Author Topic: Quick and dirty Sine bar setting.  (Read 12201 times)

Bogstandard

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Quick and dirty Sine bar setting.
« on: August 15, 2012, 11:31:44 AM »
To help people understand what is and how to use a Sine Bar, and maybe understand a little better the post that Dave has done about his Sine Plate.

http://www.modelenginemaker.com/index.php/topic,487.msg3828.html#msg3828

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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 good 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 bars and the related slips gauges that are normally used with them. But help is at hand.

These are what is called 'value' sine bars, the 5" one cost me less than 20 pounds and the small one, which I purchased recently was less than 6 pounds. You can spend hundreds on buying one, but for general workshop use, one of these would do just fine.

This shows you what they look like.

http://littlemachineshop.com/products/product_view.php?ProductID=3760

Sorry that they are no longer available from that source, but it does give you an idea of how much they cost and what to look for.

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.




You first need a small engineering conversion program installed on your computer, this shows the one I use the most. It must have a right angle triangle calculator program within it's walls. I have gone through the getting the bit you need stage in numerical order, so it should be very easy to carry out.


You can obtain it from here, free of charge.

http://home.scarlet.be/mini-draaien-frezen/engels/program-01.html




How to use.

1) Select 'Right Angle Triangle', this main page appears.

2) These bits are to do with what you are trying to achieve. The Hypotenuse is the distance between centres of YOUR Sine bar, and the angle is the one you want your bar to sit at. You need to find the length of Side 2. So select 'Hypotenuse and Angle A'.

3) This is where you select your input and output figures. Mine is set to Imperial with Degrees, Minutes and Seconds (DMS). If you wanted Metric with Decimal Input and Output, then just select those buttons.

4) This is where you input your figures, the top figure is the distance between centres on YOUR particular Sine bar, then you input the angle you require, again, this shows what I entered in DMS, you could enter yours in decimal if you had selected that option. Underneath the input, you will see a button for selecting the accuracy of output. I have selected 3, which gives the output to 3 decimal places, in fact in thous (mils) if you are in Imperial. If you are using metric, then I would suggest #2. You could select 6 decimal places, to give you super accuracy, but I think you would have trouble getting your spacer pack to the right height.

5) That is the figure you require for your spacer pack height, that you sit under one of the Sine bar rollers to give you the angle that you require.

It does look rather complicated, but it isn't. Just look at the ovals in order, input your figures, and once you have done it once, you will never have trouble again.

Marv also has a little program the he has written that will also do the same function, I am sure if he reads this he will show you all about it.

There are many ways you can obtain that figure, even by the use of a normal scientific calculator.

The choice is all yours.

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, they need to be at 90 degrees to stop things rolling about.

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.

John
« Last Edit: August 15, 2012, 11:44:28 AM by Bogstandard »

Offline steamer

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Re: Quick and dirty Sine bar setting.
« Reply #1 on: August 15, 2012, 11:46:46 AM »
Great write up John!
 :NotWorthy:
That will absolutely work.   I've even used an adjustable parallel as the sine "stack"  set with a micrometer.

Lot's of ways to skin the cat. 

Dave
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Online Jo

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Re: Quick and dirty Sine bar setting.
« Reply #2 on: August 15, 2012, 12:32:39 PM »
Thanks John, :pinkelephant:

They do that software for real operating systems: I can use it on my Linux net book. :whoohoo:

Jo
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Offline mklotz

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Re: Quick and dirty Sine bar setting.
« Reply #3 on: August 15, 2012, 04:10:54 PM »
If you're concerned about using something less accurate than gage blocks to set the sine bar height, you can calculate the expected error in the angle resulting from an error in the stack height.

A = angle
L = sine bar length
dh = error in stack height
dA = error in angle resulting from stack height error dh

Then

dA = dh/(L*cos(A))

where dA is in radians.  (Multiply by 57.29 for degrees.)  Once converted to degrees, multiplying by 3600 will give the angle error in arc seconds.

Keep these angle errors in perspective.  Remember that one arc second corresponds to a 0.017" offset at a distance of 100 yards.

My SINEBAR program carries out these error calculations as well as the calculation of the stack height for a given angle.
---
Regards, Marv


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Offline FLG

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Re: Quick and dirty Sine bar setting.
« Reply #4 on: August 15, 2012, 10:17:36 PM »
Great info!, I never understand until now why a sine bar was so preferred against a normal angle plate.  :thinking:

But there is something that I still cant figue out, lets said I make a setup with the sine bar to mill in angle, then, how do you clamp the piece to the sine bar, and the angled sine bar to the mill table?? (asuming that you have the plain sine bar style like the Bogstandard?s one, not the sloted one that Dave has shown to us) ??

Saludos

Online Dan Rowe

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Re: Quick and dirty Sine bar setting.
« Reply #5 on: August 15, 2012, 10:43:06 PM »
The sine bar goes in the vise like a set of parallels and the work is clamped by the vise jaws. There is a right angle stop on one end of the top bar so the work will not slide completely off the ramp.

Thanks for the program tip John. :ThumbsUp:

Dan
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Offline FLG

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Re: Quick and dirty Sine bar setting.
« Reply #6 on: August 15, 2012, 11:40:12 PM »
Thanks Dan, but that mean that several sine bars are requiered in different sizes to acomodate different works... $$$$  :Doh:

Offline steamer

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Re: Quick and dirty Sine bar setting.
« Reply #7 on: August 15, 2012, 11:47:29 PM »
You could also use the sine to measure the angle.....with the sine bar sitting on top of the work.


Dave

« Last Edit: August 16, 2012, 12:06:48 AM by steamer »
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Offline steamer

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Re: Quick and dirty Sine bar setting.
« Reply #8 on: August 16, 2012, 12:09:34 AM »
If the plate is a bit wider, and has some tapped holes....it gets easier to hold on to work.

Dave
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Damned ijjit!

Offline steamer

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Re: Quick and dirty Sine bar setting.
« Reply #9 on: August 16, 2012, 12:18:39 AM »
It can also be used to set a spindle to the correct angle for a cut

"Mister M'Andrew, don't you think steam spoils romance at sea?"
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Online Dan Rowe

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Re: Quick and dirty Sine bar setting.
« Reply #10 on: August 16, 2012, 12:45:57 AM »
Good point Dave and Johns mill tram tool will be very handy for the angle and the reset to vertical.
http://www.modelenginemaker.com/index.php/topic,416.0.html

Dan
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Bogstandard

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Re: Quick and dirty Sine bar setting.
« Reply #11 on: August 16, 2012, 07:40:34 AM »
It looks like this post is now well on it's way, just as I had hoped.

I think that once the method was explained, more people would like to know about it.

There are many things you can use this technique with, even Sine vices. But I also use it for very rough and ready angle setting.

If I have a piece that needs an angle machining on it, as long as I have the base length, I can work out the stack height for the angle required, and then just ledge it carefully under one end of the base before tightening up. It isn't perfect, but it will get you plenty close enough for most jobs. See C-o-C at the bottom.

John

Offline vcutajar

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Re: Quick and dirty Sine bar setting.
« Reply #12 on: August 16, 2012, 03:07:02 PM »
Thanks John and Dave for explaining how a sine bar works.  It was always a mystery how to use it.  Now I'm off to download that programme.

Vince