finding angles for shelf in garage ??

[Anonymous-0]

Hello everyone . I got a nice power mitre saw for x mas and I am going to make a nice shelf in garage . I want the shelves to be 30 " deep and supported by 2"x4" on a 45 degree angle from front of shelf to 2x4 on wall . . I will cut the supports in a 45 degree angle to set flush to bottom of plywood and screw directly to studs on wall at bottom . How long do the 2x4's need to be before I make my 45 degree cuts ? I know this is a dumb question , but everythings easy when you know how .... Thanks in advance

 

[Anonymous-0]

Lay out the shelf on a piece of plywood first. Then measure the 2x4's for the sides.

 

[Anonymous-0]

Tuff to hold the tape measure at a perfect 45 degree angle to get measurement? Must be some algebra formula that will give measurement ? I only do basic Hillbilly math so Im in trouble ... LOL

 

[Bruce S IL]

To get the length for a 45 degree you multiply by 1.414. 30 X 1.414 = 42.42 about 42 7/16.

 

[Anonymous-0]

30x30=900 is top side squared + same for vertical/wall side= 1800. Square root of 1800 = 42.42 or about 42 3/8. That would be the longest edge of the brace. That is the extent of my geometry.

 

[Anonymous-0]

Same answer. That's a new one on me. Trig?

 

[Stan in Oly, WA]

Hi Lumbrjakman,

What you want to find is the hypotenuse of the right triangle formed by the shelf, the wall, and the brace. The brace is the hypotenuse. The Pythagorean theorum (a squared + b squared = c squared) is one of the most useful formulas for carpentry. In this case the shelf can be a, the distance down the wall can be b, and the brace is c. You're cutting the ends of the brace with 45 degree angles so that makes the distance down the wall the same as the width of the shelf, 30". 30 squared + 30 squared is 900 + 900 which equals c squared. c squared = 1800 so the length of the brace is the square root of 1800, or 42.43" which is 42-7/16". The square root is the number times itself which equals the number you are working with.

Since almost nobody nowadays remembers how to find square roots long hand, you have to use a calculator, and not all of them are set up with a square root key. If you don't have such a calculator, it's pretty easy to find the square root by trial and error. Almost all calculators will square a number by entering the number, then pressing X (times), then =, which makes it pretty fast to try different numbers. So you might take a guess that the square root of 1800 is about 50 but that comes out 2,500. So you try 40 and it comes out 1,600. Then you know that the number you're looking for is closer to 40 than to 50. A few more tries and you'll have it close enough for carpentry. That's my experience, anyway.

Merry Christmas, Stan

 

[riverbend]

Geometry ? A right triangle has a 90* corner and the sides are equal length. If the short sides were 1 foot long, the long side would be the square root of 2 (~1.414). All right triangles are proportioned the same so the long side is always 1.414X the short side.

Greg

 

[LilFarmer]

From what I remember (which isn't much, sometimes) a right triangle has a 90 degree corner, but not necessarily equal sides.

An isocales (spelling) triangle has a 90 degree corner and equal sides therefore the 1.414 would work.

Not picking at anyone here, that is a new one for me too and I learned something, it just won't work on every right triangle. Have to be careful where one uses it.

 

[Anonymous-0]

Very good Greg. I've used math all of my life in construction layout. Never used that particular method to find the "C" length, but I would have had I been aware of it. Worked 35 years and learned something new tonight. Life is sweet!

Paul

 

[Dusty MI]

On a 30*60* 90* triangle the hypotenuse is 2x the length of the short side. In bending offsets in conduit we always used 2x for 30* and 1.4141 (or 1.5) for 45*.

Dusty

 

[Stan in Oly, WA]

Hi LilFarmer,

It's isosceles, but you're exactly right. I just spent about ten minutes on Google trying to find the name of the right triangle with equal legs, and it was in your reply (which I had just finished reading). I used to have a better excuse for this type of behavior when I spent much of every afternoon about half in the bag. Now I've got no choice but to take full credit.

Merry Christmas, Stan

 

[LilFarmer]

I knew the word, just not how to spell it and didn't take the time to look it up.

I am glad you did, but I probably still won't remember how to spell it tomorrow.

I will, however, try to remember the 1.414 formula!!!!

 

[MarkB_MI]

As others said, the ratio between the hypotenuse and side of a 45 degree right triangle is the square root of 2 (= 1.414). 1.414 is also the sine of 45 degrees. And the cosine of 45 degrees.

When I'm doing something like this, though, I always cut pieces a little long and trim to fit. Easy to do with a miter saw. The thickness of the lumber will trip you up, unless you're real careful in your calculations.

 

[Anonymous-0]

The others are perfect in their answers, however.... Are you sure you want the brace to extend clear out to the edge of your shelf?


And do you want it to go clear to the floor making it hard to clean with a broom? Might want to raise it a few inches off the floor so one swipe with the wifes borrowed broom will do the job faster so it lessons the chance of her knowing that you used it!

 

[huntingreen2day]

30 divided by the cosine of 45 degrees which is .7o711 = 42.42 inches

 

[Mike M]

Run the supports UP this way you have the area under the shelves OPEN to park stuff under them.

And if you do run them down WHY settle on a 45* angle ? this may put the braces down farther in the way then needed so another angle might look and work out better.
Just stick a squared off board up to the end ,hold it where it works out the best and draw a line on it then match this angle with your saw.

 

[rustyj14]

Cut it off twice and it'l still be too short!