# Waste From Square Blanks



## KDM (May 21, 2010)

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!


----------



## KDM (May 21, 2010)

*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.


----------



## Boodrow (May 21, 2010)

My Head Hurts!!!! LOL..............

Just kidding, that's a neat formula and a surprising amount of waste.


----------



## David Keller (May 21, 2010)

Interesting.  Nerdy but interesting.


----------



## Jgrden (May 21, 2010)

This is clever???


----------



## seawolf (May 22, 2010)

RESIN SAVER MOLDS. Either from our vendors or home made.
Mark


----------



## KDM (May 22, 2010)

seawolf said:


> RESIN SAVER MOLDS. Either from our vendors or home made.
> Mark



Totally!


----------



## KDM (May 22, 2010)

Jgrden said:


> This is clever???



No. This is curiosity. Clever is making a pen while playing the bagpipes. On a unicycle.


----------



## Jgrden (May 22, 2010)

KDM said:


> No. This is curiosity. Clever is making a pen while playing the bagpipes. On a unicycle.


:biggrin::biggrin::biggrin:


----------



## B727phixer (May 22, 2010)

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!:biggrin:


----------



## Fred (May 22, 2010)

Is this now the new Pen Math for Dummy's Forum? ... as I fall down many, many times trying to figure out why my head is spinning.

Actually, I do believe the formulas show all of us turners just how much "money" we are having to waste as we turn great wood into worthless chips and dust. No matter how one looks at it there is a lot of waste, either in sawing or turning.

Now someone get busy and figure out how many inches of wood are cut out by the table saw blade. Take for instance, cutting .75"x.75"x8' square strips of Cocobolo or some other expensive wood using a Forrest II table saw blade vs a thin kerf blade. Then one begins to understand the idea behind using a thin kerf blade. I do believe the expense of the blade is saved in short order.


----------



## KDM (May 23, 2010)

1TJTurner said:


> 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!:biggrin:



It was obvious that square moulds were fairly wasteful. I just wanted to know how much!

TBH, the square mould hasn't lost its place: there are still layers and patterns and stuff you can't do with a small round mould. And I really like turning them round...


----------



## Jgrden (May 23, 2010)

You need a master's degree to belong to this forum Heh, heh, heh.


----------



## ericw95 (May 23, 2010)

No.  I just finished mine (graduation is in 2 weeks) and my head hurt the first AND second times I looked at the formula.


----------



## Pens By Scott (May 30, 2010)

Has anyone tried casting PR with the brass tubes build in?  This would also see a further reduction in the volume of PR used and likely glue (CA, Epoxy...)


----------



## phillywood (Jun 4, 2010)

You thought that was bad lisen to this. I was watching a video on bowl turning few nights back. The guy was a tall guy and he had to muscle this log on to a heavy duty lathe, and I am not talkig about Mini like we use I am talking about a 850 lbs. as he said it lathe. then, by the time he was finihsed with the bowl just for being green turned the darn thing was about maybe 1/6 of the original size. now that's WASTE.


----------

