm at an angle to the gear. This is determined by its diameter.

Your lathe may come with a chart for screwcutting circular pitches, but in essence, you need a set of gears that approximate pi (so 22 and 7 will feature as factors). Note also that 355/113 is a very good approxiamtion of pi.

Thinking in terms of degrees will not help you. Obtain for yourself a copy of Ivan Law's Gears and Gearcutting as well as Martin Cleeve's Screwcutting in the lathe. These two little books will tell you all you will ever need to know.

A useful ratio for a rotary table is 120:1 which is not too hard to get to from 135:1 (need a 9 and an 8).

 

[roofman]

I would of thought it would be better to buy a cheap small unit and mount your bigger (flywheel) table to it...No thinking/time/or machining needed except the mounting side.

 

[AndyStobbs]

For it to mate correctly, you do not have any choice over the pitch of the worm. It has to match the circular pitch of the gear and the ratio you will get will be 135:1

You will need to mount the worm at an angle to the gear. This is determined by its diameter.

Your lathe may come with a chart for screwcutting circular pitches, but in essence, you need a set of gears that approximate pi (so 22 and 7 will feature as factors). Note also that 355/113 is a very good approxiamtion of pi.

Thinking in terms of degrees will not help you. Obtain for yourself a copy of Ivan Law's Gears and Gearcutting as well as Martin Cleeve's Screwcutting in the lathe. These two little books will tell you all you will ever need to know.

A useful ratio for a rotary table is 120:1 which is not too hard to get to from 135:1 (need a 9 and an 8).

I knew there was a flaw in it somewhere. So obvious now you say it about the worm matching, but I just couldn't get my finger on it.
So any gearing has to applied between handle and lathe.

Brian, I probably won't ever get around to it and will buy one no doubt when one crosses my path. Was just playing with numbers, trying to keep my brain sharp between mindlessly boring vehicular jobs.

 

[roofman]

I knew there was a flaw in it somewhere. So obvious now you say it about the worm matching, but I just couldn't get my finger on it.
So any gearing has to applied between handle and lathe.

Brian, I probably won't ever get around to it and will buy one no doubt when one crosses my path. Was just playing with numbers, trying to keep my brain sharp between mindlessly boring vehicular jobs.

I know what your like Andy...always thinking and game planning

 

[AndyStobbs]

Hoping to nip into bells and get some plate next week. For our gears. Incidentally if you have any friends with a hiab, I know where there are 5 road plates doing nothing.

 

[AndyStobbs]

For it to mate correctly, you do not have any choice over the pitch of the worm. It has to match the circular pitch of the gear and the ratio you will get will be 135:1

You will need to mount the worm at an angle to the gear. This is determined by its diameter.

Your lathe may come with a chart for screwcutting circular pitches, but in essence, you need a set of gears that approximate pi (so 22 and 7 will feature as factors). Note also that 355/113 is a very good approxiamtion of pi.

Thinking in terms of degrees will not help you. Obtain for yourself a copy of Ivan Law's Gears and Gearcutting as well as Martin Cleeve's Screwcutting in the lathe. These two little books will tell you all you will ever need to know.

A useful ratio for a rotary table is 120:1 which is not too hard to get to from 135:1 (need a 9 and an 8).

Citroën/Peugeot have 120T starter ring on some vehicles. Usually about £40.
I do ALOT of flywheels but mostly dual mass and they don't lend themselves very well to solid mounting of things.