How to work out the size of the disks for the mold
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Before
sweating over these equations, see the tip at the end of the page...you
won't need them for 25mm flares
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Here, we will work out the diameter of disk2 Disk1 just fits inside our pipe, so its radius = (pipe internal diameter) / 2 The radius of disk2 is larger than disk1 by the amount shown in the drawing as x To work out x we need to know b b^2 = a^2 - c^2 .........Pythagorus' theorem b^2 = (flare radius)^2 - (flare radius - thickness of disk2)^2 taking square root of both sides b = sqr( (flare radius)^2 - (flare radius - thickness of disk2)^2 ) now x = ( flare radius ) - b x = ( flare radius ) - sqr( (flare radius)^2 - (flare radius - thickness of disk2)^2 ) The radius of disk2 = (radius of disk1) + x thus....
A 25mm flare radius is about the largest achievable for 90mm stormwater pipe with a 2mm wall thickness. Internal Diameter of pipe 86mm for a Flare radius of 25mm using a disk thickness of 18mm Radius of disk2 = (pipe internal diameter)/2 + ( flare radius ) - sqr( (flare radius)^2- (flare radius - thickness of disk2)^2 ) Large Disk radius = 86 / 2 + 25 - sqr ( 25^2 - (25 - 18)^2) Large Disk radius = 43 + 25 - sqr ( 25^2 - 7^2) Large Disk radius = 68 - sqr ( 625 - 49) Large Disk radius = 68 - sqr ( 576) Large Disk radius = 68 - 24 Large Disk radius = 44 Results Disk1 diameter is 86mm Disk2 diameter is 88mm Thin disk to be used as scraper is 50mm diameter Stop line on baseboard drawn with a diameter of 140mm
A 25mm flare radius is about the largest achievable for 103mm sewer pipe with a 3.5mm wall thickness. Internal Diameter of pipe 103mm for a Flare radius of 25mm using a disk thickness of 18mm Radius of disk2 = (pipe internal diameter)/2 + ( flare radius ) - sqr( (flare radius)^2- (flare radius - thickness of disk2)^2 ) Large Disk radius = 103 / 2 + 25 - sqr ( 25^2 - (25 - 18)^2) Large Disk radius = 51.5 + 25 - sqr ( 25^2 - 7^2) Large Disk radius = 76.5 - sqr (625 - 49) Large Disk radius = 76.5 - sqr (576) Large Disk radius = 76.5 - 24 Large Disk radius = 52.5 Results Disk1 diameter is 103mm Disk2 diameter is 105mm Thin disk to be used as scraper is 50mm diameter Stop line on baseboard drawn with a diameter of 157mm
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As you can see, for 25mm flares, the difference in disk sizes is very small. It's much simpler to just make all the disks the same size as the internal diameter of the pipe. So you'll use a bit more bondo. Big deal...
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| This style of mold could be used in conjunction with fibreglass to make huge flares. In that case it would be worth doing the maths.... |
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Last update to this page 31st August 2006
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