Friday, March 24, 2017

Straightening twisted timbers in post-and beam construction

Re-milling timbers is not the only solution to lumber that has twisted prior to construction.

We had our logs milled into 8 x 8 timbers, technically known as “cants.” They were then stacked, stickered and covered for several years before we begin building with them. During that time, they twisted a few degrees. This posed a couple of small problems.

I came up with a solution – after many, many sleepless nights thinking about it – to “straighten” the timbers without losing any of their original thickness. (Re-milling the timbers would have made the walls shorter, which causes problems in non-log parts of the structure.)

I tested this theory with a small tool I had laying around, advertised as a miniature log mill for a chainsaw. Three of us kibitzed for a couple of hours over one log with this tool. My theory worked.
This mill attachment was not ultimately the best tool for the job, but a beefier, industrial-strength attachment was.
Testing the theory using a small chainsaw and cheap attachment from Bailey's.

This is pretty much impossible to explain verbally – I tried that with several people and just got blank stares – so hopefully, wherever you’re reading this, it came with all the pictures.

Essentially, we removed the effect of the twist without trying to on twist the cant. With a chainsaw in an attachment, and a straight piece of lumber as its guide, we cut away the offending part of the twist.

In addition to a good chainsaw and the attachment, we needed a few small spirit levels and a couple of rechargeable drill drivers. A straight 2 x 6 and a box of 5/16 inch lag screws with fender washers got us through the project.

We started by resting each timber on some sturdy sawhorses and marking the middle of the length of the timber. The middle part would not be trimmed. Only the ends.

Next we put a level across the timber at the middle mark. Using small plastic filling wedges (and later the wood wedges that are a byproduct of this operation) we would adjust the timber so that the center was level.

Pencil marks indicate where the chainsaw bar aligns to start the cut.
Then I would go to one end of the timber and lay the level across the butt. I made marks where the saw would start cutting. At first I measured the halfway point between the corners, but soon I was able to eyeball that distance.

The only way to understand why the marks go where they do is to examine the pictures carefully.

The 2 x 6 was attached to the top surface of the timber. There were elongated holes in this piece so we could attach it with lag screws to the log, then make minor side-to-side adjustments. The adjustments were necessary to align the chainsaw bar with one of the marks I just made.

The 2 x 6 had a little twist of its own, but it needs to sit level side-to-side. We attached the 2 x 6 to the middle of the log first, where we knew it was already level. Out at the business end, where we would start cutting, we attached it with the lag screw and set a level across it as we tightened. That way the full length of the 2 x 6 was level across. (Level the long way didn’t matter here.)

Ben trims a cant using the chainsaw mini mill technique.
The 2 x 6 serves as a guide for the attachment holding the chainsaw bar vertical. With everything in place, it was a matter of running the saw from the butt toward the center. As the saw moves from the end to the middle, the amount of wood being removed tapers off to nothing.

A long, pointy piece of scrap wood falls to the ground. The wide end of this piece is technically half as wide as the timber (about 3-3/8 inches in our case) except that the saw kerf made it about 3 inches wide at most.

If this is a situation you’re dealing with, and the explanation above isn’t making sense, contact me and I’ll post a video of the trimming operation for you!

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