Though I liked high school as much as a three-year-long colonoscopy, there are sometimes when it takes a high school teacher to teach you something.
In this case, it was a high school physics teacher who taught me an important lesson about tenon saws. Here’s the story.
For the last few years, I’ve been trying to explain to people how a freakishly huge tenon saw is actually easier to balance on your work (no matter what the size of your work) than a smaller tenon saw or sash saw.
“It’s the higher center of gravity,” I implored to a room full of blank stares. “It’s higher – that gravity thing – so it’s… easier. You know?”
This is a truth I know in my gut. The Wenzloff & Sons Kenyon-style tenon saw I’ve been using for the last couple years is a breeze to balance. This is despite the fact that the blade is 19” long and it feels like there is almost 6” of blade under the huge and heavy brass back. When you see this saw, your first instinct is to think: That saw is going to tip and stagger like Gunsmoke’s “Festus.”
But once you try this saw, you think differently.
But try explaining that to people. After my feeble attempt, a high school physics teacher jumped into the conversation. He said this is easy to explain: Try balancing a broom up in the air on a few fingers. If you have the bristles on your hand, it’s harder to balance the broom than if you have the bristles in the air.
This, he explained, is why the big tenon saw is easier to balance in the air. Having the weight up in the air makes it easier for you to sense if the saw is out of balance and to make corrections. This, I concluded, is a brilliant explanation.
Back in our shop in Cincinnati I tried this experiment with our shop broom. It really was easier to balance it with the bristles in the air.
So I used this analogy last weekend to explain the tenon saw to a group of 40 or so woodworkers. To demonstrate, I looked around for a broom. No luck. So I picked up my Warrington hammer to show them how this works.
First I put the hammer head in my palm and showed how shaky it was. Then I balanced it with the head in the air. And my precious and very early Warrington hammer plunged to the concrete floor.
Dang. I still dislike school.
— Christopher Schwarz
Ha! I didn’t see that one coming. That’s hilarious (when it’s not you, that is).
Or, perhaps you meant "When it’s not me." After all, tragedy is when I slip and fall. Comedy is when you slip and fall.
An alternative explanation:
Try balancing a 4-foot broom vs. a 1-foot broom. The 4-foot broom is easier since the adjustment at the hand does not need to be as precise to maintain the balance.
If the back of a 2" deep saw is displaced laterally 1/16" the effect on the kerf angle is greater than if the back of a 4" deep saw is displaced laterally the same amount.
So now we’re all going on eBay and get a pair of 26" Disston miter saws, filing one crosscut and one rip so that we can have uber-freakishly huge carcase and tenon saws. If some is good, more is better, right? Well, at least that applies to ice cream.
Chris,
Being the proud owner of the same freakishly huge tenon saw I know first hand from whence you speak. In addition I have certain limitations that have taken away some of my strength, but once this saw is in place on a board that is to be cut, it is childs play to use.
As you know I cut a tenon with this saw that was only 1/4" thick that you deemed best of a class of tenons cut with other saws.
One really needs to use the saw to understand why it’s so easy to use, only then will others realize the hidden strength of this great saw.
Michael
Dang, I just finished renovating two old Disston backsaws, and I filed the smaller saw rip and the larger saw cross-cut. Based on this explanation, I should go back and refile so the the large saw is rip and the smaller is cross-cut. Correct?
Chris,
For your readers who may want a more scientific explanation (and to start putting my 4 years of engineering education to use) the reason for the Kenyon saw being easier to use is due to its larger Moment of Inertia compared to the commonly sized tenon saws we see today.
In its simplest form, Moment of Inertia describes how difficult it is to change an objects angular motion around a fixed point, or axis. In this instance (the Kenyon saw) the axis would be the point of contact between the wood and the saw teeth, or in the broom example, the tip of the handle and the palm of your hand.
The role of moment of inertia in saw design can also be seen in dovetail saws, where the low moment of inertia (due to its short blade height) helps the sawyer to more easily make corrections to the saw plane in order to follow the layout marks.
Now before you all put your current tenon saws up on eBay, they still have a valuable role, and that is when it comes to cutting tenons on odd shaped pieces that when clamped in your bench, do not present a vertical tenon, or sawing plane, and thus the saw must be tilted to saw. Tilting will be easier accomplished with a lighter, and easier to handle saw.
For more information, just type Moment of Inertia into Wikipedia.
Rob Plumridge
Chris, I understand how your tenon saw is easier to use. What I don’t understand is how you remember Gun Smoke! I don’t think you’re old enough for the original shows, so you must have caught "Festus" on reruns.