Woodwork joint

[Rick Hughes]

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:

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.

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.

[Rick Hughes]

forgot to add the overlap would be twice t he depth ... at least 400mm

[JonT]

Lap joint?

[dom]

The beams are horizontal edge beams I presume?

Is there any load on the joint, or is it well supported either side of the joint?

Is this just spruce floor joists, or some fancier timber?

Long time since I've done a scarf joint, IIRC there tends to be some chisel-work hand-fitting to get a stiff, stable joint. Not so suited to machine cuttinf, although as you say, you could make a router jig.

I might favour a lap joint with a 400mm overlap (twice the joist depth) in the vertical plane. So 100mm depth overlaps 100mm, and several 180mm screws from top and bottom (or go right through with coach bolts). Quick and easy to machine cut.

Alternatively a butt joint, timber fishplate behind say 400mm section of joist, and lots of coach bolts through. Exposed coach bolt heads in a neat pattern look ok. Stainless steel coach bolts now fairly cheap.

[Bob Minchin]

These are dead easy to cut

Make a plywood template, mark out and cut with a handsaw. Once a pir of fold wedges have been fitted they are really strong. I used them for the ridge board for my workshop which is 10m long made from 3 x 3.9 lengths.

[The Medway Handyman]

Use some 100 x 47 & some 50 x 47. Cut the angle on the 100 x 47 & laminate it between 2 x 50 x 47 using exterior wood glue & screws.

No doubt harryagain will be along shortly to suggest using cams & dowels....

[Rick Hughes]

Open to any other ideas.

Couple of points here ... no fishplates, gangnaile plates or metalwork of any kind, would spil the look. Quick explanation ... 10m long Pergola being built ... 100x100 posts forming parallel run of uprights, along top of these posts will be bolted the 200x47 forming the side beams. i.e. on edge as you summized.

Will put 'gallows braces on first and last post pairs 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.

[Rick Hughes]

I had seen these ... thought they looked even harder to get cut right ... care to give any tips on how to do them in practise.

Great name "Stopped, Splayed, Keyed, and Doweled Scarf Joint "

I guesss it's a form of "Ridge scarf 2" on this page with addition of a slot for wedges.

[Rick Hughes]

You lost me on that ... there is no 100 x 47

Only 200 x 47 ... that I need to join end to end

[Unbeliever]

Isn't it about time you learnt to comprehend the written word and rather clear diagrams? LOL

OP quote "I have to join some 4.8m lengths of 200 x 47 timber" and not 100 x

47 - *AND* - "This is on show so no desire to use fish plates or any metalwork" - so why are you suggesting screws for the job?

Also, the solution you are describing isn't nearly as strong as the mentioned "Stopped, Splayed, Keyed, and Doweled Scarf Joint" (which is very similar to that used to join ridge boards in cut roofs) - far too much reliance on glue and screws, as per normal for you as you are incapable of jointing any two pieces of wood properly.

Now that's what you get when The Medway Handy Prat thinks he's a tradesman rather than an odd-jobber. You should have stuck to the salesman's job - ah, you weren't too good at the either.

As for your dig at harry, in fact, it is possible to make that joint with hidden handrail bolts - but again, it would be a weaker joint.

In your case, a little knowledge is rather dangerous -- and you want to write a book.... ROTFL

Time to put you back in the bin - you're much safer there.

[Jon Connell]

Why not just use a regular scarf joint without the ridges if you don't need it to support significant weight? Like this:

A wedged scarf like you linked to is, from what I can see, generally used in construction projects like barns.

If you really want to do a wedged scarf, then I think I would go with a table saw rather than a router. That should be plenty precise enough for the angled cut.

Jon

[Dave Liquorice]

Haven't you just said metalwork will "spil the look"?

Can't you just arrange the joins in the 200 x 47 to be supported by the posts and the 200 x 47 beam simply lapped and wedge dowelled to keep it together.

[Rick Hughes]

Yes ... but these are concreted in anchors, and will be totally hidden by a wooden collar.

Not sure what you means by wedge dowelled .. can you educate me ? Was intending to use Ridge scarf joint as all load will be in tension/compression, nothing in bending moment (deflection)

[Rick Hughes]

I have table saw and chop saw ... but could not figure out how to cut the 'stopped end scarf' as per

It would cut off the 'stops'

Or do you just cut it as far as you can and finish with hand saw.?

Might be me being dense as I have never done this type of joint before.

[Jon Connell]

Yep, that's how I'd do it. Keeps the hand work on that big ol' bit of timber to a minimum. If it was a smaller joint, I'd go for the router approach you suggested.

There are some other "black belt" variants that really would need a router:

Jon

[Dave Liquorice]

Lap joint with holes drilled through for dowels, slits in ends of dowels to take hardwood wedges to spread the dowel in the hole so it ain't going to pull through. Bit like how heads are fitted to shafts.

I don't follow that deflection ie up/down loading by the beams own weight or extra load produces compression in the top of the beam and tension in the bottom.

[The Natural Philosopher]

ITHM that he isn't using it as a 'beam'... A proper truss structure minimises bending in structural elements.

[fred]

Just use a standard straight scarf joint. The longer the better. Glue and cramp it. Add a few dowels for extra holding. Keep it simple.

[harryagain]

A scarf joint is the strongest. This is what they use to repair wooden aircraft. It can be glued or glued and screwed. The more acute the angle, the stronger the joint, but more wood is wasted.

All you have to do is lay the two bits of wood on top of one a nother and cut both together, Smooth the cut with the plane if it's a bit rough. Clamp them in the vice side by side & do them together. Make sure cuts are square.

Or cut one and use it as a template to cut the other.

Also good for joining ply. More care needed here.

[dennis]

So the joint is just a feature. So you may as well make it nice. So butt joints and carved plates either side or something similar.

The cross members can just rest on top and avoid the notch, just put a screw in. Unless you think it looks better with a notch. Why not shape the end so there isn't a very precise notch at all.