Metalcutting Circular Saw Cutting Recommendations, Tips, Tricks & Troublshooting

compiled & edited by Bernard Martin

As more and more of our customers are using Martindale Gaylee Circular saws we put together this guide to the commonly asked questions such as "Is there a rule-of-thumb for the number of teeth?" or "How much side clearance should I have?" Here we cover a lot of the fundamentals of selecting the right circular saw blade configuration, some tips, tricks, and troubleshooting for when things go wrong. 

Circular Saw Feed Rates

These are general cutting speed recommendations for circular saws used in metalcutting from Martindale/Gaylee. The may vary from application to application but are basically some general suggestions starting parameters when using high speed or carbide saws. 

• HSS Saws: .002”-.006”  (IPT-inch. per tooth / CLPT-chip load per tooth)
  
• Carbide Saws: .0002”-.0015”  (IPT -inch. per tooth / CLPT - chip load per tooth)

This is a conservative recommendation as a starting point for feed rates, and may vary depending on material being cut and cutting speed (SFPM).

Selecting the Proper Number of Teeth in Your Metalcutting Saw

Generally speaking, deep cuts and soft material require fewer teeth for chip clearance and stronger teeth (landed) Thin material requires more teeth, but keep-in-mind that at least 2 teeth on the blade need to be engaged in cut.

Hard materials and narrow slots (under .025”) likewise require more teeth.

Hard Materials require more teeth, and  give a smoother cut,  but at a much lower production rate.  ​

Alternately beveled teeth keep chips from sticking in the cut and in the tooth gullets.

And Remember that there should be at least 2 teeth engaged in the cut at all times.

Increase Number of Teeth For:

• Thin material 
• Thin cuts under .025”
• Slow spindle speeds
• Hard material
• Sand castings 
• Thin castings 
• Work hardened materials
• Known inclusions or Hard spots 
  

Decrease Number of Teeth For:

• Free cutting material​
• Soft Gummy long chipping materials.
• Deep cuts (over 1/4”)
• High speeds Machining Applications
  
• Chip clearance and tooth strength (Consider Metal Slitting or Copper Slitting style saws.)
  

Rake Angles and Side Clearance Angles

SIDE CLEARANCE (Tangential Clearance Angle)
This is also known as dish or hollow grind.  You measure down the side of the tip and the difference it is the difference between front and back.  As you cut, material it gets compressed and springs back after the cutting edge passes.

​A steep side clearance angle gives plenty of room for the material to expand and prevents thermal expansion of the base material.  Keep in mint that a very flat side clearance angle can provide a smoother cut in some materials.  For stainless steel and tenacious metals such as copper, zinc, tin or lead an increase in the side clearance is desirable as these materials tend to "spring back" (thermal expansion) on the blade. 

RAKE ANGLES
Rake angle is the term used to describe the direction of the blade’s teeth, as referenced from the rotation and central axis of a saw blade. If you imagine a line going from the exact center of the blade to each tooth, having the front of the tooth directly on that line would be a zero degree rake angle. The rake angle of the blade is described in comparison to that imaginary line.

A positive rake angle meana that the teeth are angled more towards the angle of rotation, while a negative rake angle would mean that they are angled backwards, away from the direction of rotation. Generally speaking, the preferred rake angle is:

• 5° to 10° positive for other soft materials.
• 5° negative for yellow brass
• On center for steel.

Why do Circular Saw Blades Break?

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.