Why Do Circular Saw Blades Break?

compiled & edited by Bernard Martin

Breakage, Wobble and Rubbing problems are often caused by how the washers are mounted on either side of saw.

It's commonly known that when saw thickness is less than 0.125″, keyways can cause stress risers and cracks.  That is why washers are often used.  However, Breakage, Wobble and Rubbing problems are often caused by how the washers are mounted on either side of saw. 

Remember, washers drive the saw in the absence of a drive key. They must always be clean, flat and bur-free. A speck of dirt will let saws wobble and cut oversize. 

If a saw breaks, it may score the washers. Always check for scoring marks around saw hole for dirt, chips or grit.  Shiny spots, as small as a pinpoint, indicate that chips where imbedded under washers.

Circular skid marks indicate the nut was not tight.

Generally speaking:

• Thin saws should especially be supported by washers as large as possible.
• Washers must be of equal diameter or they will flex out saw dish and cause one side of saw to rub.
• The nut must be wrench-tight.

Saw Blade Teeth most often break as a result of:

• Too high a feed rate.
• Spindle bearings are worn.
• Drive belts  are loose or sheaves worn.
• Improper tightening: If saw blade pauses momentarily in its rotation while feed advances, it WILL break.
• Workpiece indexed before the saw has cleared the slot.
• Improper workholding - The workpiece not tight or not well supported.
• Saw is dull, even the best tools do eventually wear out.

NOTE: ​HSS saws will turn colors as they heat during cutting. A straw color is the limit. The saw will lose its temper when it starts turning blue.