I found the section of text I submitted into an old GW article (actually written in 2002 and published Jan 07).....here it is slightly modified
It can be daunting faced with 12 foot long, variable width boards to understand how many you need - I translate any cutting list into a timber length most efficient for the project (in this case I used 900mm with a few at 1200mm), work out the total width needed to get all the components and then divide this into 125mm (5") wide planks - it’s lot easier in a timber yard to know you need to get 29 such planks of oak as these can be visualised. Also, a 900 x 125 x 25mm plank (i.e approx 3’ x 5” x 1”) is close to 0.1 cu ft - 29 planks = 2.9 cu ft of Oak. as a check, the cutting list finished dimensions gives 1.7 cu Ft of oak - allowing 40% wastage on thickness (25 mm to 18 mm finished), 20% width wastage due to circular saw and planing and 10% extra because you will make mistakes, have waney edges &knots to avoid - gives a massive 70% uplift - ending up as 2.9 cu ft.
As you can see, this gave a 70% uplift but that was for rough sawn timber, if you are using planed or square edged timber and your individual component lengths are short then the wastage could be less.
The other reason I worked on 125mm wide planks was for ease of planing and thicknessing - wider boards often cup and need to be ripped to this type of width anyway.
Also try and find out the standard lengths the timberyard keep for the chosen timber - applying the above principle can highlight how a slight change to dimensions makes a difference - for instance if the timberyard stocks 2.4m boards and not 3m or 4.8m a design that has components 1200mm long will typically not get 2 out of a 2.4m length, but you would get 2 x 1180mm - so a potentially minor design change could save money.
Dave
Dave
