: So long as the jig ensures a straight joint it is doing its job.

: On the question of scarf angle, I have some opinions to offer.

: There are lots of ratios around, ranging from 12:1 or even 16:1,
: which I have encountered in older publications, right down to
: 3.2:1 which I calculated was the minimum based on the properties
: of the wood and glue. I made and broke several test samples and
: the joint was stronger than the wood in most cases, the break
: usually occuring across rather than along the joint. For those
: of a technical bent the minimum ratio is given by root(WGS/ACS)
: where WGS is the with-grain strength and AGS is across-grain
: strength. For most wood species the WGS/ACS ratio is around
: 10:1.

: Having said all that, normally I use a 6:1 scarf which gives a
: safety factor of 2 to accommodate the possibility of long-term
: glue degradation, although I will go up to 8:1 for a joint that
: is going to be bent during hull assembly. I also use 8:1 for
: highly absorbent material like plywood, where it is difficult to
: ensure a fully-wetted joint, and for difficult-to-glue materials
: in general.

: The much higher ratios given by older authorities were - I suspect
: - adopted because scarf joints were not glued back then due to
: the lack of waterproof glues; for a nailed joint a much longer
: joint is clearly necessary.

: The downside of short joints is their tendency to slide apart as
: clamping force is applied. I use Titebond III which has a fast
: grab time, and leave the joint in the jig until the glue has
: started to grab so it no longer acts as a lubricant; I use the
: time to cut the next scarf because I usually need a batch. With
: a slow setting and slippery glue like epoxy, a longer joint may
: be required to eliminate the sliding problem. A tack through the
: joint will eliminate the sliding, in which case it is perfectly
: OK to use the shorter joint length PROVIDED there is no
: possibility the glue will be degraded at some time in the
: future.

For normal stripping of a canoe/kayak where it'll be glassed the strength is in the glass. On the sheer strips you just need long straight strips, otherwise I just butt join the strips, easier and it works fine.

Bill H.