T.P.I. vs P.P.I.

If you’re like me and you find yourself falling further and further down the rabbit hole we call hand tool woodworking, then you no doubt have a laundry list of questions that are waiting to be answered by the long deceased hand tool deities. So, it can only be expected in my quest to revive the once grand love and labor of hand sawing that my list includes everything from how much set should a hand table saw have to what the heck did they do in the “jimping room” at the Disston factory?!?

One such question that was on my list for a while was the difference between the traditional English pitch measurement, and the American measurement. Pitch, in case you are wondering, is the number of teeth that a hand saw has per inch and is given in two different standards: teeth per inch (TPI) is the traditional/British measure and points per inch (PPI) is the American gauge.

It’s fairly simple to determine the difference between the two (we’ll get to that in a minute) but it is entirely another animal to know what gauge a person, sawyer, or even saw smith is using with certainty, because I found many people using the two gauges interchangeably. And even more annoying, I found that very well versed people would do so. Just because someone said 6 ppi didn’t matter because they could in fact be measuring full teeth and not in fact the points as ppi would indicate. And just so you know I’m not harping on insignificant details, I’m referring to major hand tool retailers, makers and users….and in situations where they were describing goods and services (and no, I’m not talking about the Home Depot website…I’m talking our people here!)

So, in case you’re like me, and you long for accurate language, then here’s a quick tutorial of what I’ve learned and how to gauge the pitch of a saw:

Teeth per inch (TPI) is the traditional method that Englishmen brought over from the old country. When measuring the teeth, you measure from gullet to gullet, and count only the number of full teeth in one inch. I like to imagine the teeth as little mountains…only count the mountains that have a full left face, peak, and a full right face. I use little brass calipers to make it easier.

Now, points per inch (PPI) on the other hand, is a measure of only the peaks, or points, of the teeth and NOT the full tooth including the left and right face. Because PPI only measures the points and not the full teeth, there will always be one less tooth than points. So a 6 PPI saw and 5 TPI saw are one in the same. American makers like Disston, Atkins, etc., actually stamped the pitch of their saws on the heel…that’s what that number under the handle is…a measurment of the saws pitch, or PPI.

How about some pics to demonstrate…

Here’s a pic of a 4 TPI rip saw…

See how the calipers measure from gullet to gullet and show 4 full teeth?  That’s the 4 “T” in 4 TPI.

Now here’s the exact same saw, but measured in “points”…

See how the calipers measure from the point of one tooth to the point of another tooth in one inch? When you measure this way, you pay no regard to gullets, the faces of the teeth, or anything…just the points. That’s how to gauge PPI. That means this saw is 5 PPI. And if you’re following along at home, you now know that 4 TPI = 5 PPI.

So you see how things can get confusing, right? Here we’ve got the same saw measured two different ways and having two different pitches. The problem in converting from one to another…as you often have to do when buying an English saw…is that you don’t actually know for sure if the measurer used one method over another based solely on the number. What I mean is, its not like converting yards into meters, where the number changes by some small fraction and gives the conversion away (like 1 yard = 0.9144 meters). This is what I was running into in catalogs, websites and blogs….companies or dealers or craftsman would say PPI, but mean TPI and I had no way of knowing what they actually meant without measuring the darn thing myself!!!!!

Like i said…annoyance. But, then again, it was really a matter of just sitting down and first understanding the real difference myself.

Here’s a couple more examples…

Measured in TPI, this saw has 4 and 1/2. Measured by PPI, it equals 5 and 1/2 PPI.

But (and here’s where it gets a little more tricky) because this saw has no negative rake to the teeth, that means the gullet and the top of each tooth are at the same linear point along the tooth line, meaning that you don’t even need to move the calipers to change gauges. Get it?

 As stated above, 4 and 1/2 TPI = 5 and 1/2 PPI….one less tooth than points.

Here’s one more…

Here’s 2 and 1/2 TPI…

And measured in PPI…

…it’s 3 and 1/2 PPI.

So, figuring out the two methods was an important step forward for me. Its important to be able to refer accurately to a saw’s pitch for learning its function, selecting the best saw for the job, and conversing via internet about a perspective purchase.

Confussed? No worries, apparently, half of the hand tool world is too! 🙂

Happy sawing!

-Matt

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Published in: on December 16, 2010 at 8:34 pm  Comments (11)  

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11 CommentsLeave a comment

  1. Why does it have to be an integer number? Why not measure 5 or 10 inches and give the average. Then TPI and PPI would be the same number. If the number is small and this rounding is a real issue then go for more averaging. Thats just my opinion, but we talk about pitch all day and all night at my work, but we measure in nm.

    http://jewelscy.blogspot.com/2006/08/how-long-is-your-micrometer.html

    But I do love my hand tools and my curly maple as much as anyone.

    Great blog, love it!

    • Cyrus
      Good question…but 1 is the lowest demonenator…imagine if people started using other denomenators…then we’d really be confused! Athough I like the idea of using ten.
      -Matt

  2. Can’t we just all use PPI ;). Chris Schwarz goes over this quickly in this sawing fundamentals DVD but your explanation goes into a lot more detail. Thanks for the post.

  3. Hi Matt,

    I allways laugh when I read 5 1/2 ppi. What should half a point be? There is no such a thing.

    Cheers
    Pedder

  4. Okay, I have a stupid question. I am a newbie to the sawyer world. If two people look at a saw together and one says 4TPI and the other person says 5PPI. Isn’t it the same as “you say tomato and I say tomato”(said with english accent and pronunciation).

    Can this mistranslation lead to real differences in the cut?

    BTW, I can appreciate your quest for proper jargon. 🙂

    yaakov….

    • A great question….and yes, it can lead to not only real differences in the cut…not only in finish quality on the cut edge, but the speed of the cut as well.

      Believe me…a 5 PPI saw cuts a hell of a lot faster than a 6 PPI saw…if you’re spending big money on a saw online, you want to know for sure its got the proper pitch!

      Also, being a big saw geek, i like to have saws of different pitches….like D-8 thumb hole rip saws…I like to have a 6, 5 1/2, and 5 PPI. Now this isn’t absolutely necessary, but like I said..I’m a saw geek!
      -Matt

  5. I think that was my point. If you measure 12 inches worth of teeth and come up with 64 teeth — that gives you a better estimate of the real tooth “pitch” of 5.33. No problem with this, it doesnt have to be in integer. Count more get better statistics on your ppi estimate. Also you will get the same number for tti and ppi.

  6. Oh, I get it! That helps a ton.

  7. Matt,

    I am with the understanding that the number we see stamped below the handle of most saws made in America is the number of points per inch. That is if we only measure the number of points in one inch. If we measure the number of teeth in more than one inch, we must then refer to teeth per inch.

    Yes, it is confusing and need not be. If the American saw makers had chosen to stamp the number of teeth per inch below the handle we would not be discussing the issue over and over.

    When I buy a saw, say, on Ebay, I always make sure that the seller tells me how many points per inch, because it is easier for them to measure points.

    You did a good job explaining the differences.

    • Thanks Marv! 🙂 I agree…maybe that’s why American manufacturers changed…they wanted a gauge that was easier to measure?
      -Matt

  8. Hi Matt. Attachment shows the start of my first handsaw build. Regards Stewie

    Hope this attachment works. Let me know if it doesnt.

    http://www.woodworkforums.com/f152/1st-hand-saw-build-128799/


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