Do you agree?

[Ed62]

I'm trying to learn more about blades, and I'm reading an article about them. Part of what is said is "The more teeth, the faster the blade dulls, for three reasons: First, when there are a lot of teeth, each tooth takes small chips, which gives a smooth surface with little breakout and chipping, but each tooth hits the wood more often, and the initial impact against the wood is a serious dulling factor."

I'm certain the author knows much more than I do about blades, but how would the number of teeth affect how often each tooth hits the wood? It seems to me that the blade speed, not the number of teeth, would determine how often the tooth cuts the material. Is the reason he's saying what he says because more teeth typically means slower feed rate (thereby more revolutions)? Why doesn't the text register correctly in my small brain?

Ed

[cabinetman]

Ed

This is an excellent question. There is a mathematical solution to answer this in a manner that is easily understood. You take the number of teeth and divide that number by the circumference in inches, which will give the number of teeth per inch of circumference. Circumference = PI x D. You should use a tailors tape because not all 10" blades are 10" in diameter.

After you have figured all that out, realizing that the absolute determination of how many times a tooth hits the wood depends on how fast it is fed and the ultimate angle created by how high or how low the blade is set, and the thickness of the wood in relation to how many teeth per inch of the blade.

So, in the final analysis, the more teeth a blade has is proportionate to how long the teeth stay sharp. What I'm saying is that I'm trying to give you an answer that will allow you to finally get this off your chest so you can get some sleep at night. I know what you're going through. Dilemmas like this throw my whole schedule off.

The more teeth a blade has may not stay sharp as one with less teeth, if you use it more than the one with less teeth. Other factors affect the outcome, such as the ambient temperature each blade was used, and how much heat was created in each set of teeth for the different woods that they may have cut.

I will say one thing though, considering the criteria needed to determine this is that a sharp blade cuts better than a dull one.



A THING OF BEAUTY IS A JOY FOREVER - John Keats

[Ed62]

I understand the last part. Now I'll go back and read the rest. You're right about not sleeping when things like this happen. Thanks for the post.

Ed

[cgallery]

I'm certain the author knows much more than I do about blades, but how would the number of teeth affect how often each tooth hits the wood? It seems to me that the blade speed, not the number of teeth, would determine how often the tooth cuts the material. Is the reason he's saying what he says because more teeth typically means slower feed rate (thereby more revolutions)? Why doesn't the text register correctly in my small brain?

Ed

Well, actually, don't be certain the author knows more than you do. Quite often the author majored in journalism or mass communications and has a minor (if you're lucky) in the field he is explaining.

I look at it in terms of the amount of material being removed divided by # of teeth. More teeth should actually translate into staying sharp LONGER. However, more teeth also implies a finish quality blade. That means you are going to want to keep it sharper than a rip blade (for example), to maintain high cut quality.

So more teeth means staying sharp longer. However, it also means that it has to be kept super-sharp, so may actually require more frequent sharpenings than a rip blade.

Someone please feel free to shoot this down if I'm wrong.

[Ed62]

That's a good thing about forums like these. People have different ideas about things. Often two people can look at something from a different point of view, and both come to the same conclusion. Of course it didn't work that way this time. Any other thoughts on the subject?

Ed

[Knottscott]

I don't know the answer with any certainty, but it doesn't make alot of intuitive sense to me that a higher tooth count blade would dull faster than a lower tooth count blade (assuming all else is equal). The teeth on the higher tooth count blade aren't under as much stress as the lower tooth count blade...the work load is shared more per inch of cut and the amount of material removed is much smaller with more teeth. The logic should be similar to a planer with a 3 blade cutterhead vs 2 blade. The 3 blade should leave a smoother surface, and shouldn't dull as fast.

[lcm1947]

I would think that a fewer tooth blade would dull quicker. Don't you feed the wood faster through with a fewer tooth count whereas it's taking bigger bites whereas dulling it faster?

[jseklund]

Well, actually, don't be certain the author knows more than you do. Quite often the author majored in journalism or mass communications and has a minor (if you're lucky) in the field he is explaining.

I look at it in terms of the amount of material being removed divided by # of teeth. More teeth should actually translate into staying sharp LONGER. However, more teeth also implies a finish quality blade. That means you are going to want to keep it sharper than a rip blade (for example), to maintain high cut quality.

So more teeth means staying sharp longer. However, it also means that it has to be kept super-sharp, so may actually require more frequent sharpenings than a rip blade.

Someone please feel free to shoot this down if I'm wrong.v

I think you may be onto something here. I think most of us would agree that more teeth should mean that during each revolution, more cuts are made. For instance, if I have 20 Teeth Per Inch (TPI) than one revolution will hit the wood 20 times. If I have 30 TPI, it will hit 30 times in one revolution. This, to me, would mean that more teeth disperse the labor of a cut, all other things being equal, over more surface area. In other words, more teeth should actually mean that a cut takes less of a toll on each individual tooth, and thus the blade should stay sharper longer.

However, in the quote above, an important point is mentioned. Higher TPI is used for finishing. Maybe sharpness, like time/space, is relative. Sharp has to do with the angle of two planes meeting at a point. One of the factors in creating a blade is it's purpose. For instance- a surgeon's knife has two planes that intersect at a very small angle but does not have a lot of metal behind it. This is perfect for slicing through delicate objects with precision. An ax on the other hand isn't quite as fine an angle, but has a hunk of metal behind it for support. If you try to cut a tree down with a surgeon's knife- it will be sharp, but will dull very quickly (and probably won't cut down the tree anytime soon). If you use the ax- down comes the tree. You won't make a fine cut with it on a human though. So, do to the construction of the blade, the ax will stay sharper longer than a surgeon's knife when used for it's application.

Another point to consider- after a few hack's at the tree with the knife,the blad will have dulled, but if it's not broken yet- you can probably still cut yourself on it and think it's pretty sharp. It just won't be sharp enough to do surgery with anymore. A few more hacks and it will dull even quicker. Relative to it's purpose, it will lose sharpness very quickly, but will still probably be sharper than the saw by other measures (like shaving).

So, if any of that makes sense- the higher TPI may techically stay sharper longer, but if you use it for the wrong purpose (ripping,etc)- it will lose it's sharpness relative to its purpose very quickly.

Hope this makes sense. Also- it's total conjecture based on what little I know about sharpening....

[Ed62]

I would think that a fewer tooth blade would dull quicker. Don't you feed the wood faster through with a fewer tooth count whereas it's taking bigger bites whereas dulling it faster?

You might be taking more stock off with a lower tooth rate, but you are also taking fewer "bites". I'm not saying you're wrong (because I don't know), but I'm giving something else to consider.

When I know the "Why" of something, I feel like I know what I'm talking about. Without knowing the "Why", I might form an opinion on something, but really have nothing substantial to back up my thoughts. Keep 'em coming!

Ed

[Knottscott]

In my initial response, I answered using the assumption that all other parameters except tooth count were equal. "jseklund" brings up a good point that makes more real world sense than the assumption used in my example....the geometry makes too large of a difference to ignore. His other excellent point is intended use.

High tooth blades usually have a very different geometry, grind, and configuration than a ripping blade, or even a general purpose blade. The type of grind used makes a big difference in how a long an edge stays sharp....possibly a bigger difference than tooth count. Many high count blades use an alternate top bevel ATB grind, while most rippers use a flat top grind (FTG) which definitely wears better than an average ATB....the steeper the bevel, the sharper the point, and the faster it will dull. Some of the high count blades actually use a steep bevel....some even crossover into what's known as a Hi-ATB grind. In contrast to a Hi-ATB, a triple chip grind (TCG) has chamfered edges on many of teeth, which wear really well...the balance of the teeth are FTG which also wear fairly well.

The hook angle can make a big difference too....a low to negative hook angle creates less impact force on the tip than a steep hook. Combine a negative hook, a TCG grind, and a high tooth count, and you've typically got a blade that'll wear very well if used for the intended purpose. In fact, most non-ferrous metal cutting blades are an 80T TCG with a negative hook. It seems logical to me that a 24T ATB ripper with a steep hook angle like the Freud LU87 would dull faster in aluminum than a non-ferrous 80T TCG with a negative hook angle because the sharp points would abrade rapidly in the aluminum. Inversely, the non-ferrous blade would overheat in thick hardwood, and would result in a burned cut and premature dulling relative to the LU87. I could be wrong, but that's my logic.

[jackellis]

Tell me again. How many angels fit on the head of a pin?

[LCHIEN]

I'm with CGallery on this one. Never assume someone whose article is posted on the web is smarter than you.

I used to say anyone with a $10 account could post on the web, but now there's free accounts all over the place.

Anyway, you have to rate the website and the authors credentials and the possibility it was counterfeited (e.g. attributed to so-an-so, a trustworthy person, but it was not really). And the possibility he just made a mistake or is dead wrong. I see so many wrong things posted on the web, esp.
on news sites like AP and Reuters about technical subjects that I know a bit about, so I question everything.

[Ed62]

This article actually was not posted on the web. It's from a book I got from the library. The book is "Power saws and planers--The best of Fine Woodworking". The author was Jim Cummins, who was an associate editor of "Fine Woodworking". The book's first printing was 1990, with the second printing in 1993. Since he was/is? an associate editor, I think it's safe to say he knows a lot more than I do about the subject. I could follow most of what he had to say, but there was a time or two that I had a hard time understanding.

Ed

[Black wallnut]

Ed I for one suspect everything I read. For what exactly makes an author an expert at anything other than perhaps writing. My thinking is that with HSS blades he is correct but with modern carbide tipped blades I am doubtful that he is corrct. Yet he may be wrong on both counts. With hand saws I'm pretty certain that lower tooth counts stay sharp longer due to the size of each tooth but with round blades I think the sharpened edge on each tooth is the same with each different profile. A flat cut grind tooth's sharp edge will be the same size no matter what the count per blade. I am not saying that all teeth are the same, just that all teeth of the same shape will be the same as long as the blade width remains the same.

I think the frequency of use and type of use, i.e. ripping, crosscutting, or type of wood cut, will have a much higher imopact on length of usable sharpness than tooth count. To wit the blade you use the most will dull the quickest. Which for me is an 80 tooth blade, but I also will have cut 100's of feet of all types (or at least the types I use) of lumber and many different types of cuts i.e. rip, cross, planeing ( taking just a small amount off, not even a tooth width). Just about everything other than dado.

Final answer: I think he is wrong.

[onedash]

Isnt heat what causes sharp objects to dull faster than normal?
A hand held chisel "probably" never gets heated up during use.
A saw blade, drill bit, router bit jointer and planer knuives all get hot when used.

So based on what I have read about bandsaw blades the high teeth count blades can not move material out of the cut as effectively as the low teeth count blades and would heat up faster and wear the blade out prematurely.
Now carbide might be a whole seperate issue but wouldnt the same hold true?