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Optimum wood?

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mattnelson

Optimum wood?

Post by mattnelson » 02 Jan 2012, 03:40

Hey guys,
What is the best wood to use? Balancing ease of use, strength, longetivity and cost?
Ply?
MDF?
Hardwoods?

and what is the idea thickness to take the screws etc

garycdewitt

Re: Optimum wood?

Post by garycdewitt » 02 Jan 2012, 12:35

Plywood and MDF are going to be the most structurally stable builds with wood. Each for different reasons. I found that plywood tended to chip out at the narrow corners (i.e. triangles). But these woods are easy to split when driving screws. (I did find that the self tapping screws minimized this and did not split the pine).

If I build from scratch again, it will be all MDF. No pine 2x4's. I would glue together 2 thicknesses of MDF to create a 1 1/2 inch thick board.

You would have to look at the stability charts for the different hardwoods. They all have different characteristics and responses to changes in moisture. Hardness is not, in my opinion, the primary quality you would want. The builds would not be subject to much wear and tear such as furniture and floors. Eastern White Pine appears to be one of the more stable woods. Yellow pine is right in the middle. http://www.planethardwood.com/documents ... yChart.pdf

BUT, proper construction technique can help minimize instability. Putting a finish on the woods, especially open end grain, can help minimized instability. 3 or more coats of a moisture resistant finish such as polyurethane would be needed. Perhaps 5 coats on the open end grains. You will find that the cut ends of wood will soak in the finish.

So looking at all of this, I would stick with MDF or Plywood from a cost vs. stability perspective.

As far as taking screws. If you use a soft wood such as pine or MDF, then coarse threaded screws are the best. You can sometimes find screws made for working in MDF.

If screwing through thickness of pine into other wood, it depends on the screw type and what you are screwing into. If it is another thickness of pine, and they are self tapping screws, then I don't drill pilot holes (or if using pocket hole screws). If it is through the wood and into an edge, drill pilot holes.

Splitting can be minimized by lubricating the screws with bar soap before use.

If you are putting screws in the "edge", then 3/4 inch or wider. 1/2 inch tends to split unless you take care to pre-drill and use small screws. MDF always needs to be pre-drilled. Plywood is a 50-50 risk on splitting. I had 1 of the 4 triangles split while using self tapping screws.

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daniel_reetz
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Re: Optimum wood?

Post by daniel_reetz » 02 Jan 2012, 14:45

I have also found that countersinking screw holes in wood makes a very big difference.

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jck57
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Re: Optimum wood?

Post by jck57 » 05 Jan 2012, 13:23

Every type of wood or wood product has its place, though I don't like MDF board for making stuff. Because the fibers are so short this product is weak structurally and splits easily. Plywood is better. OSB is not as pretty but just as good functionally. Screwing into the edge grain of plywood or OSB is to be avoided. Make corner blocks or cleats out of fir (most 2x lumber). I don't use much solid pine (1x lumber) because it's usually crooked, full of knots and splits more easily than fir. Be careful not to drive screws too close to the end of a softwood board or it will split. I use oak for bits that need great strength with the grain. Solid oak is hard but easily split. Drill pilot holes for screws.

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Re: Optimum wood?

Post by rob » 17 Jan 2012, 12:53

My own opinion and experience is that Baltic Birch plywood (I'll refer to it as BBP for the rest of this post) is the best. I've found that with a little humidity, MDF swells somewhat, but BBP is quite stable. The key characteristics of BBP over regular big-box store grade plywood is that BBP is (1) made of Baltic Birch, a high-quality wood from the Baltic region, (2) made of more numerous, thinner plies, (3) strong, (4) good-looking, and (5) has far fewer defects in each ply. A good informative article on BBP is here.

But beware: you will not find true BBP at a big-box home improvement store. The "baltic birch plywood" sold there consists of a top and bottom layer of true Baltic Birch, but the middle plies are ordinary crap, with all the defects and poor quality that implies.

And as always, pre-drill holes for screws regardless of what side you're screwing on.
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Re: Optimum wood?

Post by ssmdiy » 06 Feb 2012, 14:41

I'm hoping to use plywood or OSB. How thick is it supposed to be?

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Re: Optimum wood?

Post by rob » 06 Feb 2012, 16:16

3/4" (which is actually about 0.72 inches) is what we're using.

By the way, I didn't mean to say, above, that you shouldn't go with the birch plywood that you find at Home Despot or BLowes or where ever else you shop. That plywood is far superior to whatever other plywood they sell. It's just that if you want something even better, you have to go with pure BBP, which these stores don't sell.
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Re: Optimum wood?

Post by jck57 » 06 Feb 2012, 21:48

ssmdiy wrote:I'm hoping to use plywood or OSB. How thick is it supposed to be?
My suggestions on wood were for general home shop work. If I was going to pay for CNC router shop time, I would follow Rob's recommendation and use first quality plywood such as Baltic Birch. In no case would I use OSB or construction grade plywood.

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