View Full Version : Sine vice setting angle

Hexhead

07-17-2006, 03:01 PM

How do you set the angle using a sine angle vice. Do you use gage blocks stacked up. If so how do you keep the blocks from slipping I got a sine vise from little machine shop Part # 1756 ( really good deal) but I too much of a newbe to know how to set it right.

Thanks

Millman

07-17-2006, 03:20 PM

Yeah, or you can machine a block and make your own. You're probably not going to need sec. of a degree anyway.

mklotz

07-17-2006, 03:25 PM

Here's a little writeup I did for our club that may help you.

SINE BAR ERRORS

In the metalworking books, when you see a picture of a sinebar in use, the

stack used to form the angles is generally composed of gage blocks, the

accuracy of which is measured in millionths of an inch. Are gage blocks, a

moderately expensive item for the amateur, really needed? Or is it possible to

get by with a homeshop-made stack that's only accurate to a thou?

The equation for a sinebar is:

sin(A) = S/L

where:

A = desired angle

S = stack height

L = sinebar length (i.e., roller center-to-center distance)

With a little bit of differential calculus, it's possible to write the error

equation for the angle due to errors in the stack height.

dA = (1/cos(A)) * dS/L

where:

dA = the error in the angle due to an error of 'dS' in the stack height.

(For purposes of this discussion, we'll ignore the effect of any error in 'L'.)

Let's plug in some numbers...

A = 10 deg

L = 5 in

dS = 0.005 in

Then:

dA = 1.01543 * 0.005 / 5 = 1.01543E-3 rad = 0.0582 deg

or about one milliradian error. That's pretty small. Think about it this

way...If I make a one milliradian error pointing my rifle at a target 100 yards

away, I'll miss the bullseye by 3.6 in.

If I'm any kind of machinist, I should be able to machine the block I'm using

for the stack to within 0.001 in, which would reduce the error to 0.2

milliradian, or a target miss of 0.72 in at 100 yards.

The error depends on the angle for which the sinebar is set. For:

L = 5 in

ds = 0.001 in

it looks like this:

5 0.0115029

10 0.0116359

15 0.0118634

20 0.0121946

25 0.0126438

30 0.0132319

35 0.013989

40 0.0149589

45 0.0162057

50 0.0178273

55 0.0199784

60 0.0229183

65 0.0271147

70 0.0335043

75 0.0442748

80 0.0659906

85 0.131479

where the first column is the angle, A, in degrees and the second column is

the error in A, dA, in degrees.

Since a sinebar is seldom used for angles greater than 40 degrees, we can

count on an angle error of less than 0.015 deg (0.25 mrad) if we can machine

the stack block to an accuracy of one thou. Unless you're making highly

critical components, don't be afraid to machine your own blocks for setting

the sine bar. Setting an adjustable parallel with a mike is another option.

Peter N

07-17-2006, 03:34 PM

You have to set the height up with a gauge block set, and use trig to work out the height you need. If you know the angle you want to set it to then you would multiply the distance between the sine bar centres (4” in this case) by the sine of the angle to give you the height of the gauge block stack.

For example if you wanted to set an angle of 38 degrees it would be 4” x 0.61566 (sine 38 deg) = 2.46264”, then use this figure to set your stack to the closest you can get.

I don’t know why they didn’t use 5” centres (keeping the overall size down perhaps?) as if they had then you could just use the table of sine bar constants from Machinerys Handbook.

A word of caution here – these vices are meant more for light machining operations like grinding where you are only removing a few thou’ at most – rather than for a heavy milling operation.

Peter

Edit - Oops! I see you've already been cautioned about the application of this vice in another thread. Still good advice though.

Millman

07-17-2006, 04:20 PM

Wring your blocks well, clean and lube before storing. Hell, you knew that already.

Hexhead

07-17-2006, 05:06 PM

Thanks I don't need any close tolorances, i'm making custom parts for motorcycles and small steam engines and the like. I am also using a HF mini so the cuts are light. Nice write up Mklotz I copied that down as well as the other formulas or equations (if that's what you call them) I got from you guys. I think I will make my own blocks because money is an object (one I don't have). I need another angle vise for a machine, do any of you know of a good small angle vise designed for milling?

Thanks

Millman

07-17-2006, 05:58 PM

Just go by the weight, mass. The heavier, the better.

mklotz

07-17-2006, 07:57 PM

I don’t know why they didn’t use 5” centres (keeping the overall size down perhaps?) as if they had then you could just use the table of sine bar constants from Machinerys Handbook.

The numbers in MH are 5 * sin(angle). He can still use them by multiplying them by 0.8:

4 * sin (angle) = (4/5) * [ 5 * sin (angle)]

But what a waste of time. Scientific calculators can be had for < $5 these days. Punch in angle, hit 'sin', multiply by 4...done. Beats fussing around with a gigantic book.

Charlie Rose

07-17-2006, 11:26 PM

You do'nt need to make different blocks,just use your set of adjustable parallels and set them with a micrometer.