Reading rotary table????

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DianneB
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Reading rotary table????

Post by DianneB » Tue Apr 09, 2019 12:12 pm

No matter how hard I try, I always seem to screw up the angle-setting on my rotary table! :cry:

It is 90 turnes of the handwheel for 360 degree rotation = 4 degrees per rotation of the handwheel

The major scale on the handwheel is marked 0, 1, 2, 3 = 1 degree per indication.

The minor divisions on the handwheel are 0 to 60 seconds on a vernier scale (which I am not overly worried about).

So, if I am trying to lay out a 4-bolt circle, starting from zero, I advance 4 revolutions of the handwheel (88 degrees) PLUS 2 minor divisions (1 dgree each) for a total of 90 degrees. To hit 180 degrees, I need to advance another 22.5 turns and end up on the 0 marker on the handwheel. For the 270 location, advance another 22.5 turns to end upon the 2nd minor division on the handwheel.

Are you confused? I sure as heck am! I always screw it up and end up with one (or more) holes out of place!!!

Of course all this changes when you have 5, 6, or more bolts in the circle!

Is there an easier way to keep track of the positions on a bolt circle or to figure out how to advance to the next position? (I can't afford a DRO.)

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mklotz
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Re: Reading rotary table????

Post by mklotz » Tue Apr 09, 2019 12:43 pm

"So, if I am trying to lay out a 4-bolt circle, starting from zero, I advance 4 revolutions of the handwheel (88 degrees) PLUS 2 minor divisions (1 dgree each) for a total of 90 degrees."

4 revolutions of the handwheel = 4 * 4 deg/revolution = 16 deg. You meant 22 revolutions.

For N holes in the bolt circle...

360/N = angular separation between holes = A

A/4 = a number that looks like I.F where I = intger = full turns of the wheel, F = fraction = Fractional turns of the wheel.

Examples...

N = 4

360/N = 90

90/4 = 22.5 ; 22 full turns and one half turn (2 deg)

N = 5

360/N = 72

72/4 = 18.0 ; 18 full turns of handwheel, 0 fractional turns

N = 6

360/N = 60

60/4 = 15.0 ; 15 full turns of handwheel, 0 fractional turns

N = 7 (not likely, just an example)

360/N = 51.43...

51.43/4 = 12.857 ; 12 full turns, .857 fractional turn (.857 * 240 arcmin = 205.7 arcmin = 3 deg and 25.7 arcmin (call it 3 and 26)
Regards, Marv

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SteveM
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Re: Reading rotary table????

Post by SteveM » Tue Apr 09, 2019 12:53 pm

Instead of laying out the circle with angular movement, just use the X/Y coordinates of each hole.

There are bolt circle layout programs on the web, and I'm sure Marv has one. They are essentially the same calculations that are done in a DRO to tell you where each hole should be.

Here's one:
https://littlemachineshop.com/mobile/bolt_circle.php

A tool like a spin indexer is useful when you are doing something that is divisible by 36, so for example, you are doing 6 holes, you use a sharpie to mark off every 6th hole and there's no mistaking it. You can't do 5, so there are limits.

This is where a super spacer really shines - you put in the plate and it makes sure you don't screw up.

Oh, and somehow I had the feeling Marv was going to post before I got finished typing, and he did.

Steve
Last edited by SteveM on Tue Apr 09, 2019 2:14 pm, edited 1 time in total.

RSG
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Re: Reading rotary table????

Post by RSG » Tue Apr 09, 2019 1:10 pm

Not sure if I'm missing something but if I think you are asking for a simpler solution to make circular hole patterns on a rotab. This is how I would do it.

Don't bother counting revolutions. Just remember any even number around the table will land on either a "0" or "2" on the dial. So with that said, starting with a hole at zero for a 4 hole pattern drill your first hole at "0" then dial the handwheel until you get close to "90" on the table then land on either "0" or "2" on the hand wheel hand you are good to go.

Even if it's 5 holes you want just divide it by 360 = 72. Again you will want to land on the "0" or "2" on the handwheel once you get close to the number on the table.
Vision is not seeing things as they are, but as they will be.

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mklotz
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Re: Reading rotary table????

Post by mklotz » Tue Apr 09, 2019 2:46 pm

RSG wrote:
Tue Apr 09, 2019 1:10 pm
Don't bother counting revolutions. Just remember any even number around the table will land on either a "0" or "2" on the dial.
Hmm, I don't think so. Let's look at 24 divisions.

360 / 24 = 15 says we have to move 15 degrees between each location. At 4 degrees per revolution, that's 3 and 3/4 revolutions.

That's not an isolated example...

360 / 72 = 5 ==> 1 and 1/4 revolution

360 / 48 = 7.5 ==> 1 and 7/8 revolution
Regards, Marv

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tornitore45
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Re: Reading rotary table????

Post by tornitore45 » Tue Apr 09, 2019 3:22 pm

There is no easier way to use a RT than understanding how to calculate the hand wheel rotation following the process outlined by Marv.
To expand on Marv procedure... at the end one has to crank the handle a certain number of Whole turns Plus a Fraction of a Turn
Like for example 4+3/37 4 turns is easy. What about the 3/37 of a turn? Move 3 holes on the 37 holes wheel.
Sometime the result may be decimal like 3.375 turns in that case 0.375 = 375/1000 = 3/8 Move 3 holes on the 8 holes wheel
Darn NO 8 holes wheel in sight
Move 6 holes on the 16 holes wheel

The process can be entirely automated on a spreadsheet.
Mauro Gaetano
in Austin TX

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mklotz
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Re: Reading rotary table????

Post by mklotz » Tue Apr 09, 2019 3:41 pm

tornitore45 wrote:
Tue Apr 09, 2019 3:22 pm
There is no easier way to use a RT than understanding how to calculate the hand wheel rotation following the process outlined by Marv.
To expand on Marv procedure... at the end one has to crank the handle a certain number of Whole turns Plus a Fraction of a Turn
Like for example 4+3/37 4 turns is easy. What about the 3/37 of a turn? Move 3 holes on the 37 holes wheel.
Sometime the result may be decimal like 3.375 turns in that case 0.375 = 375/1000 = 3/8 Move 3 holes on the 8 holes wheel
Darn NO 8 holes wheel in sight
Move 6 holes on the 16 holes wheel

The process can be entirely automated on a spreadsheet.
You're describing the process for a dividing head fitted with hole plates. What the OP is talking about is a rotary table; it's a different beast, though mathematically similar to a dividing head in operation. It has no hole plates, just the calibrated wheel. With a gear ratio of N:1, the wheel will be divided into 360/N degrees, the angle turned through for one rotation of the table's worm gear.

For the OP, N=90 and the wheel is divided into 4 degrees, each of which has 60 arcminutes. So it's a bit like a 240 hole plate on a dividing head. Your 3/37 would then become...

240 * (3/37) = 19.46

so you would move ~ 19.5 arcmin on the dial.

And yes the PROGRAM (spreadsheets are for accountants) DIVHEAD on my page will solve any dividing head problem. There's no specific program for rotary tables (because the calculations are so simple) although DIVHEAD can, with a bit of interpretation, be used for rotary tables.
Regards, Marv

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Harold_V
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Re: Reading rotary table????

Post by Harold_V » Tue Apr 09, 2019 3:48 pm

Hmmm. I must be missing something.
I use a BP 12" rotab, which has degree markings on the table periphery, along with a pointer. The hand wheel is calibrated in minutes (not seconds) on a vernier scale, so splitting degrees is easy and reliable. I start with the rotab on "0", so the marks make sense.

When I use the rotab for drilling (rarely done--I generally just use the proper coordinates and the machine screws), I use a grease pencil and mark the proper stopping points on the table. That eliminates the need to count turns, thus virtually eliminating any errors.

A dry run before drilling parts serves to verify the marks. With the dry run, a tiny dimple is placed on the item to be drilled, which then allows for a quick check with a ruler (a habit hard to acquire, but one of the best possible ways of eliminating scrap).

H
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SteveHGraham
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Re: Reading rotary table????

Post by SteveHGraham » Tue Apr 09, 2019 4:40 pm

For stuff like this, I write things on a sheet of paper, double-check it, and then follow the list.
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RSG
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Re: Reading rotary table????

Post by RSG » Tue Apr 09, 2019 7:51 pm

Marv, I understand it doesn't work to the exact minute/second but it's so close it's not going to effect the balance of what ever the OP is trying to do.
Vision is not seeing things as they are, but as they will be.

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DianneB
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Re: Reading rotary table????

Post by DianneB » Wed Apr 10, 2019 5:13 am

mklotz wrote:
Tue Apr 09, 2019 12:43 pm
...4 revolutions of the handwheel = 4 * 4 deg/revolution = 16 deg. You meant 22 revolutions.

For N holes in the bolt circle...

360/N = angular separation between holes = A
A/4 = a number that looks like I.F where I = intger = full turns of the wheel, F = fraction = Fractional turns of the wheel....
Thanks! When I sat down with the calulator and a paper and figurd it out - now it makes sense. I wrote down the sequence and will post it on the mill so I don't get myself confused in the shop by over-thinking it LOL!
SteveM wrote:
Tue Apr 09, 2019 12:53 pm
Instead of laying out the circle with angular movement, just use the X/Y coordinates of each hole.
You must have a CNC machine or a great love of Trig! ;) My milling machine is calibrated in Metric and I am working in Imperial so I'd rather NOT do so much math! ;)
RSG wrote:
Tue Apr 09, 2019 1:10 pm
Don't bother counting revolutions. Just remember any even number around the table will land on either a "0" or "2" on the dial. So with that said, starting with a hole at zero for a 4 hole pattern drill your first hole at "0" then dial the handwheel until you get close to "90" on the table then land on either "0" or "2" on the hand wheel hand you are good to go.
That's what I figured out - thanks!

Thanks for all the responses guys! I'll make a list and TRY not to get mysrlf confused again LOL!

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tornitore45
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Re: Reading rotary table????

Post by tornitore45 » Wed Apr 10, 2019 6:42 am

(spreadsheets are for accountants)
True, all accountants need, circular functions, hyperbolic functions, complex numbers and the occasional MOD function.
Mauro Gaetano
in Austin TX

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