World's simplest indexing head

[mklotz]

Fooling around with my sine bar protractor

http://www.homemodelenginemachinist.com/index.php?topic=969.msg6664#msg6664

the other day, I realized that the principle could be used to build what may be the world's simplest indexing head. I have no need for it and thus no intention to build a prototype so I'll throw the idea out here for anyone who may wish to use the concept.

Imagine a circular plate that can pivot on a stationary base. A pin of diameter d1 is mounted to the base near the plate at a distance r1 from the center rotation. A pin of diameter d2 is mounted near the edge of the circular plate at a distance r2 from the center of rotation. Call the "zero" angle of the table the point where the two pins are as close to each other as possible.

Now, if I want to rotate the plate to an angle theta relative to this zero, I calculate the chordal distance from the law of cosines.

c = sqrt [r1^2 + r2^2 - 2*r1*r2*cos(theta)]

then, with the definition

d = (d1+d2)/2

I set my calipers to a distance equal to s = c + d and rotate the plate until the distance between the pins corresponds to s. Piece of cake.

While this probably won't replace a real indexing head for repetitive operations, it has some real advantages for the tool-bereft novice...

No need to buy pricey tooling to set a one-off oddball angle.

Accuracy determined only by one's ability to measure simple linear distances.

If one can tolerate a pin hole in the part (or machine the hole away later), the part itself can replace the "circular plate" I refer to above.

If anyone tries this idea, please report on what you did and how it worked.

---

BTW, if you wish to use the idea and are overcome by the mathematics of calculating "c", let me know and I'll write a program to do it for you.

 

[zeusrekning]

Marv, I need a sketch. I think I get it but I probably don't.
Tim

 

[mklotz]

Your avatar made me too dizzy to do a sketch.

Draw a small circle inside a larger circle - both with the same center. Mark a point within the big circle (but not within the small circle) at radius r1 from the center. Mark a point within the smaller circle at radius r2.

Draw a triangle connecting these two points and the center of the circle. The angle between the two radii is theta. The points represent the locations of the two pins. The big circle is the fixed plate. The smaller circle is the rotating plate.

 

[zeusrekning]

Ya like it huh? Thought it was time for one.
I drew out like you said and see what you are going for. How were you thinking of it being used?
Tim

 

[mklotz]

It reminds me of M. C. Escher on drugs.

I think its use is pretty well outlined in what I wrote originally.

 

[zeusrekning]

??? Sorry.

 

[mklotz]

Ok, Tim, just for you I've attached a sketch of what I described in words.

I hope you'll be able to understand what I had in mind. The basic idea is that, when you want to accurately angle one piece relative to a fixed base or other reference, all you need is two pins and a calipers or other tool capable of making accurate linear meaurements.

 

[zeusrekning]

Thank Marv, I was able to come up with a sketch thought, I was just wondering if you had envisioned a 5c indexer using this method or some kind of rotary table. Basically if you had ant intentions of implementing this a certain way. But I think I get it now that it could be used many different ways. Be patient we me man it may take me a while sometimes.

Anyway, MC Hammer did drugs???

 

[mklotz]

Tim,

Originally I was thinking of what amounts to a simple dividing table where the work is clamped or bolted to the table. Basically, it would be a "get it done" dodge for a novice who doesn't have a rotary table but needs to do some angled work "now". However, as you grokked, the idea is useful wherever one needs to angle something moderately accurately.

Who is "MC Hammer"?

 

[zeusrekning]

OK, That's what I was wondering. Great Idea.

LMAO :big: :big: :big:

I'll tell you who MC Hammer is if you tell me who MC Escher is.
Tim

 

[mklotz]

Escher is a famous Dutch artist. There are numerous websites devoted to him (Google is your friend) but here's the Wikipedia reference.

http://en.wikipedia.org/wiki/M._C._Escher

I see from Wikipedia that Hammer is somehow associated with (spit) rock music. Don't bother telling me anything else about him. I treasure my ignorance of anything having to do with that abomination to the senses.

 

[zeusrekning]

Yeah , I googled it while I was posting last, also had to look up "grokked".
I thought you meant my inability to understand was like Escher on drugs. :big: Now I see you meant my avatar. Man I have to start getting more sleep.
Tim

 

[mklotz]

I thought you meant my inability to understand was like Escher on drugs. :big: Now I see you meant my avatar. Man I have to start getting more sleep.
Tim

I think you've been staring at that freaking avatar too long! ;D

 

[Powder keg]

I thought it was just me that was starring at that thing

Wes

 

[Lew Hartswick]

I thought it was just me that was starring at that thing

Wes

I can hardly read any post that still has that avatar showing on the screen. Talk about "distracting"
it's a KILLER.
...lew...

 

[SmoggyTurnip]

I can hardly read any post that still has that avatar showing on the screen. Talk about "distracting"
it's a KILLER.
...lew...

yep

 

[zeusrekning]

OK Guys,
Let me know if this one is too much for you.
Tim

 

[mklotz]

To be frank, it's too much for me.

Stuff that blinks or wiggles rapidly is meant to attract attention and does so very well. It's very distracting and conveys no meaning. After all, how does a stick figure say anything about you?

If you insist on an animated avatar, try constructing something that moves at a very leisurely pace, e.g., a beam engine turning over at one or two rpm.

Personally, I think animated avatars should be forbidden. I'd even like to get rid of those stupid little purple smileys that hop up and down.

 

[zeusrekning]

Marv,
I would actually like to see more smileys out of you. I think the fact that the stick figure does not say anything about me directly yet I put it there says something about me . And it made me grin :big:. I come here to get away from having to reason and have reason. And hell the purple smiley is my favorite. So, you hate rhinestones, animated avatars, and purple hoping smileys??? Ever see the soup Nazi on Seinfeld?
;D ;D ;D
But hey you knew it was purple so I at least know you are not using a black and white monitor.

Having fun with you Marv.
Tim

 

[mklotz]

Yabut, the soup nazi has control of the ladle. :big: :big: :big: :big:

Having fun with you, Tim.