Busted power feed

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 .

-------------------------------

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 .

You can easily write a spreadsheet that gives the indexing settings. I used free OpenOffice. Type in what's between the quotes below.

I type the file name in cell A1.

Enter "Divisions" in A2, "1" in A3, and the formula "=A3+1" in A4. Copy and paste A4 down column A as far as you want. You can always extend it.

Enter "90" in B2 and the formula "=$B$2/A3" in B3.

Change the format of B3 to Fraction and change the code to '# ???/???". "# ??/??" is OK up to 100., and neater.

Copy and paste B3 down as far as you did A3.

Column A lists the number of divisions, B gives the full and fractional turns for it.

If I run into roblems calculating the turns I just refer to Ivan Law's gear cutting book from the workshop series - #17 IIRC . I do this so seldom that I'd lose the spreadsheet ...