[modeleng] Re: coarse threads

I can cut 27 tpi by using a 16 tooth gear as a stud
gear, 72 teeth as an idler gear, and a 54 tooth gear
for the screw gear.  Don't ask me how with all even
numbered gears it can do this and, No, I have not
tried it as I have had no cause to doubt the gear
chart.

Al Messer


--- Chris Crosskey <chris.crosskey@xxxxxxxxx> wrote:

> 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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