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Why not Small Endmills?

Last Updated: Jan 22, 2016 09:39AM EST
Our standard MetalMax DC kit measures endmills down to 3/8" with some effort, down to 1/2" very easily. Here are reasons why smaller tools are not recommended.
 
YOU CAN’T GET THERE FROM HERE
Let’s assume you have a 10,000 RPM machining center with a ¼” endmill cutting aluminum. The manufacturer recommends a surface feet per minute (SFM) of 2000. To reach that recommendation you would have to run the tool at 30,558 RPM (SFM x (12/π)/Diameter = RPM). Since the largest and widest stability lobes are generally near the highest RPM, you won’t be able to access them with a 10,000 RPM spindle.
 
OF COURSE THEY HAVE A PROBLEM WITH SMALL ENDMILLS
Small tools break for all kinds of reasons other than dynamics. Small tools will be their problem areas, but, it doesn’t mean they will pay for it. See below
 
THEY ARE CHEAP
Small carbide endmills are inexpensive. For example a ¼” Niagara A345 endmill sells on Amazon for $22.50, the ½” is $60.73, the ¾” is $218.84. Tool life savings will be virtually meaningless. There is no room to absorb the cost of a Dashboard into a small endmill’s consumption costs.
 
THEY FAIL FOR ALL KINDS OF REASONS OTHER THAN DYNAMICS
Carbide is brittle. Small tools break from mishandling. They break in shipping. They break from overtightening the collet. They break in the cut for reasons other than chatter. The impacts of unbalance or runout of the toolholder are disproportionally greater. We open ourselves to failure, not caused by dynamics, by tapping small tools.
 
THEY ARE HARD TO TAP TEST
You must use a miniature hammer and accelerometer, which are difficult to master and to get repeatable results. That expensive hammer and accelerometer will only extend the range down to 1/4" diameter, but will add thousands of dollars to the cost of the kit.
 
HERE'S THE PROCESS FOR SMALL ENDMILLS:
  1. Use a balanced toolholder. Make sure it was balanced with the retention knob. Small tools do not impact the imbalance forces that much, but still should be measured as a full assembly.
  2. Make sure the assembly is concentric. Measure the assembly by rotating it by hand in the spindle with a 50 millionths dial indicator. Make sure the spindle and the taper are clean. 
  3. Run the tool at the maximum recommended SFM that the machine will allow.
  4. Measure the cut with VP Harmonizer.
  5. Send the Harmonizer file to BlueSwarf for a resonance test. We will calculate any possible resonant speeds that should be avoided.
Here are some recommendations from Makino, CLICK HERE
 

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