: I use a glue jig that looks and works remarkably similar to Uncle
: Jay's.

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.