--It's been so long since I used my rotary indexer that I've lost track of the nice little printed table of turns and fractions-of-turns that I used to get divisions right. I've got a project where I need to have 28 equal divisions of a circle for a bolt hole pattern. Can anyone point me to a table I can download? --Thanks,
Ed, Is yours a 40-turn table ?
--Not a table, but an indexer, but yeah I think so. It's the kind that takes index plates, so there's no dial like you'd see on a rotary table.
isn't it just down arrow left arrow, 28 enter enter............sorry, my universal indexer is under the lathe keeping that spot on the floor clean
40/28 = 1 & 12/28 = 1 & 3/7 1 full turn and 3 holes on a 7 hole plate or 6 holes on a 14 hole plate or 9 holes on a 21 hole plate... etc.
Ed,
I don't have a table but the drill would be:
Divide 40/28 = 1 + 3/7 ; That means 1 full turn of a 40 turn table plus 3/7 of a turn remaining for each of the 28 holes. Using your plates and sector arms find plates of the following numbers of holes: 7; 14; 21; 28; 35; 42, etc. Hole numbers to be sectorized on the appropriate plate(s) would be, respectively: 3; 6; 9; 12; 15; 18.
Bob Swinney
Get yourself a TI 30 calculator. Find the ratio of your table, be it 40:1 or 90:1 Enter the number as a fraction. 90 / X Display shows the number of turns, and a fractional turn, reduced to a lest common denominator.
If you have a 90 turn table, you type in 90 [a b/c] 35. Display: 2
4/7So, it takes 2 and 4/7 of a turn to index 35 times. Easy. No Charts to decipher.
--Here's a little follow up. The part that needed 28 holes was 1/4" thick steel plate, 17" dia. The holes were to be 3/8" dia, one inch in from the edge. One problem was that the size of the plate made it impossible to read the vernier dial on my big rotary table. Another problem was that if I put it on a mandrel and tried to use my indexer the part would have required a bunch of parts being made to mount it that the guy I was doing it for considered overkill. Third problem: I've got a really neat little Sherline cnc rotary table but the part's weight was too much for the stepper motor. Sooo what I wound up doing is using a circular piece of 1/16" aluminum and I made a template, using the Sherline rotary table. Template had a 3/8" center hole, so that it could be centered on a piece of 3/8"-16 allthread that fits the tapped center hole on the rotary table. I had to raise the template on 1" risers, so that it would not interfere with the stepper motor housing and then it was off to the races! I used a small diameter bit, making holes just big enough to center a pin punch, which I used later in the process to transfer hole locations to the steel parts. It turns out there was a small discrepancy, maybe 1/8", when the rotary table had indexed its way back to hole #1, but it wasn't enough to bother us in this application. Still and all if anyone uses these little cnc rotary tables and has to make high-number divisions of a circle it's something to keep in the back of your mind... --Anyway the template worked great, the two steel plates are all drilled, chamfered, etc and when I went to take photos I discovered that the camera batteries were dead!! Ah, well, my pal Mike will snap a few shots and send 'em along soon, then I'll post them to my page.
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