OT Rotab indexing

[SGW]

OpenOffice, which is free, will run the spreadsheet just fine: http://www.openoffice.org/

You don't need Microsoft Office...for anything.

[Jaakko Fagerlund]

Most rotary tables can be fitted with indexing plates, just like the ones used on indexing heads. I plan to do this for mine when I get the chance.

If you are worried about making accurate hole circles, it can be easily done in any shop using only the rotary table itself. The worm gear in the table acts like an accuracy amplifier when making hole circles so you can start out with a very, VERY inaccurate one and two generations later have one that is as accurate as your rotary table itself is. You can do it like this:

For each number of holes you need in a circle:

1. Mark out a circle and divide it by HAND. Do it as accurately as you can without taking too much time but don't worry about accuracy at this point. If each hole is +/- as much as one degree, you will be just fine. They do not even have to be evenly spaced. Drill those holes.

2. Use that rough, 1st generation plate to make a second generation plate. Now each hole on that plate will be 40 or 90 times more accurate due to the division by the worm gear. So, +/- 1/40 or 1/90 of a degree. Take a moderate amount of care in making this plate.

3. Finally use the second generation plate to make a final, third generation. At this point you want to be very careful. Watch backlash at all times. This third generation plate will again be 40 or 90 times more accurate than the second generation one. So it will be +/- 1/1600 or 1/8100 of a degree. That translates to 2.25 arc seconds or 0.44 arc seconds. Unless you have a really expensive rotary table, it will not be that accurate. Mine is specified as +/- 30 arc seconds and reads to the nearest 10 arc seconds.

Since they will only be used once, for making the third and final plate and each hole will only be used once; the first and second generation plates can be made with aluminum or plastic. You could even use plywood for the first generation plate. I would use a good steel alloy for the third generation plate.

Or just make one good plate and be done with it, no need to make it again and again.

[Paul Alciatore]

But how do you make that "one good plate"? Easy if you have something like CNC, but then, you probably can sell the RT.

I described a method that guarantees accuracy.

Or just make one good plate and be done with it, no need to make it again and again.

[Jaakko Fagerlund]

But how do you make that "one good plate"? Easy if you have something like CNC, but then, you probably can sell the RT.

I described a method that guarantees accuracy.

You mentioned a rotary table, so I presume it has a handle with degrees marked on it.

[tom_d]

Not sure if it was this site or an other, some one had posted a site where if you put in the number of spaces it would give you the coordinates in degrees , minutes and seconds cumulative . I think the site was from Canada could really use it. I only have a rotary table at home.

Are you looking for the degrees when positioning an even number of spaces, like you would find on a bolt circle? If so, then give this site a try: http://theoreticalmachinist.com/BoltCircleCalc It's a simple web site, so no need to download a program, and will give you the angle in degrees to a decimal, which can be converted to minutes and seconds.