Cutting Carlin Joints
Sometimes just watching someone do something is enough to figure it out yourself
The carlin joint is possibly one of the most interesting of all joints to tackle. It is both intimidating at first glance and dead simple in geometry and layout. The actual cutting is mostly simple but if attempted at more extreme angles it may require some skew chisels to complete. This is also more challenging to do small than large.
In wooden boatbuilding we don’t tend to get vey complicated with our joinery. Mostly scarf joints, dovetails. The odd mortice and tenon or bridle joint. The carlin joint is one of the more complicated ones, yet it is in fact quite simple to execute and the secret is in the layout.
All the layout is reliant on choosing a constant depth and then using half of that depth to layout the various features that are unique to this joint.
The finished result looks good. It takes a fastener without forcing the joint out of alignment. It can take compressive loads in two different directions, and with a fastener, can take a tensile load too. The downward load is shared by both the haunch and the sloped shoulder preventing the deck beam from splitting at the haunch. Because the notch for this joint is full depth, the deck beam resits twisting or rolling. While it’s tensile capabilities are not what a dovetail might provide, in larger boats, bronze or steel rod collar ties are usually worked into the deck structures provide that. Carlin joints also allow the least possible compromise to the strength of both components and to top it off, allows water to drain out of it too.
Practice this with some scrap. I assure you, you will get the hang of it pretty fast and a couple hours of fiddling around in the workshop will be well spent.