Screw compressors are more well suited for high volume applications (like superchargers) than high pressure. This is because the geometry of the screws is difficult to sustain with very high tolerances. Small leaks aren't a problem when you're talking 10-50psi, but the 'high side' pressure of an A/C system is typically over 200psi.

My Dad made the screws for screw compressors back in the 70-90s... He primarily worked for joy/lovejoy, but also made screws for ingersall and a few others.

It was amazing to me how small the screws were for say, a shopping mall unit.. and how PRECISE the machining was.

The math behind the profiles was insane to, it was a 'self generating' curve.. You calculated a point on the curve, and that was fed in to generate the next point. Generating a new profile shape was a HUGE process... Wonder what it would be like with today's computers :-P

That's awesome! Seeing how wholly dependent modern manufacturing is on CNC makes me respect those early machine operators even more. They were constantly innovating on how to apply physical geometry and minimize incremental errors in order to build parts with tolerances that would still hold up today.

My Dad used to do a 'trick' where he would zero out a 6 decimal place readout on the big ground glass comparator..

You could then move the table anywhere you wanted in X/Y, cover the display, and he would bring it back to 0.0000X by eye :-)

He actually went to some institute in Sweden that did ultra-accurate measurements to show them how he did it. I think the 'trick' was, he moved the shadow till it was just past the blueprint, and back it off till a sliver of light shone thru, rather then trying to 'walk' the shadow up to the blueprint..

Neat stuff - but I decided on a tech career when I was mucking out the Holyroyd mill and he turned the cutting pumps on :-P Being drenched in cutting oil convinced me I liked computers better :-P