No Hackery

The idea of using a 1.5" square with shims turned out very ugly, especially having to glue the shims to the square.  But I had some slightly oversize 1.75" squares from when I bought the ill-fated Harbor Freight horizontal bandsaw (two of them, one stillborn, the other suffered infant mortality).  So I ran these pieces through the mill to fit in the tubing.

Because the Y axis controller is currently inoperable, I was running Y by hand.  This was far quicker than I expected; faster than I dared run the mill in CNC mode.  Furthermore, I finally had occasion to understand why climb milling is better than conventional milling.  Not only was the finish beautiful  and shiny with climb milling, the 3/4" end mill seemed less interested in grabbing the metal, even at feed rates as fast as my hand could turn the handwheel.  I was able to trim these to a size that fits into the 1.75" inside (actually more like 1.73" inside) square tubing.

Tapping aluminum this thick with the Tapmatic was a bit more adventure than I expected but I was finally successful.  I think I learned the needed lessons.  Also, when screwing the 8-32 screws that hold the block in the tube requires no tapping in acetal.  Aluminum requires tapping.  Not sure if the Tapmatic can be trusted for this small a tap, but putting it in my cordless screwdriver with max torque set near 0 seems to do the job quickly and square enough for this purpose.  As you can see, this block was a little small, although adequate for my purposes; in the future I will mill them closer to the needed size.  No more acetal after the current batch is exhausted; aluminum looks better and is about half the price.