Ground Thread Dies?

[Pete W.]

Hi there, all,

This isn't so much a 'How do I?' but more a 'How do they?'

It concerns ground thread dies primarily but I guess some of the answer will also apply to ground thread taps.

How do they profile the grinding wheel to suit the thread profile?  Having profiled it, how long does it stay within the required tolerances?

Bearing in mind we could be talking about 12 B.A. or even finer and that a grinding wheel is, by definition, friable.

[Lew_Merrick_PE]

Pete,

Today, they use Cubic Boron Nitride abrasive "bonded" to hard steel forms.  Back in the dark ages, they used hard steel forms that were "fed" abrasive like unto lapping (abrasive in oil or grease) compound.  Going back even further (when "pets" were all still lizards), they used very hard "stone" for the grinding wheel.

As an apprentice in the mid-1960's, I made a whole set of lapping taps when I made my micrometers.  I screwcut the control-nut a couple of thou undersize and then brought them up to size and finish over several days of lapping.  (I was even required to hand grave the first internal thread hole I made -- talk about pain and frustration!)

[rotorhead]

Hi Pete,

Thanks for asking that question as I've often wondered how it was achieved...

And thanks to Lew for the answer..