I think if the dro were to want start and finish angle and zero was given for both values, a guy might get a 127 hole pattern by asking for a 128 hole pattern. I'm not at all sure about that, but If that's how mine worked I would sharpie it out and verify my theory. I'm curious myself. I only have a nice dro on the mill. Knowing what to expect out of my chinese glass set up wouldn't hurt at all.
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Dividing head math for large # of gear teeth
- Thread starter LEEQ
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I just checked my Grizzly DRO and if the start angle and end angle are the same or differ by some multiple of 360º, (360º, 720º, etc.) the number of holes entered will be correct. However, if the end angle differs by even .001º. As an example, drilling a four hole bolt circle; center 0,0, diameter 2, start point 0º, end point 360º will put holes at -1,0; 0,-1; 1.0; and 0,1 However, entering 359.999º for the end point, the holes are located at -1,0; -.866,-.5; -.5,-.866; ans 0,-1.
To answer Bill's question about entering negative angles, the negative angle is converted to its positive equivalent. For example, drilling four holes between 0º and 90º, center 0,0, diameter 2, start point 0º, end point 90º, the holes are located at -1,0; -.5,.866; .5, .866. If the end point is -90º, it is internally converted to 270º and the holes are located at -1,0; 0,-1; 1.0; and 0,1.
This is on a 16 y.o. DRO, model nos. H6087 -H6098, running software version 8M-B
To answer Bill's question about entering negative angles, the negative angle is converted to its positive equivalent. For example, drilling four holes between 0º and 90º, center 0,0, diameter 2, start point 0º, end point 90º, the holes are located at -1,0; -.5,.866; .5, .866. If the end point is -90º, it is internally converted to 270º and the holes are located at -1,0; 0,-1; 1.0; and 0,1.
This is on a 16 y.o. DRO, model nos. H6087 -H6098, running software version 8M-B
You may want to look into Compound Indexing (which is different than Differential Indexing), which can allow you to increase the indexing combinations available beyond plain indexing.
(You could also look into Differential indexing, which adds a gear train to the compound, so you get indexing plates and a variable gear train.)
In Compound indexing multiple hole circles are used simultaneously on a given indexing plate. This may include counting forward a certain number of holes on one hole circle, and in some instances even backing up a certain number of holes on a different hole circle. By combining the use of multiple hole circles, its possible to improve the resolution of your indexing. It may not be exact, but if you can get the resolution small enough, it may not be noticeable.
(You could also look into Differential indexing, which adds a gear train to the compound, so you get indexing plates and a variable gear train.)
In Compound indexing multiple hole circles are used simultaneously on a given indexing plate. This may include counting forward a certain number of holes on one hole circle, and in some instances even backing up a certain number of holes on a different hole circle. By combining the use of multiple hole circles, its possible to improve the resolution of your indexing. It may not be exact, but if you can get the resolution small enough, it may not be noticeable.
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Hello SoCal. I'd love to see references for figuring "compound indexing". A how to, kind of thing. It sounds like you are working with one plate on an indexing setup like mine. I am curious about backlash if you are working in two directions.
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Both of these books will fill in the gaps for anyone new to dividing. I would also like to give an honorable mention to Kurt Moltrecht for his chapter on dividing- like most of his work, he conveys the concepts clearly.
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Okay, the B&S manual is 6 MB, too large to attach. Here is a link:
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Okay, the B&S manual is 6 MB, too large to attach. Here is a link:
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So to drill 127 equally spaced holes, I would either enter 128 for the number of hole with the start and end point the same or I would enter 127 for the number of holes and the end point would be 360 x126/127 = 357.165.
On a 8" bolt circle, the holes would be .1979" apart. You would probably want to drill two or three rows with staggered holes depending on your hole and plate size.
Incidentally, this issue came up in another thread some years ago. https://www.hobby-machinist.com/threads/prime-number-division-without-gearing.62486/
Post #33 on this thread has my concept for a 127 hole dividing plate.
On a 8" bolt circle, the holes would be .1979" apart. You would probably want to drill two or three rows with staggered holes depending on your hole and plate size.
Incidentally, this issue came up in another thread some years ago. https://www.hobby-machinist.com/threads/prime-number-division-without-gearing.62486/
Post #33 on this thread has my concept for a 127 hole dividing plate.
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I always was in awe of how Brown & Sharpe engineered standards for threads, gears, measurements I preferred B& S over Starrett in many tools