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Author Topic: scarf joint story  (Read 2979 times)

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Offline canopy

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scarf joint story
« on: February 08, 2014, 04:12:51 am »

I am really sold on making a jig for scarf layouts. Not really to save time, but to be sure it is laid out exactly the same in every instance. I preferred to make my jig from thick paper rather than wood so that it could be made easily just by scoring the edges with a knife and I only have to worry about 2 dimensions compared to thick wood where there is extra work to make sure both sides are perfectly the same.

First saw the front end far enough to knock the end off with a chisel as already done here.

Then saw along the surface, going 2 chisel widths further and kerf and clean out that portion.

Now there is enough room to fit a saw in to get the last long saw cut in.

And finish it.

Here are 3 plates wedged and test fit to a 44' span. These timbers vary in thickness so are not flush on the outside but I will shave them to be later. The timbers are teak 6x8's.

Offline Thehardway

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Re: scarf joint story
« Reply #1 on: February 10, 2014, 03:20:16 pm »
Nice looking scarf work!  Must be interesting working with teak.

I have usually observed that particular scarf joint oriented 90 degrees to what you show in the test fit assembly, placing the driven wedges horizontal rather than vertical.  What is the final application for this joint?

I would try making the template from aluminum or metal which would be slightly more durable.
Norwood LM2000 24HP w/28' bed, Hudson Oscar 18" 32' bed, Woodmaster 718 planer,  Kubota L185D, Stihl 029, Husqvarna 550XP

Offline canopy

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Re: scarf joint story
« Reply #2 on: February 10, 2014, 08:20:01 pm »
In the last photo the plates are laid on their side (I'll explain why below) so the wedges and blades do ultimately go horizontal. And note the engineer further recommends using timber screws in the scarfs in addition to the wedges.

One thing that was really tough was the test fit. The standard procedure is to put them together and only then perform layouts. Since my timbers are out of square and scarfs laid out to chalk lines it means there is no reference surface on any side. So I first had to level a plate front to back and side to side using laser and bubble levels to the original layout lines, then attach the next plate after much work to get it the exact same level end to end, and then again for the 3rd one. Then have to go through the whole process again and again to chalk line the other sides. It really does not seem like a practical method.

If a jig is to be used more than once it could make sense to use a more durable material but unless you are really good it may not be as accurate. I first experimented with plywood and it was becoming a really big job before the light bulb went off to go for a 2D instead of 3D jig material. A paper jig can be discarded and a new one for a new job can be made in just a couple minutes. What I really like about thick paper is scoring lines with a knife are just so dead on straight and on line and on both sides.

Teak is a hardwood but not as tough as a lot of other tropical hardwoods. It is valued for its termite resistance and there are a lot of those critters around. Sometimes there are termite blooms that create massive clouds of them flying the air looking for their next home. Locals like to put a bucket of water under a light on such nights. The termites are attracted to the light and fall into the bucket. Then they are scooped out and fried up.