Reading rotary table????

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mklotz
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Re: Reading rotary table????

Post by mklotz » Wed Apr 10, 2019 8:59 am

RSG wrote:
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.
No, depending on the number of divisions, you can be off by as much as a degree or more. For a one degree error on a bolt circle with a 4" radius that amounts to a hole placement error of:

4 * (pi/180) = 0.070"

I'm not willing to tolerate errors like that just to avoid doing some simple, trivial math.

Like it or not, math, and the understanding thereof, is an essential part of machine work.
Regards, Marv

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DianneB
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Re: Reading rotary table????

Post by DianneB » Wed Apr 10, 2019 11:21 am

Writing down the sequence worked the charm (for my feeble mind).

I was doing a set of IBLS steam-operated cylinder drains with four #2 screws each and screwed one up yesterday with one hole slightly out of position so I had to enlarge the clear holes on that one.

I made three more today (WITH my list) with all the drilling and tapping on the rotary table in the mill and all 3 tops will match all 3 bottoms and each will mount in any of the four positions so I guess I got it "close enough"!

(I used to say "I am no machinist" but if I keep this up I will have to stop saying that ;) )

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SteveM
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Re: Reading rotary table????

Post by SteveM » Wed Apr 10, 2019 3:19 pm

DianneB wrote:
Wed Apr 10, 2019 5:13 am
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! ;)
Actually, the little machine shop calculator does the metric for you. You would only need to convert the circle diameter, the starting X/Y coordinate and (for some reason) the hole diameter.

So, for a 4-1/2" 5-hole circle, it calculates the following coordinates in millimeters (assuming that 0/0 is the center of the circle):

1 0° X = 57.1500 Y = 0.0000
2 72° X = 17.6603 Y = 54.3529
3 144° X = -46.2353 Y = 33.5919
4 216° X = -46.2353 Y = -33.5919
5 288° X = 17.6603 Y = -54.3529

Some of you may recognize this as the bolt pattern for a Toyota.

At least you don't have to work in radians!

Steve

whateg0
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Re: Reading rotary table????

Post by whateg0 » Wed Apr 10, 2019 4:58 pm

And it varies from RT to RT! If it's something that is going to be confusing, I usually will lay it out first, then if the tool isn't close to my mark, I know I need to go back and rethink what I did. That is with a RT or not.

TBH, unless I'm doing a bunch of holes, I don't use the RT. I will use cartesian coordinates. It's just way faster since I don't have to take the vise off and mount the RT and then switch them back. YMMV

Dave

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NP317
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Re: Reading rotary table????

Post by NP317 » Wed Apr 10, 2019 9:46 pm

Happily, my milling machine DRO has bolt-circle subroutines.
I enter the center of the circle. Then the radius of that bolt circle, the number of bolt holes, and the angular offset of Hole #1.
Press ENTER and it provides X-Y coordinates that just need to be moved to zero, which is the hole location.
Press ENTER again, zero the x-y values, and you are at the next hole.
Repeat.

Hold my glass of wine and watch this...
RN

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SteveM
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Re: Reading rotary table????

Post by SteveM » Thu Apr 11, 2019 6:49 am

The Moore Tool book, "Precision Hole Location" is about half textbook, and half tables of x/z coordinates for hole circles.

Of the three Moore books, it's the only one not still in print, which tells you how much the DRO has replaced it.

Steve

RSG
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Re: Reading rotary table????

Post by RSG » Thu Apr 11, 2019 4:52 pm

mklotz wrote:
Wed Apr 10, 2019 8:59 am
RSG wrote:
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.
No, depending on the number of divisions, you can be off by as much as a degree or more. For a one degree error on a bolt circle with a 4" radius that amounts to a hole placement error of:

4 * (pi/180) = 0.070"

I'm not willing to tolerate errors like that just to avoid doing some simple, trivial math.

Like it or not, math, and the understanding thereof, is an essential part of machine work.
There is no denying what you are saying is the right way to do it, and as such should be addressed correctly when being asked about it.
Vision is not seeing things as they are, but as they will be.

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