Joining plywood
bgeorges
questions. I need to join two pieces of ply end to end and I would like your
opinions on the methods available. 1. the scarf joint, how is this made? is
there a special tool for doing this? 2. Using 4 inch fglas tape and epoxy
resin..my concern is that this will be a weak point especially when I have
to bend the wood over the frames.
3. the butt connection I do not see this as practical for use in the hull.
These are just the opinions of a first time builder. Any other approaches
will be welcome. Again thanks in advance
--
Bradley Georges
Bob Walters
However, a simple scarf joint is easy to make and only takes a few minutes.
It sounds like you are making panels for a hull. If so, pre joining them is
usually the way to go and a scarf joint will give you the least trouble
later on. In spite of what others may say, a butt block will make a hard
spot that you will have problems hiding it. You can hide the block itself
under a seat, but the hard spot is something Mother Nature will not
overlook.
The fiberglass joint is better and plenty strong, but not without it's own
problems to solve. I'd suggest a scarf joint if for no other reason than
you should know how to make one if you're going to call yourself a boat
builder, even a part time amateur one.
Any good book on plywood boat building will give details, but the idea is to
stack the two sheets of plywood, measure back from the edge eight times the
total thickness, i.e. eight inches for two sheets of half inch ply, and make
mark parallel to the edge.
Now simply remove the wood from the mark to the edge in a nice even taper
using the glue lines in the ply as your guide. If you're good with your
Skill saw, you can remove a good chunk of the wood with a rough cut, but you
might cut off a finger and/or wreck a nice piece of ply if you're not
careful.
The low angle block plane is perhaps the best tool for this work. I contend
that everyone who builds anything should have a low angle block plane. I
have a couple of Stanley models around the shop and use them for everything.
I have no use at all for an ordinary (high angle) block plane and I actually
wonder why they were invented in the first place. The key to success is the
low angle. I repeat, LOW ANGLE.
Don't buy this tool unless you also buy a good stone and one of those
inexpensive blade holders that will allow you to sharpen the plane iron
easily and accurately. This tool must be sharp to function properly.
I actually use a John Henry Scarfer and it's a fabulous tool, but it costs
over a hundred bucks plus you need a power planer. Not worth it for a part
time builder. Do not buy the Gougeon Brothers scarfer. If you need to do a
lot of scarfing, use the John Henry for sure.
By the way, I didn't mention all there is to scarfing here. You must
support the edge well, etc. but that information will be found in any good
book on ply boat building. If you don't have one, get one and READ IT. I
like The Gougeon Brothers on Boat Construction, but there are many others.
Good luck.
Bob Walters
bgeorges <bradley...@sprint.ca> wrote in message
news:rrQH4.2840$Bq2....@newscontent-01.sprint.ca...
KF4call
>opinions on the methods available. 1. the scarf joint, how is this made? is
Bradley,
In the advice from Bob Walters, you have heard from someone whose ideas
reflect a really expert and useful knowledge base. I think he is correct
about scarphing, even for a first time builder. I was a complete novice to any
type of wood working at all when I did my first scarphs. They are not all that
hard to do.
I used a jig for a circular saw, which I built from plans and scarphing
instructions provided by Tracy O'Brien, a West Coast boat designer,
http://www.localaccess.com/tracy/boatpage.htm
I don't know if he sells the plans for the jig individually.
Regards, Warren
D.W.L
Building Manuel
In summary :
The butt strap joint causes an unfair "hard spot" when bent to a curve.
Used a 4" fglas tape, epoxy resin and fglas mat over a butt joint. one side was
layed with just the 4" tape.The other side a hollow was sanded out of the
length of the butt joint, filled with a piece of mat and lots of resin.The
second piece of 4" tape was put down over this .(ply over 3/8 recommned
hollowing both sides of the joint).
Apperently they tested(by breaking it over their knee) a piece of 1/4" of ply
and broke in the wood and not the joint. He called the joint "the Payson Plywood
Butt Joint".
I would also test a sample too i suppose , just to make sure. : )
bgeorges wrote:
> Hi and thanks to all who contributed to my last post. But I have more
> questions. I need to join two pieces of ply end to end and I would like your
> opinions on the methods available. 1. the scarf joint, how is this made? is
Chris Crandall
: questions. I need to join two pieces of ply end to end and I would like your
Scarfing is a good choice, and it's the best joint, but . . .
It costs you inches. If you make an 8-to-1 scarf joint,
in 1/2 inch ply, you lose four inches across the two sheets.
It might make no difference to you, or it might make a large difference.
Some designs use all 8ft of a ply sheet; these are usually designed with a
butt block or double-tape joint in mind.
John R Weiss
3" fiberglass tape on each side. High-stress joints have additional layers of
tape and/or plywood built up on the inside. The outside of the butt joint is
very smooth, with an almost-undetectable bulge.
The butt joint will be stiffer than the wood around it, and can be made
stronger than the surrounding wood.
-----------------
John Weiss
Lake Forest Park, WA
Remove *nospam* from reply address
bgeorges <bradley...@sprint.ca> wrote in message
news:rrQH4.2840$Bq2....@newscontent-01.sprint.ca...
> Hi and thanks to all who contributed to my last post. But I have more
> questions. I need to join two pieces of ply end to end and I would like your
August Depner
find nonstandard lengths of ply so he could avoid scarfing the wood... did scarfing
suddenly become anathema to good craftsmanship?
My understanding and experience (4 small craft and some home projects, so you can
judge) is that a scarf joint is always stronger than a butt joint, since the surface
area of the scarf joint, hence the area over which the glue holds, is larger. Of
course, butt joints have been used forever, but the concerns over unfairness seem
justified - I've seen problems like this. The person building from 4mm ply surprised
me - with wood that thin, you don't lose all that much length with a scarf joint,
and all that tape over a butt joint is unnecessary with a scarfed join - so less
time fairing. Good luck whatever you do - but scarfs are easy to make and work
well. Good reasons not to limit your bag of techniques.
"D.W.L" wrote:
> Hi, I have no boat building experience at all(not yet). But i read the book Boat
> Building Manuel
> In summary :
> The butt strap joint causes an unfair "hard spot" when bent to a curve.
>
> Used a 4" fglas tape, epoxy resin and fglas mat over a butt joint. one side was
> layed with just the 4" tape.The other side a hollow was sanded out of the
> length of the butt joint, filled with a piece of mat and lots of resin.The
> second piece of 4" tape was put down over this .(ply over 3/8 recommned
> hollowing both sides of the joint).
>
> Apperently they tested(by breaking it over their knee) a piece of 1/4" of ply
> and broke in the wood and not the joint. He called the joint "the Payson Plywood
> Butt Joint".
>
> I would also test a sample too i suppose , just to make sure. : )
>
> bgeorges wrote:
>
> > Hi and thanks to all who contributed to my last post. But I have more
> > questions. I need to join two pieces of ply end to end and I would like your
> > opinions on the methods available. 1. the scarf joint, how is this made? is
> > there a special tool for doing this? 2. Using 4 inch fglas tape and epoxy
> > resin..my concern is that this will be a weak point especially when I have
> > to bend the wood over the frames.
> > 3. the butt connection I do not see this as practical for use in the hull.
> > These are just the opinions of a first time builder. Any other approaches
> > will be welcome. Again thanks in advance
> >
> > --
> > Bradley Georges
bde...@mindspring.com
how easy it is to do with a good sharp plane.
Bill Denes in Chattanooga
John R Weiss <jrweiss@*nospam*attglobal.net> wrote in message
news:38f7a...@news1.prserv.net...
> I am building a kayak using 4mm plywood joined with butt joints reinforced
with
> 3" fiberglass tape on each side. High-stress joints have additional
layers of
> tape and/or plywood built up on the inside. The outside of the butt joint
is
> very smooth, with an almost-undetectable bulge.
>
> The butt joint will be stiffer than the wood around it, and can be made
> stronger than the surrounding wood.
> -----------------
> John Weiss
> Lake Forest Park, WA
> Remove *nospam* from reply address
>
> bgeorges <bradley...@sprint.ca> wrote in message
> news:rrQH4.2840$Bq2....@newscontent-01.sprint.ca...
Al Gunther
> Hmmm... I just got through replying to someone else in this group that
wanted to
> find nonstandard lengths of ply so he could avoid scarfing the wood...
did scarfing
> suddenly become anathema to good craftsmanship?
>
> My understanding and experience (4 small craft and some home projects,
so you can
> judge) is that a scarf joint is always stronger than a butt joint, since
the surface
> area of the scarf joint, hence the area over which the glue holds, is
larger. Of
> course, butt joints have been used forever, but the concerns over
unfairness seem
> justified - I've seen problems like this. The person building from 4mm
ply surprised
> me - with wood that thin, you don't lose all that much length with a
scarf joint,
> and all that tape over a butt joint is unnecessary with a scarfed join -
so less
> time fairing. Good luck whatever you do - but scarfs are easy to make
and work
> well. Good reasons not to limit your bag of techniques.
What John is building is a Pygmy kayak kit. They specifically design the
butt joints to fall in the center of the kayak where there is little if
any bend. Their reason for favoring butt joints in a kit is that they have
better experience in the builder getting the proper alignment of the two
pieces being joined with butt than with scarf joints. Certainly scarf
joints are not difficult to make with practice and the joint bends fair.
But, hundreds of these kayaks have been built and they are very well
accepted for their looks as well as for their strength and performance, by
well seasoned kayakers. The 4mm thickness allows them to weigh slightly
over half what a fiberglass kayak of the same dimensions would weigh and
yet they are as strong and stiffer, I believe.
--
Al Gunther, Kingston, WA <---- 47° 48.1'N, 122° 30.0'W
http://www.silverlink.net/~agunther/
August Depner
with the Pygmy construction - what a shame, too, since they're in my area and
their boats have a great reputation. I suppose the main thing is follow the
designer's recommendations. As a general rule, my point about scarf joints
being stronger than butt joints is true, but one needs to build the boat as
designed. I'm taking on the building of a catamaran that utilizes butt
joints, and I'll build it that way, too.
Bill Walker
I doubt that boat designs are so precise that if you use one instead of the other,
your boat will explode at the first wave and sink tragically to the bottom. Nah,
the material science and the engineering is not that precise.
There is a very compelling photo in CLC's pamphlet (the bending difference is
obvious).
How proud do you want to be of the finished product? When I brag about my boat,
one of my favorite bragging subjects is the scarf joints. I've never bragged about
a butt joint. My motto is:
Butt-joints are for butt-boats.
Mark Weaver
Bill Walker <bwa...@alaska.net> wrote in message
news:38F9EDCF...@alaska.net...
> The ol' butt-joint vs. scarf joint argument is a regular issue in this NG.
>
> I doubt that boat designs are so precise that if you use one instead of
the other,
> your boat will explode at the first wave and sink tragically to the
bottom. Nah,
> the material science and the engineering is not that precise.
>
> There is a very compelling photo in CLC's pamphlet (the bending difference
is
> obvious).
>
> How proud do you want to be of the finished product? When I brag about my
boat,
> one of my favorite bragging subjects is the scarf joints. I've never
bragged about
> a butt joint. My motto is:
> Butt-joints are for butt-boats.
>
I've just recently started reading this newsgroup since embarking on my
first boat-building project and I thought I had read that the proper term
for my stitch-and-glue dink was a 'goo box', but now you're suggesting
'butt-boat' instead. Hmmmm. How about a 'goo-butted box-boat'? Well,
anyway, here's what it looks like as of this afternoon:
http://people.mw.mediaone.net/mlweaver/images/Spindrift3.jpg
Mark
Nicholas Carey
> What John is building is a Pygmy kayak kit. They
> specifically design the butt joints to fall in the center
> of the kayak where there is little if any bend. Their
> reason for favoring butt joints in a kit is that they have
> better experience in the builder getting the proper
> alignment of the two pieces being joined with butt than
> with scarf joints.
I believe that the reason Pygmy uses butt joints is at least
as much a pratical business decision as it is an engineering
decision.
Pygmy's (and CLC's for that matter) boats are designed to be
sold in kit form. The feather edge of a scarf joint is
*fragile*. Using butt joints instead of scarfs ensures that
fewer shipments are damaged in transit. Thus, Pygmy's
choice of butt joints ensures a fewer customer complaints
and problems -- always a good thing if you're running a
business.
And from a manufacturing point of view, the use of butt
joints simplifies manufacturing of the kits. It's speedy and
simplee for the CNC router they use to cut a simple 2-D
shape out of flat stock. Cutting a 3-D taper on one end
would complicate things and slow down manufacturing.
Any designer has a lot of stakeholders to answer to, all of
whom have differing (and often conflicting requirements).
The designer needs to craft a compromise that suits all the
stakeholders.
> ... hundreds of these kayaks have been built and
> they are very well accepted for their looks as
> well as for their strength and performance, by
> well seasoned kayakers. The 4mm thickness allows
> them to weigh slightly over half what a fiberglass
> kayak of the same dimensions would weigh and yet
> they are as strong and stiffer, I believe.
And the choice of a butt joint wasn't made to meet a
requirment that the joint be the "strongest and most
flexible joint possible", but that is merely be "strong
enough and flexible enough". I'm sure that Pygmy's butt
joint *is* strong enough and the designer(s) addressed the
flexibility issue by placing the butt in places where
little flexibility is required.
N.
--