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Steel Saw Plate

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Steel Saw Plate

Ideally saw steel would stay flat no matter how thin it was.  It would also resist the repetitive stress of entering and leaving the cut as well as any impact stresses caused by hitting foreign objects.  See our article on making The Best Saw Blades to see the importance of Quality Steel Saw Plate and the impact it has on the finished saw blade.  Also, refer back to the Saw Blade Index for other articles about saw blades.

In real life, the very best saw steel is no where near the ideal.  Quality saw steel has to be imported into the U.S. because it is simply not made here.  Saw plate is rolled to make it flat.  It is then shipped in flat plates so it does not have the memory of being coiled. 

Saw plate is laser cut to shape.  Then it is heat treated to achieve the proper hardness.  It may be heated more than once.  It is ground to bring it to the proper thickness and flatness.  The grinding and heat treating may be done in different order by different operations. 

The carbide tips are brazed on the saw plate.  The heat of brazing changes the structure of the steel in the heat affected zone.  If there is too much heat applied it may be necessary to temper the saw plate after brazing. 

As a saw blade comes up to speed it wants to distort.  The outside of the saw blade wants to move away from the center.  The effect is similar to twirling a rock on a string around your head.  The string gets tight and the rock wants to move away from the center.  This is also described as the outer rim wanting to grow faster or get bigger than the inner rim.  If this happens the saw blade will want to form a cup or a potato chip shape.  To compensate for this the saw blade is tensioned with a stretch roller. 

The blade is passed between two hard rollers that compress the steel into a narrow band.  This serves as a divider and separates the areas on either side of this.  In effect this makes a single piece of steel into two joined circles of steel with different properties.  This may be done one or more times.  On smaller, less expensive saw blades this is typically not done.  On ten inch saw blades the thickness of the steel is sufficient to maintain shape against the stresses inmost cases. 

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In ten inch saw plates they may consider a 0.090” plate thin.  In saw mills they will use a 0.090" plate on thirty inch saws and the plate may get as thin as 0.060”. 

As a final step the plate is examined with a flat edge and hand hammered to correct high and low spots as well as to ensure proper tension in the steel.  

A circular saw must be tensioned to operate properly; the larger the saw is, the more important it is to have the proper tension. As the saw comes up to speed, the rim stretches much more than the center of the saw, due to centrifugal force.  

An untensioned saw will be loose and floppy at speed and will wander out of the cut and heat up. 

Tensioning is done by "Hammering"; the saw is placed on a saw anvil, mounted on a "hammering horse" and controlled blows are applied in a specific manner to adjust the tension. Almost all hammering is done equally on both sides of the saw, preferably with the hammer blows exactly corresponding. Blows applied INSIDE the center of the radius of the saw will add to the tension, blows applied OUTSIDE the center of the radius will lower the tension. A saw that is going to be run at higher speed will have to have more tension than one operated at slower speed. See our article on Recomended Saw Blade RPM. 

The person doing the hammering must know exactly what the RPM of the saw is while in the cut, how much power is on the mandrel, and whether the mill is Left or Right Hand. (The "hand" is determined by which side of the sawyer the log is on as it enters the cut; if it's on his left, the mill is Left Hand).  

Once the saw is properly tensioned, it's a good idea to remove all the lumps in the plate. This is done on an anvil that's padded with very thin leather or several layers of heavy paper. The saw should have no shiny spots on it after it's been in operation for some time.  A saw that needs work will wander out of the cut, especially if it's not perfectly sharp. That causes poor lumber and heating of the saw. 

Besides the anvil and hammering horse, the blade smith must have an accurate straightedge, a tension gauge, and a dog-head hammer.

As the saw blade runs the plate heats up.  This heating allows the steel to relax and become soft.   Many saw blades are changed while still sharp because the plate needs service.


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