Friday, October 4, 2013

Zinki: Powell’s Tone Hole Extrusion Process

By Steven Wasser - President, Verne Q. Powell Flutes

What’s in a name?  In this case a lot, but the name itself is something we just made up because it sounded like fun. 

Zinki is the name we’ve given to Powell’s patented process for extruding tone holes on one of our CNC machining centers.  

The "Zinki" CNC Machine
The traditional process for extruding tone holes generally involves at least 3 separate steps, each one involving a different setup on a different machine, as follows:
1.      Make a small hole in the tube where the tone hole is going to be.  Usually this involves drilling or punching an egg-shaped hole.
2.      Load solid pulling balls into pockets in an arbor, then slide the flute tube over the arbor and place on a machine.  Position dies over each tone hole.  Connect a spinning shaft to the pulling ball and pull up through the die, pulling flute tubing with it to form the tone hole.
Traditional pulling ball.
3.      Remove the tube from the pulling arbor and place it on another machine.  Face each tone hole level with a cutting tool, then use a special tool to roll over the tone hole edge to (a) eliminate the sharp edge and (b) reinforce the tone hole.  
The process normally takes 30-45 minutes and uses both extrusion - a brute force technique - and spinning to form the tone holes.  The force required has a tendency to pull metal from the tube into small ripples alongside the tone holes.  And each time a flute tube goes from one setup to another, accuracy is lost.
Powell’s Zinki technology delivers the pulling ball from the outside of the flute tube, rather than pre-loading it on an arbor inside the flute tube.  In order to do this Powell needed to figure out how to put a big ball through a small hole.  Instead of a single large ball, the Zinki pulling ball is actually a series of small balls which can expand and contract. The details can be viewed at U.S. patent #7,420,109B2.

Close-up on Zinki pulling ball.
With Zinki the balance between extrusion and spinning shifts to spinning.  The result is a highly accurate tone hole with little if any rippling on the tube.  The last step in Zinki is to “kiss” the top of the tone hole with a diamond facing tool to make sure that it is level.  And all this takes place in a fraction of the time for traditional tone hole extrusion.

Powell Conservatory (Drawn Tone Holes)
Close-up on drawn tone holes.  Red arrow points to the rolled edge.


  1. I like your post and it is so good and I am definetly going to save it. One thing to say the In depth analysis this blog has is trully remarkable.
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  2. Very interesting...I have a Powell Sonaré PS-709 & as I've learned more about the Powell flutes in general I've been curious about what made your drawn tone holes different. Now I know! Thanks Powell!


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