Archive: Jun 2021

Router Bit Tool Geometry

Leave a Comment

There are a lot of different geometries involved in making a router bit—clearance angles, grinding angles, hook angles, axle angles, side clearance angles, radial clearance angles, and side rake. For the purposes of our discussion we will only talk about the basics.

  • Tool size is a determining factor in how fast you can cut and what types of geometries and clearance angles are possible—all major factors in productivity, finish, and consistency of parts.
  • For stability, choose the shortest cutting length possible. You should have sufficient shank to fill 80% of the collet. Longer router bits will deflect more—run-out is more exaggerated the longer the tool.
  • The larger the diameter of the tool the faster you can go—up to a point. While a 3/4” diameter bit will be able to handle a much larger chipload than a 1/8” diameter bit, larger bits require slower speeds for safety reasons. The following are general safety guidelines:
    • Up to 1” Diameter—Maximum of 24,000 RPM
    • 1” to 1-1/2” Diameter—Maximum of 18,000 RPM
    • 1-1/2” to 2-1/4” Diameter—Maximum of 16,000 RPM
    • 2-1/4” to 3” Diameter—Maximum of 14,000 RPM
    • 3” to 3-1/2 Diameter—Maximum of 12,000 RPM
  • Use the largest shank possible. However, cutting diameters smaller than the shank diameter cause stress points at the transition and can contribute to breakage. Solid carbide tools larger than 1/2” in diameter can be expensive and are designed when extra long lengths are needed. The following are safety guidelines with relation to shank size and head diameter:
    • 1/2” diameter shank—Maximum large diameter is 2”
    • 1/2” diameter shank—Maximum small diameter is 1/2”
    • 1/2” diameter shank—Maximum overall length is 4”
    • 5/8” diameter shank—Maximum large diameter is 3”
    • 5/8” diameter shank—Maximum small diameter is 5/8”
    • 5/8” diameter shank—Maximum overall length is 4-1/2”
    • 3/4” diameter shank—Maximum large diameter is 3-1/4”
    • 3/4” diameter shank—Maximum small diameter is 5/8”
    • 3/4” diameter shank—Maximum overall length is 5”
CNC Manual

Free CNC Manual

We cover this topic in more detail in our free to download CNC Manual.


For more, refer to our CNC Manual. 

To peruse our online catalog or to place an order, visit EOASAW.com or call us at 817-461-7171.

Have any questions? Feel free to ask us in the comment section, give us a call, send us an email, or visit us on Facebook!

For more informative EOASAW blog posts, visit our main Blog Page.