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My Balance Journey

Hey everyone!

I wanted to fill you in on our journey to balance the outer rings of Tungsten on our Columbia Ls2 top.  For a little historical info check it out our previous post: Columbia Ls2 Update.

First off balancing anything rotating is an art and those that do it well are master craftsmen!  My breakthrough came when I got a tip to talk to a local spindle balancing machine shop, luckily the owner Bill was willing to listen and help us get on track!  Thank you for all your continued help and expertise!

So what does it mean to balance a rotating disk?  Well I recommend starting with reading: Analysis of Balancing of Unbalanced Rotors and Long Shafts using GUI MATLAB.  This gets super in depth and really confusing quick unless your a savant or an engineer.  To boil it down we wanted to bring the center of gravity in line with the center of rotating axis. 

We researched a lot if ideas and finally honed in a dynamic balance like this one from Haimer:

...but soon found out that those are hundreds of thousands of $$$.  So, could we do the same thing here in our shop?  Well of course, how hard could it be?

It was really hard!  Really really really really hard!  Turns out that balancing in general is really hard and not many people do it well.  But up to the task we forged on and found a small unit for hobby turbines and premium drone motors from Aerobros.  For only a few hundred bucks it was worth a try but we still had to make a cradle to hold the rings and measure any unbalance. 

v1: My first design looked like below we used a motor to mount the Tungsten ring on but these tungsten rings blew out the horrible bearings in the motors too fast and there was slop in the motors.
 

v2: Moved the motor to the side and employed a drive belt but it was not accurate enough and would give out erroneous readings.

v3: After copious amounts of further research we came to realize we need to set up a dual plane balanced station and only use the readings from Plane 1.  Our first iteration ended up looking like this:

v4 through v8: This is where we are at today and we finally have a repeatable fixture (with some calibration)!  We would like it to be more accurate and continue working to create another fixture but this is a few months off still!  This one will balance a "nickle" on end tho...

 

What does the process look like to balance a ring?

  1. Calibrate the fixture by taking an initial reading on the vector graph. Here's what it looks like (the smaller the "Max" G Number the better the balance)



  2. We then affix a ring to our fixture and take another reading. This gives us our initial reading of how "imbalanced" the outer ring is.


  3. Insert magic sauce here (gotta keep some things a secret, sorry...)

  4. From #2 and #3 we compute a vector and estimated material to remove.  We take the ring over to our mill and remove this material and retest starting with step #2.  The balance marks will look something like below and our goal is to only have one on each outer ring but some may have more depending on each rings needs.

 

Our goal with each ring is to bring it less than "G-20 @ 10,000 rpm."  When we launch and test our hand spins come in around 2500 rpm which would bring this number in line with a G-5 specification.  We determined this number by testing Columbia Copper rings and they all test withing this standard and spin excellent!  As we get better we hope to bring this number down but one thing we have learned is: "to embark on a balance journey is not an easy one and just when you think you have something figured out, you don't..."

 

Special thanks again to Bill for your continued support and Keep Calm and Spin On!



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