Posts + Gallows brackets

Im in progress with an external structural timber project. Part of this is a number of 150 x 150mm (6 square) treated softwood, which support roof beams. The posts will have 45 degree struts coming off them aka Gallows brackets. Again out of same size stock. The leading edge of the 45 degree joint is to be cut into the vertical posts, effectively giving it a stop to rest against (and transfer load I assume) point, the design calls for this stop to be let in 20mm (~3/4)
Sketch of joint is on: http://tinyurl.com/6nr2jp
Is there any technique for doing this type of joint (dont even know what they are called), some posts will have one gallows bracket others will have a pair .. in both cases there are galvanised steel plates through bolted providing structural strength. Sketch of double one is at : http://tinyurl.com/574dhz
I do not have the option to move posts form their now vertical permanent position, so I am looking for technique for cutting in-situ, maybe its just a case of getting in there with a chisel, but thought I would ask.
Intent is to glue the joint as well with quality polyuretane glue ... but mainly to prevent water ingress, steel plates will provide the strength.
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Timberframers call theis a "brace".
http://www.tfguild.org/joinery/part4.pdf
Look at the fourth page of this document (upper left). It illustrates brace joinery which meets your need to install into a preexisting T-shape. The bottom mortise for the brace is extra tall. The brace it inserted into the lower mortise, and lifted straight up so that the upper tennon inserts into the cross-member mortise. A block is then inserted below the lower tennon to fill the oversized mortise.
The document has a few other approaches to brace joinery that might also meet your needs.
If you need specific pointers on how to to the layout for these, just ask I've done a "barn-load" of them.
Cheers,
Steve
Im in progress with an external structural timber project. Part of this is a number of 150 x 150mm (6 square) treated softwood, which support roof beams. The posts will have 45 degree struts coming off them aka Gallows brackets. Again out of same size stock. The leading edge of the 45 degree joint is to be cut into the vertical posts, effectively giving it a stop to rest against (and transfer load I assume) point, the design calls for this stop to be let in 20mm (~3/4)
Sketch of joint is on: http://tinyurl.com/6nr2jp
Is there any technique for doing this type of joint (dont even know what they are called), some posts will have one gallows bracket others will have a pair .. in both cases there are galvanised steel plates through bolted providing structural strength. Sketch of double one is at : http://tinyurl.com/574dhz
I do not have the option to move posts form their now vertical permanent position, so I am looking for technique for cutting in-situ, maybe its just a case of getting in there with a chisel, but thought I would ask.
Intent is to glue the joint as well with quality polyuretane glue ... but mainly to prevent water ingress, steel plates will provide the strength.
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Good document .. but I those 'housed' or 'tennoned' joints are too complex for this job. The strength in this job is being provided by the steel plates ... just need a way of 'stopping' the leading edge of the 45 degree brace, maybe I just have to cut the end timber of the brace to 50 degree rather than 45, square off the point and try and scribe in this to the post.
Just wondred if there was a technique to doing this.
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Just mark the joint out carefully on the three sides of the post, score all of the lines with a straightedge and box knife, then use a skillsaw to cut the square shoulder. A few minutes with a sharp chisel and a mallet will get the rest of the waste down to the lines, and you're done. It's not rocket surgery.
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Yup.
Make the housing a consistent depth rather than tapered, and just cut the top edge at a 45-degree angle. This way it's easy to cut out the bulk of the material with a series of through crosscuts with a circular saw. Cleanup with a chisle becomes much easier
The top edge does not have to be tight as braces are designed to work just under compression. The side and bottom faces of the housing bear all the force. Typically a gap will develop there anyway with the inevitable lumber-yard wood shrinkage.
-Steve
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To check what you mean here ... the post is meeting beam at a 45 degree angle, if I read you right, I should cut housing a constant depth, then cut angle on the end of brace to match ? keeping brace location overall angle at 45 degree.
I
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If I follow you, as per this sketch: http://tinyurl.com/5764b5
Is it worth putting any dowels or biscuits in as well, the steel plates will be providing the structural strength, just wondedred if dowels or pins would help keep joint tighter together. I will be gluing up with Polyurethane (Gorilla Glue)
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If I follow you, as per this sketch: http://tinyurl.com/5764b5
Yup... that is what I meant. It's just easier to cut the joint with a cirrcular saw that way.
Is it worth putting any dowels or biscuits in as well, the steel plates will be providing the structural strength, just wondedred if dowels or pins would help keep joint tighter together. I will be gluing up with Polyurethane (Gorilla Glue)
If you are going to use a steel plate and bolts to keep the brace in the housing, you don't need to do anything more. The housing itself should handle all of the primary forces of the joint.
To clarify: braces only work under compression; that's why are generally implemented in pairs. Each brace resits wracking forces in the opposite direction. The compressive strength of white pine (really soft stuff) is around 500psi (side grain) and nearly 10 times that for end grain.
http://www.matweb.com/search/DataSheet.aspx?MatGUID ec7114d2524b63826044c3cc6c344c&ckck=1
I think your 6x6 brace will do just fine. :-)
Don't even both with biscuits glue or pins.
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