Question on plastic injection molded guitar pick

[ik918]

Hello all, I'd appreciate any expertise you may have on the following injection mold question: I am working with a supplier to make guitar picks using plastic injection mold. The material is Dupont Delrin. I received the samples and noticed a strange result when the sample picks were tested on a guitar. When strings are struck with the pick, the tone is different depending on which side of the pick (core side vs cavity side) is used to strike the strings. Both sides of the pick have identical dimensions, so I would expect the tone to be identical. However, one side gives a tone that lacks bass. The other side gives a tone that lacks treble. Is it possible the material properties could be different between the core side and the cavity side, perhaps due to the cooling process, flow rate, or air venting in tooling? Any other possible reasons? For clarity, an image is attached showing the pick's tip, which is completely symmetrical between the two sides. Note, plastic injection molding is a commonly used process for making guitar picks, so I was not expecting any issues. I'd greatly appreciate any input on this!

 

[Erich]

Is the radius along the edge and around the point the same on each side?

I would make a fixture to clamp the pick like you hold it. Apply a load to the tip and measure deflection. Measure it with deflection in both directions.
Are they the same? How is the part gated? Where are the cooling lines on each side of the mold? Its a mystery to me why it should play differently but injection molds are inherently assymetrical things, so I would focus on those areas.

 

[ik918]

Thanks very much for this feedback. I will check on the gates and vents. Also, it is possible that the tip has some slight non-uniformity, even though the drawing has a perfectly symmetrical tip. If you have any suggestions on best practices for tooling, flow rate, cooling, etc.. to ensure the tip gets made perfectly symmetrical (per drawing) without excess material at parting line, that would be super helpful. Thanks!