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PeterSibley
02-03-2015, 12:20 AM
I have been getting out the staves for my main mast, it's about 18 foot 6 inches (5.6m )long and every stave will have a least one join in it.

I assume scarfs are the normal method of joining sections together ? About 6 to 1 ?

But another possibility seems to be the way all commercial architraves are joined .... the ones here seem to be made up of a multitude of sometimes very short sections but are quite rigid. By this I mean a finger joint.

I bought a finger joint router bit a while ago but haven't used it yet, has anyone had experience of this and how did it go?

Mine is a stacked set of cutters like this .

http://feihonghsu.com/mchenry/photos/1pc-finger-3d.jpg

StevenBauer
02-03-2015, 01:00 AM
Of course David is correct, if you are thinking of a standard finger joint. But some of us old timers might remember how Ken Hutchins got out his full length planking on his exquisitely built Tally-Ho. Instead of cutting the planks square and then using the finger joint bit he cut the boards at a 8 to 1 taper and then used the finger joint bit. He tested this method thoroughly and was sure that it was as strong or stronger than a regular scarf.
I don't have any pictures but if you don't get what I mean I could work something out in the morning.

Here's a thread from the olden days where Rob H shares some test data he produced showing that this works: http://forum.woodenboat.com/showthread.php?4662-Finger-joints-for-planking



Steven

Gib Etheridge
02-03-2015, 01:42 AM
I was surprised to see that David said it's not enough. I've always thought that finger jointed 2x4s were as strong as solid 2x4s, and, indeed, I have that same bit and have used it quite a bit and never had a joint fail using T III so long as I clamped the joints endwise while the glue set up, so I took measurements from the image.

The material is 33mm thick. The 11 glueing surfaces are 9 mm long. That's 99:33, only 3:1, so sure enough, less than ideal. Then again, each glued joint will be backed on both sides by solid wood. That's worth an experiment. If I had to place a bet before experimenting I would bet in favor of the finger joints holding if the rest of the joinery is well done.


Not recommending anything here though Peter, just saying.

MN Dave
02-03-2015, 02:03 AM
see post # 12 http://forum.woodenboat.com/showthread.php?9019-Wood-mast-and-boom The finger joint is not perfect, about 75% of the strength of a solid stave. The joints are supported by the surrounding staves, which makes a lot of difference. I suspect that the strength would be adequate, but it is a gamble that is difficult to recommend to someone else. Various threads have recommended anything from 6:1 to 20:1, with some consensus around 8:1 for scarf joints in birdsmouth masts.

More information
http://www.duckworksmagazine.com/08/howto/birdsmouth/index.htm see links at end
http://forum.woodenboat.com/showthread.php?85042-Building-Durandal-a-Marisol-Skiff

PeterSibley
02-03-2015, 02:17 AM
Of course David is correct, if you are thinking of a standard finger joint. But some of us old timers might remember how Ken Hutchins got out his full length planking on his exquisitely built Tally-Ho. Instead of cutting the planks square and then using the finger joint bit he cut the boards at a 8 to 1 taper and then used the finger joint bit. He tested this method thoroughly and was sure that it was as strong or stronger than a regular scarf.
I don't have any pictures but if you don't get what I mean I could work something out in the morning.

Here's a thread from the olden days where Rob H shares some test data he produced showing that this works: http://forum.woodenboat.com/showthread.php?4662-Finger-joints-for-planking



Steven

I do remember Ken Hutchins scarfs and the finger joints .... which is why I thought of it. It seems to me that the joins in a birdsmouth mast are many and widespread, so even if an individual joint is not as strong as an 8 to 1 scarf it is also taking very little of the load .

Thanks for that link Steven, it's the one I was looking for but couldn't find .

Here's an cut and past of one particularly useful post . The ''shallow angle join'' he mentions sounds very interesting, it's also crossed my mind that this could be a useful joint for joining strips in strip planking.

07-09-2000, 02:39 PM
#20 (http://forum.woodenboat.com/showthread.php?4662-Finger-joints-for-planking&p=567114#post567114)
Rob H (http://forum.woodenboat.com/member.php?1665-Rob-H)
http://forum.woodenboat.com/images/statusicon/user-offline.pngSenior Member



Join DateMay 2000LocationWest Newbury, Ma. USAPosts131


http://forum.woodenboat.com/images/icons/icon1.png
Low tech finger joint test.

Wednesday afternoon I took a chunk of 8/4 Eastern White Pine and ripped it into strips 3/4 x 1 1/4 and scarfed or finger jointed them using a router bit, glued them with Gougeon's epoxy, unthickened, and let them cure until this morning.
This morning I milled the sticks down to 1/2 x 7/8 and cut them into 23" lengths with the joints centered at the midpoints.. I also took another chunk of EWP and milled it to the same dimensions, to use as a control and to "calibrate" my test.
I placed two benches 21" apart to support the sticks. Each stick was placed across the gap with a canvas tote bag hanging from its middle. Then I started gently loading the bag with 5 lb pigs of lead and continued adding pigs until the stick broke. When the stick broke, I weighed the bag on a balance scale.After a first try, I left the bag loaded to 41 lbs and added lead from there.
I tested 8 sticks, 4 with joints and 4 without.

Piece # Joint Weight at failure

1 None 57 lbs
2 None 64
3 12/1 scarf 87
4 None 67
5 8/1 scarf 92
6 Finger @ 90 deg <41
7 Finger @ 15 deg 92
8 None 63

Piece #6, the 90 deg finger joint, was the only one that broke significantly on its glue surface. It broke as I was lowering the 41 lb bag into position, so its breaking point was likely somewhat lower. Less than half the strength of the other joints.
All the other jointed pieces broke across the grain "ignoring" the glue joint. This says to me that these 3 joints were all at least as strong as the wood.
The joint made with finger joint routerbit crossing the piece at 15 deg to the grain was just as strong as the 2 scarf joints.
The piece of pine I milled to use as a control sample was significantly weaker than the piece I used for scarfing and finger jointing. Both were clear, straight-grained stock, with no runout. Both came from the same lift of lumber from a reputable dealer. But one was nearly half again as strong as the other. Curious...

SO, to the point in question: Is router bit finger jointing a suitable substitute for a good glued scarf joint? Answer: no.
At least not at the standard 90degree angle.
But if it is laid out at a long shallow angle to the stock, it behaves much more like a scarf joint and has some potential as a "board stretcher".
I would definately recommend more extensive research before trying this idea around an actual boat.
I realize that this test would not pass muster in a laboratory. Too few test pieces, not enough control over the test conditions, etc.
On the other hand, it gave a rough, ballpark idea of the relative strength of the joints in question.

If anyone wishes to expand on this in a more formal manner, I'd love to read the results.
Cheers,
Rob

Gib Etheridge
02-03-2015, 02:20 AM
Still thinking about it.

I've always liked the look of a well done tapered finger joint. If I had to make one with hand tools and it came out as well as the one produced with a router bit or shaper cutter I would call it some mighty fine joinery.

If the joints were oriented so that all that showed in the multifaceted blank was a straight across glue line then the rounded mast would have interesting and maybe even beautiful features if enough material had to be removed to show two levels of fingers.

Now that's got me imagining what puzzle joints and dovetail joints would look like.

My gut tells me they would all be more than adequate in a situation like a bird's mouth mast or a laminated beam where each "scarf" would be backed on each side by solid wood.

Somebody with nothing better to do should do some testing. :p

WX
02-03-2015, 02:24 AM
I did 8:1 Peter.

Gib Etheridge
02-03-2015, 02:29 AM
I do a bit of strip planking and use a simple 10 degree scarf, which is very close to 6:1, to make full length strips with WRC. I have picked up 100 or so strips, often by one end, and never had the scarf let go, and I've twisted the heck out of some of them while bending them at the same time and never lost a one. Once they are backed/glued on each edge to solid wood they can't possibly fail. Applying the same principle to a mast with finger joints sounds better to me all the time.

No, I'm not trying to stir the pot, just thinking out loud.

PeterSibley
02-03-2015, 02:39 AM
I'm thinking too, lots of material in a very short time !

Cutting scarfs is quick and easy, gluing the things up perfectly sometimes isn't but a bit more thought and a few simple jigs would solve that too.
I guess on of the attractions of the finger joint idea is the self aligning set up, apply glue and press together and no sliding around . That would certainly be great in strip planking as it would align the strips , whether it's the right way with the mast is undecided !

Gerarddm
02-03-2015, 02:42 AM
Finger joints work in 2x4 studs because they are solely in compression. Not so with masts and spars. 8:1 scarfs are about right.

Gib Etheridge
02-03-2015, 02:45 AM
Key words Peter...."press together".....unless you use epoxy.

PeterSibley
02-03-2015, 02:58 AM
Key words Peter...."press together".....unless you use epoxy.


Press together with epoxy. BY:D

Gib Etheridge
02-03-2015, 03:14 AM
Let it soak in for a while, then reapply.

Would you have the finger joints show or turn them 90 degrees and show not as much?

PeterSibley
02-03-2015, 03:16 AM
I do it flat across so they don't show.

Gib Etheridge
02-03-2015, 03:21 AM
So you get those nice curves when you round the mast. Nice.

Christ, it's after midnight here, and I have to get up early. Bye for now.

slug
02-03-2015, 03:25 AM
What kind of jig will you use to cut fingers into the end grain of a long board ?

PeterSibley
02-03-2015, 03:32 AM
I have a few jigs in mind , it shouldn't be too difficult.

slug
02-03-2015, 03:43 AM
All the jigs I can think of are just to much trouble for a couple joints. Thats why the slash scarf is used. The finger would be nice because it wastes less precious timber. i just cant figure out a simple way to do it.

PeterSibley
02-03-2015, 03:50 AM
I'll very likely use my router table as if it were a spindle moulder and using a cross slide in the slot , cut square across the end or as has been suggested , at a 2 to 1 angle.

Likely 20 joints to cut around those horrible knots in fir !

slug
02-03-2015, 03:50 AM
Why not make up two 90 degree finger staves , glue up the two staves with staggered joints, then break test the glued pair
Ive got a feeling that the multi stave construction and staggered joints will be plenty strong

PeterSibley
02-03-2015, 03:58 AM
I'll certainly run tests , as I mentioned earlier this could be very useful for strip planking .

slug
02-03-2015, 04:11 AM
Stagger the finger joints in the same ratio as a scarf...say 12 to one.

a birdsmouth is made of many staves . Your first test implied that the mast was built of a single piece with a finger joint.

PeterSibley
02-03-2015, 04:21 AM
Stagger the finger joints in the same ratio as a scarf...say 12 to one.

a birdsmouth is made of many staves . Your first test implied that the mast was built of a single piece with a finger joint.

Ah ! Silly me, that explains a bit . In an 8 stave mast it could be OK.

slug
02-03-2015, 04:24 AM
I like the idea of fingers to conserve valuable timber. Modern teak decks are made this way.

Jay Greer
02-03-2015, 08:21 PM
Just in the back of my mind, common sense tells me that a finger joint placed in a mast, while strong, may create a hard spot in a spar that is subjected to lateral flexing as well as vertical thrust loading. In my own shop when we build a mast long enough to require the scarfing of staves, we stack all stock that will need scarfing after the first rough 12:1 surfaces have been roughed out with an adze. This only takes a short while to accomplish. The staves are stacked on 2X4s on the floor for this so that the worker can stand with a leg on either side of the pile as he dubs the rough scarf angle on them all. Then the stock is stacked and clamped on the bench in such a way as to form a rough 12:1 surface that is then buzzed off with a power plane.

Once this is done, a sharp jointer plane is used to clean and true the final surface. I still use my Grandfather's old wood bodied jointer plane for this final truing. Here, this takes a total time of an hour or less. Then the stave scarfs are glued up on the bench using a couple of box nails to keep the scarf from sliding out of register under clamp pressure. If needed, we may do a run through the surface planer but that is, most often not needed. Usually this kind of work takes about s total of five to six hours, not counting drying time, to complete. We end up with a set of full length staves that should have scarfs located at different heights. Placing the thin end of the outer scarf ramps towards the heel of the mast insures that vertical loading of the joint is aimed inward towards the core of the stick and insures better supported by the adjacent staves. This also presents the least amount of grain to the sun's angle thereby lessening the chance of radiation grain checking. Scarfs should be staggered so that no two end up along side on one and other. I always try to create the longest space between scarfs as possible.

This is knowledge that was passed on to me by my mentors many years ago when I was just learning the trade of spar and boat building. They were guys that really understood how wood works and should best be handled for boat building.
Jay

Kevin Moroney
02-04-2015, 11:20 AM
Just a question, How do you taper the staves for a mast. Do you use a jig on the table saw, router, planer? How do you make them all the same and how do you know how much to taper each stave?

Measures Once Cuts Twice
02-04-2015, 11:54 AM
Just a question, How do you taper the staves for a mast. Do you use a jig on the table saw, router, planer? How do you make them all the same and how do you know how much to taper each stave?

http://www.duckworksmagazine.com/04/s/articles/birdsmouth/


Excellently written, includes tapering - run the calculatoR for the 2 Diameters of the taper (ie 4" tapering to 3") keeping The other variables constant and mark them the length of the taper (ie the last 4 feet) Nip off the wedges and instant tapered mast

http://i334.photobucket.com/albums/m410/alfajimBBK/DarkHarbour/5A1A8287-C61D-4105-A5E4-B4EFE322A228_zpskvkfk2mb.jpg

A great place for test pieces to build confidence!

And now "Back to this thread"; do you make the scarfs before or after cutting the birdsmouth wedge out? I'm guessing before but worry about the manhandling of the single stave while working on it.
Though better to break now then later I guess.

good luck!

StevenBauer
02-04-2015, 11:57 AM
Tapering the staves for a Birdsmouth spar is the whole point. That's why it saves time and effort over building solid spars. Figuring out the taper is pretty straight forward. Just calculate the stave size for the max and min of the mast diameter.

For example if your mast is 3" in diameter the Birdsmouth calculator says the stave should be about 1.1" wide. If it tapers to 2" you use the calculator again and get .53". So you make all your staves 1.1" wide to start. If the taper is in the top 3' you just need to taper the last 3' of the staves from 1.1" to .53" This can be done by making a simple jig on the tablesaw or by hand plane, power plane or even belt sander. I've even roughed them out freehand on the bandsaw then finished them with a hand plane.
It's easy to make them all the same, just clamp them together on your bench and plane them all at once.

WoodnMetalGuy
02-04-2015, 12:28 PM
Just a question, How do you taper the staves for a mast. Do you use a jig on the table saw, router, planer? How do you make them all the same and how do you know how much to taper each stave?

Kevin -

I tapered mine by clamping all the staves together, marking the taper on the two outside ones, and planing them down to the line. There are some photos here: http://woodnmetalguy.blogspot.com/2014/08/mast-boom-and-yard-making-some.html

-- Dave

Kevin Moroney
02-04-2015, 12:48 PM
Kevin -

I tapered mine by clamping all the staves together, marking the taper on the two outside ones, and planing them down to the line. There are some photos here: http://woodnmetalguy.blogspot.com/2014/08/mast-boom-and-yard-making-some.html

-- Dave

Thanks Dave!

David G
02-04-2015, 12:59 PM
Tapering the staves for a Birdsmouth spar is the whole point. That's why it saves time and effort over building solid spars. Figuring out the taper is pretty straight forward. Just calculate the stave size for the max and min of the mast diameter.

For example if your mast is 3" in diameter the Birdsmouth calculator says the stave should be about 1.1" wide. If it tapers to 2" you use the calculator again and get .53". So you make all your staves 1.1" wide to start. If the taper is in the top 3' you just need to taper the last 3' of the staves from 1.1" to .53" This can be done by making a simple jig on the tablesaw or by hand plane, power plane or even belt sander. I've even roughed them out freehand on the bandsaw then finished them with a hand plane.
It's easy to make them all the same, just clamp them together on your bench and plane them all at once.

The better designers will give full info on the configuration of the taper - mostly via diameters at selected heights. That's so the flex will be sufficient, and correctly located, to work best with the sail specified. If not, more generic layouts are available from other sources: Skenes; Leathers; etc.

I use the spar layout to creat a single, accurate pattern out of 1/2" plywood. I then use that pattern to mark the layout on each stave. I use a bandsaw or jigsaw to cut just outside those layout lines. Final step is to put the pattern onto each stave with double-stick tape and use a router with pattern bit to trim to final shape.

That way, you put all your fussiness into one pattern, and get it right. Then, all the staves will come out the same (and, presumably, dead accurate).

BrianMCarney
02-04-2015, 09:50 PM
This is a timely thread for me, as I've just scarfed up eight staves for a birdsmouth mast. The mast is about 15'6" for a balanced lug rig on a Goat Island Skiff.
However... My stock was all 8' long. So the scarfs are all in the middle of the staves. The scarfs are 8:1 and cut across the wide faces of the staves, so in the finished construction the seams will run from the outside in or inside out.
I was sort of hoping that if I flipped adjacent staves end-for-end, I wouldn't need to worry about staggering more than that. Of course I don't want half my last to land in the drink either. Am I being foolish? Should I consider buying additional stock and adding a second scarf to half the staves so that only four of them are scarfed in the middle?
thanks!

David G
02-04-2015, 10:04 PM
Yes, you need to stagger those scarfs.

BrianMCarney
02-04-2015, 10:37 PM
I was afraid you'd say that. :confused:

PeterSibley
02-05-2015, 01:46 AM
Yes, you need to stagger those scarfs.

As all have agreed that an 8 to 1 scarf is as strong or stronger than the original timber ..... why ?

I can see an aesthetic argument for spreading scarfs but how about an engineering point of view ?

slug
02-05-2015, 02:22 AM
Dont know. In the shipyard there is a broken box section spruce mast. The scarfs didnt fail, the glue joint holding the box together failed. I didnt measure the scarfs...they are long 10 or more to one.

The mast glue joints appears to fail first at the solid blocking zone near the spreader . This solid blocking appears to have put the joint in tension rather than compression and broke the bond.

BrianMCarney
02-05-2015, 08:21 AM
As all have agreed that an 8 to 1 scarf is as strong or stronger than the original timber ..... why ?

I can see an aesthetic argument for spreading scarfs but how about an engineering point of view ?
This is a very good question Peter. I suppose it could be extra insurance against bad scarf jobs? Anyone have any thoughts? David G?

Hugh Conway
02-05-2015, 08:47 AM
If the glued scarf joint ends up stiffer (or weaker) than the surrounding wood, staggering them would reduce the stiffness differential in a single spot.

David G
02-05-2015, 10:41 AM
If the glued scarf joint ends up stiffer (or weaker) than the surrounding wood, staggering them would reduce the stiffness differential in a single spot.

This. Unless a scarf is very long, it will induce a slight hard spot. A kink in the flex profile of the stave. You can either ameliorate this effect by scattering the scarfs throughout the elevation of the spar... or you can multiply the effect by grouping them together - and thereby substantially increase the chances of a failure.

Jay Greer
02-05-2015, 01:13 PM
Dont know. In the shipyard there is a broken box section spruce mast. The scarfs didnt fail, the glue joint holding the box together failed. I didnt measure the scarfs...they are long 10 or more to one.

The mast glue joints appears to fail first at the solid blocking zone near the spreader . This solid blocking appears to have put the joint in tension rather than compression and broke the bond.
I never use blocking other than at the head of the mast. Blocking defiantly creates hard spots. Masts more often than not break at blocking spots.
Jay

David G
02-05-2015, 01:27 PM
I never use blocking other than at the head of the mast. Blocking defiantly creates hard spots. Masts more often than not break at blocking spots.
Jay

Just so. And this is why I use 'crown blocking' when blocking is required. The tapered crown points help eliminate what would otherwise be a 'stress riser'. --

https://farm4.staticflickr.com/3728/9225728465_4fb0a25c67_b.jpg

WX
02-05-2015, 04:50 PM
This is a very good question Peter. I suppose it could be extra insurance against bad scarf jobs? Anyone have any thoughts? David G?

My understanding of it was the scarf is a weak point and therefore should be staggered.

stromborg
02-05-2015, 07:02 PM
Best practice is undoubtedly to get some distance between scarfs. But you need to view the scarf in context too. Unlike say a plank it doesn't stand alone but has backing on both sides to reinforce it when used on a birdsmouth mast.

WX
02-05-2015, 07:48 PM
My understanding of it was the scarf is a weak point and therefore should be staggered.

I should point out that at least one of the staves in my mast has at least 4 scarfs in it. The mast is nine metres in length.

john welsford
02-06-2015, 02:31 AM
Peter, there are two different profiles of fingerjoint, and different sizes within each of those two. What you have there is a "non structural" fingerjoint cutter set. These are nowhere near as strong as a "structural" type. You wont find a router set for the latter, they are in practical terms only used on the big production fingerjointing machines but you can tell which is which by the blunt or squared off tips on the non structural ones and the other type has a different slope and sharp points.

I'd use, in fact I am using ( see todays post on my blog http://jwboatdesigns.blogspot.co.nz/ . Not "advertising" even though its the second time Ive mentioned it today) a 6/1 slope scarf for a pair of 8 stave birdsmouth free standing masts that I'm in the midst of making from pin knot grade Baltic spruce.
I made a couple of test pieces, and neither broke on the joint.

Just make sure that you have each scarf three or four mast diameters away from any other, and preferably keep them in the top section of the mast where the stresses are a bit lower.

John Welsford



I have been getting out the staves for my main mast, it's about 18 foot 6 inches (5.6m )long and every stave will have a least one join in it.

I assume scarfs are the normal method of joining sections together ? About 6 to 1 ?

But another possibility seems to be the way all commercial architraves are joined .... the ones here seem to be made up of a multitude of sometimes very short sections but are quite rigid. By this I mean a finger joint.

I bought a finger joint router bit a while ago but haven't used it yet, has anyone had experience of this and how did it go?

Mine is a stacked set of cutters like this .

http://feihonghsu.com/mchenry/photos/1pc-finger-3d.jpg

PeterSibley
02-12-2015, 02:38 AM
I took everyone's advice and scarfed the joins but being the kind of person who likes to mechanise processes I made a jig for my table saw . It works well and fast . A few photos will be better than a written explanation.

http://i1062.photobucket.com/albums/t487/PeteronTweed/JIM/P2120402.jpg


http://i1062.photobucket.com/albums/t487/PeteronTweed/JIM/P2120403.jpg


http://i1062.photobucket.com/albums/t487/PeteronTweed/JIM/P2120404.jpg

This is the way they turn out, 10 to 1 and nicely smooth .

Thanks everyone for the discussion and advice .

WX
02-12-2015, 04:25 AM
Have looked at my birdsmouth howto thread yet?:-)

PeterSibley
02-12-2015, 04:31 AM
OK,OK, now !

PeterSibley
02-12-2015, 04:38 AM
I have and very good it is too ! Y>

WX
02-12-2015, 04:40 AM
Ta.:-D

Redeye
05-16-2016, 02:59 PM
I saw this nice little doohicky and thought to add it here to Peter's thread. it's not scarfing but...

Although the standard method of using your table saw set to 45 give quick and adequate results for birdsmouth spars, would this be an improvement? Or would it not?

My thoughts are that one might lose some of the stability during glue up that the simple 45 gives, and perhaps result in a lower glue surface area. But this option would result in an already smoothly 8 sided spar that might allow better clamping and a cleaner glueup...

Thoughts?

https://lh3.googleusercontent.com/-D2X1PMSX4XU/VzokyDWIniI/AAAAAAAABt4/_5BDtRldSiYShcq31L53gpD_-1B0RfJQACCo/s640/Screen%2Bshot%2B2016-05-16%2Bat%2B7.25.05%2BPM.png

matching pair for ONLY 404.00 CHF + tax ... ouch!

Redeye
05-16-2016, 02:59 PM
Actually, the more I think about it, the less I like it...

Especially as you plane down to round, you lose more and more glue surface...