Setting Out for walls

[bobloes]

I am building retaining walls and a couple of them will connect to my boundary wall. Obviously I want the two to be at right angles. I am using Pythagoras to attempt to get the two walls at right angles but ... The length of the end of the wall from the boundary wall is 450cm and I have used string to produce the right angled triangle. Needless to say I am not confident that this has worked properly as the string stretches. I have also used a piece of wood 200cm long to provide a more 'stable' measurement and then extended another 250cm from the measured point. My mark one eyeball says that it looks ok. I do not have a 10 metre metal tape measure. I have even calculated the likely error. ie if opposite and hypoteneuse are in error by 10cm (one longer one shorter) then the angles only changes by less than two degrees and the end point will be out by 7cm. Am I being anal? Should I trust the eyeball? Is there a guaranteed method which does not involve me buying items which will never be used again? Any non-abusive suggestions gratefully received.

 

[freddiemercurystwin]

£4.10 is hardly likely to break the bank is it?
http://www.machinemart.co.uk/shop/product/details/10m-tape-measure-2/path/measuring-and-marking-out

 

[bobloes]

Thanks Freddy for waking me up. Tightfistedness can stop me seeing the wood etc.... Cheers

 

[Chukka63]

buy a square

 

[Nige F]

Make one using pythag.. 3-4-5

 

[noseall]

We use a foldaway ally builders square to initially set up the lines, then fine tune them with some metal tape measuring.

As Nige has said using the 3-4-5 method is most simple. You will get a fairly accurate representation of squareness if you measure out 3m, 4m and diagonal of 5m.

Trying to achieve anything more accurate than this is pointless in most domestic situations.

 

[Thermo]

using a 345 square and string lines will get it more than accurate enough

 

[Nige F]

Note for the DIY`ers it`s 345 any distance eg a random length of wood. It`s the ratio that makes a square

 

[noseall]

Note for the DIY`ers it`s 345 any distance eg a random length of wood. It`s the ratio that makes a square

Multiples work also, i.e. 6, 8, and 10.

 

[Thermo]

also length of string is not an issue. Its twice as long from the middle to the end

 

[bobloes]

Multiply all sides by the same factor difference and it works for any lengths. Anyway as I said to Freddy in message three I bought the tape measure and did the job in five minutes. The mark one eyeball was at least 10 cm out. Cheers all.