Huge Dado (?) for 6x6 Pergola post and beam

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Hi,
I plan to build a Pergola that will be based on 6x6 posts and beams. I want the beam to have a 6" wide, 6" long and 3"deep "pocket" that will accommodate the post. I have no tools to do such cuts. I have no band saw and the jigsaw and circular saw I have cannot cut as deep. I have a table saw that will probably bog down in seconds… so, how do you suggest I do these cuts?
Thanks, Izak.
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Izak wrote:

Don't you mean 5 1/2 by 5 1/2? (Just kidding)
Since your going all the way across, what you can do is make several saw cuts (closely spaced) accross the pieces that will overlap and then break them out with a chisel.
NJBrad
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Brad Bruce wrote:

You can start the cuts with a circular saw and then finsh with a handsaw...
NJBrad
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izaks asks:

Handsaw and chisel. Charlie Self "Inanimate objects are classified scientifically into three major categories - those that don't work, those that break down and those that get lost." Russell Baker
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A panel saw (Disston) is a labor saving device in this case. :-)

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Circular saw to make multiple cuts close together, then use a chisel
I would NOT try this on a table saw if the 6x6 is going to hang off the table top by any significant degree
RAS would work as well
John
On 8 Aug 2004 07:57:11 -0700, snipped-for-privacy@walla.co.il (Izak) wrote:

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As would a hand saw...
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Izak, Every now and then, you have to get back to the basics. I think this is such a time. Lay out the joints with a try square and pencil and make the cuts with a handsaw. Knock out the waste chunk with a hammer and clean it up with a chisel. It'll be good for you.
DonkeyHody "Every man is my superior in that I can learn from him." - Thomas Carlyle
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On 8 Aug 2004 07:57:11 -0700, snipped-for-privacy@walla.co.il (Izak) wrote:

A handheld circular saw, biggest and chunkiest you can find. Saw across the grain to mark out the edges, then saw more cuts to split it into 3/8" sections. You can split these short-grain sections out with a chisel.
You'll also want a square (like the Stanley roofing square) that can be clamped onto a beam and is thick enough to give a firm and reliable guide for the saw.
Then find a book on timber framing (like one of Sobon's) and do some redesign. If you go for the simplest of designs in timber this size, you'll get problems with joints opening up with movement. Commercial pergolas are held together with steel strapping, but that's ugly.
I'd probably cut a stub tenon on the end of the post and a blind mortice in the beam to locate them. Blind mortices are a nuisance to cut, but it's more weatherproof - maybe in .il you don't need to worry. To hide the end of the post (after the inevitable shrinkage of the beam) I'd cut just a very shallow dado (maybe 3/4") across the beam, probably with angled shoulders.
If you're doing a "three dimensional" pergola, not just an arch, then look at Japanese framing and especially their multi-way joints. European and America framing is based on making vertical flat frames on the ground, then lifting them up and holding them apart with the wallplates. A pergola looks better if made with an Eastern approach, where the design is based more on horizontal layers.
You'll also want a drawknife for shaping and for final decorative chamfering. If you use any diagonal braces, it's well worth the effort to curve their outer edges, not just leave them straight. . Use treenails to pin any tenons, not metal fittings. The finished effect is well worth it.
--
Smert' spamionam

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There have been a lot of replies to this but as I understand your question, none of them will work. You threw everybody off by indicating you want to cut a dado, but your description describes a pocket. Two very different animals. For a 6x6x3 pocket, I'd drill a series of holes 3in deep and chisel out the edges to make them square. Use a one inch or bigger bit and put a tape marker on it to indicate your depth, and you'll be all set.
--

-Mike-
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On 8 Aug 2004 07:57:11 -0700, snipped-for-privacy@walla.co.il (Izak) wrote:

Three inches is too deep for that pocket.
You don't want to waste more than a third of the horizontal member.
If'n you want to do something that is both structurally sound and really cool, make a dovetailed joint between the two.
I'd make this an inch and a half deep and this would allow you to use a hand circular saw to do most of the work.
I'd make the bevel at somewheres between a four-to-one and a six-to -one.
Make your bevel cuts first and then waste the remainder with vertical cuts.
When you're done with that, treat yourself to a nice slick and clean up the roughage.
I don't like trying to make these sorta things dead flush, so I'd reduce the width of the vertical member and run a chamfer on the horizontal member's mating surfaces. It'll look slicker'n'snot.
(btw - the good news about the dovetail is that it will work in tension as well as in compression - this may not seem like much of a concern until you get that pergola loaded with foliage and have it go through a good windstorm - this may not be the case with your project - but, then again, who knows?)
Regards, Tom.
Thomas J.Watson - Cabinetmaker (ret.) tjwatson1ATcomcastDOTnet (real email) http://home.comcast.net/~tjwatson1
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wrote:

I can see using one of those funky little Japanese cogged joints on the horizontal joint surface to hold it against twisting, but what's this dovetail for ? Where's the vertical tensile force coming from ?
--
Smert' spamionam

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On Mon, 09 Aug 2004 12:23:50 +0100, Andy Dingley

Too many folks build as though compressive forces were the only ones in play. The uplift caused by wind can be significant.
I don't know where you live but around here hurricane straps are used to tie the framing together from the roof to the mudsill.
The pergola wouldn't provide much sail area in relation to its weight - at least if it remains just bare sticks, however, I would anticipate the possibility of foliage and trellis material adding a great deal more sail area - to the degree that I would want to address the uplift issue.
The dovetail that I've described would be easier and faster to cut than the mortise and tenon, would have better mechanical properties, and would add a bit of detail.
Regards, Tom.
Thomas J.Watson - Cabinetmaker (ret.) tjwatson1ATcomcastDOTnet (real email) http://home.comcast.net/~tjwatson1
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Here's a beam sitting on three posts:
+-------------------------------------------------+ | | +-------------------------------------------------+ +--+ +--+ +--+ | | | | | | | | | | | |
With everything straight and new, the beam certainly only exerts compressive forces on the ends of the posts. But, put the thing out in the rain for a few years, and maybe the beam will warp a bit. Depending on which way it warps, it'll either try to hump up the middle (putting tension on the middle post), or pick up the ends (putting tension on the end posts).
Alternatively, let a hurricane blow through and try to tear the roof off. Building codes in areas prone to hurricanes require that roofs be strapped down to prevent them from being lifted off in storms.
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I would simply cut a 2"x6" tenon 6" long on the post end and a matching 2"x6" mortise full depth in the beam. You can do the tenon with a handsaw and the mortise with a drill and a chisel.
--
Ross
www.myoldtools.com
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On Sun, 8 Aug 2004 20:11:06 -0500, "My Old Tools"

I don't hold with this, and here's why.
You've described a through mortise and tenon and that exposes the sucking endgrain of the tenon to the elements. Open joinery in this situation is a mistake (IMHO). You've also interrupted the beam in such a way as to create a potential for cracking and splitting along the lines of the mortise.
An included joint would be my preference and I'll stand by the dovetail, but would be open to a stubbed tenon that was pinned.
(and the pin could be a nice feature)
Regards, Tom.
Thomas J.Watson - Cabinetmaker (ret.) tjwatson1ATcomcastDOTnet (real email) http://home.comcast.net/~tjwatson1
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Thank you all for your excellent suggestions. I certainly have changed my original design and approach for this job.
The modified design will still have a beam mounted on top of the 2 post but the posts will be placed 20" from each end of the beam. This way, I will not do a pocket but a big dado 6" wide by 6" long and only 2" deep so not to expose the post end grain to the elements and will gain better structural design for the horizontal beam.
Further more, 2" deep cut I can do with a hand held circular saw and a guide and then chisel out the waste.
By the way, the pergola is 17 foot long and 11 foot wide so using a table saw is out of the question anyway…
Thank you all for sharing your experience and knowledge.
Izak.
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On 8 Aug 2004 07:57:11 -0700, snipped-for-privacy@walla.co.il (Izak) calmly ranted:

Sharpen up your 8tpi Disston, son. Finish up with a 2 or 2-1/2" slick. It's really good cardiovascular exercise. DAMHIKT
- Gently-used Firestone tires for sale at discount! ----------- http://diversify.com Website Application Programming
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Take the circular saw that you have, make 2 length wise plunge cuts to your 3" deep layout lines and keep them within your 6" crosscut layout lines on both sides. This will give you a clean joint line. Then make several kerf cuts across the beam within your layout. I'm betting this will leave about a 1/4' depth to get downto the first plunge cuts. Finish off the cross kerfs with a bow saw if possible then knock out the waste with a hammer and clean up the surface with a chisel so that its level from one plunge cut to the other. If this is green treat keep the circular saw tooth count down to about 24 tooth blade. A little practice and you will knock 'em out about 20 minutes a piece.
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Eric Johnson writes:

Not a whole lot of basic circular saws will make a 3" deep cut. Maybe one with a 10" blade, but otherwise, this depth requires a handsaw.
Why would a plunge cut be needed for a dado?
Charlie Self "Inanimate objects are classified scientifically into three major categories - those that don't work, those that break down and those that get lost." Russell Baker
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