HF 7x10 gear charting

The HF 33684.pdf manual labels the top gear A. A drives B. C is the gear on the shaft with B. C drives D, which turns the 16-pitch lead screw. The tpi formula is 16*B/A*D/C, so you get the same tpi when A and C are interchanged with each other, or when B and D are interchanged with each other. For 27 tpi, use gears ABCD = 20 45 80 60, per gears.c program. 16*(45/20)*(60/80) = 27.

Thank you for the advice.

That may be because the supplied gears don't include what you need.

Well ... you seem to be assuming that everyone knows the specs of the HF 7x10 and its accessories -- or that only those who do will answer.

First off -- in my 12x24" Clausing, to cut 27 TPI, I simply select it from the quick-change gearbox.

But many quick-change gearboxes do not offer 27 TPI -- it is (for whatever reason) a relatively uncommon thread -- mostly seen in

3/8-27 electrical threads for mounting lamp sockets derived from old gas light fittings, and the somewhat larger 5/8-27 thread used for microphone mounts -- perhaps from the same origin.

What you need to know is first the pitch of the leadscrew. You should have that in your manual -- or be able to measure it.

Then calculate how far you need to move per rotation of the spindle (1/27th of an inch, or 0.037037").

Now -- assuming that your leadscrew pitch is say 10 TPI (Sounds reasonable for a 7" lathe, but it could easily be something else), that gives you 0.100" per full rotation of the leadscrew, and divide that into the distance you *want* to move (0.037037") to get how much of a rotation you need the leadscrew to turn to produce that, That turns out to be 0.37037 rotation.

So -- the ratio is 1:0.037037 or 2.7:1. Convert this to get integers on both sides, which becomes 27:10.

So -- you now need to find a combination of gears (taking into account all gears from the spindle to the leadscrew) which will give 10 turns of the leadscrew for 27 turns of the spindle, or perhaps 54:20 would give more reasonable gear choices and is the same ratio in reality.

Now -- it comes down to *you* knowing what gears *you* have, and figuring out whether any combination which will physically fit into the headstock can be made from what gears you have available.

It may turn out that you will need to *make* a 54 tooth gear to mesh with an existing 20 tooth gear in your set.

There have been people who have written programs (spreadsheets or C programs or BASIC or whatever) which when fed a list of the available gears will tell you which you need to use. Maybe one of those will post.

Good Luck, DoN.

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good stuff

Let the group know how you make out.

Unka' George [George McDuffee]

------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).

Thank you Don for your input.The workaround was to use a friend's lathe with the capability of 27 tpi.I didn't have the correct gear for my lathe.I needed to make a connector for a faucet that had a 13/16 x27 threading.It all worked out.