I work at a machine shop with high-volume parts and a lot of threaded holes. Common sizes are 1/4-28 STI and 10-32 STI. Every hole gets a helical insert. We have always had major issues with the 1/4-28 STI holes. Some inserts will go in with no problem, some will not even go halfway in. These are holes that have been through the same process and tapped with the same tap. What can be some causes of this? Also, we never have problems with any other hole size. Just 1/4-28 STI. We use pneumatic drivers and also dip the inserts in a liquid before inserting. also, every part gets anodized.
Started doing some research and testing. Like debris in the holes from buffing and tumbling, or anodizing thickness causing issues. These are all still in development.
Final questions: Has anybody had similar problems and did you find a solution? Does anodizing leave a thick enough layer to affect this? What about Alodine?