Wall Slots with the Craftsman Twin Saw

By Duane Sellman (reprinted from fall 2009 newsletter)

Duane Sellman

The “Twinsaw” from Craftsman can be a very useful tool. It has 2 circle saw blades that rotate in opposite directions minimizing the kickback tendency as the blades make contact with the material you are cutting. The two blades apparently have no set on one side as they are mounted very close together. I have found mine very useful in cutting wall slots and yesterday cutting off character post branches where they make contact with the stress-skin panels in the ceiling of the great room. After cutting, the sheet rock will be able to slide between the ceiling and the branch.

As purchased, the Twinsaw has the blade guard retraction lever in the way for my purposes. I cut this lever off and attached a wire to form a finger loop to utilize for retracting the blade guard. See photo. Now that the lever is gone, I can lay the saw with this side on a flat surface such as the ceiling and move it into the branch and score the branch all around. I say score because the blade can only penetrate an inch or two before the saw body contacts the wood. Once scored, a reciprocating saw, handsaw, or electric chainsaw may be your saw of choice to complete the cut. As purchased, the Twinsaw cuts about 5/8‟s of an inch from the surface it is against. This gives plenty of room to slip ½ inch sheetrock. I have not tried 5/8 inch sheetrock.

To utilize for wall slots, we have two options. The first is to make a jig to attach to the wall in the proper location for the wall and run the saw along it. Use the saw to score the outside of the wall slot without any tear out of wood fibers. Then use the electric chainsaw to deepen and clean out the wall slot to its full width. I make slots for the sheetrock on each side of the stud, not for the stud itself. My first stud is plumb and against the log which protrudes the farthest. I may have to notch into one or two logs so my stud contacts at least one log high on the wall to receive the timber screw of some type. This screw goes into the top of a slot cut in the stud to allow for settling. It is put in only snug, not tight. I like to cut 3” squares of ¼” plywood to act as wooden washers so the screwhead or standard washer does not dig into the stud restricting settling. It won’t actually restrict setting. More likely it would break the screw. The Twinsaw needs more than one and ½ inch width to rest against so I add a stud for additional width or custom cut blocks between the jig and wall. The saw may lose contact with the jig before penetrating the log without these blocks.

The second option, which I prefer, is letting the homeowner (or me) frame the partition stud walls and use the end stud to guide the jig as mentioned above. It may still be necessary to add a stud or blocking.

Another variation is having a pre-varnished trim board sit on top of the sheetrock. The advantage here is that slivers of unpainted sheetrock do not settle down into view over time. This recent house may be the first time I have done this. So this time I do not need a ½” slot for sheetrock, but a ¾” slot spaced ½” out from the framing. In theory, if I temporarily screw a 5/8” thick plywood to the framing to guide the Twinsaw, the outside of the scoring saw kerf should be at 1 and ¼”. Just right for the ¾” wood on top of the ½” rock. Actually I aim for at least 1/16” oversize; otherwise you will be cussing as the material will not go into the slot.

The depth of the wall slots is always a question. Ideally, the slot would go in to just make contact with the lateral groove thereby closing all gaps. Going too deep reduces the structural integrity of the logs sideways strength. There should not be two slots on opposite sides of a log at the same point as this would really reduce this integrity. This depth of the slot would be easy in the rare situation where all the laterals are 4” wide and are in perfect alignment. That does not occur in my houses with character (crooked) logs. So sometimes my sheetrock ends are not cut square. If they are not square, I have to ensure that after settling there will not be an absence of sheetrock at the lateral groove. It takes a little figuring for me to be sure the sheetrock goes straight up from each lateral groove at least as far as I expect that point to settle down. With the trim board on top of the rock, that board could be removed later and corrected, but with the sheetrock you are kind of stuck! Another place for sprayfoam, trim it, sand it, and paint it. That would work in my house, but not for my customer!

Of course, everyone knows that if the sheet rock is scribed with points to go in between the logs, those points can eventually break off as the logs settle. Some people think after a year or two the house is done settling. Myself, I estimate my houses settle to 80% in three years. I know of two log homes within 20 miles of mine that had settling occurring at 12 years. I find this hard to believe but the homeowners told me first hand. One of them was a log home builder also. Both of these homeowners came home and could not open the door because the settle board had come down enough to interfere with the door opening. Now this is a cut and dry situation. Either the door touches the settle board or it does not touch. So at 12 years of age, two log homes still had settling occurring. One was smaller red pine logs by our standards, but the other was probably 12” mid-diameter logs. I actually spent a week fitting logs on that house when it was built in 1982 and put an addition on it several years ago. Now they want more room again and I talked to them about another larger addition.

Another variation is wall slots for ¾” material such as pine tongue and groove. For this, I added a spacer onto the saw metal housing around the blade. This entailed drilling and tapping the thin metal for screws to attach the aluminum material I used for my spacer. I could see duct tape being used here!! Yesterday I removed my spacer since the plywood on the framing gave me more spacer thickness which I needed.

I recently purchased two “DUAL-SAWS” from the TV infomercial. I was sure they would work great. And the first one did for a while. On TV they even cut a car body in quarters. Cutting brass and aluminum requires the use of a lubricant stick which looks like a hot glue stick. Anyway, this 3amp saw worked for a few slots, but got hot with the continued use. Five minutes to cut a slot, 10 minutes to set up for the next, and so on. It started to smell like a hot motor. A couple days later 5 minutes cutting a window (2‟x4‟) extension jamb down and it quit running.

The craftsman is 7 amps. I have to remember to give it sufficient cool down time! I may have paid $189 at Sears 4 or 5 years ago after Jim Grieb showed us his Craftsman Twinsaw at a conference.
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About gllca

The Great Lakes Log Crafters Association is chartered as a non-profit organization in the State of Wisconsin, USA. The Board President, Board Members, and Officers are elected by the general membership and serve as stewards for running the association
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