[felenish]

Hope this is the correct forum for a question. I have a somewhat weird project I'm working on for a friend. He has me building a toe-pincher coffin, which is fairly simple in itself. My big problem is the way he wants to lid to come out. Here is a picture.

I know dimensions are tiny. I'm also attaching the SketchUp file for a better view.

View attachment coffin.zip

I am having a hard time getting the angles for the side pieces to match up correctly. any help on how to calculate that are an easier way to go about it is greatly appreciated.

Thanks

 

[woodnthings]

if it were me

I'd make the layout lines on the back side, turn it over and use a circ saw set at about a 20 degree angle from vertical, and saw to the lines....you can use a straight edge guide clamped in place for better/straighter cuts. You have to allow for the offest from vertical....probably about an inch or less and make your layout oversize....I'm just spitballin' here...guessin' UNLESS those dimensions are the bottom and the top can be whatever it turns out?

Is this a glue up? How thick? :blink:

 

[GeorgeC]

I cannot open the .zip file and cannot read the dimensions on the sketch.

Who are you and what is your woodworking experience?

George

 

[felenish]

I'm a hobbyist with a few years experience. Mostly I've done bookshelves and entertainment centers. Couple of chairs. I know a bit about calculating angles from computer work its just the mix of an angles crosscut as well as an angle on the joint that is messing me up. The angled rise on the edge is throwing me way off somewhere.

Here are a couple closer pics of the dimensions and an unzipped sketchup file. No idea why the zip wouldnt work.

Sketchup File - View attachment coffin.skp

 

[Sorrowful Jones]

The angles are as follows: Starting at the top the angle is 60 degrees, the side angless are 50 degrees and the bottom is 70 degrees. If you are mitering the joints, just cut your miters 30, 25, and 35 degrees respectively. As for the angle for the edge of the lid, I would just guess about 20 degrees.

 

[mdntrdr]

Use the Sketchup protractor to read the angles. :smile:

 

[felenish]

thanks for the quick answers guys. If someone could point me at someplace to learn the math for that that'd be awesome. And this is my first project with sketchup so I'm still getting used to all the features.

 

[Sorrowful Jones]

I dont use sketchup. Those are angles I used to build some coffin shaped pistol cases. As far as the math... just add up all the angles around the box. If you add 70, 50, and 60 you get 180. Double that you get 360 degrees.....which will get you all the way around. That combination of angles is not the ONLY combination that can be used, but whichever combination you use needs to add up to a total of 360 degrees. Not really sure if that was your question, but hope it helps

 

[rrich]

If someone could point me at someplace to learn the math for that that'd be awesome.

It's just high school trigonometry. (Actually I learned Tangent, Sine and Cosine in first year algebra.) With a book of trig functions and working everything into right triangles it's not difficult.

- The right angle 90° is not used in the calculations and the side opposite the right angle is called the Hypotenuse.

- By knowing the length of any two sides, the angles and third side can be calculated.

- By knowing one side and one angle the other angle and sides can be calculated.

Tangent of the angle = the opposite side divided by the adjacent side. Look up the Tangent and read the angle.

Sine of the angle = the opposite side divided by the hypotenuse. Look up the Sine and read the angle.

Cosine of the angle = the adjacent side divided by the hypotenuse. Look up the Cosine and read the angle.

The sum of the angles of a triangle always equals 180°. In a right triangle the two non right angles are complementary or subtract the angle that you know from 90° to determine the other angle.

When making a rectangular frame with mitered corners, the outside length of a side equals the inside length plus twice the width of the side.

It's the kind of thing that can be learned in a couple of hours if you accept the nomenclature and the process. I used to know where and how the trig functions were derived but it is not important.

A word of warning, some of the books of trig functions may indicate that the values of the functions are positive or negative. This has meaning for surveyors in coordinate geometry but for woodworkers always assume positive values.