Help Calculating Angles

Pontiac Freak

Pontiac Freak

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Maybe someone could shed some light on how to calculate angles easily. I am trying to figure out how to duplicate a bend on a fender. I need to cut out 2 triangles essentially or 1 large one so the sides will be equal when they come together. The finished angle needs to be 38°, the side is 2" tall. Make any sense? 20151226_090116.jpg
 
I'll give you something to think about. The height is immaterial.

What happens if you cut two 2 x 4"' @ 22.5° angle and join the angled faces? You can do this and see if you have some scrap around.

Or take some solid wire and play with it and a protractor. It's better to go through some exercises than for someone to just give you an answer, when possible.

And yes, just one triangle cut is what you need on each side of the channel.
 
In this case you need a 38 degree included angle, with the center line on the bend line, then cut 19 degrees on either side of the C/L. Add a bit of clearance in the bottom of the ''V'' because the metal will bunch up a bit when you bend it.
 
What Jim said.

I would add that the centerline is perpendicular to the edge rather than as you have it marked. The two cut lines have to be equal lengths.
 
Another consideration: When you bend metal, the outside of the bend stretches and the inside compresses. Usually the outside will deform more than the inside and you have some growth in the overall length. The amount of growth depends upon the radius of the bend and the thickness of the metal. If you have somewhat critical dimensions, as in bending up a box, this needs to be taken into account.

For a simple bent configuration, you can make the bend first and trim to length afterwards. Otherwise you need to calculate the amount of correction needed. There are bend tables to help with that process. Another way would be to take a piece of scrap material of the same thickness and measure its dimensions. Make a trial bend similar to the desired bend and remeasure. You should then be able to calculate corrections for the bends.
 
This is the easiest math that you will ever do in a machine shop, I do however recommend using the center line of the material as the baseline rather then one of the surface planes, this will reduce the error to roughly 1/2 of the material section.
 
All of the above. You've got the info now go for it. the only thing I may consider is to nick the inside face of the surface from web to web this helps make the bend sharp on the outside surface if you want you can weld it up after you get the fold tacked
 
JimDawson said:
In this case you need a 38 degree included angle, with the center line on the bend line, then cut 19 degrees on either side of the C/L. Add a bit of clearance in the bottom of the ''V'' because the metal will bunch up a bit when you bend it.
Click to expand...

Thanks everybody for the replies, still trying figure out how to get the angles for myself for next time. JimDawson, trying to see what you are saying. Are you calling the 90° vertical centerline - 0° and going 19° either side of it? Or are you refrencing the bottom where the bend will be 0° and going 19° either side? 90°-19°=71° & 90°+71°=161°?
 
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