When designing the CNC Lathe toolpaths for the Porsche AN Fuel Filter fitting, we decided to employ gang tooling alongside turret tooling to increase the speed and precision of the 500 part batch.
With this approach came a new challenge: how do we perfectly orient the center points of the gang tools along the X-axis of the lathe?
With a gang setup, each tool has its own unique center relative to the lathe chuck, and each and every one of those centers need to be found and programmed into the lathe.
Ideally, a multi-position gang block, used for mounting multiple tools will have its “distance between centers” known. For example, our 3-gang block has a listed distance of 1.250” between centers.
But, we don’t like the idea of simply trusting a spec. sheet and entering in a 1.250” offset into the CNC... I’d rather we verify.
This brought us to the purchase of a 2D Coaxial Indicator.
A 2D Coaxial Indicator allows for accurate component centering and positioning in many machining applications. What makes the indicator so handy is that it can be used at any angle and the dial remains stationary, in this case, allowing us to spin the lathe chuck while reading the gauge.
Let’s begin...
Step one is just mounting the dial indicator into the lathe chuck. Our indicator has a 0.375” shank diameter, and while we could’ve mounted it into a 0.375” 5C collet for dead-on accuracy, for our application, mounting it into the chuck is appropriate.
Step two has us jogging the lathe to place the 1st hole of the gang block approximately center to the coaxial indicator.
What we need to do is to make sure the indicator is under a gentle “load” when we insert the feeler into the bore. We want to make sure as we rotate the indicator, it is in constant contact with the wall of the bore.
We hand-rotate the chuck to ensure the feeler is in constant contact for the entire 360 degrees of rotation. At this point we don’t care how off-center the chuck and gang tool holder are, we just want constant contact.
Step three, we begin to adjust the x-position of the lathe, while hand rotating the chuck – the goal being to lessen the swing of the indicator with each adjustment.
NOTE – we could run the chuck at a low-rpm (our indicator requires less than 800RPM) while we adjust the X-position, but we’re not yet brave enough to risk destroying our new tool… so we’ll continue to turn the chuck by hand between adjustments.
When the indicator has the smallest amount of deviation, you have found the center of the gang tool, and therefore, have lined up the lathe chuck on-axis with the gang bore.
Step four: At this point you can “zero” out your tool in your CNC program.
Now, for step five, we want to verify that our chuck is on-axis with the gang tool holder when we dial in G0X0.
Our 3-position gang tool has a 0.750” bore, so we machined a piece of 0.875" Carbon Steel Round Bar A36 Hot Rolled stock to a final diameter of 0.7495” as a test piece.
Step six: We drove the lathe to a random position in X and Z, and then sent the machine to X0. We loaded up the test piece in the chuck and began to move the gang tool towards the chuck in Z.
As we carefully approached Z, our test piece perfectly slid into the gang tool bore, aiyooo!!!
And with that, we’ve perfectly centered the first tool to the lathe chuck, we simply repeat the process for tool 2, and tool 3, respectively.
NOTE – we can speed up the process remembering the distance between centers on this gang block is spec’d out to be 1.250”, helping dial in the center that much faster.
Have fun!
E