How to calculate machining angle 20 MOA taper

Thankyou for making it very easy to listen . I tend to freeze up when confronted by complicated math . It is a hang over from my very bad experiences at school. I think it happened again right here when I tried to work out John Kiellys simple easy method and I got that stupid result .
Something dislexic is happening and I think I see the wrong numbers or something . I can't explain it really. When I tried it again very slowly it was perfect. I actually tried many times to recreate that wrong answer and could not get anything like it.
How the F*ck could I screw up 20.94 / 600 but I did totally , the first time.
I know it happens because I used to see it on math exams that I got back after marking. Later when the stress is gone and I sit down and look at the mistakes I can do the sum correctly. It has ruined my life really because math is so important.
 
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Math anxiety is fairly common. That is why it is so important that beginning students get as much help and practice as is needed to feel confident in the subject, early on. There is a wide range in the amount of work it takes for students to master the subject, and schools can't customize their curriculum to the degree needed to overcome the problem. The trick is extra work early on.

In the case of older students who have issues at a level above the basics, even though they know their math facts well, spending time on how problems are approached and viewed can be productive. Developing a sound plan before beginning calculations is the key.
 
Trig isn't all that difficult . .

Anyone that can multiply and divide can do Trig. at least that is what a Tool Design Teacher once told me. The one thing that opened the trig door to me was so/sa= Tan. The Side Opposite and the Side Adjacent will move and that is the confusing part to most people starting out doing Trig. . . depending on which angle you are looking for. If you hit the wrong angle and get some really oversize numbers - hit the inverse function and you will most likely have the correct answer.

I used to pick up a bunch of Trig Tables at Machine Shows and give them to the guys in the shop for references, to double check their calculators with - :eek:. If you look in a trig function book and want 20' of angle it will show you .00582 under the Sine of the angle, and if you use a 6" sine bar . . just multiply that by 6.00 and you will come up with the .03492, put that under a 6" sine bar and you have your 20' of angle, or a #65 (.035) drill blank.

My HP15 does it a little different than most calculators, RPN gives a different aspect to working the problem. If I want 20' of a degree, I push the 0.2 and hit the f-degree and get .33333 hit the SIN and get .005818 multiply that by 6. and get the .034906 . . and with the JOB Blocks that is what goes under the 6" sine bar. . .

But the easy way to do trig is to start out with the SO/SA=TAN and all will come together if you practice with it. Being a Mold maker for years you get really handy with TRIG. . everything is an angle . . there is nothing straight in molds . . :eek:

I had the same problem with math teachers, they were more interested in flirting with the girls in the class than they were in teaching the subject. Some people don't catch on to math as well as others, and I was one of them that had a hard time with it. It took me years of night school and lunch times working with the numbers to get a good grasp on it. One of my teachers had a great way of simplifying it - that equation above was the answer for me, once I had that the SO & SA were movable - Trig was easy from there on out . . And I still keep a Trig Function book handy. . just to unwind the mind with at times. . .:rolleyes:
 
I got, "Well, I've got..............

24 others in this class, if you don't 'get it', you'll just have to sit there, because I don't have the time to hold up the class for YOU!" :eek::confused: And, another one bites the dust...... Amazing how this post after alllll those years, still brings back those painful memories.
 
Yes I agree something that affects you forever is hard to forget.
So I now understand the small angle calculation and can switch it around for different amounts of MOA .
My next logical question is .
What do you use for larger angles over 2 degrees?
I think I am going to regret this but what the hell.
 
Sine of the angle times sine bar length equals stack height for that angle.

Convert the angle to degrees and/or decimal degrees. For example 31 2/3 is 31.667, 40 MOA becomes .667.

Enter the number into a scientific calculator

Push the SIN key

Push the X key (for multiplication)

Enter the length of your sine bar, in inches(not the OAL, but the specified length, from where the round under one end touches the surface you are working on to where the one at the other end touches.). In the previous example, the length was 6"

Push the = button.

The answer is your stack height in inches.

This is for angles less than 90 degrees.
 
Ok thanks Boyd. It's the normal sine function that I have in my stack height program anyway.
However programs break down so I would like to understand it manualy also.

How do I work out this part . I have difficulty with fractions.

" Convert the angle to degrees and/or decimal degrees. For example 31 2/3 is 31.667, 40 MOA becomes .667. "
 
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If you're using a 6" Kurt Vise as I am, and your stacking your shim stock under the one side of the vise at the bolt down ears you'll notice that the ears aren't 6 inches apart. You may want to refigure to get a closer value to the actual spacing of the bolts.

Paul
 
Geeze Paul

Why would you want to abuse a vise like that??? :eek:

I've got a fixture mock-up of a Remington long action. There's two dowel pins precisionally located sticking out the side spaced exactly 6" apart. I machine the bottom of the rail, bolt it to the fixture. I place shim between the dowel pins and the vise jaw to give me the correct MOA angle and then machine the top of the rail.

That's why we don't let millwrongs play with our precision equipment...


:D
 
I new it could not last . It was only a matter of time before insults started to fly.
If you can respond Boyd please email or PM me as I am out of here.
 
AJ300MAG said:
Why would you want to abuse a vise like that??? :eek:

I've got a fixture mock-up of a Remington long action. There's two dowel pins precisionally located sticking out the side spaced exactly 6" apart. I machine the bottom of the rail, bolt it to the fixture. I place shim between the dowel pins and the vise jaw to give me the correct MOA angle and then machine the top of the rail.

That's why we don't let millwrongs play with our precision equipment...


:D
Click to expand...

Great Al,

Ok Smartiepants. What do you do if you're starting with a blank section of Rail like brownells sell and machining the bottom of the rail to fit the top of your action with 20 or 15 moa as needed? I have cut my soft jaws to hold the rail upside down and cut across the top (bottom)... but this method would require seperate jaws for each moa offset.

Paul
 
Paul they make a sine plate that has "T" slots for bolting a vise on, or you can make a fixture to hold the rail to machine the bottom.


Last thing I'd do (meaning NEVER) is try warping the bottom of one of my vises OR putting divits into to top of a mill table by bolting something to it that isn't clean and flat. Thats why we stone off the table and vise bottom before bolting down a vise... every time.
 
A jig can be made to hold damn near anything. Machine the angle
into the jig. Its completely repeatable and simple to set up at
a moments notice. You can make a fixture/ jig as ornate as you want,
just think it thru ahead of time. No shims under the vise please
 
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