Do taps and dies actually get dull from plastic?

[jj9ball]

Someone please help. I am having huge issues with threads on all my pens feeling too tight. It has actually gotten worse the past couple pens I have made. Is it possible that the plastic and alumilite have made my taps and dies dull over time? I have made a 100-150 pens with them. I use pam to lubricate the taps and dies when I am using them. I also blow them out with compressed air when I am finished using them. I normally turn my tenon about .15mm undersize (11mm x .75 threads gets a 10.85mm tenon). I use a drill that is around exactly the size (example above would get a 10.30mm hole. The biggest issue is that I haven't changed any of my methods and all of a sudden everything is fitting wrong. Any help would be GREATLY appreciated. Thank you for any and all suggestions.

 

[bmachin]

Any chance that the adjusting screw in the die got tightened? That would open up the die thus giving you a larger minor diameter.

Have you changed drills? I've noticed that the shanks of the drills in my metric set tend to run about 0.1mm undersize.

Bill

 

[1080Wayne]

Bill has given you the most likely answers to your problem . To give you the theoretical answer to the dulling question - probably , given enough usage on the harder plastics , but I think the more important issue is the inorganic pigments used to colour the blank . Some may be fairly abrasive . I suspect Trustone and similar products would be the worst .

 

[bmachin]

One other possibility comes to mind. If you have changed to a softer more resilient blank material your drills and lathe tooling may be compressing the material as you cut. When the material "bounces back" you will end up with an oversized tenon and an undersize hole.

The reference that I have regarding machining urethane warns against this effect.

Working from memory, that reference recommends a 15 degree back rake and a 30 degree front rake for turning if you are using a metal lathe.

Bill