What’s a joint like you doing
in a boat like this?
[‘Shiplap’ vs Scarf vs ‘Butt’ joint]
Tim and All,
Let me see if I can answer six 'messages' at one go . . .
Tim, I already sent you a direct answer about a technique to
'solve' the 'movability' issue.
I don't have any problem with either the 'device' or the 'joint',
per se. I just said it was VERY over-priced, and the particular
joint was 'inappropriate' for the use specified. I have several
routers and am always on the look-out for a more efficient way
of doing things. However, 'More Power !!' and 'high tech' tools
sometimes take more time & effort to do ONE of anything.
It's the SET-UP, that takes the time & effort . . . not
the 'doing'. For ONE 'sheet' {the Scarf Jointing
of two standard 4x8 sheets}, nothing beats the short time &
high efficiency of laying them down in a 'stair-step' and a
few minutes work with a sharp hand plane. The positioning of
the sheets, the ply's, and the clamping boards assure a straight
cut. Applying the epoxy & cloth, and the clamping is the
same, regardless of the actual cutting. If I have to do multiple
sheets, I will use a belt sander for the initial work, then
a pass or two with a bench plane.
One of the features of Bolger's plans, and often times Dynamite's
interpretation, is the concept of, 'Boats for the 'Everyman'
' A big 'Production' shop, even if it is a 'Custom' shop, doesn't
really concern itself with 'waste'. It calculates materials
based on a 'per increment' basis. They can't buy a 1/10 of a
sheet of ply, so they use the cost of a full sheet in their
pricing calculations. Even if they do have a 'scrap' area, it
probably doesn't pay them to keep less than a ½ sheet.
Bolger tries to use, 'everything but the squeal'. Payson probably
illustrated the philosophy best when he said he wanted to, '
. . . sell plans {of boats} that actually got built'. A Butt
Joint may not be 'pretty' {and it 'flags' through thin
materials}, but is really an 'elegant' use of materials. The
builder is able to use the FULL LENGTH {or width} of the materials
he has purchased. The 'backing board' is cut from left-over
scraps and sometimes not even illustrated on the actual plans,
just mentioned in the text. Overall, it is the 'SIMPLEST' joint.
One step up from this, and an indication that 'modern materials'
are 'brought into the mix', is the 'Payson Variation', or 'Taped
Butt' Joint. A little messier, it still may 'flag'
through, and it takes a bit more care & practice to be done
well. While it has been proven. ' . . stronger than the surrounding
wood . . .', some people add more time, cloth, and epoxy to
make the 'Hollow Taped Butt Joint'. Could be
for further piece of mind, and it doesn't 'flag' {?} - or at
least not as much.
While some of these 'messages' extol the virtue of the “JointAbility”
as 'quick & neat', others recommend the 'modified
finger' joint that requires a template to be done well.
It is hard to believe that it will beat a Scarf Joint in 'fairness'.
A properly done Scarf will NOT have a 'flat spot'. It is certainly
not 'easier' in concept. Maybe in exception, but the template,
length of 'fingers', and the cutting tool are critical elements
{costly ?}.That 'interlocking joint' is very
good. In fact I have a couple of plastic storage boxes whose
attached lids close with it. To use it, the edges must be CLEAN
which means a SHARP cutting tool, used well, a good & accurate
template, and careful set-up. Again, for 'one-time' use ?? What
does it add, mechanically ?? Will the boat be built from $100
a sheet cosmetically beautiful marine ply and 'clear coated
? Or plain A/C ply and painted ?
Other than the 'Wood Backed Butt Joint', the CARE of assembly
is critical, and just about the same for ALL the 'epoxy methods'.
How carefully you 'stack' or clamp the joint will effect the
surface appearance. All of the Butt Joints, and the 'Interlocking'
Joint use the full sheet - there is no 'cutting loss' in the
length {or width}. The Scarf Joint does cause
a loss, how much depends on the ratio of the scarf - maybe 2
inches over-all for a 1 to 8 with 1/4 inch sheet goods. However,
it does allow the 'fairest' curve . . . more so as the curve
gets tighter.
Well, I think that responds to everything, and the villagers
are lining up with their torches & pitchforks. Each of these
approaches has their place - they have all been 'around forever'.
The builder has to make HIS decision. A lot of the plans out
there have also been 'around forever'. What was a good idea
in 1950, may have been supplanted 50 years later. A specifically
mentioned material may no longer even be available. If you have
gotten the plan from a reputable designer, he probably included
an 'update sheet' or sent you one. I know that's what Dynamite
did with the "taped joint' and later 'hollow joint'. In
addition, if you have a question, or an idea concerning the
latest concepts in physical chemistry or materials, or building
concepts . . . write a letter to the designer. All it takes
is a bit of patience and a bit of ink.
Regards & Good Luck,
Ron Magen
Backyard Boatshop
> Ron, thanks, this is most helpful. I'm interested in this
joint because I have a curious problem, building Topaz in a
long garage. . . .
> best,
> SNIP
> Tim.
- - - - -
SNIP
> I think the biggest advantage of the JointAbility is that
the router bit rotates sooooo fast that the surface is much
smoother than a saw or an electric plane can give. Plus, the
jig ensures a straight line.
- - - - -
> I experimented with another type of joint about four years
ago. It seems to work even better than the scarf joint and is
a lot easier to construct. It also produces less of a stiff
spot than a scarf.
>
> Basically, it is a type of finger joint. The fingers were
1.5W X 2.0 deep and the roots and crests were radiused. These
dimensions were optimized for 6mm ply but would probably work
just fine for ½".
> Doug
- - - - -
> I'm using this sort of joint in some glued lapstrake ply
construction, and the joints are both invisible in curved panels
. . . and appear to be very strong . . . .
> One important point: wet the edges out thoroughly with
unfilled epoxy so they are completely saturated, then push the
joint edges together with some lightly filled epoxy that COMPLETELY
fills the joint and squeezes out. We then squeegee the joint
and apply smooth plastic with weights on it until the epoxy
is cured. The resulting joint requires little or no sanding
to finish.
>
> David
- - - - -
SNIP
Plans call for Payson-type butt joints hollowed and glassed,
not with backing blocks. But it seems to me that ship-lap joints
would be quicker and neater. . . .
> --Tim.
- - - - -
> SNIP
> Could it be that the 1" lost in cutting a shiplap
joint costs you an extra sheet of plywood?
>
> Bolger often spends an amazing amount of effort in utilizing
sheets of plywood efficiently.
>
SNIP
Ron Magen
