Gallery, Projects and General > How to's
Quick and dirty sine bar setting
bogstandard:
This post isn't for those people who do everything by the book and only use the best equipment.
What I am about to show you is a relatively cheap method to get reasonable levels of angle accuracy.
Whether you know or not, the sine bar is a method of producing very accurate angle measurement, if you know how to use one.
It can also be a rather expensive way of doing it, due to the cost of a top quality precision sine bar and the related slips gauges that are normally used with them.
These are what is called 'value' sine bars, the 5" one cost me less than 20 squid and the small one, which I purchased recently was less than 6 squid. You can spend hundreds on buying one, but for general workshop use, one of these would do just fine.
Here is just one place you can get them from.
http://littlemachineshop.com/products/product_view.php?ProductID=3760
Even though they are cheap, it doesn't mean you should throw them about, you treat them as you would any other precision instrument. If it doesn't come with a storage box, they should be stored by resting on one of the sides, as shown by the small one. The top top face and the bottom of the rolls are the critical bits.
This is how they are normally used, either sitting on a parallel, or another true flat face. One end is supported on a stack of slips that have been built up to the required height to put the top face at the correct angle.
Getting that required height can be rather daunting for the newcomer, because of the calculations involved.
I am going to show you a way where the calculations are done for you, and you should get acceptable accuracy on your angle.
This method will only work if you are working with decimal versions of the angle you require ie 7.25 degrees, if you want to use degrees, minutes and seconds, on this post, you are on your own.
So the first thing you should do is go to the downloads section under public domain, and download the Workshop Calculator that I have put there.
This little program you can drop onto anywhere, say your desktop and run it from there. It doesn't instal, it is just a small free running proggy. Just delete it if you don't want it on your comp.
Open it up and go to right angled triangles.
This pic shows what you need to do.
First off is to select the units you will be working in, and that depends on whether your sine bar is imperial or metric. A sine bar's length is given as the distance between the centres of the two rollers.
Then enter your required angle in the box 'Angle B', followed by your sine bar length in the box marked 'Side C-B', then press 'Calculate'
Within microseconds, the results pop up.
You are after the box marked 'Side A-C', that is the height that is required to be put under one of the sine bar rollers to set the top face at the correct angle. It will be in the units selected at the start, either metric for a metric sine bar and miracle of miracles, imperial if you input imperial coords.
This is the controversial bit, what to use instead of those very expensive slip sets.
I have two of the expensive ones, donated to me many years ago, but I always use these little jobbies that a friend picked up for me when he visited the US with his work.
http://littlemachineshop.com/products/product_view.php?ProductID=1757&category=988300808
So you still don't want to fork out any more cash?
Then grab your trusty mic and go around your shop measuring the thickness of things, and by holding the bits together, and using a set of feeler gauges as fine tuning, you will soon find you can get to the height you want.
If that is too much like hard work, then dive in on your lathe and turn a piece of something down to the same diameter as the height you need, and depending how the sine bar is situated, you can either leave the turned down bit on the original bar, or just part it off. But remember, don't try to put the round edges against each other. Set it up like in the C-o-C at the bottom.
I hope that this has helped to explain how easy a sine bar can be used, and it is not in the domains of master machinists, as a lot of beginners suspect.
Bogs
spuddevans:
Thanks very much for that John :thumbup: :thumbup: That has explained sine bars to me, now I'll be on the lookout to get a set.
Tim
mklotz:
As an alternative to John's approach, you can go to my website and download the free program, SINEBAR, which has the following features:
You can select decimal or dms input mode for the angle.
In addition to the stack height, it calculates the error sensitivity of the setup, which shows the error in the angle that will result from a 0.001" error in the stack.
If you do use gage blocks to construct the stack, the program indicates which blocks need to be used.
Here's a sample output...
---------------------------------------
SINEBAR CALCULATIONS
Distance between sine bar rolls [5] ?
Angle input mode [D]ecimal degrees, (X) deg/min/sec ?
angle in decimal degrees [4.93468141 deg] ?
Distance between rolls = 5.000000
Angle = 4.934681 deg
Stack height = 0.430100
Stack height measured in same units as roll separation.
A .001 error in the roll distance will cause an angle error of 0.000989 deg
A .001 error in the stack height will cause an angle error of 0.011502 deg
Blocks from standard 81 gage block set needed to form stack = 0.4301 in:
0.2000
0.1300
0.1001
----------------------------------------
John didn't mention my favorite way of forming the stack when hyper-precision is not required (which is most of the time in the amateur's shop). I use an adjustable parallel and set it with my micrometer. Open the mike to the desired stack height and lock the thimble. Place the parallel between the mike faces and open to fill the gap. Then tighten the lock screws on the parallel.
Note that small errors in the stack produce very small angle errors. In the case above, a 0.001 error led to an angle error of 0.012 deg. 0.012 deg is about 0.0002 radians. If you make a 0.0002 radian error pointing your rifle at a target 100 yards (3600 in.) away, you'll only miss the bullseye by:
0.0002 * 3600 ~= 0.75"
websterz:
Marv, your site is like the Library of Congress for HSM'ists. :bow: Is there ANYTHING you don't have???
mklotz:
Well, I'm still lacking the program that calculates the meaning of life but I've got the differential equation laid out. Now it's just a matter of solving it. :)
The mix is eclectic. Many of the simpler programs (like SINEBAR) were requested by folks who, to put it shortly, didn't pay attention in math class. The more complex ones were written by me to solve problems that I encountered in my hobby work. A program is the ideal way to remember a complex calculation that will only be used infrequently. Programs have perfect memories (if programmed properly) and will remember to check all those possible error sources that are too easily overlooked if trying to reproduce the calculation from fallible human memory.
Furthermore, computers offer the opportunity to solve problems in ways that are impractical or impossible for humans. If you wanted to know what combination of change gears would produce a desired ratio, you wouldn't consider writing down all the possible combinations, calculating the ratio for each, and then calculating the error of that ratio wrt to the desired and picking the arrangement with smallest error. Doing that in a computer is perfectly straightforward and the calculation with today's machines is done in a few microseconds.
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