"Snag" wrote in message ...
On 12/9/2020 6:06 AM, Jim Wilkins wrote:
"Snag" wrote in message ...
On my bench-top mill , well it ain't busted no more ! Today I
replaced the speed control pot and reassembled it , installed it and
it's working fine now . Since I was on a roll , i decided to set up the
rotary table and engrave the dial for the X axis that I lost (original
wouldn't work with the PF) when I installed the power feed . This
machine uses 8 pitch leadscrews ... which means 125 divisions , which
requires a 25 (or multiple) hole index plate with my 90:1 worm ratio .
And I don't have one but I do have the time and material to make one !
Actually I'm making a 50 hole plate , got it machined to size and
mounted in the rotary table and almost ready to drill . I figger it's
best to bolt the RT down before I start ...
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How?
I've read of several possible ways to generate and test an index plate
or similar geometric pattern but I've only tried two, and found them
difficult without a DRO.
The messiest was graduating a crossfeed dial for an AA/Sears lathe with
a 5/16-24TPI LH thread. That's 41.67 lines per turn.
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That dial must have been a trip , how on earth did you resolve the
partial space ?
I used the rotary table to drill the 50 hole plate I needed to scribe
125 lines on the dial ... On my 90:1 RT , I moved 1 5/9 rotations per
hole - 1 full turn and 20 holes on a 36 hole plate IIRC . The dial was
36 holes on the 50 hole plate ... and what's cool is that now I know how
to do this , I can reproduce any hole pattern I need .
--
Snag
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I put the locking screw between lines 0 and 40. It didn't take long to
realize that the AA/Sears lathe wasn't practical to turn steel so I went
looking for a better lathe and found the 10" South Bend. The AA was demoted
to grinding and polishing, and drilling small deep holes. However last night
I used the SB to drill a 1mm hole in the end of a 4-40 screw for the music
wire drive pin in a gauge pointer puller:
https://www.pressuregauge.co.uk/acce...removal-tools/
I made the tool quickly and roughly from water pipe to fix the gauge, then
decided it was an interesting shape worth cleaning up and polishing.
The formula is simple, 90/125 handle revs per division, but the fractional
math can be difficult to match to available hole circles. I reduce the
numbers to prime factors, in this case 90=2*3*3*5 and 125=5*5*5, instead of
trying to convert calculated decimals to fractions. Removing all factors
common to both leaves 2*3*3 / 5*5, or 18/25 or multiples thereof.
My second hand RT is 40 turn and I made a spreadsheet that gives the turn +
hole settings. The RT had only one plate so I've had to find ways to index
what it couldn't. I indexed 13 spline grooves to fit a motorcycle sprocket
to my sawmill's transmission with the 54 tooth change gear from the AA
lathe. Fortunately the RT's plate had the 17 hole circle to mill a 68 tooth
steering sector gear for my tractor. 40/68 = 2*2*2*5 / 2*2*17