Help... Need to mark out a scalene triangle WITHOUT a compass.

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I got plans the other day to cut out 12 triangles on the sheer at work.  No angles were given, just lengths, and each length was different. Now I can use a compass but the material is 3/16ths to 1/4. And I can't get a perfect layout cause of the height of the material, and in conjunction trying to line it up in the sheer (PITA). On top of that I need to be with in 1/16th. What i have been doing is cutting the sticks to the longest dimension and using the edge of my tape as a pivot, while holding my soap stone at the desired length and swinging an arc.  Can anyone tell me a more precise way without a compass? Preferably with a ruler.Thanks
Reply:If nothing else you could lay it out on a paper scaled down. Just use 1/4 the length of the sides or what ever division will get it small enough. Then you can use a protractor to measure the angles. Then use the angles to make the full size versions.
Reply:layout 3 straight edges to form sides.  Intersect the straight edges at the given measure. mark the triangle.  Chalk line will or welding wire will work for marking sides too.
Reply:I prefer string when drawing arcs, but string and soapstone are tough to get within 1/16"If you like math, here is an example (not to scale):

Last edited by MinnesotaDave; 08-13-2016 at 12:31 PM.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Hey DAVE, I saw that on '' BIG BANG THEORY'' !!!

    Way too many numbers for me.  

I'll go for full size layout with string too. What lengths are you talking about ?
Reply:draw it in cad and then measure the unknown points and lengths.millermatic 130XPharbour freight 180 amp mig with added caps.hobart stickmate ac/dcpowerarc 200
Reply:Lay it out on paper with compass / dividers.Then center punch the corners through the paper onto the sheet.
Reply:

Originally Posted by BD1

Hey DAVE, I saw that on '' BIG BANG THEORY'' !!!

    Way too many numbers for me.  

I'll go for full size layout with string too. What lengths are you talking about ?
Reply:

Originally Posted by Fastsofa

I got plans the other day to cut out 12 triangles on the sheer at work.  No angles were given, just lengths, and each length was different. Now I can use a compass but the material is 3/16ths to 1/4. And I can't get a perfect layout cause of the height of the material, and in conjunction trying to line it up in the sheer (PITA). On top of that I need to be with in 1/16th. What i have been doing is cutting the sticks to the longest dimension and using the edge of my tape as a pivot, while holding my soap stone at the desired length and swinging an arc.  Can anyone tell me a more precise way without a compass? Preferably with a ruler.Thanks
Reply:Laying out a triangle with lines of three given lengths is most easily done with a compass.  If you have a triangle made of points: A, B, and C, first measure out the straight line AB with a ruler (1st length).  Then set your compass for the length AC (2nd length) using the ruler and the compass.  Draw an arc with the compass pivoting at point A.   Next set the compass for length BC (3rd length).  Now draw an arc using the compass from point B on the line AB.  The intersection of the two arcs will be point C.  Connect the dots.I don't know of a better or faster way than with a compass and I don't understand the reluctance not to use it.  You've described swinging an arc with your ruler which sounds like what you do with a compass.  Maybe you just don't have the right tools.Last edited by Denis G; 10-13-2016 at 11:16 PM.
Reply:Drill holes in ruler.  Stick scribe through holes.  I do it all the time for things larger than my calipers.

My name's not Jim....
Reply:

Originally Posted by Denis G

Laying out a triangle with lines of three given lengths is most easily done with a compass.  If you have a triangle made of points: A, B, and C, first measure out the straight line AB with a ruler (1st length).  Then set your compass for the length AC (2nd length) using the ruler and the compass.  Draw an arc with the compass pivoting at point A.   Next set the compass for length BC (3rd length).  Now draw an arc using the compass from point B on the line AB.  The intersection of the two arcs will be point C.  Connect the dots.I don't know of a better or faster way than with a compass and I don't understand the reluctance not to use it.  You've described swinging an arc with your ruler which sounds like what you do with a compass.  Maybe you just don't have the right tools.
Reply:Years ago I did a little gunsmithing (benchrest stuff).  I got into a "stuck" spot with some angles and asked on a forum what "that formula" was to find a certain length in a right triangle.  I was told it was the pythagorean theorum -  (a^2+b^2=c^2 - or dave's first step in his picture) and was promptly scolded that it was NOT a "formula"...  To this day that incident reminds me of the times as a kid that I would say "but I'll never need this stuff in the real world"