Preventing and fixing a slipping drill press chuck.


  • Preventing and fixing a slipping drill press chuck.

    Have you ever chucked up that big bit, say a 3" Forstner bit, and without thinking just line up your hole, power up the drill press and start drilling away only to have the drill press bog down and end up with the chuck slipping, or even falling off the taper?

    Well, the fix is plenty simple.

    First off. Avoid slipping the chuck at all. This means you need to make certain of the following.
    #1. Your bits are good and sharp. A dull bit will grab the workpiece instead of cutting it. You'd bog down a V-8 engine with some of the bits I have seen people try to use on their dril presses.
    #2. Your drill press is running at an appropriate speed for the bit in question. Wood Magazine offers up a GREAT drill press speed chart that can be found on their site at

    Once the damage is done, you need to recover. and it's not as hard as it would seem. This is also a great opportunity to inspect and lubricate the chuck.

    #1. Remove the chuck from the drill press taper shaft. If it is already spinning, you should just be able to grab it and pull down to remove it.
    #2. Thoroughly clean the chuck inside and out with a non depositing solvent such as Brake Parts cleaner, or rubbing alcohol. (care should be used on some newer chucks that may have plastic components. DO NOT use solvents on plastics!).
    #3. When cleaning the chuck, run the jaws in and out all the way cleaning as you go to clear any wood dust, dirt, grease, and other nasty debris that gets into drill press chucks.
    #4. Fully clean the taper.
    #5. Apply a dry lubricant to all surfaces where metal is supposed to slide against metal avoiding the contact areas where the jaws contact the bit, and where the chuck contacts the taper.
    #6. Fully retract the jaws.
    #7. Place a flat and parallel sacrifical wooden piece on the drill press table. Insure it is at 90 degrees from the center line of the taper from all angles.
    #8. Start the chuck on the taper, and raise the table to just under the chuck with the chuck nearly resting on the sacrificial piece, securely locking the table in place, and double checking square.
    #9. Slowly lower the handle pressing the chuck onto the taper.
    #10. Rotate the chuck 180 degrees, lower handle and press again.
    #11. Rotate the chuck 90 degrees press again.
    #12. Another 180 degrees, press again.
    #13. Remove the sacrificial piece and lower the table.
    #14. Install staight smooth rod on the chuck (I have some scrap 3/8" smooth rod, 6" long that I keep for drill press testing). Set up runout gauge on table / fence to measure runout, and measure your runout. Shouldn't be much if any. Last time I had to do this my chuck didn't measure any runout at all.

    • LCHIEN
      LCHIEN commented
      Editing a comment
      are you talking about the chuck slipping on the taper or about the bit slipping in the chuck?

      What do you do when the latter happens? Other than just making it tighter. I've had to make it so tight that the chuck key hurts my hand to get it loose. Perhaps I should spring for forstner bits where they have hex shanks.

      Another point is, if the bit grabs and locks up the motor, better kill the motor as fast as possible to prevent motor burnout or tripping a breaker. The chuck has held on the taper and the bit in the chuck. You motor just doesn't have enough torque at this point to spin the bit. If this happens a lot to you, better
      1. sharpen the bit
      2. use less feed pressure
      3. use a lower speed for more mechanical advantage
      4. get a more powerful motor/drill press
      5. drill a series of smaller to large concentric holes so the material removal is less for each pass.

    • dbhost

      Editing a comment
      I am specifically addressing chuck slipping on the taper, not bit slippage in the chuck. That is a different situation...

      In the instance I had it happen to me, by the time I could get to the switch and shut down, the chuck had slipped off the taper.

      Not sure I agree on the speed issue. Not sure why. I pretty much trust the Wood Mag chart. Hasn't disappointed yet.

      As far as bit slipping in the chuck goes. That is a really good question. I would think that you could thoroughly clean the mating face of the jaws, and then scuff the jaw mating faces (where the jaw touches the bit shank) with some 80 to 120 grit sandpaper, maybe on a dowel or something?

      Just a guess. I have never had a problem with the bit slipping, just the chuck.
      Last edited by dbhost; 09-07-2012, 01:59 PM.

    • LCHIEN
      LCHIEN commented
      Editing a comment
      the speed as suggested by the charts is idealized for smooth cutting and assumes you have a drill motor powerful enough to do the job.

      If you are limited by the power of the motor, you will have to slow the drill down to get more torque. Just like a car, too high a gear can lead to cogging and stalling the motor, shifting to a lower gear gets more torque, less speed. Lower gearing (or pullying as the case may be) for a drill gets you more torque to keep from stalling the motor.
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