What angles to cut for X leg table

http://i8.photobucket.com/albums/a40...s/drawing1.png
Dodgy drawing I know

I want to build this table but cant figure out what the correct angles to cut are.

I'm sure my old maths teachers are turning in their graves (where i put them) " QUITE BOY!!!! YOU"LL BE THE DEATH OF ME!!!!!").

I've used pythag sum sq two sides = hypot (sq root) to come up with a length. But i cant seem to get any further.
What angle(s) do i need to cut and how do I calculate that angle?

(Please show working out or you'll be given a D minus)

In case you cant see the pic. X leg table 600mm high 420mm wide..... (Width of timber used for leg 90mm)
Hypotenuse = 732.3mm

No good at maths either sorry, but can use CADD.
Attachment 317521

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Originally Posted by Picko

No good at maths either sorry, but can use CADD.
Attachment 317521

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Thanks for the reply Pico. Unfortunately I cant use CAD. good excuse to learn I guess.

Whilst you've solved the problem for this particular example that does not inform me how to work the angles out for another, different set of measurements.

Thinking on this today I realised the sum of the internal angles would be 180 but still no way of working out what the top and bottom angles would be unless its an equalateral triangle.
I guess the obvious work around is make the table top 600 wide.

Simple solution is to do a full scale drawing and measure from that. Used to do a couple a month in 100x10 mirror polished stainless.

Draw a rectangle the width and height of the X leg.
Take a piece of the material you wish to use and lay it over the rectangle on a diagonal so it just touches opposite corners of the rectangle and draw lines on each side of the material.
Repeat for the opposite diagonal.
You can then use a protractor and rule to measure all angles and lengths, and transfer these measurements to the material for cutting.

We used to do the drawing on 18mm chipboard and fit blocks etc to position the material for welding to ensure that it didn't move while welding. You could do similar if you needed to for glueup.

It's not easy to calculate a solution using geometry. Changing the top to make width and height the same won't help, as that doesn't factor the leg material width and it's effect on the intersecting angle.

I believe the geometry (?) answer is SOHCAHTOA.

GOOGLE and start reading.

I did this once ... Many many years ago when building a crossed brace for an outdoor balustrade. My father (who would have been 70 at the time) rattled it off like he used it every day ...

Ended up using a little bit of trial and error.:D

28.44°

Ok I took a guess at the amount of leg in contact with the floor. First guess was 95mm. Turns out it is closer to 102

420 - 102 = 318

I worked on 600 high.

That gives me a triangle 600 high and 318 across the base

318/600 = 0.53

0.53...... (2nd function)TAN = 27.93°

Glad you showed your workings Dave ... Or we would have to deduct marks. :)

Now to find out if it is close enough to the mark for what dadpad wants

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Originally Posted by DaveTTC

Now to find out if it is close enough to the mark for what dadpad wants

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Full marks to Dave. A+ and a Mr man stamp for you lad.

Thanks all for the tips.

The solution I arrived at was to pin the legs at the center of the X allowing a reasonable amount for off cut at each end of the legs to ensure i could open 420 wide
Using a 600 straight edge along one side I then opened the legs until i had 420 wide measured from outside of leg to outside of leg at the 600 mark.
I marked the 600 points. Then joined these marks using another straight edge.
I had to ensure the 600 and the 420 straight edge were at right angles (using a square) to each other (near enough) or the cross over could have been lower or higher than desired and make the table lopsided.

then without moving the 600 straight edge up or down the legs do the same for the bottom. Whilst in position I marked the rebates for the cross over. Then removed the center pin.

Once i had it on the drop saw it just a matter of getting the drop saw angle to match the marks.

Accuracy wasn't really a priority as the table was an outside table made from pallett wood and sitting on grass but I like to do the best/neatest job I can.

Seems so simple now I feel like a bit of a doofus. Shows how over-thinking things can buy you a bunch of trouble.

This also goes to show that we teach geometry the wrong way at school.
I recall sine, cosign and tangets being taught in maths class.
Also recall thinking what a useless waste of time it was and where in hell was i ever going to use something like that.
Know I know..... but its taken me 40 years to find out

I use it often with roofing angles. Particularly with reno's


Dave the turning cowboy

turning wood into art