end to end Scarf Joints

[RickH]

I have to join some 4.8m lengths of 200 x 47 timber ... end to end
This is on show so no desire to use fish plates or any metalwork ....

The solution seems to be to use a Scarf joint i.e:
http://tinyurl.com/ptks6ln

I have only created sliding scarf joints, not these ones with stops.
Is there a particular technique to doing these ...

Opt A ... I thought of simply marking out and hand-sawing as best I can ... then using the one 'cut' to be the template for the next end.
The issue is trying to get a very neat joint in 8x3 timber with a jack saw may be stretching things ......

Opt B .... rough cut to within 1/4" or so, and make a template out of plywood and run a router with collar and 2" worktop cutter around template.


Would cut such that angled 'glue area' is twice the depth, i.e., at least 400mm long.
Once I have them cut will put in plenty of PVA D4 glue clamp, and also drill some holes from underside through the joint and glue in some 10mm dowels, they won't go right through so not open to rain form above.

Open to any other ideas, or practical tips.

 

[freddiemercurystwin]

This a structural joist?

 

[RickH]

It's an external structure

Quick explanation ... 10m long Pergola being built ... 100x100 posts as uprights, along top of these posts will be bolted the 200x47 forming the side beams.
Will put 'gallows braces on first and last post for rigidity.

Across the top of the posts spanning between the 2 parallel runs of posts will be 100x47 cross beams, notched to depth of 30mm where they will be glued over the 200x47 beams.

There is nothing on top ... no dead load other that timbers own weight.
http://tinyurl.com/odmhukq

 

[big-all]

if you have no central support the 8x2" on its own would break at the join assuning 30 ft/9m
what is the actual unsupported span of the 8x2"??

 

[RickH]

There are upright posts every 2m to which beam will be fixed.

 

[big-all]

so if i understand this right the posts are on the 4x2" which are supporting the 8x2 on the end as a cantilever effect
the 8x2" are supported every 2m along the given length
so in other words the maximum gap is 2m as a cantilever you are only ever keeping the inbuilt stresses in check so any joining method you choose will be fine
finger half lap simple scarf

 

[RickH]

The posts are 2 parallel runs bolted to ground anchors, each post 2m apart, and 2.18m between the runs.
At the top of each of the post runs running longitudinally and parallel with the post run is a 200 x 47 beam, bolted to each post.

Hence supported every 2m.

between the parallel runs are 100x47 cross beams that are notched to slot over the 200x 47 beams ... glued & clamped.

 

[pinenot]

Here's some alternative scarf joints too the simple one you've provided. Notice the folding wedges that provide a drawing of the joints linearly. assuming the supports are well positioned in relationship to the joints, I believe they provide good support too the structure...pinenot

 

[RickH]

nothing attached ?

 

[pinenot]

Oops -

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• pinenot
• 4 Sep 2013
• 1

...pinenot

 

[big-all]

Oops -

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• pinenot
• 4 Sep 2013
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...pinenot

216 is the easiest as you can clamp in place and run a saw through both ends to give you identical touching surfaces

 

[Dave54]

Oops -

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• pinenot
• 4 Sep 2013
• 1

...pinenot

216 is the easiest as you can clamp in place and run a saw through both ends to give you identical touching surfaces

Should be reasonably easy with a table saw and a bit of careful hand work. To the OP the secret of getting stuff like this right is to have timber which is square with parallel faces, and the same dimensions. Mark out with a knife, a square and a sliding bevel, and then as out old woodwork teacher used to say "Cut on the waste side of the line" I don't really know much about structural joints in timber frames, but I thought that traditionally these joints were used either directly on top of a post, or on a beam where it actually runs through a mortice in a post. They're intended to give a strong joint in tension I assumed.

 

[big-all]

you can scrub my comments about running a saw through it its a"V" shape

 

[RickH]

Oops -

Untitled

• pinenot
• 4 Sep 2013
• 1

...pinenot

216 is the easiest as you can clamp in place and run a saw through both ends to give you identical touching surfaces

Tenoned scarf looks interesting ... but a lot of work.

maybe the dowelled scarf joing (1st in pic) is way to go ..

Anybody cut one of these, just wondered if there is any tip to get a tight fitting joint.

 

[pinenot]

As I already noted, look at the folding wedges within the designs which effectively lock the joints, making the board almost one continuous length.
Oh! and it's only fair to give recognition to the book these scarf joint diagrams come from - woodwork joints (THE WOODWORKER SERIES) Evans London, date unknown (but probably c 1930's) available at http://www.gutenberg.org/files/21531/21531-h/21531-h.htm ...pinenot