Calculate thread pitch and feed rates...

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John Hill:
John, I did some more research today and much to my suprise I learned that inch is exactly 25.4mm, for some reason I always assumed that was an approximation.

Anyway, as we have a 127 tooth gear and 127 is the lowest integer mulitple of 25.4 I believe the imperial threads should be as accurate as the metric threads. Of course the issue may be that instead of, say, 20 TPI the nearest is something else, but at least I should be able to calculate them!

Tonight is Coronation Street so thats only one hour in the play shed this evening, heck! It is Coro St tomorrow night too, at this rate I will never get anything done! :doh:

John Hill:
John, Mr Bagstandand Sir! What size change gears do you have for your lathe? I am ready to plug those into the program.

bogstandard:
Hi John,

These are my bits.

Paired gear - 127/120

Other gears - 22, 24, 26, 44, 48, 52

Leadscrew - 3mm pitch

It will be very interesting to see how things turn out.
I have also attached scans of my gear layouts for the lathe, to see if they match up with yours.

John

John Hill:
Bogstandard, this is the image you get when you run that program I sent you..(hopefully).

The first time you run it the list boxes will be empty so you need to load in all the values, your ever reliable Artful Bodger has already done that but you still need to click on the 'Load' bar, then wait, and wait, and wait, you will have enough time for a cuppa while it calculates all the combinations possible with your lathe if you had all the change gears you have, plus all the change gears I have, plus all the change gears that are issued with the same lathe in the imperial version. There a about 2.71 squillion combinations! So just wait, OK? :coffee:

It will make a file on your PC so it does not have to calculate them again and when you press the Load button after that you will have only time to blow your nose while it loads them.

You can do two things with Thread Finder, you can put in a desired thread pitch in the top left boxes, only one at a time of course, click the 'Find' button and it will find that thread in the big list which you will be able to scroll up and down. There are quite a few possibles for most pitches and my idea is that you choose the one that matches the change gears you have on hand, clever eh?

The other thing you can do is calculate the pitches available from a particular setup of change gears, just enter the values in and click the 'Calculate' button, you will get 50 lines in the smaller list which is the 50 pitches available from the combinations of the three change levers.

Notes:

D is the driving gear close to the spindle

X1 is the intermediate gear that D meshes with.

X2 is the gear paired with X1, or the same gear which is usual when doing metric threads.
(So if using just one intermediate gear, or just one of a paired gear, enter X1 and X2 as the same)

Z is the gear which X2 meshes with, i.e. the gear on the change box.

Note that metric 1.25 is shown on the lathe table but we cant get it with our gears, the closest is 1.24 but if you really, really wanted 1.25 you could see from Thread Finder that there are a few ways you could get it, for example:

20.3200" 1.2500mm A1 D=60 Z=48 X1=120 X2=120 M=1

..so cut yourself a 60 tooth gear (or hit the supplier up for one) and you are there!

1.25 is just one I decided to check on, there could be others like this.

Have fun, I have not attempted to make the program dork proof so if you ask it dumb questions by putting in daft values it may well spit the dummy.

John

Darren:
Hi John H, that looks like you've worked hard :thumbup:

If one could change the leadscrew pitch, could it work for any lathe and gear set?

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