Having seen that ER Collet Chucks can perform well, it’s also important to realize that some care is required to ensure maximum performance from an ER Collet Chuck. Maximum performance means:

      The shank of the tool can’t slip during machining, nor can it be pulled out or pushed in.

      Runout should be minimized.

      Those are really the two issues we want to focus on, and here are the Tips you need to Maximize Performance in these areas:

      Tip #1: Collets and even the collet chuck nut are consumables.

      If you’ve taken care of all the other factors and still can’t get the performance you expect, replace the collet.  If the problem traces to a collet chuck, try replacing the nut as well.  Both are readily available separately–you don’t have to buy collets in a set and you can purchase collet chuck nuts separately too.  Treat them as consumables because they can wear out.

      Inspect collets for undue wear before each use.

      Look for fretting and scoring on the collet that indicates it spun inside the collet chuck.  Similarly, check the inside bore for the same kind of wear, indicating a tool spun inside the collet.  If you see such marks, burrs on the collet, or gouges of any kind, its probably time to replace the collet.

      Tip #2:  Keep it clean!

      A tiny chip stuck in the collet, chuck nut, or the chuck’s interior collet pocket can introduce a huge amount of runout and may also prevent the collet chuck from gripping the tool shank properly.  Make sure everything is squeaky clean when you assemble a tool and a collet chuck before putting them into the machine.

      Also, a little residue of oil or cutting fluid can rapidly reduce the collet’s holding power.  Hit all the components with some degreaser before you assemble them so they’re dry and oil free.

      Tip #3:  Torque the Collet Chuck Nut to Proper Spec.

      Most machinists don’t realize just how much torque is needed to properly tighten an ER collet nut. When you hear a machinist talking about having an endmill slip in an ER collet chuck, you have to wonder two things:

      – How clean was the chuck and cutter shank when they were tightened together?

      – How much torque was used to tighten the collet nut?

      Are you torquing your ER32 collets to 100 ft/lbs? That’s a bunch more than a lot of folks expect going on feel alone.

      To hit the higher specs comfortably and reliably, you’ll need a fixture to hold the toolholder while you tighten the nut.  Don’t rely on tightening it in the spindle of the machine.

A torque wrench is ideal for tightening the nut if you want to make sure you’re hitting the torque spec.  

      Whether you use a torque wrench or not, make sure you’ve at least got a nice wrench for your chuck. The single pin spanners are the worst for me when I have to apply a lot of torque.

      Over-tightening is just as bad as under-tightening because it can deform the collet in a way that leads to increased runout.

      Tip #4: Consider ball bearing nuts for your ER Collet Chucks

      Here is another interesting factoid gleaned from my research: ball bearing nuts for ER Collets can improve their performance even further. A ball bearing nut has about 14% more static stiffness for surface finish, but a whopping 50% more damping, which helps keep the chatter out when you have to get aggressive with a cut. I can tell you from experience that the ball bearing nuts are much nicer to use too–applying enough torque with one is much smoother.

      The disadvantage of ball bearing nuts is they have moving parts, and so are difficult to keep well balanced for high rpm applications.

            Tip #5:  Worried about the cost of all those collet chucks?  Use a mix of collet chucks and set screw holders.

ER Collet Chucks are pretty cheap as toolholding solutions go, but sometimes we want an even cheaper solution.  Many machinists worry about collet chucks slipping too, so between that and the cost, they use more setscrew (Weldon shank) type holders.

      Here’s the problem with those setscrew holders.  Tests indicate that a standard ER collet chuck is 15-58% statically stiffer than a Weldon shank end mill holder. That and the much reduced runout (Weldon end mill holders grip the cutter from one side which adds runout) make them preferable for surface finish.

      The thing is, larger diameter endmills can tolerate more runout and generate higher cutting forces, so they’re better candidates for set screw holders.  Consider using endmill holders for roughing with larger cutters and collet chucks for smaller cutters.

      If you can afford them and take proper care as described in this article, you’ll wind up putting the setscrew holders aside over time, though.

      Tip #6:  Avoid Weldon shanks on endmills–they’re more likely to slip in a Collet Chuck.

      If you use a Weldon-shank cutter in your ER collet chuck, expect holding power to be reduced by up to 30%, which is the amount of surface area that can’t be gripped because of the Weldon cutout.

      Tip #7:  Assemble your collet chuck properly

      There’s a right way and a wrong way.  The right way is to snap the ER collet into the collet nut before threading the nut onto the chuck and tightening.

      Tip #8: Make sure you insert tools deep enough in the collet

      Collets have a rated minimum tool depth.  If you don’t insert them deep enough, they will have increased runout.  Typically, you will want to use at least 2/3’s of the collet’s length.

      Conclusion

      ER Collet Chucks are an excellent workholding solution, and with a little extra care, you can ensure you’re getting the best possible performance form your ER Collet Chucks at all times.