laser beam splitter for setting out a right angle

jim_in_sussex presented the following explanation :

How perfect is 'perfect'?

Most people manage to make an accurate enough right angle out of three good straight pieces of wood forming a triangle.

One of the prisms in an old pair of binoculars might just be a 45 deg(?).

Two lasers?

Shouldn't be hard to bond to an engineer's square and fabricate a micro-adjust?, should be a lot cheaper, too.

Just a thought... DIY and all

Use trigonometry. The hypotenuse will be the square root of the sum of the squares of the other two sides. If yours were both 3m, then the hypotenuse is sqrt(3² + 3²) = 4.243m. The easy one to remember is a 3-4-5 triangle... sqrt(3² + 4²) = 5 Make up a loop of string (preferably as non-elastic as possible), which is 3+4+5=12m long, and mark it at the 0m, 3m, and 7m positions. when pulled taught (but not stretched), the angle between the 3 and

Yep. 3 straight pieces of in the ratio 3:4:5 guarantees a right angle as accurate as you can make the ratio.

The corners of an 8x4 sheet of reasonably thick MDF or ply are also very good right angles (unless bashed!)

Regards Jeff

You could use something like this and direct the beam at a prism as you suggested.

Pricey though.

Dead right. Worked OK for the pyramids in Egypt didn't it?

Dave

"The3rd Earl Of Derby" wrote

Regards Jeff

Bad catch 22 situation. The laser beam cross needs to be aligned vertical to the surface on which the line are shown, or else the lines won't be at right angles. How do you get this right angle in the first place without using a set square, or possibly a plumb line if the laser is pointed down to a flat floor.

john

Spirit level?

In article , jim_in_sussex Sun, 1 Jan 2006 14:49:46 writes

I have one I bought when building my loft. It has two lasers at right angles.

I don't have the details to hand but I think it cost about £150

QVC (UK) sell a tripod mounted laser device that projects a vertical line and a horizontal line. Each line is separately switcheable. The Vertical and horizontal lines are pendulously self correcting [within reason] and the tripod arrangement allows the projection head to be adjustable in height (heave axis) via a rack-and-pinion winding gear; rotation (yaw axis) is achieved by manually swivelling the laser head. The 'right angle' projected is "close enough for government work" and more that suitable for D-I-Y.

is there something wrong with using a spirit level?

NT

If he doesn't care about levelling, all he needs is a tape measure.

The Egyptians didn't have trigonometry. They had some geometry (including 3:4:5 triangles), but not that much.

Then buy a Cowley level or similar off eBay. Full-blown theodolites are cheap (tripods are harder to get hold of) and there are plenty of simple-to-use builders' levels and similar gadgets that can accurately lay out a level or a plan right-angle with minimal complexity.

Lasers are of negligible use here. it's easier to do it with eyeballs and a telescope than a projected spot. For 3m ranges outdoors you'd have to spend serious money to get a laser that was remotely easy to use or accurate.