"DoN. Nichols" wrote in message
...
On 2008-06-16, DazFNQ wrote:
Ha It gets better, in the Hare & Forbes brochure it says theat the
leadscrew
is metric, but another source of information for the same lathe says that
it
is an imperial leadscrew.

Looking at the threading charts, it looks as though it is using
transposing gears (typically 100 tooth plus 127 tooth) to drive the
leadscrew for metric threads, but direct (just an idler, which is likely
to be the larger of the pair of transposing gears) for imperial
threading, which suggests that it is an imperial leadscrew, not a metric
one.

Checkout the image of the standard gear setup:

http://www.metalworking.com/dropbox/...dard_Gears.JPG
dropbox link



Have discovered that its pitch is 3mm and it has 8tpi (butress thread)

This is now not correct, calcs originally based on the chinese manual:

After measuring the carriage travel based on leadscrew revolutions

Leadscrew Revs Dial Indicator Gauge
1 0.125
2 0.250
3 0.375
4 0.500



Interesting. Do you have the machine directly available? (I
guess so, given the photos). Why not cheat and try *measuring* the
leadscrew's pitch? Of course -- it might be possible that it has two
leadscrews, one of each pitch.


Yep, with a Unified 60 degree pitch gauge measuring over an acme
square thread can be problematic but does appear to be 8TPI as nothing
else comes remotely close.


And normally for Imperial that would be an Acme thread, not a
buttress thread. IIRC, the included angle of the buttress is 30
degrees, and the Acme is 29 degrees, so that part would be pretty
difficult to tell without really precise measuring tools. :-)

I'll just keep digging.

And *confirm* things by *measuring* what you can get to. No
matter what lies the "manual" may tell, you can tell which is the truth
by actual measurement.

Your absolutely right, those chinglish manuals are crap.

Therefore, based on my original message snipped

Leadscrew = metric 3.125 pitch

Change gears 1 Set: M=1.25 (pitch) Z=22T, 44T, 26T, 52T, 38T
(Where it appears that Z = Z axis )

Simple gear train of
Driver 24T
Intermediate 127T
Driven 48T

Im not sure as to which calc method from my reference book to
choose here. Is there a resource on the net that can answer these
questions?

Thanks DazFNQ