Steel plate bending strength and thickness?

[tomwalz]

How does the strength of a saw blade change as the thickness of the plate changes?

If one saw blade has a steel saw plate 0.125” thick and another, otherwise identical, has a steel saw plate (body) that is 0.100” thick, then what is the difference in strength? Does the same ratio apply for a saw body (plate) thickness of 0.075”?

We are looking for differences in strength as related to susceptibility to bending during cutting. Bending would occur from feeding deviation or differences in material such as knots or rocks in wood.

The source for this question stems from a discussion on just how much more dangerous are thin kerf saw blades than standard kerf saw blades.

Thank you,
Tom Walz


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[Maui]

Tom, it's essentially a beam strength problem. The proper bandsaw blade thickness is not only a function of what you are cutting, but also the wheel diameter of the machine. For example, see page 55 of this book under "Blade Thickness":

http://books.google.com/books?id=dL...ge&q=saw blade thickness beam bending&f=false

Maui

http://www.EngineeringMetallurgy.com

 

[tomwalz]

Very impressive answer. Thank you.

Unfortunately I neglected to include "circular saws" in my description.

These blades tensioned by hammering or rolling the metal.

Assume everything else is equal and only the metal thickness varies.

Tom

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[tomwalz]

It looks like it is about the cube of the of the difference.

A 20% reduction leaves you with app. 51% of the strength.

Tom

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[Maui]

Tom, a circular saw blade's teeth have to make a wide enough cut to allow the blade plate to pass through the kerf. And for the blade to operate smoothly and make a true cut without a lot of scoring on the edge of the cut, the blade plate has to be substantial enough to absorb vibration and to handle the heat generated during the cut. For a full kerf saw blade, a kerf width of about 0.125 inches is generally considered standard. But for consumer saws that are usually underpowered (under 3 HP for a table saw) a full 0.125" kerf has another effect: drawing too much power from the tool. If not enough power is delivered to the blade, the saw slows down causing excessive friction. And the blade heats up as a result, and can become distorted or burn the cut surface. This is where the thin kerf blades come in - they require less horsepower to run so these power challenged saws can make the necessary cuts. But thin kerf blades are more susceptible to distortion from temperature gradients, especially near the rim where the temperature gradients are the greatest. And because their mass is lower than a thicker blade, they tend to heat up more, which can aggravate distortion issues. The following article provides a good description of this:

http://www.thinkerf.com/Downloads/HeatFlow.PDF

Maui

http://www.EngineeringMetallurgy.com

 

[tomwalz]

Dear Maui,

Thank you.

I finally found my answer on Dr. Lehmann's site as well.

http://www.thinkerf.com/Downloads/ThinKerf.PDF

John Schultz of SuperThin Saws took a direction similar to yours and provided a nice list of additional factors.

The paper I read was based on 0.080" plate as compared to 0.040" plate. Does the same hold true for 0.125 diameter to 0.090" or 0.085"?





Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[Maui]

Tom, the same relationship between blade thickness and stiffness should hold true. An easy way to remember this rule is that cutting the blade thickness in half reduces the stiffness to roughly 1/8 of it's original value, all other factors being equal.

In your original post you mentioned blade strength, not stiffness. The stiffness is primarily dependant upon the elastic modulus of the steel and the blade geometry, and is very insensitive to steel grade and heat treatment. The blade strength however is strongly dependant upon the grade of steel and the heat treatment that it receives. Which of these two are you interested in?

Maui

http://www.EngineeringMetallurgy.com

 

[tomwalz]

The thin kerf blades seem to be often regarded as a miracle cure for under-powered saws. Very little attention seems to be paid to the downside.

I have seen enough industrial saw blades to know the problems that can arise. I was looking for some way to convey the need to be more careful with thin kerf blades.

Attached is an 0.070" saw blade that had a few problems.

Thirty years ago I started working on saw blade brazing. Fifteen years ago I started working on learning carbide. Now I am trying to learn something about steel.

Tom

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[Maui]

That is an ugly failure. I'm surprised that this blade wasn't taken out of service before it failed catastrophically. It sounds like your interest is expanding into ever broader fields. If you're trying to learn something new about steel alloys, there is a great deal to learn. And there are plenty of books on the subject, several of which have been discussed here in these forums.

For a discussion of why the elastic modulus is so insensitive to changes in chemical composition/heat treatment/cold work see

faq330-1441

Maui

http://www.EngineeringMetallurgy.com