View Full Version : geometry of saw blade teeth

03-08-2009, 04:18 PM
i have spent nearly 3 hours googling to try to find information about sharpening round saw blades, both carbon and carbide to no avail.

im looking for tooth geometry stuff.

could someone point me in the right direction ?

i did find some u-tube clips showing some guys doing it with some explaination that i found useful but i would like more, including drawings.

i want to sharpen blades with my adrian ace grinder. . .

my tool repair business is really slowing down around here and i need to use some of my hobby stuff to help buy food and pay the dang bills until things pick up..

any help would be greatly appricated.


doctor demo
03-08-2009, 04:59 PM
i have spent nearly 3 hours googling to try to find information about sharpening round saw blades, both carbon and carbide to no avail.

im looking for tooth geometry stuff.

could someone point me in the right direction ?

any help would be greatly appricated.

David, it has been My (limited) experiance that every blade maker has a slightly different tooth config.
I have sharpened cheap carbon Skillsaw blades by hand with a file and it works well, if you don't let the blade get too dull.
I guess that You are talking more along the lines of more than a blade or two though.
Machinery's Handbook has a section on sharpening mill cutters, and a lot of the same principals would apply. If You have a copy give it a look , back clearence etc. is shown.

On the cutters and blades that I have sharpened for myself or as a favor for friends, I just match all the existing angles as best that I can. No body has complained yet.
I have sharpened : 7-1/4 '' through 12'' saw blades, Rotobroach cutters, holesaws and other misc stuff along with mill cutters.


Paul Alciatore
03-08-2009, 06:30 PM
Each tooth on a saw is essentially a single point cutting tool. There are just a lot of them in a row. So the basics of cutting tools apply directly to saw teeth. Each tooth must have a rake angle, back clearance, and side clearance just as a lathe tool would have.

The front face of the tooth forms the rake angle. It is measured from a perpendicular to the line of action as it cuts. It can vary depending on the material the saw is intended to cut. Wood saws would have a larger rake and metal saws a smaller one but this is not hard and fast and you may find examples contrary to this. Most saw teeth have a combination of back and side rake: more on this below.

Any cutting edge of point must have clearance in order to actually cut. If there is no face clearance, the edge can not penetrate the material being cut: the side lands on standard twist drills are an example of this. These lands on the sides of the drill flutes give it a zero sideways clearance so that they will not cut sideways (at least not easily).

Saw teeth have back clearance formed by the rear face of the tooth. A problem arises here since usually the same cutter is used to cut the front of one tooth and the back of the previous one. The simplest cutter used to sharpen saws is a file, ususlly a triangular one with 60 degrees between adjacent faces. So, the back clearance on many saw teeth is relatively large. Using a triangular file, the clearance angle automatically becomes 90 degrees - (the rake angle + 60 degrees) or 30 degrees - the rake angle. Hence the most common saw tooth form that you will see. I guess this turns out to be a good thing as most saws are sharpened in this manner. However, a second sharpening operation on the tip of the tooth can reduce the clearance angle to any smaller amount desired.

Side clearance is also needed or the saw will stick in the kerf. This can be generated in different ways. One is to offset the teeth alternatively; left, right, left, right, etc. This is done by just bending them and special tools are made for this purpose. They can also be offset in other patterns such as the wavy set where they are offset in a sine wave like pattern and ten or more teeth form one cycle of this pattern. Another way of providing side clearance is a hollow ground or tapered saw blade. This is where the cutting edge of blade is thicker than the rear or inner part for circular saws. So the cutting edge of the teeth is wider than the blade behind it and it effictively has side clearance.

I spoke of a combination of back and side rake above. Saw teeth that have an alternate offset will often have alternating side rake also. This allows the teeth to cut sideways a bit better, which is good for allowing you to follow a curved line when cutting. Or to make adjustments to follow a straight line better. So when sharpening staggered teeth, it is desirable to change the angle of the tool for every other tooth. Or more likely, do every second tooth and then change the angle and then do the other half. This can also be done on wavy set teeth, but several teeth would be ground at each angle.

The above is just some basic ideas. There are many, many tooth forms on saws designed for many different cutting situations. One of the most important things to do when sharpening saws is to observe the original form and duplicate it as appropriate. Also, any good shop book should have information on saw tooth form and sharpening.

On a grinder you would probably want a cup style wheel with a 60 degree edge. But much can be done with a triangular file. Same number of strokes and same pressure on each tooth. With a little practice, angles can be set by eyeballing it. Observe the results under magnification (5X or 10X) and adjust technique accordingly.

john hobdeclipe
03-08-2009, 07:54 PM
Wood cutting saws or metal cutting saws?

03-08-2009, 10:31 PM
both if possible.

thanks for the info so far. lots to consider.

03-09-2009, 12:24 AM
I dont know what your grinder is capable of, but for wood cutting circular saws, you will probably see mostly, rip and "combination" styles with the rare crosscut. But most important, they will only be DULL; they will still have the original tooth angle, (at least on SOME of the teeth!) Something you might consider is sharpening chain saws. I will say this to a group of machinists:-most chainsaw owners HAVE NO IDEA how to properly sharpen a saw, or worse yet, WHEN it needs sharpening. The same is true of kitchen knives. Be honest now, how many of you, (us?) can hold your, (our,) hand over the candle and truthfully say "my kitchen knives are all sharp and therefor safe!" All that being said, you would have to come up with some realistic pricing to generate the business. But there is absolutely no question that the dull tools are out there. Duffy

03-09-2009, 04:48 AM

Most people can't sharpen a kitchen knife because they are pieces of crap. Most are serrated, saws, which can't cut anything.

Any that are actually edged are so soft they will MAYBE cut one slice of bread, then be dulled.

A 50 buck knife, and a good steel with it, maybe you can slice the annual ham.

I can say MY kitchen knives are sharp and safe. Mine are carbon steel, and good carbon steel, and the ones I use daily are some you would not use. Dexter, Russel made, and I'm down to my last dozen. 1/32 thick and bend 180 and they come back straight.

Two of my kids love them. The other hates them because you shouldn't HAVE to clean them after every use. They SHOULDN'T rust if you use them and throw them in the sink.

So I don't give her any more of them. She can keep chopping at stuff with blunt edged crappy cutlery.

Carbon or steel blades, saw wise, you have to decide if you want life or cut from them. Sharper angle, better cut, shorter life between grindings.

Carbide, what the hell, most is neutral to negative rake. A sharp tooth doesn't cut much better than other blades. Carbide cuts a more coarse chip and takes more power to turn.

I prefer steel blades on my saws.

Chainsaws, I will agree with Duffy, everybody grinds the hell out of the tooth and feels they got it, but if you don't grind down the gaugers and rakers you got ****.

Anybody looks into the "Chain Saw Derbys", 2 foot log in 10 seconds will see that they have really radical grinds. Most saws would probably not take the punishment, BUT, chains can take one hell of a cut. Way more than the pussie saw you will get from HD or Lowes or Sears.



John Stevenson
03-09-2009, 06:10 AM
From watching professional saw sharpening machines work I noticed that they ground each tooth off the blade.
By that I meant that the direction of the grinding wheel threw the burr to the outside of the blade.

Some of the German swing grinders swap rotation of the wheel every swing so they can do it tooth by tooth, some of the ones working on the flat do every alternate tooth then swap rotation and do the other teeth.


03-09-2009, 08:33 AM
my "Ace" is designed to run both directions. uses a 3 or 4 inch cup wheel or diamond blade (i don;t have the diamond yet) and will sharpen up to, i believe,16" blades. plus cutting tools, anything with a straight tooth.

really a neat 1200 lb grinder.

they are still sold at about 22 grand plus fixtures. . . . i stole the thing. fixtures are pretty straight forward so i;ve been whittling a way at building them.

i should take a pix of it and post it after i get more of the fixtures done.

03-09-2009, 11:51 AM

These get good reviews from woodworking mags. You can glean some info from their specs.

http://www.foley-belsaw.com/ has large catalog of sharpening tools and supplies, maybe information.

john hobdeclipe
03-11-2009, 08:53 PM
I used to do this in a production environment, for a large furniture factory, and would like to pass along what I remember from those days (25-30 years ago.) This is all concerning carbide tipped saws use for cutting wood.

Woodworking saws will have hook (or “rake”) angles that vary from about -5 degrees to about +20 degrees or sometimes more. You never know, when you first get a saw, exactly what the hook angle is, or was intended to be. Often a previous saw guy will have ground it poorly, and you have to decide whether to try to follow his work or try to get it back to the factory specs.

To grind the faces, you'll need to determine the hook angle. I'm assuming you have an attachment for your grinder that will adjust for various saw diameters and also allow you to swing the saw around to adjust the hook angle. You'll need a flat plate that fits on your grinder in place of the diamond wheel. I made mine from the aluminum body of an old worn-out diamond wheel. Put it on your lathe and machine a flat on the face (where the abrasive would otherwise be) that is, say, to 3/8” wide. Or you can mount the wheel on the grinder, spin it up, and machine the flat in situ, with a lathe tool mounted to the grinder's bed.

To determine the hook angle, mount this set-up wheel on the grinder, put the blade on the blade holder, bring a tooth face against the index finger, clamp the blade, drop the finger out of the way, and carefully bring the blade up to the set-up wheel (the wheel is NOT turning,) tweaking it into position so that you can see, with a magnifier, if the tooth face is parallel to the machined face of the wheel. Adjust accordingly until the tooth face and the wheel face are as close to parallel as you can get them. Make a note of the hook angle.

Now you can replace your set-up wheel with a grinding wheel and start grinding the faces, taking off no more than .001” per pass, preferably a bit less. Make one pass on each tooth face, all the way around the blade, then if needed start another round. How many rounds you need to make depends on how dull the blade is. Don't try to get all at one time, the blade, blade holder, and grinding wheel will find a way to flex and give a bad, un-flat grind. There is a definite limit to the volume of carbide that any particular grinding wheel can remove in a given amount of time. Try to take off more than that, and something has to flex, or break, or overheat to the point of damage.

Take about half of the worn edge off by face grinding, and get the rest of it when you top grind.

Remember that a degree or two one way or another from the original factory grind will never be noticed...it just doesn't matter as far as the cutting action goes regardless of all the advertising crap that the popular name brand blade sellers will tell you. But it's important to stay as close as you can to grinding parallel to the BACK of the tooth, to maximize tooth life. You'll need to obtain some special, thin rimmed diamond wheels to do the faces of saws with a lot of teeth, as the space in the gullet in front of the tooth can get pretty tight.

Setting up to grind the tops of the teeth is about the same, except that you have a much smaller area of carbide to try to line up to the set-up wheel. You can fake it here, though. 8 to 10 degrees top clearance will work for just about every wood cutting situation. You need more clearance in wood cutting saws than in metal cutting saws, because the wood fibers spring back a bit after the edge passes, and will rub and cause heat build up. But too much clearance simply makes the cutting edge weak and the saw will dull more quickly. If you must go down to about 5 – 6 degrees to keep from grinding the steel behind the tooth, that won't really hurt anything. Less than that and the tips will quickly gum up behind the cutting edge and create more heat.

Side grinding is the hardest part to do. You don't have much room between the tooth you're grinding, the teeth in front of and behind it, and the saw plate. If you don't have a double side grinder, which does both sides of the tooth simultaneously, you have to set up a very rigid system to keep the blade from flexing as the grinding wheel tries to push the tooth away. Some machines are designed to flat grind the sides, others do a hollow grind. Some grindermen prefer one way, some the other, and it gets argued endlessly. I don't care. It's still a pain without special equipment. My experience is solely with a double side grinder that did hollow grinds. We used 1/2 to 2 degrees of radial clearance, and 2 degrees of tangential, if my memory is correct. Radial clearance is where the top of the tooth is wider than the bottom, tangential clearance is where the face of the tooth is wider than the back. It's important to keep the tooth ground so that it is exactly centered on the plate, and to have all the teeth the same width.

One problem with hollow grinding the sides is that, as you progressively grind away the face, you lose tangential clearance until you need to re-grind the sides whether you want to or not.

Our practice was to run a sharpening cycle, thus: 1. Face grind. 2. Face and top grind. 3. Face grind. 4. Face, top and side grind. Repeat the cycle until the blade needs to be re-tipped. I had a log book of every blade in the factory, (a couple hundred or so) and kept running entries of everything we did to the blade. The log book included info on the blade diameter, plate thickness, bore, number of teeth, hook, top, and side clearance angles, and which machine it was released to, run time, problems, etc., plus our service to the saw, such as grinding, tooth replacement, retipping, outside work, etc. If you are sharpening saws for the public, this may be pointless, but on the other hand if you have repeat customers, it may save a lot of time and money. At the very least, when you finish a saw, take an engraver and write the specs on the blade, down close to the bore where it won't get polished off by the next guy.

Below are three scans of explanatory drawings from “Armstrong Carbide Filer's Handbook” posted with the kind permission of Armstrong Manufacturing Co. (http://www.armstrongblue.com) This book is a good source for info on carbide saw grinding, terminology, etc. It's targeted more for the sawmill crowd, but has a lot of good info that can be applied to smaller saws too.

And this is a good outfit to get diamond wheels from (assuming they will fit your machine, or can be modified to fit.) plus other saw servicing supplies. Equipment Ltd. (http://www.equipmentltd.com)

The Hanchett Saw And Knife Fitting Manual is available from Hanchett Manufacturing. (http://www.hanchett.com) It also targets the sawmill industry, but has an excellent discussion of saw plate stresses, hammering, leveling and tensioning.

Usual disclaimers apply...I'm not connected with any of these companies in any way.

If I've only managed to confuse you with all this, let me know, and I'll be pleased to confuse you a bit more.




03-11-2009, 10:27 PM
that was the pictures that i was hoping for. thanks all of you , for the information. . . . carrying forward and hoping. . . .