Archive for April, 2009

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Here’s My Pitch … on Progressive Pitch

April 22, 2009

Despite my best intentions to revive my blog, about the closest I’ve come thus far is having numerous ideas for blog entries while working in my shop! So let’s see if I can do a little better. Let’s get into some saw stuff.

I recently met with a customer who asked me what I thought about progressive pitch. Most of you probably know, but for those who don’t, progressive pitch is when the teeth at the toe of the saw are finer than the ones at the heel. And they gradually progress in fineness, from their finest point at the nethermost part of the toe. You can do it so that just the first so many inches of the saw have progressively bigger teeth, before the full sized teeth are reached and obtain for the rest of the blade. That’s what you see on old rip saws. Or you can do it so the size of the teeth slightly increases down the entire blade, like you see on the Le-Nielsen progressive pitch dt saw. In either case the idea is to take stress off the toe of the saw by making the teeth smaller. Depending on how you start your cuts, this feature can make starting your cuts easier, but moreso it eases stress on the toe of the saw with every single stroke.

So what do I think about progressive pitch? That’s one of those things that you get asked a lot as a saw maker. At first blush it seems like something that would be a great idea for every saw in the universe. Easy start, easy reentry, get a big bite back near the heel, etc., etc. But like lots of things with saws, it is a bit more complicated than that once you think about it a little more closely.

Here’s the deal–to ease the cut at the toe of a saw that already has relatively fine teeth, placing yet finer teeth in front of them is not actually necessary. The teeth that are already there are fine enough that you can simply adjust their rake and achieve the effect you desire, a simpler solution to the same problem. What’s more, I find that easing the rake of the teeth is a much more sensitive way to tune the saw than messing with its pitch. Adjusting the rake gives you essentially infinite adjustability, whereas progressive pitch is kind of a one shot deal. Of course you can adjust the rake on a saw that has progressively pitched teeth, but if you are going to adjust the rake, why bother with the progressive pitch to begin with? So basically I don’t think progressive pitch is of much use for a backsaw. I just don’t think it is the best solution.

Progressive pitch actually becomes necessary when the teeth of a saw are large, and adjusting the rake of those teeth near the toe would not sufficiently ease their aggressiveness there. This is what makes progressive pitch very useful for full size rip saws. The large teeth at the toe can grab and cause the saw to bow. In fact I think progressive pitch is the perfect solution to that problem.

You might wonder, then, what if you made a backsaw that had pretty large teeth near the heel and had tiny teeth at the toe. Maybe you could get the best of all worlds–an easy start and a super aggressive and fast cutting saw. Well, here’s one thing that is very true about saws–they are extremely symbiotic tools, in that all of the elements in a given saw affect each other and need to exist in a kind of balance. So with big teeth, that means that the work done by the saw is going to be divided among fewer teeth, and therefore it will place greater strain on each tooth—-and therefore bigger teeth require a thicker plate to support the bigger teeth. Big teeth on a thin plate can make the blade buckle or distort. How much thicker does a plate have to be to support bigger teeth? I don’t know, thicker than I want to use. On tenon saws, the backsaws with the largest teeth, I still find adjusting the rake to be a superior way to tune the saw.

And lastly, I’ve seen the idea floating around out there that modern saw makers don’t do progressive pitch simply because the vintage machinery they use to tooth their saws does not do it, and the makers let the machinery dictate the design of their saws. I can’t speak for everyone of course, but for me at least that is nonsense. For most saws, there are far better reasons not to do progressive pitch than that.

(Please Note: Chris’ question below is based upon a previous draft of this entry in which my thoughts were not as clearly stated. After answering his question and rereading my entry, I decided it would be best to edit the entry for clarity as opposed to leaving it the way it was and leaving so much clarification in the comments.)

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