Useful Responses From Readers

I mentioned how much work tapping in steel is compared to aluminum, and aluminum compared to acetal, and a reader said that I needed to use a spiral point tap (often called a "gun tap" because of the industry that it came out, as did many of our basic machine tools) instead of a plug or bottoming tap, the type commonly sold in hardware stores. 

It turns out that some of my taps are indeed, gun taps, and work wonderfully well.  Others are the traditional bottoming tap.  This is the right choice if you are tapping a blind hole.  Still, it is faster to use a gun tap to start the hole, and then use the bottoming tap to complete it.  For through holes, the gun tap is the right choice.  I was completing an order for a customer in Illinois earlier, and for that, I was tapping 1/4"-20 holes in aluminum tubing--and with a little thread cutting oil on the tap, it went through just beautifully.

I noticed an interesting statement in the Wikipedia article:

The largest tap and die company to exist in the United States was Greenfield Tap & Die (GTD) of Greenfield, Massachusetts. GTD was so irreplaceably vital to the Allied war effort from 1940-1945 that anti-aircraft guns were placed around its campus in anticipation of possible Axis air attack.

 I actually own a number of Greenfield taps and dies, by the way.