heavy timber oramental truss

[mel]

I've been asked if I want to attempt building 3 heavy timber trusses. 4' tall x 20' long. Top and bottom cords are 6x10 cedar and the web members are 6x6. I'm figuring on mortise and tenon joinery and hardwood pegs. These are strictly for looks and will not need to support any load other than itself. Any guidance?

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[Edwin Pawlowski]

According to my very rough estimates, a 6 x 10 x 20' piece of wood is going to weight well over 200 pounds. You have 6.25 cubic feet and even light wood can be 30 to 40 pounds a cubic foot. The truss complete could be 600 pounds or so. What is going to support this and how are you going to move it??

Is there some historical significance to the project? If this is just decorative, I'd consider making the thing from 1 x boards made into a square hollow tube configuration. Ed

[My Old Tools]

Do it all the time in timber framing. M&T is the way to go. I use a big

16" Makita skil saw to cut the shoulder and cheeks within 1/16th or so and finish with a #10 Stanley and a slick. Mortises can be done with a Makita chain mortiser, an antique boring machine (see my website), or a power drill or a brace and bit followed by a chisel. We use 2" tenons on most things. They will be heavy and appropriate wall support will be needed. Cedar wouldn't be the best for supporting loads, but it should be fine for this application. 1" pegs are pretty standard.

[mel]

What is going to support this and how are you going to move it??

This is a decorative truss going in a builder's personal house. The truss will bear on the top plate of a 2x6 wall with adequate studs underneath.... as far as moving it goes a forklift & flatbed truck for delivery.... a crane and 20 Mexicans for setting it in place ought to do it.

[My Old Tools]

yep, that ought to do it.

[mel]

question for you Ross. Do you think we ought to design a stiff-back to go across the tops of these to keep them from sagging?

[My Old Tools]

The sketch you showed should be self supporting for a 20' span. It is dry timber isn't it? Even wet, it should be ok, but it will check badly. We typically build with green timber. As long as it is joined and dried in place, it works fine except for checking.

[mel]

we are going to use either green cedar or more than likely doug fir. Richardson mill in Carrolton is going to size 8 x material to a net 6". There is a huge difference between the cost of cedar over the fir. I noticed you are in Greenville. Just curious, where do you get your timbers? BTW, I peddle lumber for Foxworth/Galbriath Fort Worth