Monday, September 1, 2014

Lock Notches, Why and How

I have to say that log cabin building is not as straight forward as most would think. Get some logs cut some notches and pile them up. How hard could it be? Everyone did it 150 years ago and just with hand tools. No chain saws.

Well if you have been following the construction of cabin #3 you know there is more to it than meets the eye. Lock Notches are just that. Take a look at the picture below of the first one in this cabin.
Can you see it? Well lets take a look at the why and how of Lock Notches...

With the log sitting on the rough notch and the final notch scribed in orange you can see that if cut this deep (over 1/2 of log diameter) it would weaken the log at the notch. The solution is to cut a  Lock Notch. This will be a block of wood left in the notch. The orange horizontal line going through the middle of the notch shows the size of the block to be left in the notch. About 3 inches in this case.

With the log rolled over the notch is cut to the depth of the block to be left in the notch.

After being cleaned out the width of the block to be left is laid out. The material on either side of the block (marked by X's) can now be chiseled out as per final scribe.

Next the receiving notch for the block is laid out in the lower log.

Both halves of the lock notch cut and ready.

Walla! Now do you see the lock notch?

Tuesday, August 26, 2014

Round two completed

The logs for round two of the cabin are completed. This was a good chance to fine tune the process of calculating, scribing and cutting the saddle notches to the correct depth so the tops of the logs for even numbered rounds will be at the same height. Looks easy enough, right? But when you think about it the logs are tapered and different diameters on the ends, maybe not.

The tool that makes it possible is the Log Scribe. A dividers with a point on one leg and Ink pencil on the other.

What makes it work are the two levels that keep the dividers in the correct planes while you move it along marking the line for the saddle notch and groove cuts. You keep your eyes on the levels, not the pencil! This takes some practice to get the hang of.

With the lines marked I like to chisel the line for a positive reference so as not to over cut it when using the axe or saw.

And if all goes well this is what you get. All four corners at a height of between 21" and 22" with a minimum 3" wide groove making contact with the log below it. When the EM Seal expands in the groove the joint will be air tight.

With the new school year starting this brings to mind the old saying about learning and it applies here for sure. "I hear it I forget. I see it I remember. I do it, I understand!"