The Great Plywood Scarf Question
Jane Sheridan & John Rankin
pile of okume ply, a roll of soft wire and 10 gall West epoxy in my garage.
This question may have been beaten to death before--but I have been
researching plywood scarfing techniques and it all seems frightfully
difficult, unless one is prepared to buy a planer and an attachment --which
probably won't get much more use after this. I did try an experimental
scarf using a belt sander --not very successful and since I have about 20
feet of scarfing to do not very appealing either.
So I found a site on the net which talks about a fiberglass scarf-- perhaps
that would do but it seems a bit crude. Would it be strong enough in a
panel 5 feet wide?
What about shiplap? Might be able to cut it with a saw. How wide would it
need to be--the scarf is supposed to be 4" on 1/2 inch ply.
So the question is--is there an easy way for a complete amateur who only
owns hand held tools and a router (which hasn't arrived yet) to cut a good
scarf or shiplap? John Rankin
Chris Crandall
: So the question is--is there an easy way for a complete amateur who only
: owns hand held tools and a router (which hasn't arrived yet) to cut a good
: scarf or shiplap?
With your ply, there are two techniques I can recommend.
1) The butt joint. Two varieties
1a. Fiberglass butt joint. Place two pieces of plywood next to
each other, sand down the adjoining area enough to place a strip
of fiberglass tape in. Do this on both sides (may have to be done
in sequence). then, coat edges of plywood with epoxy, lay in
fiberglass tape, and coat and cover with epoxy. When this sets
up, turn over (carefully!) and repeat. This is a pretty strong
joint.
1b. Classic butt joint. Take a piece of plywood the same size as
you are joining. Butt the two together, and cut a piece of
plywood in a strip, 6 to 8 times as wide as your plywood is thick.
Coat the two sheets of plywood and the bott block (strip) with
epoxy, and screw the butt block into place (from the other side of
the plywood, through the hull, into the butt block).
It is important to put your butt block on the *inside* of your
hull. :-)
Once this is completed, you may wish to add a fiberglass tape
joint on the outside of the hull.
I have used this joint . . . it is very strong.
2) Scarfing.
There are lots of ways to do this. If your wodd is no more than
1/4", then several places sell scarfing attachments to circular saws.
Apparently they work (I havent' used one).
Classic scarfs are not hard to do with a well-sharpened plane.
Line off where they belong (measure out 4 inches on 1/2" plywood), and
plane down. The glue lines (maroon-colored resorcinol) will act as
guides.
Since you're buying a router, one can also create (and maybe
purchase) jigs for scarfing that use a router. Basically, these are a
couple of inclined planes that serve as guides.
Me? If I didn't need visual perfection, I'd go for a butt block approach.
Time-tested, easy, and guarantees good line up between plywood pieces.
For perfection, I'd get a good, reliable and sharp hand plane, and go at
it.
In between? Anything else.
Glen C Davis
I agree that the plane is the simple approach for most people. I have used
a small plane for years to scarf Okume ply when building Kayaks and boats
up to six meters. The most common ration is around 8:1. If you are
scarfing 3mm ply then you multiply that by 8 and get a 24mm scarf section.
Stack one panel on top of the other and offset the ends by the length of
your scarf section (say 24mm). Clamp them down to a work bench and plane
from the line 24mm in from the end of the top sheet to the edge of the
bottom sheet. The overall length of the section you are planing will be
48mm for the two sheets.
Once you have a good eye for this technique, and this takes some practice,
you will be able to knock them out pretty quickly. Watch that the ply
bands develop the same width as you plane. Nice straight lines and even
bands indicate you are doing it right.
When the slope is straight and the bands even, unclamp and flip them over
to check the lineup.
Good Luck and enjoy the building. Great therapy.
Regards
GD
Frank W Gundaker
<www.common-sense-designs.com/boats/step_scarf.htm>
It loods easier than an angle on a regular scarf joint. I personally
like the KISS theory. (ie. butt joint)
Good luck
Frank
PS- What design are you getting ready to build?
Glen C Davis
their techniques.
Sorry Frank but the butt joint does not look professional. You also are
left with that butt block on the interior to remind you forever more that
you did not take the time to do it right.
GD
Steve Miles
isn't very encouraging.
Insisting on perfection or "professional" results is fine for those who
desire it and for those who are building a high class, show finish boat,
but otherwise it borders on snobbishness.
BTW, professional only deals with making a living from what you do, it does
not necessarily equate with craftsmanship. The average production boat can
be pretty rough, and I have seen caravel planked wooden boats, built by
professionals (in the business for years) with sizable gaps between inside
edges of planks. In fact with exceptions for some talented and lucky
professional builders, I suspect many amateur built boats have a higher
level of craftsmanship, skills may be lower, but time is free.
Some boats are built to be perfect by those with the time, skill and money
to do so and some are built just to get used and enjoyed. (I have built
boats with both butt blocks and scarf joints, I prefer scarf joints but
will use whichever makes sense or suits my fancy at the time.)
If we all insist on perfection in our own efforts and those of others, we
will discourage too many potential builders. I think it is better to
accomplish something with average results (flaws and all) than to never
start because the bar has been placed too high by others.
For a simple boat, or a boat that will be painted, a well executed, neat
butt block is perfectly acceptable. With any luck the butt block can be
placed where it isn't obvious.
Butt blocks have been used in traditional caravel planked boats a very long
time; true they are smaller and perhaps less visually offensive, but still
butt blocks and still visible.
Plywood boats were being built for decades before epoxy glues came along
and allowed the average homebuilder to get a reliable scarf joint. Until
this point, butt blocks were pretty standard if you didn't/couldn't pay for
factory scarfed sheets.
Just my $.02
Steve Miles
Glen C Davis <gcd...@bigpond.com> wrote in article
<01be1f28$34539b80$296d868b@gcdavis>...
Dave Carnell
by laying up the joint on fiberglass wet with epoxy. Details at:
<http://home.att.net/~DaveCarnell>
Dave Carnell
Chris Crandall wrote:
> Jane Sheridan & John Rankin (fin...@health.nb.ca) wrote:
> : So the question is--is there an easy way for a complete amateur who only
> : owns hand held tools and a router (which hasn't arrived yet) to cut a good
> : scarf or shiplap?
>
Kmmu2
>From: "Jane Sheridan & John Rankin" <fin...@health.nb.ca>
Asking about scarf joints:
I've another perspective. I used a router to scarf 1/4" plywood for a stitch &
glue dinghy. It's really easy. I did a few destruction tests with sample
pieces (driving over them with a car and standing on small strips of scarf)
until I was convinced that the plywood past the scarf was weaker than the
joint. It always broke at the edge of the fiberglass taping.
Set your router to slightly more than half panel thickness to allow for glue in
the joint. I say about because plywood really varies in thickness, even across
a single sheet. Then cut a rabbet (woodworker types correct me if I'm off
here) 4" wide on each plywood edge. Then glue the edges with slightly
thickened epoxy and tape over the seams with 1 layer of 4" wide tape. If this
is for a larger vessel than a dinghy, I'd use 2 or 3 layers of tape.
What I'm describing is a simple lap joint - see art below:
-------------------------------------------------------
|
-----------------
|
---------------------------------------------------------
< - 3-4" - >
It's really quick to do with a router and very tidy. Make several test cuts on
some scrap to get depth of cut just right, allowing for some epoxy thickness.
It helps to screw down a board into the joint (over a piece of plastic) while
things are curing to ensure that the plywood mates nicely.
Good luck, Evan Gatehouse
Michael Neverdosky
The but joint has a long and respected history, but it needs to be used
correctly.
Quick check;
Does the part have to be bent or curved?
Yes - use a scarf joint
No - use either a scarf or butt joint
I prefer scarf joints and after doing a few, I find that I can do a scarf
about as fast as a butt joint and it uses less material.
I do use the occasional butt join in flat locations and they work fine,
but I still like the scarf better for most work.
michael
Gabriel L Romeu
> a small plane for years to scarf Okume ply when building Kayaks
Which kayaks have you built Glen? Any on you were particularly happy
with? I have been looking at the Pygmy, CLC and laughing loon and
thinking long and hard...
Is there any others to be looking at?
--
gabriel l romeu
http://members.aol.com/romeug studio furniture
http://members.aol.com/romeugp paintings, photos, prints, etc.
http://members.xoom.com/gabrielR a daily photo journal
Al Gunther
> I don't mean to be rude, but ......the "its got to be perfect" message
> isn't very encouraging.
>
> Insisting on perfection or "professional" results is fine for those who
> desire it and for those who are building a high class, show finish boat,
> but otherwise it borders on snobbishness.
Pygmy Boats Inc. in Port Townsend, WA has been marketing kayak kits since
1986. These kayaks are considered by serious kayakers to be top of the
line in performance function and beauty. Their excusive use of butt blocks
is explained as being superior to scarf joints for kit boats because the
pieces are all precut and alignment of the butts is accurate. Their sucess
speaks for itself.
BTW, I don't own a Pygmy kayak and once scorned butt block joints myself,
but the reverence by people who have really used these kayaks has
convinced me that butts blocks do have a definite place even in top of the
line products.
--
Al Gunther, Kingston, WA <---- 47° 52.7'N, 122° 30.9'W
Joseph Palazzolo
angle iron to the far edge of the ply with screws. Attach a 1 3/4 inch length
of angle iron 12 inches above and parallel to the 3/4 inch angle. You now have
a 12-to-1 slope between the tops of the angle iron. Make a long (24 inch) sled
for the router to set in. With a planer bit you can now rout 12 to 1 scarf
joints all day long.
Jane Sheridan & John Rankin wrote:
> Hi ----I'm new to this group and a complete neophyte boatbuilder with a
> pile of okume ply, a roll of soft wire and 10 gall West epoxy in my garage.
> This question may have been beaten to death before--but I have been
> researching plywood scarfing techniques and it all seems frightfully
> difficult, unless one is prepared to buy a planer and an attachment --which
> probably won't get much more use after this. I did try an experimental
> scarf using a belt sander --not very successful and since I have about 20
> feet of scarfing to do not very appealing either.
> So I found a site on the net which talks about a fiberglass scarf-- perhaps
> that would do but it seems a bit crude. Would it be strong enough in a
> panel 5 feet wide?
> What about shiplap? Might be able to cut it with a saw. How wide would it
> need to be--the scarf is supposed to be 4" on 1/2 inch ply.
> So the question is--is there an easy way for a complete amateur who only
> owns hand held tools and a router (which hasn't arrived yet) to cut a good
> scarf or shiplap? John Rankin
Rick
RN
Joseph Palazzolo wrote in message <36682ADF...@compuserve.com>...
Peter Ring
I've tried scarfing by electric planer and circ. saw with attatchment.
It's faster to use the saw and it's easyer to get started with the planner.
I think a router setup made by you in scrap wood sounds like the best
solution, as 20' of scarfing isn't much. I haven't tried it, but it must
make a very precise scarf. Planer scarf, electric or not is slightly
difficoult, if you want a perfect scarf, by it works.
I have made my own attachment using a West/Gougeon Bros. attachment as
inspiration. Theirs can tak up to 1/4" ply, my enlarged version can take
3/8" ply. I can not recommend this method in thicker panels, unless You are
willing to plane the rest away. My saw is a 2kW Makita and i wouldn't try
handling anything heavyer in that use.
Ps. I've made more than 300m of scarfs in a summer that way including
building the the entire hull. So if you know any with a saw and a
attachment, he'll probably spend the one hour needed to scarf Your 20'. A 8'
scarf should not take mor than 10-15 min. incl setting up.
Best of luck
Kind regards
Peter Ring
Alaska Bill
>
> Hi ----I'm new to this group and a complete neophyte boatbuilder with a
> pile of okume ply, a roll of soft wire and 10 gall West epoxy in my garage.
> This question may have been beaten to death before--but I have been
> researching plywood scarfing techniques and it all seems frightfully
> difficult, unless one is prepared to buy a planer and an attachment --which
> probably won't get much more use after this. I did try an experimental
> scarf using a belt sander --not very successful and since I have about 20
> feet of scarfing to do not very appealing either.
> So I found a site on the net which talks about a fiberglass scarf-- perhaps
> that would do but it seems a bit crude. Would it be strong enough in a
> panel 5 feet wide?
> What about shiplap? Might be able to cut it with a saw. How wide would it
> need to be--the scarf is supposed to be 4" on 1/2 inch ply.
> So the question is--is there an easy way for a complete amateur who only
> owns hand held tools and a router (which hasn't arrived yet) to cut a good
> scarf or shiplap? John Rankin
My first scarphs were made with a home-made wood jig, C-clamped on my
Sears 7ź cirsular saw. Worked OK. Lots of noise and heat, but, with
patience, it succeeded.
I now use a big planer with the John Henry jig...but, as you indicated,
that may be a bit much if you have no other use for the planer....
--
***************************************************************
Someday we'll look back on all this and plow into a parked car.
***************************************************************
-----------------------------------------------------------
Ski trails anyone?
http://www.alaska.net/~bwalker/wtg/wtghome.htm
...sorry, this website has no porn, yet...
A Auerbach
a jig to produce a dovetail or jigsaw-puzzle type of joint?
I have seen this discussed in kit boats, and have seen
such jigs used for furniture. Would seem to be a natural
alternative to conventional scarfing.
Alex
Rick
about the fiberglass reinforced butt joint with added biscuit joint
reinforcing. It seems that the main problem with glassing a butt joint is
in getting to the other side. Biscuit joints added along the joint would
make it much easier to maintain alignment when flipping the plywood over to
tape the other side. Would this make a significant difference? I haven't
had to join plywood yet, but my next project will require it.
Rick
Gabriel L Romeu
This was my first thought, but quickly dismissed it for the following
reasons:
the plywood is far too thin
it woould probably bend differently than the plywood resulting in great
difficulty in fairing
they are meant to be used with a water based glue sso they would expand
in the joint, epoxy is not.
the cutout is larger than the biscuit and MAY result in voids (though
these probably could be filled before final glueup.
I would love to be proved wrong in this, so if you try it and are
successful, let us know.
Joel Tobias
why bother. With the Leigh, you can make a variety of joints of dovetail
or similar shape, but the big advantage of that joint is that it is
mechanically styable to traction forces. This is why it is traditional to
use this toye of joint on a drawer side - it is constantly being pulled as
the dwarer is opened and closed. To use such a joint to join two pieces of
plywood where the forces applied are mainly bending seems to me to make
little sense.
That said, yes you can do it and rather easily either freehand with the
usual dovetail drill, or with the Leigh jig.
In article <boya2.1798$I04....@typhoon-sf.snfc21.pbi.net>, "A Auerbach"
<auer...@aapr.com> wrote:
Joel A. Tobias
2210 Hillcrest Rd.
Medford, OR 97504
go...@mind.net
Jane Sheridan & John Rankin
I have just finished a rowing boat kit from Wayland Marine (the Merry
Wherry) and the kit arrived with finger joints in a sine wave pattern which
were just butted together with West Epoxy Putty. The outside had glass
cloth and the inside was sited at a frame. 3/16 ply. It has been perfect
so far and the panels were about 15 feet longafter jointing. Took up a
curve with no hard spots too.
I was relucuctant to try anything like that in my present sharpie project
because of the fear of finding out too late that the engineering was
insufficient. (I have a cousin whose concrete hull cracked on launch
day--horror.)
Dave Carnell
once. That is, lay up the fiberglass and epoxy on the underneath side and lay
the plywood on it. Very thoroughly fill any voids between the butted edges
with thickened epoxy. Then lay the upper surface of the joint and cure the
whole thing. I have laid up a sandwich of two joints in one operation and it
works fine.
Dave Carnell <http://home.att.net/~DaveCarnell>
Bud
see what's happened until after the epoxy has set up.
I am dealing with 1/2" plywood, ending up with 28' lengths. It appears the best
method for me will be to align and join the plywood sheets with lap joints, apply
fiberglass to the joints on one side, and let it set up Then turn the whole 4' x
28' muther over and apply fiberglass to the joints on the other side. Pray for me
-- I'll need it!
Bud Stych
Traverse City, MI
Dave Carnell wrote:
> Avoid the flipping operation, which is hair-raising, by laying up both sides at
> once. That is, lay up the fiberglass and epoxy on the underneath side and lay
> the plywood on it. Very thoroughly fill any voids between the butted edges
> with thickened epoxy. Then lay the upper surface of the joint and cure the
> whole thing.
> Dave Carnell
> Rick wrote:
>
> > While discussing alternatives to scarfing plywood, Biscuit joints added along
Bud
several alternatives to traditional scarfing. Similar to biscuit joinery would
be the keyed joint shown, in which a spline is inserted into the edges of the
plywood. This is using 3/8" plywood, I believe.
Bud Stych
Traverse City, MI
Gabriel L Romeu wrote:
> Rick wrote:
> >
> > While discussing alternatives to scarfing plywood, I have been thinking
> > about the fiberglass reinforced butt joint with added biscuit joint
> > reinforcing. It seems that the main problem with glassing a butt joint is
> > in getting to the other side. Biscuit joints added along the joint would
> > make it much easier to maintain alignment when flipping the plywood over to
> > tape the other side. Would this make a significant difference? I haven't
> > had to join plywood yet, but my next project will require it.
> >
> > Rick
>
Bud
fiberglassing either side. It failed quickly with just my weight on it!
Bud Stych
Traverse City, MI
Joseph Palazzolo
seperated by 3/4 inch plywood the width of my router base. Leave a section (the
size of the router base) open for the router to sit in.
Dave Carnell
Then you lay them together and proceed with the upper surface. Then you won't need
any prayer.
Dave Carnell
Bud wrote:
> I have qualms about laying up fiberglass on the blind side and not being able to
> see what's happened until after the epoxy has set up.
>
> I am dealing with 1/2" plywood, ending up with 28' lengths. It appears the best
> method for me will be to align and join the plywood sheets with lap joints, apply
> fiberglass to the joints on one side, and let it set up Then turn the whole 4' x
> 28' muther over and apply fiberglass to the joints on the other side. Pray for me
> -- I'll need it!
>
> Bud Stych
> Traverse City, MI
>
> Dave Carnell wrote:
>
> > Avoid the flipping operation, which is hair-raising, by laying up both sides at
> > once. That is, lay up the fiberglass and epoxy on the underneath side and lay
> > the plywood on it. Very thoroughly fill any voids between the butted edges
> > with thickened epoxy. Then lay the upper surface of the joint and cure the
> > whole thing.
>
> > Dave Carnell
>
> > Rick wrote:
> >
> > > While discussing alternatives to scarfing plywood, Biscuit joints added along
Alex Zimmerman
I'd like to wade in with a variation on the technique suggested by Joe Palazzo.
It involves building a wood and pipe jig for use with a router set in a plywood
"sled" or base plate. I found the design for it in a back issue of Wooden Boat
(I don't remeber which one off-hand). If you are interested I could root
through the pile and find out the issue for you.
There is probably a limit to the width of ply that could be easily accommodated
by a jig of this type. I built 4 CLC kayaks with it, using Okoume plywood, but
the widest piece was only a foot or so. It turned out very nice results,
though, and the wood took a very smooth bend across the scarf. I also did a
test joint before I did the real thing, and loaded it to destruction. The
plywood broke away from the scarf, so the joint is at least as strong as the
ply.
Alex Zimmerman
Paul VandenBosch
fiberglass on one side will probably crack as you try to turn the
combined panel.
Get some slow curing epoxy.
Lay a sheet of plastic down on a flat surface.
Wet out the bottom side of the panels where they will be joined with
epoxy and glass, be generous, and adding a little filler to the epoxy
is not a bad idea.
Put the glass strip on the plastic sheet and wet it out, generously.
(Note: for 1/2" you may need more than one layer of glass)
Set one of the panels on the wet-out glass, aligning it to cover half
of the glass.
Clamp it down or weight the panel so it can't move.
Lay the other panel down and align the joined ends.
With clear epoxy (or with just a little filler), wet out the tops of
the panels.
Make up some thicker filler (mayonaise) and pour it over the joint.
Squeegee it in, forcing it into the joint, try to get any bubbles out.
Lay on the top strip of glass, and wet out.
Tap the panel far end with a hammer to set the joint tight.
Clamp or secure the panel.
Put a piece of plastic sheeting on top
put a flat board or piece of ply on the joint.
Load on bricks, full pails, weight, avoid stepping on the panel or
bumping it.
I got this system from Dave Carnell's site and it worked for me on 2'
wide panels.
I made one mistake by trying to line up the long ends of the panels to
make a baseline for lofting. The joined ends were not exactly aligned
and left a 1/16" to 1/8" space between them with just filler between
the glass layers.
I also have a bubble or two between the panel ends.
I tested them all by lifting them with one hand on the joint and
pushing them up to see if they would break.
One panel broke after I sanded it almost to the weave.
Joining your panels this way will be easier than glassing one side at
a time.
Good luck with your project!
Paul VandenBosch
South Haven, Michigan
The Guide to Sailing and Cruising Stories
http://personalpages.btc-bci.com/~vdbosch/
On Mon, 07 Dec 1998 10:44:47 -0500, Bud <bst...@gtii.com> wrote:
>I have qualms about laying up fiberglass on the blind side and not being able to
>see what's happened until after the epoxy has set up.
>
>I am dealing with 1/2" plywood, ending up with 28' lengths. It appears the best
>method for me will be to align and join the plywood sheets with lap joints, apply
>fiberglass to the joints on one side, and let it set up Then turn the whole 4' x
>28' muther over and apply fiberglass to the joints on the other side. Pray for me
>-- I'll need it!
The Guide to Sailing and Cruising Stories
http://personalpages.btc-bci.com/~vdbosch/
Jane Sheridan & John Rankin
numerous times before.
Well here you go. I set up the first scarph using Dave Canell's invisible
fiberglass scarph technique. 5feet wide in 1/2 inch marine ply. It was
great! Came out fairly pretty and as strong as I was willing to test it.
Not perfect since there were quite a lot of folds in the poly over the top
that needed sanding and filling but the next one which is curing right now
will be better. This time I pinned the lower layer of poly down on a board
first and took great care to get the fiberglass flat without wrinkles--not
relying on pressure to smooth them out. The top layer is covered by poly
and then a layer of 3/8 ply which I hope will bend a bit and conform better
to the "hump" of fiberglass and resin and aid in smoothing it out.
I like this so much, and I can do it on my own without help, that I think I
will use it for all seven scarphs required.
THANK YOU ALL for your many replies and good wishes. If the boat falls
apart when I hit the first wave I will be sure to let you know. John Rankin
building 18x7 ft Kayleigh OB sharpie (Tracey OBrien designs)