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Old 05-21-2010, 04:34 PM   #1 (permalink)
KDM
 
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Default Waste From Square Blanks

Is this worthy of a tip/trick/FAQ?

Square Mould Turning Wastage

The calculation for the amount of material wasted when turning a square moulded blank into a cylindrical shape yields a really surprising number. Here’s the science part:

Assuming the desired cylindrical blank is the same length as the initial right cuboid moulded blank, the length can be disregarded for percentage wastage calculations.

To calculate wastage when turning blanks of a given size down to resultant cylinders of a given diameter, we may use the following simple equations:
b = s^2
c = π (d / 2)^2
w = (b - c) / b * 100
Where:
s is the length of side of the square section of the right cuboid moulding.
d is the desired diameter of the cylinder
b is the cross sectional area of the mould
c is the cross sectional area of the cylinder
w is the percent wastage.
Example

We start with a right cuboid moulding 22mm of square side. We aim to turn this into a cylindrical blank of 15mm diameter.

The cross sectional area of the initial blank is
b = 22^2 = 484mm^2
The cross sectional area of the cylinder is
c = π (15 / 2)2 = 177mm^2
This is a wastage of
w = (484 - 177) / 484 * 100 = 63%
This is pretty staggering. Even for a blank of 15mm sides (the bear minimum) and wanting to turn this down to a 12mm slimline, we still lose a massive 50% of the initial material.

Conclusion

Using circular moulds as small as possible where we can is likely to save at least 50% on the raw casting compound and increase the amount of use we get from the cutting tool before re-sharpening!

Last edited by KDM; 05-23-2010 at 02:49 AM. Reason: The superscripted 2's looked OK when I typed them but when I submitted, they weren't superscript.
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Old 05-21-2010, 04:37 PM   #2 (permalink)
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Further Thoughts on Waste From Centre Drilling

Centre drilling the blank produces even more waste. To take into account the waste from centre drilling, the equations given above are extended / modified as follows:
b = s^2
c = π ((d / 2)^2 - (k / 2)^2)
w = (b - c) / b * 100
Where:
s is the length of side of the square section of the right cuboid moulding.
d is the desired diameter of the cylinder
k is the diameter of the hole in the cylinder
b is the cross sectional area of the mould
c is the cross sectional area of the cylinder with the hole cut
w is the percent wastage.
Example

We start with a right cuboid moulding 22mm of square side. We aim to turn this into a cylindrical blank of 15mm diameter with a 7mm centre hole.

The cross sectional area of the initial blank is as before

b = 22^2 = 484mm^2

The cross sectional area of the cylinder with the hole cut out is

c = π ((15 / 2)^2 - (7 / 2)^2)= 138mm^2

This is a wastage of

w = (484 - 138) / 484 * 100 = 71%

In the example of the blank of 15mm sides turned down to 12mm with a 7mm hole, this is a loss of 67% of the material.

Conclusion

Using circular moulds as small as possible with the centre hole moulded into the blank is likely to save at least 65% on the raw casting compound and increase the longevity of your drill bit and chisel.
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Old 05-21-2010, 04:41 PM   #3 (permalink)
 
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My Head Hurts!!!! LOL..............

Just kidding, that's a neat formula and a surprising amount of waste.
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Old 05-21-2010, 04:50 PM   #4 (permalink)
 
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Interesting. Nerdy but interesting.
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Old 05-21-2010, 04:51 PM   #5 (permalink)
 
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This is clever???
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If you see some one building an ark, it might be wise to stop and help.
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Old 05-22-2010, 02:58 AM   #6 (permalink)
 
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RESIN SAVER MOLDS. Either from our vendors or home made.
Mark
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I think my head is now full of sawdust and shavings, every time it rains the swelling wood causes splitting headaches.
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Old 05-22-2010, 11:44 AM   #7 (permalink)
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Quote:
Originally Posted by seawolf View Post
RESIN SAVER MOLDS. Either from our vendors or home made.
Mark
Totally!
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Old 05-22-2010, 12:38 PM   #8 (permalink)
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Quote:
Originally Posted by Jgrden View Post
This is clever???
No. This is curiosity. Clever is making a pen while playing the bagpipes. On a unicycle.
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Old 05-22-2010, 04:29 PM   #9 (permalink)
 
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Quote:
Originally Posted by KDM View Post
No. This is curiosity. Clever is making a pen while playing the bagpipes. On a unicycle.
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Old 05-22-2010, 06:25 PM   #10 (permalink)
 
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My eyes glazed over after the first equation....
So what your saying is use round moulds as close to the diameter of your pen as possible...Right?: Whew...I didn't know I needed all that math to figure that out!
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