Broken Router Bits

Router bits broken due to improper feeds and speeds
Broken router bits

Broken Router Bits

About once every six months we hear from someone who breaks router bits regularly. They always seem to break in the same way so I thought I would do a blog post and a video about this breakage.

There seems to be the same two problems. The router bits are burnt by which the customer means that  the router bits got hot enough to get discolored. The other problem is that the router bits break and they typically break right at the top of the flutes.

Quite often the reason the router bits discolor is that they are run too slowly. Router bits are designed to be run at a certain speed. If you run them too slowly, they bog down in the material, friction builds up and they can get to hot.

With CNC router bits you need to match the speed at which the router bit rotates with the feed rate or how fast the router bit moves through the material. Router bits have a gullet which is the notch or trough behind the cutting edge. This collects the material as it is being cut off. You don’t want to try and feed the router bits so fast that you overload these gullets or notches or troughs or whatever you want to call them.

However you want to keep the router bit moving through the material fast enough that that friction and the heat from friction don’t become an issue.

Tungsten carbide may be flexible depending on who you talk to. Tungsten carbide, as it is ordinarily used, is actually grains of tungsten carbide cemented together with cobalt. Because there is a metal matrix, tungsten carbide can be somewhat flexible.

People who are experts on metal think that tungsten carbide is rigid which it is by comparison with most metals. Ceramics experts think tungsten carbide is pretty flexible because ceramics are absolutely rigid. We tungsten carbide people pretty much come down on the side of “don’t try and bend the tungsten carbide” because it generally won’t bend enough to notice or to do you any good before it breaks.

If you’re trying to plow your router bit through a sheet of material with a CNC machine you can put enough pressure on the router bit to snap it.

It typically snaps at the top of the flutes because the characteristics of the router bit change greatly here. The fluted part of the router bit is thinner, with less material and thus bends more readily. If you are pushing the router bit hard enough with a CNC machine to bend it then the fluted part will pretty well bend in a single curve.  Once that curve reaches an area of thicker material there is a discontinuity in the curve. And, if you’re reading this, you’re probably more than smart enough to know that materials that are bent to the breaking point are most likely to bend where the material changes for some reason.

If you are burning router bits or breaking router bits on a regular basis, please check your feeds and speeds.

If you don’t know what feeds and speeds you should be using, please contact us and we will contact the engineer or the manufacturer and get you the correct data.

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3 Responses to “Broken Router Bits”

  1. Bob Roberts says:

    Thank you for your article —

    I was cutting some thin stainless steel with a .020 2 flute bit from Performance Micro tools. My initial attempts were successful but now I am breaking bits while using the same material and the same feed and speed rates.
    I am running a CNC Shark Pro plus with a Bosch Colt router-
    Running at 35,000 RPM with a feed rate of 21 —
    Any thoughts as to why i am suddenly having the bit breakage problem-
    Thank you


    • admin says:

      My fist thought would be movement someplace such as material fixturing, worn collet, loose bit.

      You don’t say how long you run the drills. As tools run longer they get duller and this puts more force on them. The dulling accelerates with use at a geometric rate rather than linear. Instead of dulling as 1-2-3-4 it dulls as 1-2-4-8.


  2. bing says:

    Your style is so unique in comparison to other folks I’ve read stuff
    from. Many thanks for posting when you have the opportunity, Guess I’ll just book mark
    this page.

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