Post 16 in a continuing series….
Continuing work on the inverted ’T’ support beams, which connect to one another with mitered half laps.
After the pieces were cut to length (see the previous post), I laid out the half lap shoulders with a marking gage:
The Matsui layout tool is sufficiently precise in its adjustment that I can reliably offset for half of the mechanical pencil line thickness, @ 0.25mm:
The pencil lines, since I always check my cut out by measurement, are there mostly in a symbolic role, conveying clear information about what is supposed to be cut and what isn’t. Still, I strive to put the lines in precisely. I find it helps to use an Optivisor to closely check some of the layout lines. Most of the offsets I mark out are calculated based on measurements of the actual pieces. Try to put the lines in as accurately as I can, and afterwards when I measure I am sometimes surprised to find my layout lines could be more accurately placed yet.
I decided to drill the mortises this time, using an undersize brad point drill:
This was the first time I used the t-bolt hold downs on the mill table, and I’m a fan already. Nice to have the feeling that the end stops I have clamped in are simply not going to move anywhere after cinching down the nuts a modest amount.
Setting the plunge location by eye, I aim to leave just enough meat in the mortise for square-up and dimensioning work with a chisel later on:
After the mortising, a round of kerf-wasting of the lap itself was done on the sliding table saw:
The cut shoulders were clean and coincident for the most part:
Then it was time to machine the rough-cut lap surfaces smooth, a task for which I again turned to using the milling machine. This time I hoped to learn from my mistakes the previous round with the pillow blocks:
After the laps were trimmed, then it was on to the 45˚ abutments. A few rounds later, I had parts which were starting to fit together:
A closer look:
The other side:
A little bit of fit massaging later, this end was down:
A tiny bit of tear out happened from sliding the joint apart. Hard to avoid, but regrettable all the same.
The other side:
Seems like it came out okay. I am getting closer to figuring out the ideal sequence for cutting the half lap with mitered abutments. I’ve tried cutting it many different ways in the past, however the milling machine is getting me closest to the desired result.
I should have the remaining fitting completed tomorrow, and hopefully the mortising cleaned out to the lines as well. Step by step, we move forward.
Thanks for visiting the Carpentry Way.
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