A reader emailed me today asking about why his 5 point Disston rip saw isn’t cutting any faster than his Lie-Nielsen 11 point thin plate tenon saw. I get this kind of question a lot and thought it would make a great post. Here’s my response to his question….
I think you’re comparing apples and oranges here. Should the Disston be faster than the L-N? Well, that really depends on what you are cutting. Is the point of a 5pt rip saw to cut faster than an 11 point tenon saw? Not exactly. Speed of cut is important and one of the benefits of using a coarser saw, but there are limits. You wouldn’t want 5 points on a 0.020 thick tenon saw plate (which your L-N has)….the teeth would heat up and deform, and the plate would turn into spaghetti in the kerf. Bigger teeth need a thicker plate to disperse the heat generated by friction in the cut, so 10 or 11 points is about the limit in size for a saw plate of that thickness. Generally speaking, coarser tooth spacing (= bigger teeth = lower ppi) cut faster because they take bigger bites of wood. So why not use a thicker plate on a tenon saw and make bigger teeth so it cuts faster? Because a thicker saw plate means cutting a wider kerf, which requires the removal of more wood, and that slows the saw down because it has more work to do and you gain nothing.
Look at it like this: Your big Disston rip saw with 5 points per inch has a saw plate around 0.042 inches thick and should be set to cut a kerf around 0.050 inches total width. But your L-N tenon saw has a 0.020 thick plate and should be (hopefully!) set to cut a kerf 0.024 inches thick. So…
5 pts : 0.050 inch
11 pts : 0.024 inch
Do you see a relationship?
While the 5 point Disston has teeth twice as big to do the work, it has to cut a kerf twice as wide as the L-N. So both saws are really removing a similar amount of wood relative to their tooth spacing. There are other variables at play in determining speed of cut, namely, the thickness of the work and also the rake of the saw teeth. And there’s more. Lots more. Bottom line is that there is a lot to figure when determining how fast a saw will cut.
So what does all of this mean? It means you should match your saw to your work. Thin plate tenon saws are great because they allow great precision in cutting joinery….like tenon cheeks that split your layout lines. Rip saws don’t need anywhere near that kind of precision….you want them to hog off wood like a billy goat on crack and you want a nice thick saw plate to disperse that heat so that the saw plate doesn’t warp and throw you out of true.
Hope that helps.