It’s not every day that you come across a 37-foot Glulam beam. It’s also not every day that you have to install 16” knife plates into that same Glulam. Unfortunately, commercially available chain mortisers can have a limited depth of cut, and the fact that we didn’t own one led me to seek an alternate solution.
What we did have was an awesome chainsaw — a Stihl MS362 — and a knack for simple solutions to complex problems. We took a quick trip to visit our friends at Ladner Harbour Machine Shop because we were in search of a woodworker’s best friend — Aluminium. It can be machined with our tools and is relatively easy to work with. I was able to come up with some channel and flat bar that would form the basis of the jig. Back to the shop we went.
I knew that we needed a solid guide for the chainsaw that could be easily adjusted. This would affect a precise mortise in both the beam and the supporting columns. It would have to allow for a controlled plunge of the saw, as well as be adjustable for the thickness of the knife plate which was thicker than the chain on the saw. I drilled two holes in bar of the saw (yes it hurt a little…) and affixed the aluminium guide bar to the saw with threaded ready rod for easy adjustability. I then installed the aluminium channel into some plywood and 2x6 that could be clamped to the beam and column. We had a jig!
Off we went to site again. After careful layout of the knife plate locations on the beam (you only get one shot at getting this right) we were ready to fire up the saw! Side note here: We kept the beam wrapped from the factory until is was craned into place (that may be another article) and clamped heavy duty casters to the beam so we could move it as required for the machining. The saw and jig were a perfect team! Easy to control the plunge, width and depth of cut. Simple, yet effective. We really could not have asked for more — except maybe an endless supply of mortises to plunge!
Simple materials and some ingenuity go a long way to getting the job done well.
