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How do you cut your birds mouths? #21543 10/26/09 01:28 AM
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WC Timberworks Offline OP
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Hi. I am looking for any shortcuts for cutting birdsmouths. I have 80 of them to do by hand this week. I cannot afford to buy the hema tools right now. Any suggestions or quick steps?

Re: How do you cut your birds mouths? [Re: WC Timberworks] #21553 10/26/09 12:07 PM
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Gabel Offline
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More info, please.

what size are the rafters?
roof pitch?
Heel height?
Is the material planed or rough sawn?

Re: How do you cut your birds mouths? [Re: Gabel] #21558 10/26/09 10:36 PM
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Don P Offline
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Codebook spans for lumber sheathing are;
24"=5/8" min thickness
48"-1.5" Fb270 E.34
60"-1.5" Fb420 E.66
72"-1.5" Fb600 E1.15

Off the top of my head #2 Eastern White Pine runs about Fb575 and E.9 So for 48" it doesn't take much but it does need some thickness.

Re: How do you cut your birds mouths? [Re: WC Timberworks] #21562 10/27/09 01:37 AM
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mo Offline
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WC,

Gabel has the right questions, but you might be dealing with this.

Most pitches are going to give you one cut (either the level or plumb) that your saw is not going to be able to make. I usually cut these on their backs or tops (whatever you want to call it).

In this picture it is a 10/12 which leaves the level cut at 50.19. Some saws wont make it especially 8/12 and lower (or 14/12 and steeper)

As you know it is pretty damn difficult to run an angled beam saw across a 4X. This set up is even more difficult but helpful. If you can cut with precision this way you don't even half to clean up with the chisel afterwards(if your rafters are exactly the same dimension in depth).



If you are looking for speed you might want to look into this. Create a angled block to attach to your beam saw base. Whatever the angle is of the block you can add to the maxed out limit of your 45 deg on your beam saw. Attach to the saw add some wax and be prepared to be dog tired from concentration afterwards .

*This is effecient if all your rafters are very close to the same depth. You can stay a little away from the corner and then a couple whacks with the chisel will clean it right up and save you from handsawing or having to flip 80 rafters (that would be necessary if you cut the rafters on their sides).

And if they are all the same dimension you might be able to gang cut them side by side. I usually stay away from this though, it can get hairy and sloppy.

80 Rafters might just be enough for this.

Last edited by mo; 10/27/09 01:42 AM.
Re: How do you cut your birds mouths? [Re: mo] #21563 10/27/09 01:57 AM
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oh yea, I forgot to add chainsaw. wink

Re: How do you cut your birds mouths? [Re: Gabel] #21564 10/27/09 02:48 AM
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the rafters are 4x6 clear planed and sanded douglas fir. very high end. I only produce the highest end products. The pitch is 30 degrees, there are two birdsmouths on each rafter. one at the top with a heel of 1/2" which sits 1.5" on a 3x7 ridge, and the bottom heel is 1" that sits on the 8x10 beam. Steve has a Mafell Bandsaw 12" model Z3L 220v for sale that I really want. Do yout think this machine will cut these cuts precisely? I know the newer models will cut a very accurate and square cut.

I did 4 birdsmouths the other day with my 10 1/4 makita circ saw, then finished the cuts with my japanese saw staying just away from my scribe lines. then i cleaned them up perfect with the chisel. to do four birdsmouths took me 4 hours...

Re: How do you cut your birds mouths? [Re: WC Timberworks] #21565 10/27/09 03:07 AM
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toivo Offline
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an electric chainsaw can be clean and accurate if the lines are cut with a knife, as in log building, opened up by cutting straight down and then in at an angle to that cut to relieve a splinter. then the fitting parts are all cut with an edge tool. use the tip to brush out hollow behind the edge. maybe a little gonzo for your standards, but fast. at a point snow is falling and it's nice to have a roof overhead.

Re: How do you cut your birds mouths? [Re: toivo] #21566 10/27/09 03:10 AM
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toivo Offline
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that said, last building this was done with a handsaw and an adze.

Re: How do you cut your birds mouths? [Re: mo] #21571 10/27/09 11:08 AM
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Don P Offline
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Whoops, sorry about my response, I obviously had a couple of threads open. It would look more intelligent in the underlayment for metal roof thread.

Re: How do you cut your birds mouths? [Re: toivo] #21572 10/27/09 11:17 AM
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TIMBEAL Offline
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I don't think a chain saw will cut it for WC Timberworks. I think this is bordering on philosophy, 1 hour/rafter perhaps a CNC machine is in order.

Is that scribe lines or score lines?

As per the other axe thread, how about an axe?

Tim

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