Thread: Help Calculating Cubic Meters of Timber Required For Project

Originally Posted by thumbsucker

I need some help with my maths. I doubt the validity of any calculations I do.

I will need the following pieces of oak at:

0.05 meters x 0.05 meters x 0.6 meters = 0.0015 cubic meters -- yes, but see below
0.025 meters x 0.025 meters x 0.4 meters = 0.00025 cubic meters -- yes, but see below
0.05 meters x 0.3 meters x 0.3 meters = 0.0045 cubic meters -- yes, but see below

I will need:

50 pieces of the 0.05 meters x 0.05 meters x 0.6 meters = 0.0015 cubic meters totalling 0.08 cubic meters
600 pieces of the 0.025 meters x 0.025 meters x 0.4 meters = 0.00025 cubic meters totalling 0.15 cubic meters
25 pieces of the 0.05 meters x 0.3 meters x 0.3 meters = 0.0045 cubic meters totalling 0.11 cubic meters

Making for a grand total of 0.08 + 0.15 + 0.11 = 0.34 cubic meters.

Is this correct? I only need 0.34 cubic meters for this project?

I'd do the sums this way

50 pieces x 600mm long (finished length) -- requires 50 pieces each 650mm long (to allow for snipe) = 32.5 metres of 50 x 50
600 pieces x 400mm -- requires 600 pieces 450 long = 270 metres of 25 x 25
25 pieces x 300mm -- requires 300 pieces 350 long = 10.5 metres of 300 x 30 (which might be a little hard to source)

normally I'd then add 10% for wastage (checks, knots, excessive warping, wind, cupping, etc).

Now is your 50 x 50 nominal, rough sawn or finished dimension?
likewise for the 25 x 25 and 300 x 25.

If finished dimensions you would normally start with nominal 75 x 75
the 25 x 25 might start at nominal 35 x 35 and the 300 x 25 might start at 350 x 50

so
32.5 metres of 50 x 50 becomes 32.5m x .075 x .075 = 0.183 cu.m + 10% = 0.201 cu.m
270 metres of 25 x 25 becomes 270 x .035 x .035 = 0.331 + 10% = 0.364 cu.m
10.5 metres of 300 x 25 becomes 10.5 x .35 x .050 = 0.184 + 10% = .202 cu.m

Total required = 0.767 cu.m

which is more than 2 x what you calculated, but I've worked on the basis that your dimensions are finished dimensions, if they are rough sawn and approximate lengths, then I'd just add about 10% to your number

Im a bit perplexed. Are you asking for cu m because the price quoted you is $ per cu m?

With the sizes you are nominating, the supplier will more than likely have it and is sold by lineal metre
As stated in the previous post, you have to allow for wastage and also is it rough sawn or dressed, makes a big difference.

Its for a green woodworking project for school kids that making greenwood stools, but they will get there stock from slabs as they cannot split logs being kids.

I need to purchase slabs and I want to purchase enough without buying stock that will not be used.

The dimensions above are ruff sawn size not final. 50 mm ruff will be about 42 final the 25 mm ruff will be about 20 final. The 0.05 meters x 0.3 meters x 0.3 meters is for carving small bowls.

Since it for kids I would add 20% waste (0.07 cubic meters) to my 0.34 cubic meters making a total of 0.41 cubic meters.

So to be safe half cube should cover us well and truly?

Originally Posted by thumbsucker

Its for a green woodworking project for school kids that making greenwood stools, but they will get there stock from slabs as they cannot split logs being kids.

I need to purchase slabs and I want to purchase enough without buying stock that will not be used.

The dimensions above are ruff sawn size not final. 50 mm ruff will be about 42 final the 25 mm ruff will be about 20 final. The 0.05 meters x 0.3 meters x 0.3 meters is for carving small bowls.

Since it for kids I would add 20% waste (0.07 cubic meters) to my 0.34 cubic meters making a total of 0.41 cubic meters.

So to be safe half cube should cover us well and truly?

I'm not sure where you're getting your slabs from, but can you purchase 25mm thick ones?
Also, will you need to discard the sap wood at the edges of the slab?
I ask because there was around 60% "waste" in the last two slabs I purchased -- the project I was working on needed heart wood 30mm thick and much of the slab was sap wood. The slabs were priced according to the proportion of heart wood to sap wood so I didn't feel as though I over paid.

So, redoing the sums on the basis that you're cutting strips from 50mm thick slabs

50 pieces x 600mm long x 50 x 50 = 30 metres of 50 x 55 = 0.0825 cu.m -- allowing 5mm for the saw kerf.
600 pieces x 400mm x 25 x 25 = 240 metres of 25 x 25 = 120m of 50 x 25 = 60m of 50 x 55 = 0.165 cu.m
alternatively, if you can't get a true 50mm thick slab,
600 pieces of 400 x 30 x 25 = 240 metres of 30 x 25 = 0.180 cu.m
25 pieces x 300mm x 300 x 30 = 7.5 metres of 300 x 30 = 0.0675 cu.m

Total 0.33 cu.m

normally you'd add 10% for wastage, but because you're cutting up slabs, I suggest allowing 20%, yielding around 0.4 cu.m

Hi Thumbsucker

Your project sounds interesting, and sure needs a lot small sizes. If you have trouble getting this out of oak, I have lots of 40 x 40, some 50 x 50, and plenty of 75-80 x 25 in Tasmanian blackwood, all select grade but in sizes that are not really used in our big dining table projects. They were milled from the very last pieces of the logs to get every last piece of nice timber out of them. I can get the 25mm stock ripped into 25 x 25. It is all dry, so may not fit your greenwood project, but may be a lot less work with minimal wastage. We also have 300 x 25 and 300 x 40 in blackwood if it suited your bowls.

As other members suggested, getting this out of slabs can be extremely wasteful. Recovery from most logs is about 30% sawn into boards, and up to 60% sawn into slabs, as the slabs are less selective of quality timber. So when you re-process slabs into boards to achieve cleaner timber, you often end up with that extra 30% of the log volume as downgrade waste, which represents 50% of the actual slab. These are rough random figures for natural feature grade and craft slabs. As quality increases, so does recovery, but so does price. It could be a long haul ripping 600 or more small pieces out of slabs.

PM me if you think it might help you out.

Cheers

James.