More on scarfing

[cs]

Some of you may have noticed that some clear Doug Fir tent poles have come into my poccesion. Quite a few of these are octogonal shaped and measure 1-3/4" across the octagon. This will work out great for a gaff spar for my weekender which has a diamter of 1-1/2".

The problem is that the poles are about 6' long including the metal tip on the end and the gaff is 6'-2" long. So I will need to scarf a couple of them together to get the proper length.

Now I'm not afraid of scarfing, I've had to do it on every spar I've built. But with the others I've had to laminate the spar up from 3/4" stock and thus each scarf had a soldi piece of lumber on one side or the other. With these tent poles they are a solid piece so the scarf will not be back up in a lamination with a solid piece of lumber.

I guess I'm worrying over nothing, but why don't you re-assure me.

Chad

ps I guess Gaff Spar is the correct term. It is the spar at the top of a gaff rig.

[JimConlin]

If all you need is 2" of length, I'd try to get clever with the design for the gaff jaws.

If you still feel he need to scarph something, then go for it. Use a 12:1 taper. Locate the scarph at the top end. The gaff will be tapered thinner there, so you can accommodate any misalignment that might creep into the short extension.

If you're still uneasy about the alignment of the joint, consider a clothespin scarph. Personally, i think it's more trouble than it's worth in this case.

[cs]

Jim by the time you figure in removing the metal end I've lost another 3 or 4 inches and thus it ends up being about 6" to short.

Chad

[Bill Perkins]

Chad I see it Jim's way . You're going to have to join the jaws to the gaff anyway ,so just lengthen the body of the jaws to lengthen the spar .

[htom]

I'd build one end of a clothspin scarf into the jaws, too, but I can see an argument that it would be stronger to put it out at the end of the gaff.

[cs]

Give me details of a clothespin scarf since I'm at work and can't look it up in my books, which are at home.

Chad

[NormMessinger]

It would be a "V" knotch in one sitck and a wedge to fit it in another. Sort of a regular scarf bent back on itself. Know what mean, know what I mean. I wonder it it would be any stronger than a regular streight scarf.

[Ian McColgin]

Cloths pin is like ===>>====.

It'll take up only about a foot and a half of gaff even at 12:1 since the facing surfaces are 12:1 but the whole scarf nets at 6:1.

Before you glue, cut just a bit off the male V so it's squared and will thus leave a little hole in the finished spar. Once the glue's dry, use that as a ilot hole drill it out an put in a little dowel. Really thin - 1'8" could do. That will keep the female V from spliting. Really the gule ought to do it, but we all do it down here and it works.

If your gule work is good, it won't matter where you put the scarf but, for what it's worth, the area near the jaws only takes compression strain while further out there can be big bendis strains.

The only gaffs I've seen broken were broken in the upper half somewhere, depending on how the peak hallyard bridle was arranged.

G'luck

[NormMessinger]

"It'll take up only about a foot and a half of gaff even at 12:1 since the facing surfaces are 12:1 but the whole scarf nets at 6:1."

Ah, yes. That is an advantage, for sure. Anybody have any thoughts on the relative strength of the two? I have no idea, only a hunch.

[Russell Sova]

Just make sure she does a pearling stitch every 10th row for a nice pattern.

[Ian McColgin]

I've not seen data one way or the other.

I think that in a bending flexing application, the cloths pin could be a little less desirable.

In general, the best scarf is the easiest one to make accuratly.

[L.W. Baxter]

I think a scarf joint on a stick of six feet is kind of an odd thing to bother with. Most trees are over six feet tall, so unless you're using bonzai tree lumber, seems like you could find something of proper length and use that...unless you never want to finish your boat, in which case, you could build the whole thing out of tent poles!!!

[warthog5]

Quote;

so unless you're using bonzai tree lumber.

HeHe Now that's funny. HeHe :D

[JimConlin]

I've never done one one, and I can't think of a precise way to machine the female side of a clothespin scarph. Guess that's why God made epoxy fillers.

[L.W. Baxter]

God didn't make epoxy fillers. That would be satan...

[cs]

The clothes pin scarf sounds like a good idea. I was also thinking of doing a different kind of scarf. Not sure what its called. What I'm thinking is cut the scarf 12:1 and before gluing up dowel it. Seems like I've seen this somewhere, just can't remember where.

L.W. sure I could go out and buy lumber that is longer than 6'. I would probably have to laminate it up to get the proper thickness. Than I would have to rip it down to get the octagonal shape and than I would have to start shaping with a hand plane.

My way all I got to do is add a scarf and start planing, and besides I got this stuff for free. :D

Chad

[NormMessinger]

Dowels in a joint do little except to help one keep the joint aligned until the glue dries. Same with biskets unless you are Norm-the-machinest and need to sell power tools.

[cs]

Originally posted by NormMessinger:
Dowels in a joint do little except to help one keep the joint aligned until the glue dries. That was my thought process behind this (see great minds do think alike smile.gif ) . Ya, see other times I've epoxied scarf joints they tend to want to slide till the epoxy sits.

Chad

[Donn]

I always thought that the benefit of dowels or biscuits in joinery was to increase the area to which glue is applied. :confused:

[Dave Fleming]

Some time back there was a good write up of the difference in dowels and buscuits in FWW, particularly a solid wood door.
One with dowel reinforcement and the other with biscuits. Dowel proved superior in strength.

I have never used biscuits as I am all set up for doweling in most sizes and applications

If glue area is critical then a finger joint would add significant area to the glue surface.

Splice length ie: 1:8 or 1:12 does just that increase the glue area. I too use alignment dowels for many applications. Dry fit joint, bore for dowel/s, apply glue, join, insert dowel and clamp.

[Mike DeHart]

Another take, but from a rank novice...

Scarph the individual tent poles to make up poles around 12 ft long. Use the long poles to glue up the gaff, staggering the individual scarphs so they don't all fall together.

[cs]

Mike the tent poles are thick enough so I don't have to build up with laminations. I just need to scarf for length.

Chad

[Ian McColgin]

If you have a table saw, you can make a jig to lay against the fence that will give the correct angle for either a regular scarf or a clothspin scarf. In this size, it's not so hard.

On masts where I've had to put in a clothspin scarf it was a pain as the unit was a bit large to move about and too great a diameter for any but a big band saw anyway. In the event, I found it easier to use my japanese upll saw to cut the female V, dress it as well as I could with a plane and file, and then make the male side to match, since the male end is so much easier to fuss with. Once it was close, I'd just tap it in place with a bit of carbon paper so that I could mark the high spots on the male part.

Even with a clothspin scarf allignment is a major issue - if you want the mast straight. I personally brace scarfs from all directions and at the ends and thus do not have a slippage problem. Thus never happened to use dowls but I've seen it done and think it nifty.

I can see how biscuits are helpful especially in mass assembly and for people who need more power tools but they don't add strength and I've never done enough repetative stuff to justify bothering.

Epoxy is so wonderful because it made all those fussy scarfs - hooked and double hooked and zigs and zags - mostly unneeded and opened things up for folk like myself who might get two plane surfaces to match but are definatly challenged with more than that.

I am not at all convinced that liniar scarfing should be done with thickened epoxy. If you're laminating a frame or something, there's an arguement that just working with the wood as sawn is good as there's a variginated surface for the epoxy to grab. Always struck me as a strange irony that the Googe Bros advocated this at a time they still used the term 'saturation' in their brand name.

But gluing stuff end to end means gluing across end grain, no matter how beveled. Here even a planed surface is lovely for the glue as it can take up in the grain a good ways. I like my scarfs for extending planking or spar stock or whatever to be a perfect as I can make them with the thinnest glue line I can handle. Maybe after wetting out the grain a little high strenght thickening stuff in the mix for glue up, but nothing like peanut butter consistancy. More like just tick enough that it doesn't drip out before setting up.

Even the Googes seem to encourage the idea that the thinner the glue line, the more the joint can handle flexing stresses.

[Bill Perkins]

Chad one way to get a perfect female scarf would be to rip one piece in half ,plane the perfect siimple scarfs , and reassemble .It sounds like there's enough material for you to loose the saw kerf , useing a planer blade idealy .

Makeing the gaff jaws up of two halfs would be convienient , and the female scarfs could be on the other end of the same pieces .

[ 09-23-2003, 12:06 PM: Message edited by: Bill Perkins ]

[cs]

Got 2 poles scarfed together last night. I used a 12:1 scarf and doweled it. Tonight I will get a chance to look at and see about starting to shape it.

Chad