Set Tooth v. Swaged Tooth Bandsaw Blades

Many people ask me about wide cut blades.

What are the advantages and disadvantages of using wide cut blades. I have had a good amount of experience with bands up to 12" wide, but for this particular article we will deal with the most popular applications and that is blades in the 2"-6" width.

Let's start with the tooth of the bandsaw blades.

We know that tooth load is very important with all bandsaw blades, and keeping tooth load down per square inch is the most important thing that a sawyer/sawfiler can do to preserve his bandsaw.

For an illustration of this let's look at the teeth of a swage tooth or a welded tooth band. Note that all comparisons will have to be made of equal width bands for this comparison to be accurate. The swage tooth and the welded tooth have a full tooth width at the top or the leading edge. The full tooth has three cutting edges. It has the top or leading edge and the two sides.

The tooth load is created by all edges that cut wood. The tooth width on these type blades are usually twice the width of the body. For instance, if the body is .042 then the tooth is usually created to be at least .084. So each tooth is cutting a kerf (path) through the log at least .084.

The sides of the tooth are also cutting and adding tooth load. All of the cutting load is distributed into the gullet and most of the stress is at the narrowest place of the band which is the deepest part of the gullet. The body is pulling the tooth through the cut and the tooth is under load and is pried backward in micro amounts and the steel molecules at the narrowest part of the gullet are being stretched and being put under great stress.

The bandsaw steel is, for basic understanding a spring, or spring steel. I say this because it has the ability to stretch a certain distance and return to its original shape. Remember, the term 'certain distance' this is important.

Each molecule of steel is round in shape, and can be stretched or elongated to a certain distance before it is stressed and begins to remain elongated. When a molecule remains elongated it has been distorted in the gullet from pulling too large (more than the body molecules can take) of a tooth load.

The band gullet has what we call a long front. We say this because the front has stretched but the molecules at the back of the band have remained un stretched. This condition causes a hump, that rises up in the middle portion of the band, or in other words the middle of the band will hump toward the slab side and the mirror image is on the log side being concave. At this point the band will dive into the log every time!

Note: A good spring has the ability to elongate or compress a certain or prescribed amount and return to its original shape millions of times without losing strength. It is only when the prescribed amount is exceeded that it becomes distorted and loses strength. Think of valve springs in a gas/diesel engine. They operate within their ability to extend, compress and return every time and run almost forever under harsh conditions. They do not exceed their steels ability to stretch and return.

A good understanding of the above two paragraphs is very important to understand an accurate comparison between the swage tooth band and the set tooth that we will discuss below.

Now let us look at a set tooth band of .042 thickness.

The Kerf of a set tooth band is also two times the thickness. Usually .084 (sometimes more sometimes less). The difference is the set tooth shares the tooth load between 3 teeth. Each tooth is only .042 on the top or the leading edge. The most any tooth can cut is .042 wide. The average that the 3 teeth cut is only .028. The right and left tooth only cut the set amount beyond the body width.

Only 2 of the teeth cut on the side and they only have 1 side to create side load which is very minimum. It is so small that I do not consider it to have a side load. The reason there is not a side load is the angle of the side of the tooth. The tooth is bent or set at such a sharp angle on the side that only the the top corner of about .010 touches the wood fiber. Of course, if you run your band excessively dull it does take on more side load.

Now compare the gullet stretch per tooth. Remember both band bodies are .042. The set tooth has the total kerf stress divided between 3 teeth. The swaged full tooth carries the entire kerf stress per tooth, plus the side load on 2 sides per tooth. It is easy to understand that the full tooth carries twice the load just because of the top width of .084. Then add the 2 sides of load and we have at least 3 times more tooth load per square inch than the set tooth bands have.

What does this mean? From my experience the set tooth pound for pound will perform 2 to 3 times better than a full tooth of the same band width and thickness. This is true even if a special steel is welded to from the full tooth.

Let me talk about the body of the band for a bit here. I have spoken of the distortion and how it changes the middle portion of the band to dish on the log side. This causes a band to start diving into the log in an uncontrolled manner.

Remember that distortion is caused when a band is driven with a tooth load greater than the body steel is capable of withstanding and still return back to it's original shape. Any bandsaw that is pushed to this point of stretch has become distorted. This will cause the band to not run good and it will dive into the log because of the natural change of curvature called anti-clastic curvature.

Myth of restoring bandsaws debunked

When this happens the band cannot be restored to new by the Saw Repairman/Sawfiler. However, the sawfiler can distort the middle of the back of the band to equal the front stretch/distortion.

Of course for those who know the term, this is called benching. This is when a roller or hammer is used to expand/distort the molecules to match the front distortion. The roller stretches the molecules by elongating them as it is pressed between two specially shaped steel rollers. The hammer expands the molecules in a star burst shape to achieve the distortion of making the middle of the band back longer.

The hammer needs to be crowned to give a star burst expansion. If a sawyer runs the band too hard or too dull he will distort the front. Then, when he sends it out for repair the sawfiler has no choice but to distort the middle and the back to make the blade equal everywhere. He can make the blade saw and appear as if it is restored it to original, but it is not.

Of course the tooth sharpness can be restored, but I am speaking of the body distortion. Now after 3 or 4 runs the band has been distorted by the sawyer and then distorted by the sawfiler and the molecules pulled apart (cracks in the gullets) and the sawyer or owner asks what is the sawfiler doing wrong. It is not the sawfilers fault. It is a matter of stressing the blade more than it can stand.

If you want this cracking to stop then you have to lower tension which in turn makes you slow down and pull the band for sharpening more often. Or leave the tension the same and just sharpen much more often. All in all keep the tooth load lower.

It is my opinion that a good set tooth band with correct curvature that is 1-1/2 wide will outperform dollar for yield, a band twice the width at 3 inches that has a full tooth. It is easier to keep the tooth load down on a set tooth band and it is easier to maintain a set tooth band.

Full tooth bands require a lot of attention because of the larger tooth load. They require more professional attention. This Professional attention is at a large expense.

I like the set-tooth blades best because of the ease and the lower cost of maintaining the blades.

Be sure to check out our new Cooks Super Sharp bandsaw blade. You can order these blades online through our online store any time you need them. Cooks Super Sharp is taking the sawblade industry by storm!

Until Next Time,

 

 

aka... the "Saw Doctor"
Co-Owner CooksSaw.com
Leaders in Bandsaw Technology!