Calculating waste

[Mikey the 2nd]

In my mind somewhere I know from my carpentry days there is a formula for calculating waste on a 45 deg mitre. Eg if you need a 12" piece of 1" moulding mitred there is an equation to work out what size piece you need to start with. I can't for the life of me remember it. Can anyone help please?
Mike

[Steve N]

It's not waste, it's what you need to complete a frame of any given size, so a frame with a width of 1" (from rebate to the outer edge, not the front face) you will need for a 10"x8" frame 10+8x2 PLUS 1"x8, you have 4 corner per frame (well if you are doing a 4 sided frame, not a 5 sided frame) and 2 miters per corner, so in the example above you will need 44" with no leeway

[prospero]

The important thing to remember is that a piece of moulding has TWO ends.

[Not your average framer]

There's a lot to understand about moulding waste that is not necessarily considered. Your waste is not just the bits that you cut off when mitring the corners of the frame, also the left over mounting from a full length that you have used while producing that frame. Plenty of left over moulding, never earns you a penny, but it still had to be paid for and that is also waste.

Saving up left over bits, so that you can match the bits up to make ready made frames, is a rather hit and miss way of earning any money as well, as lots of these bits never match up to make a usable frame and even if they do, there is no certainty of a customer buying that frame once you have made it. Old timers never spent time working out in detail how much to allow for waste down the last few pence.

Knowing your wastage, is unnecessary and largely meaningless to most self employed framers and generally allowing a fixed percentage of the overall cost is good enough for most of us. You hear the figures like 30%, or perhaps a third being banded about, which is probably about right. My price chart allows 40%, because I produce more waste than most and I reject any wood that has any sort of blemish, or defect.