[modeleng] Re: coarse threads

I've cut a lot of funny threads (ie metrics and BA) on my gearbox kitted
ML7.... I do own (because I'm weird) every single Myford changewheel bar
the 96 and I've found that if I swap the 12/25 compound that runs the
gearbox normally (it's an early one so it uses a 12/25 rather than the
later 24/25) for the normal Myford 25-tooth compounding gear it will
take any gear up to 48T on the stub before it interferes on the
reversing gears. That gives me a range of 28 gears (IIRC one of the
40-something gears isn't made but I think I have all the 20's and 30's)
that can go in there all of which will produce coarser threads if the
lathe is run in normal screwcutting setting on the gearbox, flip the
finefeed gear over so that it's in finefeed (divide screwcutting TPI by
9) and run the numbers on the wheels and some remarkably close
approximations to an awful lot of threads drops out, most of the small
metrics, the BA's down to about 10 or so etc.... If they're not enough I
can always reach for the DAG Brown extended range banjo and run two
compounds of changewheels into the gearbox.... I refuse to believe
there's a thread between about 1TPI and 100TPI that I can't get to
within a percentage error of less than 0.5% on....... Still don't know
why on earth anyone would design a standard lathe to cut 27TPi though,
it means you'd probably have 13.5TPI and 54 TPI in the box too, though
if the numbers dropped out easily enough I suppose it's only costing you
half an inch of box width and one gear......
It's still a bonkers number though..... 

chrisc

-----Original Message-----
From: modeleng-bounce@xxxxxxxxxxxxx
[mailto:modeleng-bounce@xxxxxxxxxxxxx] On Behalf Of Jesse Livingston
Sent: 27 January 2007 16:17
To: modeleng@xxxxxxxxxxxxx
Subject: [modeleng] Re: coarse threads

 Jesse, my old Logan-made lathe will cut 27 tpi.

 Al Messer

I wonder why?  There is no use for 27tpi except in 1/8" pipe threads.
Seems 
that it would require a bunch of extra gears to the QC box- - -- -or
does 
your lathe not have QC?  Easy to do with change gears, but apparently
not 
for a QC box lathe.

REDNECK Jesse 

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