I have attached a basic Feed and Speed calculator I found (Excel format). It allows you to enter your feed rate (celll D4) and it will calculate the RPM required to produce various chip loads.
The spreadsheet also shows the recommended chip size for various materials with 4 different size bit diameters.
I added a column to show the Dewalt Speed setting necessary to achieve the desired RPM. If the required RPM exceeds the 27,000 RPM limit of the 611 it will display “To Fast”. If the required RPM is below the minimum speed of 16,200 it will display “To Slow”. Otherwise it will display the speed setting between 1 and 6 (i.e. 2.5 is halfway between 2 and 3)
The first thing I noticed is that if these calculations are correct, I have been running my RPM’s way to high.
For example if cutting hardwood with a .125 inch bit the recommended chip size is between .003 and .005
To achieve that chip size with a two flute cutter moving at 100 inches per minute the RPM should be 16,667 or a setting of about 1.5 on the Dewalt 611.
For MDF with a Feedrate of 125 inches per minute and a .125 cutter the Dewalt should be set at 1
Please let me know if anyone finds an error with the calculations, they look pretty straight forward but wow these numbers are very different from what I have been using.
CNC Speed Calculator.xlsx (14.0 KB)