Vee Fixtures: angle of V?

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.

Goodgawd, that should have been, 90 deg V vs. a 120 deg V.

120'

Think 3-jaws chuck.

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

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.

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 90º Included Angle V's:

(D1-D2)(.7071) = CM (Centerline Move)

For 120º Included Angle V's:

(D1-D2)(.5774) = CM

For 60º Included Angle V's:

(D1-D2) = CM

D1 = Diameter 1 D2 = Diameter 2

Is seems 60º V's would be easiest to calculate a move for.

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.

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 60º 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.

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.

Vinny:

Thanks, but seriously Vinny, don't bother on my account. I have absolutely no real world need, or use, for such a program.

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....

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.

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.....

PV:

Actually, I was looking for a universal formula like you later listed. I saw that the .7071 was the sin and cos of 45º, and that .5774 was the tan of 30º, and that "1" was double the cos of 60º - but couldn't see a pattern. I was just starting to subtract 90º from the angle elements when the kinetic energy of my curiosity ran out. LOL