Will's books

Will's books


Monday, June 15, 2020

History behind the Headcutter and Seat-cut Guide

The following short blurbs are condescended from the chapter
 “Filling Needs – the Headcutter and Seat-cut guide stories” in
 From the Top Plate Up – A Production Roof Framer’s Journey

Get your copy of FTPU  HERE.

The Headcutter

Best gang-cutting tool available

By doing roof framing demonstrations in the mid-1990s incorporating the production gang-cutting methodology at JLC Live conferences, I became acutely aware of the problems everyday carpenters faced in applying these techniques on the job-site. Few possessed or could even purchase the trick roof cutting tools that I had from the track framing days of the 1970s (dado saws, sidewinder blades, etc). While the swing-table saw base was readily available to help make the seat-cuts, making the head-cuts even with the Linear Link or Prazi Saws was extremely inefficient due to their lack of power. To remedy this, I decided to undertake a project to mount a regular gas-powered chainsaw with some real horsepower on an adjustable saw-table.

Original prototype

Working on it in my spare time, I had a prototype ready within a few weeks, but it would take a year or more before I could get it out to the public. What was of great importance to me was that the saw-foot be able to mount quickly on the chainsaw’s chainbar without the need to drill mounting holes. A chainsaw accessory more or less. I also wanted the saw-table to be able to bevel well past 45°, so it could not only be used to gang-cut ridge-cuts, but also be used to gang-cut seat-cuts. Yep, a genuine “one tool does it all” solution to the age-old problem of gang-cutting rafters. I originally began by using a pair of large set screws for the chainbar fastening method, but later this was upgraded to a more beefy clamping mechanism when it went into production at Big Foot Tools, and a legitimate machine shop was fabricating the saw-table, not some guy on the tailgate of his pickup truck. My design utilized the top edge of the chainsaw bar to make the cut so wood chips were thrown away from the operator and the cut-line area stayed clean. While I had employed the “top edge of chainbar” cutting technique in other framing situations all my life, using it for the vertical milling of raked rafters was nothing short of a perfect fit.  After much deliberation I settled on the name “Headcutter” for the saw-foot. Looking back now I probably should have named it the “RafterCutter” or “Gangcutter” so the name would better incorporate all its cutting capacity, but hindsight is always 20/20.

 Headcutter can be used to make seat-cuts as well as head-cuts 

Everyone liked the “Headcutter.” Not only did it get used to gang-cut rafter ridge-cuts and seat-cuts, but it found a home precision cutting bundled TJIs and structural insulated panels (SIPs) as well. I was jazzed that carpenters finally had an adequate tool solution to the age-old problem of gang-cutting rafters.

The Seat-Cut Guide

Seat-cut Guide works on 2x12, 2x10, 2x8 material from 4/12 to 12/12 pitch

The “Seat-cut guide” arose out of another "solve a problem" situation as the “Headcutter”, but this time I found myself in the shoes of Third World carpenters. Over the years, I have spent a fair amount of time in Central America on various humanitarian aid projects. One of those projects offered me the opportunity to train up a bunch of young men in Western framing techniques by building 4 wood houses. Seeing as how I had traveled to this country by airline, I could only bring along one of my best friends, the Skil 77. My other best friend, a Homelite or Sthil chainsaw, had to stay at home since used chainsaws are restricted from cartage on commercial airliners due to a residual gas fumes fire hazard.

The job was fun and the guys were good strong workers. In no time, they had picked up floor and wall framing basics and we were moving on to the roofs. We used an area out of the rain to rack up the rafters so they could be cut. All the roofs were Dutch Hips so there was a lot of hip jack rafters to be cut. Since I did not have my swing-table for the seat-cuts or my chainsaw/Headcutter for the head-cuts, we were forced to hand-cut all the rafters. Major bummer! This was something I had not done since I was a kid, yet in Second and Third World countries it was the everyday occurrence. This would truly be an enlightening experience, and just as giving demonstrations at JLC Live conferences had opened my eyes to see the typical American carpenter’s dilemma in applying gang-cutting techniques without the proper tools being available, this similar situation now led me to see the world through the eyes of a poor carpenter who was just struggling to feed his family. He possessed few personal tools other than a hammer and the whole crew might possess one electric circular saw to be shared among all.  A chainsaw and Headcutter would make no financial sense whatsoever.

Even when hand cutting rafters, it is still best to use various production gang style techniques to save time and increase precision. Gang marking rafter layout on all the boards in a particular series of rafters is infinitely better than the age-old practice of using a full-length rafter template to mark each board individually. Even lacking specialty roof cutting tools, one can still gang-cut starter passes to save lots of time. To make the head-cut and a plumb tail-cut starter passes on racked lumber, the carpenter would adjust his circular saw’s bevel to match the pitch of the roof, and with the saw blade set to its maximum depth, make a long, rip-style saw-cut across the top surface of the racked lumber material following the appropriate snap-lines. If the tail-cut was to be cut square, the tail-cut snap-line is followed with the circular saw set square (0°) instead of set at the roof pitch’s bevel angle. Although the depth of these cuts will be far short of what is needed to complete them in most cases, they nonetheless provide an excellent physical locator to place the circular saw’s blade when it comes time to finish off the cuts with the rafter boards laid flat. Now with the head-cut and tail-cut starter passes made, the carpenter would adjust the depth of his saw blade to equal the vertical portion of the rafter birdsmouth’s notch and make a saw pass across the top surface of the racked lumber material following the heel-cut snap-line. The heel-cut dimension is found by drawing out a full-scale birdsmouth notch having a 3½-inch seat-cut length and scaling the vertical leg. The saw’s bevel would remain the same as was set previously for the ridge-cut (and tail-cut if plumb) and angle the same direction. At this stage, after the heel-cut was made, the tradesman would lay all the partially cut rafter boards flat on their sides, so he can finish off the starter cuts with his circular saw’s bevel set square (0° on adjuster). The head- and tail-cuts at each end of the board are made first, typically using a handheld adjustable saw guide (a Quick Square® will substitute) or a plumb-cut template.

Plumb-cut and birdsmouth template
Finishing off a gang-cut marked head-cut

After those cuts are made, the carpenter must draw out the seat-cut on each rafter so he will have a cut-line to follow with his circular saw. To lay out the seat-cut correctly, the carpenter’s best option is to use a template-style marking jig that characterizes the desired birdsmouth notch After removing the marking jig, the carpenter makes the seat-cut with his circular saw by following this scribe-line. Accuracy for the seat-cut can be difficult to achieve by sight considering that the cut is very short in length, and the carpenter is making this cut freehand with his circular saw balanced precariously on the very edge of the board. Not only does the front of the saw-foot obscure a good portion of the cut line, but dark-colored wood, especially pressure-treated lumber, and shadows caused by bright sunlight, can cause the cut-line to be practically invisible. All these things only serve to multiply inconsistencies in the finished birdsmouth notch. Variations in the seat-cut cause a poor transfer of roof load to the wall, make installing exposed frieze blocks difficult, create problems installing the fascia, and produce a wavy roof surface

As we waded our way through hand cutting the rafters, my mind was looking for some way to speed up the process. Marking and cutting the seat-cut was the most time-consuming aspect, so I focused my attention on that area. I settled on the idea to make a “ride over” seat-cutting jig that would use the premade heel-cut saw kerf as a reference.

The Original single pitch Seat-cut Guide made for 2x8 rafters

To use the guide, all a carpenter had to do was slide the device’s follower rail along the top edge of the board until the locator tang fell into the existing heel-cut saw kerf. Next, he would position a circular saw against the saw-fence, activate the motor, and push. It was simple and produced a perfect seat-cut every time. Gobs of time was saved since there was no birdsmouth to lay out and the actual cutting process was idiot proof. Since the seat-cut positioning was governed by the top-of-board follower in combination with the heel-cut alignment tang, the heel-stand on every single rafter was held constant. By incorporating a cutting stop on the saw-fence, excessive overcut at the notch was eliminated. By using the guide, I estimate we cut 30% from the time it would have taken to cut the rafters on those four homes as compared to without it. Everyone on the job loved that little guide. Its success got me thinking that a variable roof pitch version of the guide would be a great help for carpenters who hand cut 2x rafters individually. Eventually, I had a design that fit all the needed parameters and we christened it the Seat-cut Guide.

Cutting demo video click HERE.  
Guide setup instruction video click HERE.

The Seat-cut Guide is a great option for everyday carpenters and small builders who can not justify the expense of fancy gang-cutting tools. The device solves the common problems associated with the layout and cutting of 2x roof rafters done individually. The Guide, by functionality, automatically positions a preset perpendicular saw fence relative to an existing cut for a precise birdsmouth notch. It automatically sets the heel-stand distance equally on every board cut in a series negating the need to measure and mark each individually. A cutting stop is also incorporated to eliminate excessive over cut when making the perpendicular notch on lumber material. The Guide has been geometrically designed so that when adjusting the saw fence to any roof pitch shown on the graduated common rafter scale, the length of the resulting seat-cut will be approximately 3.5 inches long (the industry standard). If desired, the birdsmouth size can be enlarged easily by a simple adjustment.