Saw tip angles

[Tom Walz]

Saw tip angles

These are the three common angles on every saw tip. (ATB and similar are optional and treated separately. Hook angle is considered a saw blade angle and not a saw tip angle although you can influence hook angle by the type of tip you use and how you grind it.)

These angle have great deal to do with how successful a blade is any given cutting application. Some materials do better with more clearance and some with less clearance.

The two sides must match for the saw to cut straight. If the side angles are different it is like having the front wheels on your car out of alignment.

Currently best practice quality standards seem to call for the two sides to match within 0.1 degree.

This is where a quality saw blade comes in. Carbide is high wearing and thus hard to grind. It wants to “push back” against the grinding wheel. Better blades are made on larger, more rigid (and thus much more expensive) grinders. They often are ground in several passes with different grits of wheels instead of just one pass with a coarse grit.

That’s it. Just a project I have been working on.

Tom

[J.R. Rutter]

When do you think we will reach the point where we can custom order blades with these variables spec'd out for not much more $ than off-the-shelf blade designs?

This week I was wishing for an 18" version of a miter saw blade: high ATB + R, minimal radial + side clearance, negative (or zero) hook angle - doesn't seem to exist...

You've done a nice job illustrating these design variables.

[Tom Walz]

Thank you for the kind remarks.

There is web site exclusively for saw and tool builders and this is the current project. We are working on standardizing what we mean by various terms, how to measure them and what best practice is and should be.

A custom blade might be more affordable than you realize. If you wish you can call Emily Erskine at 800 346-8274 and we can get you a price?

Mostly what we build and sell are saw blades with our long life, Cermet 2, tips on them. Adding advanced tips add very little to the cost of the blade but it can increase the time it stays sharp by 2 – 5. Actually most folks are happy running it 2 or 3 times as long and don’t push it as far as they could.

Also we have put Chisels on a Wheel on line free. Chisels on a Wheel is often described as the best book on woodworking tools ever written. That is open to discussion but it is very good. It is long out of print but we got permission to reproduce it and sell it.

The entire book is online at:
http://www.carbideprocessors.com/level2store/mysite23/Chisels_on_a_Wheel_index.htm

The web site is undergoing a major overhaul this week but it should be there for a couple days anyway.

Tom

[J.R. Rutter]

Thanks - I will call to get a quote at some point, but I ended up with an Amana that was "close enough" for right now. I read "Chisels . . ." a couple of years ago - very informative. Good to know it is online.

How does the cermet 2 compare to say c4 carbide in sharpness? I am trying to get the best possible cut surface quality in end grain crosscuts. Are there any advantages other than longevity?

[Tom Walz]

Cermet 2 is our name for a family of advanced materials. We spent years (and years) testing advanced steel cutting materials to find a few suitable for wood and wood products cutting.

C4 is technically a grade for precision finishing of cast iron, non-ferrous and non-metallic materials
C-1 to C-4 are general grades for cast iron, non-ferrous and non-metallic materials
C-1 Roughing
C-2 General Purpose
C-3 Finishing
C-4 Precision

It is usually tungsten carbide grains cemented together with cobalt.

Very roughly you can expect carbide tipped saws to have an edge radius in the 10 – 18 micron range. Micro grain carbide can get to the 8 -12 micron range. Nanograin materials, such as Cermet 2, can be in the 4 -6 micron range.

Cermet 2 gives a toughness somewhere around C2 or C3 while providing better wear life than C4.

Cermet 2 also has a higher lubricity so that it slides through the cut more readily. This means you can also feed it faster. It has a very low thermal conductivity so it doesn’t heat up as much as carbide. We use an advanced binder so that corrosion is greatly reduced.

Here are some considerations in carbide wear. I add or subtract factors to it depending on the material, application and so on.

Theoretical considerations
1. Wear – the grains and the binder just plain wear down
2. Macrofracture – big chunks break off or the whole part breaks
3. Microfracture – edge chipping
4. Crack Initiation – How hard it is to start a crack
5. Crack propagation - how fast and how far the crack runs once started
6. Individual grains breaking
7. Individual grains pulling out.
8. Chemical leaching that will dissolve the binder and let the grains fall out.
9. Rubbing can also generate an electrical potential that will accelerate grain loss
10. Part deformation - If there is too much binder the part can deform.
11. Friction Welding between the carbide and the material being cut
12. Physical Adhesion – the grains get physically pulled out. Think of sharp edges of the grains getting pulled by wood fibers.
13. Chemical adhesion – think of the grains as getting glued to the material being cut such as MDF, fibreboard, etc.
14. Metal fatigue – The metal binder gets bent and fatigues like bending a piece of steel or other metal
15. Heat – adds to the whole thing especially as a saw goes in and out of a cut. The outside gets hotter faster than the inside. As the outside grows rapidly with the heat the inside doesn’t grow as fast and this creates stress that tends to cause flaking (spalling) on the outside.
16. Compression / Tension Cycling - in interrupted cuts the carbide rapidly goes though this cycle. There is good evidence that most damage is done as the carbide tip leaves the cut and pressure is released. 17. Tribology – as the tip moves though the material it is an acid environment and the heat and friction of the cutting create a combination of forces.

There is more on this at www.carbideprocessors.com. Again, the web site is being rebuilt this week so I am not sure what is up at any given time.

Tom