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metric or inperial

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luke penny02/03/2013 22:15:30
6 forum posts

how do i determin if my lathe is metric or inperial

Nobby02/03/2013 23:53:26
587 forum posts
113 photos

Is there a name on it ? or thread chart.? check the pitch on the leadscrew ? post a picture of the x slide micrometer dial.

John Stevenson03/03/2013 01:15:20
5068 forum posts
3 photos

Does it speak english ?

Ady103/03/2013 02:44:00
3112 forum posts
414 photos

Open up a cheap digital vernier a few inches

jam it between the saddle and the headstock, reset it to zero


Turn the leadscrew once and see what your reading is

On an imperial 8 turns would usually be exactly an inch (but not all)

Not sure about metric, 2mm a turn?

Or count the TPI on the leadscrew using a ruler

Line up one inch of the ruler with a crest, and count forwards(don't include the first lined-up crest)

Let us know what you get


Edited By Ady1 on 03/03/2013 02:50:57

Stub Mandrel03/03/2013 09:52:58
4304 forum posts
292 photos

What make of lathe?

It's usually the carriage leadscrew pitch that you need to check, unless it has a screwcutting gearbox.


luke penny03/03/2013 17:40:43
6 forum posts



Edited By Wolfie on 09/03/2013 00:22:41

JasonB03/03/2013 17:55:42
12342 forum posts
1096 photos

Here you go, you will soon get used to teh quirks of ME forum



Edited By JasonB on 03/03/2013 18:16:22

Speedy Builder503/03/2013 18:24:16
1415 forum posts
95 photos

Looks like a Colchester Bantam ?? As it has the screwcutting gearbox on it, and it looks like an older model, it is more than likely a Mk1 M/c.


Mk. 1 Screwcutting and Power feeds
Although most Mk. 1 Bantams were fitted with a screwcutting gearbox, numbers of "Hawk" models were supplied to training workshops with cheaper imperial or metric changewheel screwcutting. On the changewheel models there was, unlike their contemporary Harrison competitors, no 3-speed leadscrew gearbox, instead a simple 2-speed gearbox was employed where a sliding double gear on the feed shaft could be moved by a lever into one of two positions to pick up a single gear on the leadscrew - and so select either a fast or a slow rate of feed (the leadscrew on Bantams is used only for cutting threads and should normally be left disengaged).
The "Eagle" screwcutting gearbox version offered 29 English pitches from 3.5 to 80 t.p.i. (and 15 metric with translation gears) and the Condor 27 metric pitches 0.2 to 6 mm (and 26 English with conversion gears). Sliding feed rates varied from 0.001" to 0.028" on the screwcutting model; from 0.001" to 0.032" on the Eagle and from 0.02 to 0.7 mm on the Condor. In every case the surfacing (cross-feed) rate was half that of the sliding. Both models were equipped as standard with a number of extra changewheels to extend the normal threading range beyond that commonly required; if these gears are missing from a used lathe, it's worthwhile asking if they have been stored separately and perhaps overlooked. Power cross and longitudinal feeds was fitted to all models with a push-pull knob to select sliding or surfacing and with the engagement and disengagement by a flick-in-and-out lever at the bottom of the apron. To protect the power-feed mechanism against overload damage all models were fitted with a shear-pin incorporated in the top gear of the drive to the screwcutting gearbox..

luke penny03/03/2013 19:36:59
6 forum posts

the bottom lever in the picure is thew only one and like you say it operates a sliding gear on the feed sharft

Trevor Wright08/03/2013 13:23:10
139 forum posts
36 photos


Bantams from this period were imperial only.

Thanks for posting the picture…I have a Bantam mk1 identical to this but the plate that shows speeds per lever position for the spindle is completely worn away….

As for screw-cutting it would appear that the plate is showing the change-wheel settings for each thread with only the one lever. Mine has a 3 position lever and a 6-way circular handle for power feeds and screw-cutting, so yours is definitely not standard.

Perhaps a photo of just the lower plate? Should be able to figure out whether thread pitches are included in the chart.



luke penny08/03/2013 21:52:06
6 forum posts

i have mounted a mag base on the sadle with a inperial clock and then a metric clock touching the cross slide.

with the inprerial when i turn the crosslide 5 divisions on the dile it reeds 3.3/4 thows on the clock when i repeat it with the metrick clock 5 divisions on the dile reeds 5 on the clock.

so i think its a metric lathe.

the leed screw is inperial

im disapointed as i wanted a inperial bantam i would like to get a inperial crossslide and topslide for it

Edited By luke penny on 08/03/2013 21:53:18

Les Jones 108/03/2013 22:23:16
1960 forum posts
130 photos

Hi Luke,
I think there is an error in your measuments as you say 5 divisions on an imperial guage read 3.75 thou which is 0.00375" x 25.4 = 0.09525 mm but you then say that a metric guage reads 5 divisions for the same movement which I assume is 0.05 mm. This means there is an error of almost 2:1 in your readings. Either one or both guages are wrong or your interpretation of the readings is wrong. I personaly only use a dial guage as an indication of runout. Not for actual measurments.


Ady109/03/2013 00:20:41
3112 forum posts
414 photos

im disapointed as i wanted a inperial bantam

i would like to get a inperial crossslide and topslide for it


Just fit a DRO (digital read out) and it can be metric or imperial whenever you like

As far as threads are concerned all threads are TPI, be they metric, Imperial or from the planet Zog

Edited By Ady1 on 09/03/2013 00:24:59

MadMike09/03/2013 10:00:33
181 forum posts

Ady, not all threads are classified as TPI, only those using full size Imperial measure, as opposed to the over rated Napoleonic versions. the Latter are quoted as having a thread pitch of, for instance, 1.00 or 1.25 mm. Of course you can convert these to a TPI equivalent but you may get some rather strange values like 20.325 TPI.

Ady109/03/2013 12:09:15
3112 forum posts
414 photos

Actually you've just reminded me of an old TPI project

I started and half finished... a bit like my life, lol

It does all the TPI calculations for a headstock->banjo->banjo-> leadscrew setup

plus you can specify any allowable error


So 20.325 plus or minus 0.001 is a doddle to calculate

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