Calculating CNC Speeds and Feeds
U.S. Wood Industry Gets an Opportunity

One of most interesting parts of the Custom Cabinetmakers Assn. meeting at C&C Millworks in Fond du Lac, WI,  was the technical tooling presentation by Mike Serwa of Vortex Tools.

In addition to explaining the basics about CNC routers and tooling, Serwa delved into the selection factors for choosing tools - by necessity getting into the detail of how they perform within a CNC machine, and how they are designed. He explained the basic tool holding systems. Generally speaking the tighter the hold on the tool shaft, the faster the tool can spin, and the more work it can do. Here's a quick recap:

Spring: a collet-type holder, which is the most common in use, but doesn't have the tightest clamping. Since it has less clamping force on the tool it limits its spin speed. "More clamping force allows for faster spin," noted Serwa.

Hydraulic: grease pressure forces the inner diameter of the tool holder to collapse, capturing and holding the shank of the tool.

Shrink to fit: Through thermal expansion, the holder opens to accept the tool shank, then closing around it, creating a 1-to-1 union of spindle and tool shaft.

 Tribo by Schunk deforms a Triobular
opening in a setting tool (top) to ac-
cept the tool shaft (bottom).

Tribos by Schunk: deforms a triobular opening in a setting device to accept the tool shaft. When the pressure is released the holder closes around the shaft. 

 Tips for loading and changing tools:
"It is as bad to over-tighten a tools as it is to under-tighten it," said Serwa.
-Use a torque wrench to get consistent settings
-Make sure to organize your tool area
-All tool surfaces should be cleaned after use
-A proper tool changing fixture is needed

In setting a tool, "Make sure you have the right amount of tool shank in the collet," said Serwa. "It should fill at least 75 percent of the collet."

Speeds and feeds
Serwa offered these general specs on speeds:
"Most boring bits will run 3,000 to 6,000 rpm in making a plunge in the range of 4 mm. Routing bits will run at speeds of 8,000 to 18,000 rpm, Serwa said, even going as high as 24,000 rpm. "Typically, smaller diameter tools need to run at higher rpm."

How fast to run the bits is determined by the material being worked and the design of the cutting tools. The "chip load" that a tool handles is a factor of the feed rate (in inches per minute) divided by rpm times the number of flutes in the cutter. Here's the formula:

Selecting a feed rate is a factor of these values. Download a PDF of this Vortex chip load chart

The Cabinet Makers Association,which sponsored the event described here, is working with Custom Woodworking Business magazine to present a powerful educational lineup of presentations for the 2nd Annual Custom Cabinet Conference, February 24-25, 2011 in Charlotte, NC.

The Custom Cabinet Conference will be co-located with the 7th Annual Closets & Home Organization Conference & Expo. Free expo registration, a $20 value, is being offered at the Closets-Expo website through November 30. Early-bird registrants will qualify for conference discounts.

Presentations of the Custom Cabinet Conference include:
• Working with Designers & Architects by Joe Knobbe of Exclusive Woodworking
• Moving from Residential to Commercial by Rick Thaler of OGB Architectural Woodwork
• Pricing for Profit by Sean Benetin of Millwork & More
• Hiring, Firing and Motivating Employees by Scott Boschetti of America’s Woodworker
• Making Dollars & Sense from Your Advertising Expenses by Dave Grulke, CMA

More details about the Custom Cabinet Conference, Closets Expo & Conference and the all-new Wood-Tech Summit are available at and

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