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I'm trying to work out if a shower screen will fit my bath. Using a measuring tape the current screen is 700mm long along the curve, which measures 646mm in a straight line. Is it possible to work out the radius from just these 2 figures?
Alternatively, if (according to the diagram below) the centre point is 249mm from the wall, should the widest part of the shower screen be 799mm from the wall?
Method I was taught at school to find the centre point of a circle:
Draw three points on the curve, let's call them A, B & C
Draw straight lines between A & B and between B & C
Find the mid point of these two lines.
From each mid-point draw a line at right angles.
Where the two lines intersect is the centre point of the circle. You should be able to measure from that to get the radius.
Radius of your screen is around 507mm (assuming it's a constant radius). Calculated by drawing it in AutoCAD and measuring it...
Jeff
What Whitestone said.
Although (and maybe I'm missing something) why not look at the diagram and simply read the dimension that says R 585?
And on that basis the screen will be 249 + 585 = 834 from the wall
The bath apparently has a radius of ?600? (can't quite read the text clearly but seems to tie in with Rscreen) so the total will be 600 + 249 = 849
(seems reasonable the screen is slightly inward from the edge of the bath, otherwise the water will just run down the inside onto the floor)
Although (and maybe I’m missing something) why not look at the diagram and simply read the dimension that says R 585?
he's trying to determine whether the screen in the diagram will replace the one he already has. Its the radius of the existing screen he's trying to resolve.
Rather than do clever maths - what I'd do is draw the radius of the replacement screen on a piece of cardboard, cut it out, and offer it up to your existing screen to see if its a match
told you i was missing something 😉
In that case do what Mac says, who cares what the radius actually is, as long as it fits in practice.
Thanks for your help, shame the cardboard all went in the recycling this morning 🙂
Buy the new shower screen anyway then you can use the box it came in to cut your template.
When you've established the radius and confirmed its the wrong shower size but the new shower screen back in the box and take it bac.... oh.
[i]Pieface wrote:[/i]
I’m trying to work out if a shower screen will fit my bath. Using a measuring tape the current screen is 700mm long along the curve, which measures 646mm in a straight line. Is it possible to work out the radius from just these 2 figures?
In theory yes. If r is the radius and the angle is 2a (in radians) then:
350 = ra
323 = r sin(a)
so with 2 variables and 2 equations we should be able to solve that:
323 = r sin (350/r)
...at which point my maths runs out, though that's certainly easily solvable with iteration (that may be the only way)
Isn't this just a chord problem?
You know the chord length.
You know the arc length.
Measure the segment hieght.
Stick it in the formula.
Not quite, because he doesn't have the segment height, he has the arc length instead (which isn't used in the formula in the link you gave). It boils down to the equation I gave above which doesn't have quite so neat a solution.
anyway, I iterated in Excel and the answer is 508.39mm radius (which I suspect may have rather greater precision than the measurements 😉 )
It is kind of fun devising a good iteration - got to that in a handful of iterations starting from a vaguely sensible starting guess (power of 6 on the difference seems to be optimal).