thread / screwcutting and gears

hi all, just got myself a EXE lathe 3 1/2 super i think, and im trying to find out how to calculate which gears to use, it has 24t on the spindle and a small selection of other gears, i have 3 pegs to utilise if needed. Ive found a few programs/website to help calculate them. but im still struggleing a little to ensure the first gear is the fixed 24t on the spindle.

any help or advise please. do i need to have another 24t gear to start with when using these calculators?

ive tried nthreadp.exe and lathe gears.exe

cheers

also would any one know what the thread on the spindle be for a faceplate?

cheers all

Hi you could try here **LINK**

Roy

yeah read through it, its where i got the ntthreadp.exe which seams the best, i think i can add the kludge factor as a ration of spindle/1st gear. was woundering if there was a program for spindge gear and 3 pegs and then the leadscrew.

thanks by the way for helping.

Hi Lloyd

If it helps As you know leedsrew 12 tpi Mandrel 18.

is there a 24  on your mandrel ?   its 18 on mine 

leadscrew 54 idle 18 = 36 tpi
39 .. 18 = 26 tpi
36 18 = 24 tpi
33 18 = 22tpi
30 18 = 20 tpi
27 18 = 18 tpi
24 18 = 16 tpi
21 18 = 14 tpi
18 18 = 12 tpi
Example 54 divide 18 X 12 = 36 tpi

The thread is 3/4" x 16 tpi locating dia is 13/16" .812"
You can cut 10 tpi with a compound on 2nd stud 18 to 36  for LH add Idle gear

Nobby

Edited By Nobby on 08/02/2013 16:53:55

Edited By Nobby on 08/02/2013 17:08:03

Nobby,

thanks for the info, I am a bit new / green at this and have just bought the exe lathe, ive looked at the www.lathe.co.uk/exe and it looks like the 4" on there but is a little smaller and other pic's ive seen look like a 3.5. I think mines 8 tpi on the leadscrew ( if im right i turned the handle 8 times to move it roughtly 1". Im not sure if my terminolagy is correct but if the fixed gear on the spindle (or mandrel) the one behind the main bearings, is 24 teeth.

I see how you calculate the TPI now thanks, not sure i understand the cut 10tpi with a compound on 2nd stud 18 to 36.

sorry and thanks, It looks obvious when you see it explained....

regards

Hi Llyod
I should have read you original post Yours is a 3&1/2 Exe lathe mine a smaller 2&1/2"
Anyway 8 tpi leadscrew Is the same as my Myford S7 Mk 1
Have you got a comlete set of gears for it ?
Some other guys may contribute 

Example 48 on leadscrew 24 on spindle
48 Divide 24 x 8 = 16 tpi         ie 2 o1
Nobby

.

Edited By Nobby on 08/02/2013 21:05:21

i dont think so, i have in total a 47t,46t,52t,32t x2,28t thats including the one on the leadscrew at the monent but not the 24 on the spindle.

thanks

Lloyd, if you load up and save your gearset (including the 24T on the spindle) into Nthreadp, and then specify the threads you might want to cut, you can look through "driver gears" for a combination which uses 24T as one of the drivers. Don't forget to click "Load gearset" each time you start the program.

However, I've tried setting up the gearset as 24, 28, 32, 32, 46, 47 and 52T and it there are very few inch threads those gears will produce exactly. You need a better set of gears!

Andy

ok thanks, so it doesnt matter which way round i put the gears, (or how many extra idle gears i use) as long as the 2 sitting on the same pegs are the same (driven/driver), as i have no tumble reverse at the mo (id like to make/add one) i need to add or remove the change it from LHT to RHT? And if i want to do metric threads i just need to work out how many 1.5mm threads per inch to calculate it?

so i need to look for more gears, Lathe.co.uk state the teeth are the same as boxfords and southbed. Is there any gears i should be aiming for more smaller or bigger ones? whats a good starter set?

Lloyd,

First, to cut threads less than ¼” in diameter, it is probably easier to use a die than to cut them on your lathe, though the lathe can be a great help in ensuring a die-cut thread is true, if the stock is held in the chuck and the die in a tailstock dieholder. Annual rotation is probably in order, unless your slowest speed under power is very slow – 60 RPM or so is OK.

Looking at threads between ¼” and 1” in diameter, all Whitworth, BSF, Unified Coarse (UNC) and Unified Fine (UNC) threads will be covered if you can cater for 28, 26, 24, 22, 20, 18, 16, 14, 13, 12, 11, 10, 9 and 8 threads per inch ("TPI". Note that the first, second … seventh threads in that list have double the TPI of the eighth, ninth …. fourteenth.

There is a formula which works out the gears required to cut threads of the required TPI on a lathe with a given leadscrew TPI. I believe your leadscrew is 8 TPI. If your driver gear (the one on the spindle) is 24T, that formula can be simplified. Just multiply the TPI you want to cut by 3 to get the number of teeth needed on your driven gear, which is the one you need to put on the leadscrew.

So, looking at the second seven TPIs listed in the second paragraph above, the driven gear to go on your leadscrew is 24T for 8TPI, 27T for 9TPI, 30T for 10TPI, 33T for 11TPI, 36T for 12TPI, 39T for 13TPI and 42T for 14TPI (none of which you have; your 24T is already on your spindle). You will need to bridge the gap between the 24T on the spindle and whatever is on the leadscrew with one or more idler gears of any convenient size. As long as there are no compound gears in the train, the idlers (which will include those on a tumbler reverse, if you have one) have no effect on the overall gear ratio, which is determined only by the first and last gears in the train. A compound gear comprises two gears on the same shaft which are fastened together so they revolve as one. One of the two is driven by the gear above it in the train, and the other drives the one below it.

But a compound gear will be useful to get at the first seven TPIs in the list. If in place of the idler (or one of the idlers) you compound two gears together, one of which has twice the tooth count of the other, and use the larger one as a driven gear and the smaller as a driver. Then, you will get twice the TPI out of whatever gear is on your leadscrew. That will give you the first seven in the list.

I have assumed that the bore of the 24T on your spindle is such that you can’t change it for any of the other gears; if you can, then further, more complicated calculations might produce the right ratios from fewer gears.

As to metric threads, the only way to get these exact is to use a compounded pair and a 127T gear somewhere in the train. But given the rather odd tooth counts of your present set, you may be able to produce “near enough” metric threads for practical purposes.

Finally (at last!) : before investing in gears meant for a Boxford or South Bend, check that their bores match your spindles, or be prepared to make new spindles to fit them.

Andy

I've just registered and am thrilled to find another Exe 2-1/2" lathe owner. Nice to make your acquaintance, Nobby.

I've had my Exe for about 18 months and have yet to use it due to health problems. I'd been searching for one for years and having missed one or two because we were househunting and couldn't store them I eventually found one belonging to a wonderful man who wrote the history of Sunbeams.

It came without its treadle system which is probably just as well with my increasing frailty and was driven by a 1/3hp motor giving only one speed. I must create a c/shaft with pulleys that match the wide steps of the spindle pulley.

I was happy to find the spindle nose thread at 3/4"x16 was a match for my Taig lathe after very careful boring of the back of the chuck to 13/16" register. If they are rendered useless on the Taig thereafter the Taig chucks are cheap to replace. I will not modify the Exe in any way.

Mine is a very early example and the picture of bronze gears shown on Tony Griffiths' site is my actual lathe.

I will post further on this, particularly on screwcutting.

Ray

thanks you very much Andy and Nobby. i think i now understand. il have a play to confirm my calculations, then i can start to look for some "fitting" gears.

P.S.

was there a song "3 is the magic number" it seems to be in my case!!

cheers

Edited By Lloyd Bowers on 11/02/2013 08:43:52

Andy or someone can you confirm my calculations please, if im getting it right i can roll on..

so for my gears does this look correct?

and if i had a compound gears of 48t and 24t i could multiply the TPI by 2? and half the MM? like you say as near as in most circumstances will work?

So if i had my 24t on the spline turning 52t/32t compounded, and had the 46t on the leadscrew id get 25.46tpi and 0.99mm?

thanks

My interest in Exe lathes stems from a decades long fascination with the Metalmaster machine designed by the late David Urwick around 1950, a description of which here

**LINK**

He freely adoped the Exe screwcutting arrangement without modification and I can do no better than repeat his own words:

"Another excellent idea that I adopted from the
Exe lathe was the unusual screwcutting arrange-
ment. It may not be familiar. A sleeve, permanently
fitted on the mandrel, carries a 24 tooth gearwheel,
which initiates the change-wheel train, and also a
single-dog clutch, by which it takes its drive from the
mandrel. In screwcutting, this clutch is used to
engage the change-wheel train, with the satisfying
result that it is impossible to pick up the wrong
thread. The change-wheels can spin quite easily as
the saddle is traversed back to the start of the
thread.
With one exception, the numbers of teeth on the
change-wheels are all multiples of the number 3,
instead of the usual 5. These, together with the 24
tooth wheel on the mandrel and an 8 t.p.i. lead-
screw, provide a comprehensive range of threads
with simple trains. The formula could hardly be sim-
pler:

No. of driven teeth = 3 X t.p.i.

Numerous metric threads can be cut, to a tolerable
degree of accuracy, by the introduction of a 38 tooth
wheel. It will be appreciated that this wheel fitted to
the leadscrew, with two suitable idlers, gives a 2 mm
pitch (to an error of only 0.0026 in. per inch). Other
metric threads can be readily calculated as multiples
up and down from this basis. The 38 tooth wheel
also enables 19 t.p.i. (i.e. 1/4 in. and 3/8 in. gas (BSP)
thread) to be cut with a simple train."

So indeed, 3 is a magic number. The standard gearset was "rising in 3s" and in the case of my own 2-1/2" Exe is 18,21,24,27,30,33 and 36.

Simple pitches (without compounding) are thus 12,14,16,18,20,22 and 24 tpi. Several compound setups are possible - this is for a 18t spindle gear and 12 tpi leadscrew, using any 2 idlers or 3 idlers for LH threads. The formula for this lathe is Leadscrew teeth =3/2* desired pitch instead of 3*

The gears themselves are 18dp 14-1/2 deg pa - 7/16" bore and I can't imagine they were different for your 3-1/2" lathe. I have considered gears from HPC in Delrin (to protect my lovely bronze gears) but they only list 20 deg pa. I haven't contacted them yet. I'd like 38,39 and perhaps 60t.

Ray

ok, tjanks for the info ray.

Hi Lloyd,

The TPIs and metric pitches shown in your table are correct, but (apart from the first, which is close to 1.5mm as used on M10 coarse) don't correspond to any normal standard threads.

The full formula linking changewheels, leadscrew pitch and the thread which will be cut as a result is Drivers/Drivens = Leadscrew TPI / TPI that will be cut.

“Drivers” is the tooth count of the driving gears, and if more than one then their tooth counts multiplied together.

“Drivens” has a corresponding meaning in relation to the driven gears.

Idler gears are ignored.

To work out what threads can be cut by the gears you have, the formula can be rearranged as:

TPI that will be cut = Leadscrew TPI x Drivens / Drivers. Your Leadscrew TPI is 8, so if you only have one driver (the 24T on the spindle) and one driven (on the leadscrew), this can be simplified to: TPI that will be cut = 8 x Driven / 24 which simplifies further to Driven/3. This is reflected in your table.

If you include a compound gear in the train, so there are two drivers (24T and Driver2) and two drivens (Driven1 and Driven2), then:

TPI that will be cut = 8 x Driven1 x Driven2 / 24 x Driver2, which simplifies to

TPI that will be cut = Driven1 x Driven2 / 3 x Driver2.

"So if i had my 24t on the spindle turning 52t/32t compounded, and had the 46t on the leadscrew I’d get 25.46tpi and 0.99mm?"

That has a 24T driver, a 52T Driven1, a 32T Driver2 and a 46T Driven2. Using the formula in italics, TPI that will be cut = 52 x 46 / 3 x 32. I make that 24.92TPI or 1.02mm pitch. If the length of thread engagement is fairly short, that would be a practical substitute for 1mm pitch unless you were making something needing more accuracy, like a feedscrew.

Andy

Andyf

"Annual rotation is probably in order," ... ummm ??

Rgds

Bill

ok, thnaks again andy, explained very well.