Vee Fixtures: angle of V?

Awl --
For holding rounds, in particular multiple V's in soft 30" jaws, for holding rounds in Z. The rounds will be anywhere from 5/16 x 3/4", to 1 x 2".
Basically the fixture will be in a "T", with the bottom of the T being a 1x3 alum bar clamped in two 6" vises, and the top of the T being about a 1x2 or 1x3, bolted to the bottom bar, with milled V's on *both* sides. So the top of the T will have the V's.
Will hold about 60 parts, for light-ish ops, such as light facing cuts, drill/tap small holes.
Also, I will have angle alum screwed to the bottom part of the T, to act as a Z stop for parts held in the Vs. I'll proly slot the angle alum, to make it adjustable in Z.
Threaded rod/nuts will hold outside clamp rails on the parts, such that only half turns of 15 nuts will release all 60 parts.
If I do two of these fixtures, I can have a quasi-palletized system.
Also, eventually, vises can be dispensed with, and this system mounted directly on a subplate, for possibly 300+ parts per load.
I'm leaning toward 60 deg V's instead of 45 deg, bec the smaller the angle, the more "camming" into the V can occur, bec of mechanical advantage. Not a biggie biggie here, since the Kurt jaws themselves will not be applying direct force, but rather the lighter rail system above.
But, the shallower V of 60 deg will accommodate a greater range of diameters, altho each V will also consume more linear space, allowing for fewer parts.
Any opinions on the V degree? The overall strategy?
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On Jun 3, 10:23am, "Proctologically Violated"

Unless the rail that clamps is fairly "flexible" it will mostly grip the one highest rod, and/or highest V slot. Sometimes a "cushion" of rubber/neoprene etc can take up the variations. I had a job with 100's of cold sawn extrusions, that were clamped on the sawn (imperfect) faces. I added some 3/16" thick neoprene strip to the clamping bar, and they all held fine.
Another option is a series of holes, with brass tipped dog point screws to grip. If your rods are steel anyway. I've made 1000's of 1/4" D 1018 pins that were fairly aggressivley milled on the ends while being captured in a 2" X 5" aluminum bar, simply held in place with a 1/4 X 28 brass tipped dog screw each. Change the Dog point screws at the First sign of trouble.
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Goodgawd, that should have been, 90 deg V vs. a 120 deg V.

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On Wed, 3 Jun 2009 12:34:20 -0400, "Proctologically Violated"
120'
Think 3-jaws chuck.
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-JN-

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On Jun 3, 4:23pm, "Proctologically Violated"

I would use 90 degree Vees. But my choice would be because making 90 degree vees would take me less time. Cut one side with the bottom of a end mill and the other side with the side of the end mill. Of course since you are using aluminum, you could probably use a table saw to cut the Vees and use any angle.
Dan
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Real accurate grinding v blocks are not 90 degrees, they are 120. Not sure if they hold better or worse though. One thing, write yourself a simple excel gimmic, or draw something in solidworks or do what I did and make a simple perl script that you can tell how much to move when you put different sizes in from where you are. I have a perl script that prompts, "input old diameter", then "input new diameter", then it says something like "move towards vice .2185". If you are running a mill that has variables like a haas write up a simple proggy to do it. Have it dump the answer anywhere it can update. I made the haas dump it in the feedrate area when I did stuff like that. So you put your parts in the vice, dump 2 numbers in your program and hit run, and there's the number in your feedrate readout. Make the move and your right on location. Makes it real nice when playing with v block fixtures.
Also, if your making it hold a lot of parts, on the soft jaw side mill crosshatches so it will take up the space a little, so you dont end up with 1 or two loose parts here and there. Some people put a negative 1 or 2 degrees on the soft jaw side so it will push your parts downward.
As far as the floor goes, mill slots so you can slide parallels thru, or pins, every half inch of whatever you think you'll need to accomidate different length parts. Make it known numbers so you'll always know where you are in z to the top of the parts. After you build these you technically should never have to pick up again no matter what sized dia or length you put in.
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vinny wrote:

    You know, I did a Google search for a formula for moving the centerline of different diameter rounds in V-Blocks. Didn't fine any with the search terms I used, so I messed around drawing stuff in a CAM system and came up the following:
For 90 Included Angle V's:
(D1-D2)(.7071) = CM (Centerline Move)
For 120 Included Angle V's:
(D1-D2)(.5774) = CM
For 60 Included Angle V's:
(D1-D2) = CM
D1 = Diameter 1 D2 = Diameter 2
    Is seems 60 V's would be easiest to calculate a move for.
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Bottle, How did you arrive at your numbers, without a formula?
If we let the apex or tip of the V be X0Y0, the distance to the center of the round from the tip of the V is R/cos(90- A/2), where A is the included angle of the V. Let 90- A/2 = B.
So the difference between the center coord of two rounds is (R1-R2)/cosB, which affirms your numbers. I initially thought they were incorrect, esp. the 60 degree numbers!
So I get:
180: (r1 -r2) * 1/1 = r1-r2 = .5 (D1-D2) (as expected)
120: (r1-r2)*1/.867 = 1.15 (r1-r2) = .5774 (D1-D2)
90: (r1-r2)*1/.707 = 1.414 (r1-r2) = .707 (D1-D2)
60: (r1-r2)*1/.5 = 2 (r1-r2) = D1-D2 !!!!!!
30: (r1-r2) * 1/.25 = 4 (r1-r2) = 2 (D1-D2) !! (approx) Etc.
So the centerline "travel" gets quite rapid, with small degree V's, wrt to diameter change of the held object.
However, anything below 90 is proly not a good idea, as the mechanical advantage against the jaw increases rapidly.
Inneresting.... I hadn't intuitively grokked this trend, before calc'ing this out.
But ultimately what I would do is indicate the fixture, indicate one pc in one of the V's, and use that as Y, as opposed to a calculation.
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Proctologically Violated wrote:

PV:
    Drew some V's, then a few different diameter circles tangent to the V legs, then dimensioned the center points of the circles.     All my math reference books are packed away in a box somewhere.

    Yeah, the 60 number coming out to 1 was strange. It's funny I never noticed that in all the years I've been machining.
    BTW the degree symbol is ALT 0186 on my character set.

    Why should that matter?

    I'd indicate a part as well. I was just curious what the numbers might be.
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Well, if suff'ly below 90, when you opened the vise, you might not be able to get the part out! Both the part and the V jaw might be damaged, esp. if the part were tubing, even thick walled tubing.
This "travel" within a V by diff. diam rods becomes evident if you draw a very narrow V on paper, and then fit circles 1/2" diam, and then 1" diam. You'll see their spacing is substantially farther apart than the diffs in their diameters. Neat....
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Dat was perty neat, ackshooly. Your numbers were spot on.
You should show jb how you did it, this way he'll NEVER have to learn sines/cosines, or anything else with math.
Oh.... but he *will* have to learn cadcam.... Oh well.... Mebbe if it's strictly 2-D, and really really simple, and you write out very explicit instructions with pitchers....
I hope, if I'm ever in a class learning cadcam, there's a jb in there, so at least I'd only be the 2nd dumbest in the class.....
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Proctologically Violated wrote:

PV:
    Actually, I was looking for a universal formula like you later listed. I saw that the .7071 was the sin and cos of 45, and that .5774 was the tan of 30, and that "1" was double the cos of 60 - but couldn't see a pattern. I was just starting to subtract 90 from the angle elements when the kinetic energy of my curiosity ran out. LOL
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If I remember this weekend ill write a script. The math is easy enough I know, but clicking an icon on your desktop and having it prompt you for the size your at now, then the size you are using next, then it telling you clearly, move away from V this amount, etc... is pretty nifty.
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vinny wrote:

Vinny:
    Thanks, but seriously Vinny, don't bother on my account. I have absolutely no real world need, or use, for such a program.
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Would you trust this, over indication? I have never been so lucky!
It could help make the indication go faster, tho, less hunting around, f'sure.
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