The intent of the short-shot approach is to help ensure that all cavities are short during 1st stage fill. This ensures none of the cavities are packed during fill and therefore receive the same amount of packing in all cavities during 2nd stage.
Question: How do I determine 90-95% fill for a multi-cavity tools? I’m not looking for theory, just a practical procedure.
My Response: There are many opinions on this matter, but I have had great results following the guidelines below:
- Turn off 2nd stage packing and mold a short shot with all cavities short
- Incrementally decrease the transfer position and mold parts until the first cavity fills completely
- Weigh and record the shot weight of all cavities without the sprue or runners.
- Multiply that weight by 0.90 and 0.95 to determine the lower and upper limits of your target weight
- Adjust the transfer position until you achieve a 1st stage part weight between those limits