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Posted: Fri May 18, 2007 11:54 am
by Lewys
ok, i'll try to explain as best i can.
Say i want to lay a circle with a diameter of 2m.
This will give me a circumference of 6.2832m.
If i was to lay this using for agrument sake 300mm square slabs. So that each cut is the same size, i divided 6.2832m by 303mm (3mm for the join) which gives me 20.7366. Meaning there would be 20 with the outside edge being whole and 1 with the outside edge being cut to .7366 of its length.
For all cuts to be sections to be the same size will rounding 20.7366 up to 21. then dividing 6.2832m by 21 (which gives me .299mm which would be the size to cut each section.
I know that the numbers i've given above only work out to 1mm cut which would be totally pointless, but it's just to explain.
Will this way of doing it work? or is there another?
Thanks for any reply.
Lewys
Posted: Fri May 18, 2007 5:46 pm
by bobhughes
I played around with this for a bit and your calculation is right as far as it goes. You won’t end up with a circle but a 21 sided regular polygon, and you also need the angle for the side cuts because the inner circle will only have a diameter of 1400mm.
You could work it out using trig or possibly by your method above but I found this handy calculator that, if you input the number of sides and the length of each side, will work out the angles for you. Of course all the flags for the inner polygons will have to be cut at the same angle.
Have a look and try it:
http://www.1728.com/polygon.htm
Posted: Fri May 18, 2007 7:50 pm
by lutonlagerlout
lewys,i hate to tell you this mate, but just buy the circle pack,what you have described doing will look crap
the odd cut you can get away with ,but believe me i have tried many times to cut square flags into circles etc and it takes ages and rarely looks good
i know its feasible but its uneconomic
cheers LLL
Posted: Sat May 19, 2007 10:20 am
by bobhughes
I assumed this was a theoretical exercise:)
Could you imagine how long it would take to measure and cut all those slabs?
Posted: Sat May 19, 2007 2:06 pm
by Tony McC
I have a calculator (not currently online) that determines the number of "units" needed to form an arc or any radius and any length. So, if you needed to know how many 100x100 granite setts are needed to form a quarter circle edge course with a radius of 4.2m, allowing for a 12mm joint, you input the variables, click the magic button and it tells you that you need 59 setts.
It can also work out cut angles for fast arcs laid using rectilinear paving units of any size. So, if you were laying a quarter circle of Brett Alpha 210x140, laid 210 wide, to an arc of radius 1.2m, then each block would need to be trimmed by 22m for single edge taper cuts or 11mm on each edge for double taper cuts.
I have dozens of these calculators - I keep thinking I'll burn them all onto a CD and flog them on EBay!
Posted: Sat May 19, 2007 3:15 pm
by lutonlagerlout
this is paving expert bob not geometryexpert .com LOL
LLL
Posted: Sat May 19, 2007 9:42 pm
by bobhughes
And no comment from the original poster
Posted: Sun May 20, 2007 6:34 am
by Dave_L
bobhughes wrote:And no comment from the original poster
Perhaps he's away on a dirty weekend?*
*DIY :laugh:
Posted: Sun May 20, 2007 7:30 am
by seanandruby
A few years ago before you could get these circle packs. i worked with a guy who wanted to do all the finished work, ( yeh one of them ) thing is he was rough as r soles. but he was the boss. we laid a square patio to the required size, then drew a circle. well i thought it looked shite. there were so many darts, also the size of the patio reduced quite a lot. a few days later after some heavy rain and being walked on, guess what? he got rollicked from r sole till breakfast. :laugh: these houses where in the higher price bracket to.
Posted: Sun May 20, 2007 10:56 am
by Lewys
hi guys, thanks for all the replys.
sorry for the late reply bobhughes, but its the weekend! lol
maybe the example i used wasnt the best example to choose, but just wanted to know if the theory behind it was right thats all.
Thanks for all the replys, hell of a active message board!