Why check spindle drawbar force

Drawbar force is often the first thing to weaken on a CNC machining center, and it fails quietly. The Clamprite Gage measures the actual clamping force at the spindle, so you see the loss on the dial long before it shows up on the part.

• More machine uptime

  Catch force loss on a routine check, not after a crash or a scrapped batch.

• Smaller spindle repair bills

  Fix the drawbar while it is a planned job, before it becomes a spindle rebuild.

• Less wear on the whole tool chain

  Drawbars, clamping collets, pull studs, tool holders and tool tapers last longer.

How drawbar force is lost

1. 1
   The springs wear

   A stack of 100 to 150 Belleville springs pulls the tool holder into the spindle taper. They wear grooves into the drawbar, and the friction between springs and drawbar eats into the pull force.

2. 2
   The cut gets worse

   With less force the holder can move: chatter, poor surface finish, shorter cutter life and scrapped parts. Programmers often adjust the program to compensate, not knowing a spring is failing.

3. 3
   Springs break

   Fatigued springs crack and break one after another, and the force drops sharply.

4. 4
   The holder pulls out

   In the worst case the tool holder pulls out of the taper during a cut, damaging the spindle taper, bearings, tool holder, pull stud, cutter and fixture.

5. A routine force check catches it early

   Measuring the tool clamping force with the gage shows the loss in time to act, so the repair is planned, smaller and cheaper.

   Per EN 1550 clause 6.2: static instruments for measuring clamping force must be used at regular intervals (every ~40 operating hours).