SOH CAH TOA

 

snap a chalk line

Paul

 

Pi r squared

 

jtm, what does that mean? Remember, we're trying to draw an angle with nothing more than a ruler and BASIC math at our disposal.

 

Pi x r 2'd, isn't that the formula for circumference, or area, or rocket fuel? I need to draw an angle.

We can use the ruler/yard stick/tape and the 3-4-5 formula to start by drawing a ninety degree triangle.

Took me a moment to realize I'd finally seen the end of computing pi…...............

 

To be clear, I'm looking for an angle, such as twenty degrees and it needs to be within a degree.

 

I'm curious…

If a protractor is 180 degrees, how could you ever exceed its capability?

 

4 cubits / 11 cubits

 

I'm intrigued, and also horrible with most math type calculation scenarios, so I'd really like to see exactly what you're referring to.

 

Kelly, can be done but need to know, width, length constraints.
Are you needing to cut an angle from the end of narrow board or across a larger panel?

 

I started with a ninety degree angle, since it was the easiest to come by. All I had to do was use an L square, or measure 3,4 then 5 feet (measure three feet, turn, measure four feet, turn the same way and line the tape with where I started).

Once I had a ninety degree angle, I could get started, or go equal distance on each leg, measure the distance between the two points and split it in half for forty-five degrees.

Depending on how big the item was going to be, I could use eighth of an inch, quarters of an inch, halves or even larger fractions or whole numbers to represent each degree mark.

We know the entire angle is ninety degrees, so, if we use the ninety degree angle, we will need to use ninety of the chosen increments. If we used the forty-five degree angle, it would, of course, require we use forty-five of them.

Staying with the forty-five degree angle and choosing 1/8" increments, I will need a measurement 45/8th's, (5"5/8"), which will be measured across the angle from two points that are an equal distance up the two legs of the 45.

It may take a couple runs, moving the line between the two legs up or down them, before you find the position which gives you your 5-5/8" distance.

Once you find the points that will give you the 5-5/8" distance, you can double it, rather than resort to trial and error again. You could also make a chart, which I will, giving the measurements for extended points.

With your line ran between the two legs, mark eight inch increments on it for the forty-five degree marks. Mark critical positions, such as 90, 72, 60, 45, 30 and 22-1/2 degrees for easy location in the future.

Using this, you can mark any angle accurately. You can, then, use Paul's chalk line to mark your angle.

I found this useful for setting up to run 2x's for ten degree angle cuts.

and working in the area I know the angle will be, eventually, drawn,

 

SOH CAH TOA

- jtm

I've heard the lengthy story about the indian chief Soh Cah Toa… but I've also heard that back in the 60's "Some Old Hippy Caught Another Hippy Tripping On Acid". Got any other fun ones?

Anyways, the answer is to expand beyond basic math and use trigonometry. Even if you don't learn it there are online calculators that take the learning out of the equation (heh).

http://www.carbidedepot.com/formulas-trigright.asp

Punch in two values you know such as angle A as 20 degrees and side b as 10 (units don't matter, interpret them all as the same). The result is that you get side a as a length of 3-5/8". This will get you as accurate as you can measure 90deg and straight lengths. Oh, you can use this to make a big 90 as well. Put in 120" for both sides a and b and the diagonal (hypotenuse) is 169.71". Even if you round to 169-3/4" you would only be off by 0.015degree so it's pretty easy to get fairly accurate.

Also, I think that your method won't be right. You are taking a straight line and dividing it into equal segments? You need to take a circle and divide it's circumference into equal segments to get equal angles between each point.

 

School Closed Today…..... Oscar Had A Hit Of Acid

 

The reason your method won't work is because the same reason it does work for a 45. For the 45 your distance on both legs are the same, but if you try to use the original line with 90 segments to find a different angle it would be like using different lengths for each leg and that is what throws it off.

 

 

 

Pi r squared
- waho6o9

Nope…pie are round. Cake are square.

 

Get a bigger protractor. Or use a framing square. If a 12 in 12 pitch is 45 degrees, you can figure anything it out from there.

 

Altendky has the answer - sin, cosine and tangent (easy to find calculators on the web). With these, with a line of known length and a line at a right angle to it, you can readily calculate the length of other lines for a given angle to the known line, or calculate an angle between two lines of known length, etc.

This isn't that hard (your smart phone probably has a calculator with the trig functions) and will give you accurate answers and it doesn't take long.

 

I just look up angle multipliers. I use the standard multipliers all the time as an electrician for running pipe. they arent for precision work but the charts are out there.

 

Here is a link to an online calculator that will do the math for you. You give it an angle and side or two sides and it will tell you the rest. If you are doing angles beyond 90, 180, etc youll have to subtract or add 90, 180 etc

http://www.cleavebooks.co.uk/scol/calrtri.htm

 

What's a smart phone?

Altendky has the answer - sin, cosine and tangent (easy to find calculators on the web). With these, with a line of known length and a line at a right angle to it, you can readily calculate the length of other lines for a given angle to the known line, or calculate an angle between two lines of known length, etc.

This isn t that hard (your smart phone probably has a calculator with the trig functions) and will give you accurate answers and it doesn t take long.

- mnguy

 

I take it you did not try my way. If you create a perfect triangle and run a line off it when it will give you 90/8ths, for example, each eighth will be a degree. You CAN do the same with a 45. In both instances, the lines must be equal.

The calculators others offered seemed to not work, unless I, first, calculated the line lengths for both legs.

__
Punch in two values you know such as angle A as 20 degrees and side b as 10 (units don t matter, interpret them all as the same). The result is that you get side a as a length of 3-5/8". This will get you as accurate as you can measure 90deg and straight lengths. Oh, you can use this to make a big 90 as well. Put in 120" for both sides a and b and the diagonal (hypotenuse) is 169.71". Even if you round to 169-3/4" you would only be off by 0.015degree so it s pretty easy to get fairly accurate.

Also, I think that your method won t be right. You are taking a straight line and dividing it into equal segments? You need to take a circle and divide it s circumference into equal segments to get equal angles between each point.

- altendky
[/QUOTE]

 

Unless I'm misunderstanding your method!

 

I take it you did not try my way. If you create a perfect triangle and run a line off it when it will give you 90/8ths, for example, each eighth will be a degree. You CAN do the same with a 45. In both instances, the lines must be equal.

I did not try your way but I did think about it and it is incorrect. Equal angles result in equal distances along a circle not a line. If you drew a circle instead of your 45degree line and then used a curved ruler? Then your approach would be fine.

The calculators others offered seemed to not work, unless I, first, calculated the line lengths for both legs.

I didn't try the others but my calculator link works fine with a single angle and a single side.

Perhaps we do not understand exactly what you are trying to do. Often when cutting angles you are cutting it relative to an existing straight edge or line. In that case pick a distance along that line that will end up roughly at the wide end of the cut, use a normal square of appropriate size to find a right angle to the existing straight edge, use the online calculator with the first length along the existing straight edge and the desired angle, measure along the square by the distance calculated by the calculator. This gives you a point which, combined with your first corner, can be used to draw the correct angle.

If we don't get you the answer you need with writing then perhaps you can provide a picture so we can more directly address your needs.