I made spindle square so I decided to share my successes and failures in case anyone else wants to make one.
The attached images show how I made the square. It is pretty straight forward. The difficulty is making sure the “feet” of the square are in perfect relationship to the shaft.
I chose some 5/8” bar stock to use with a ½” drill rod. I was going to use a socket head cap screw to secure the shaft in the body, but since I had a .498 & .499 reamer I decided on a press fit.
I used my DRO for the hole spacing, I drilled and reamed for the main shaft. I then drilled a stepped 3/8 inch for the dial indicator shaft, and a through hole for the tip. Then cutout the arc for the dial indicators.
I inserted a 3/8 dowel in the body to act as a drive dog in the 3 jaw chuck. Then I squared the feet to the shaft by taking a skim cut at the lathe.
Here is where I screwed up. I had trammed my mill about 3 weeks prior and assumed it was right. It wasn’t. It was out of tram, so when I went to test my new spindle square I got a bad reading and started to chase my tail to find out what went wrong.
I got a piece of window glass so I could smoothly spin the indicator on top of the mill table. I later found out that the window glass was not perfectly flat. I took another skim cut at the lathe. After that I got a little rocking on the feet. (I don’t know what happened there) Then I locked it down in the mill vise and took a skim cut on the bottom of the feet. This made it worse.
Here is the bottom line. The feet don’t have to be in perfect relationship to the shaft.
All you have to do is make sure you zero the dial indicators independently of each other in the same spot. The attached photo shows how I used a ¾ inch parallel bar to zero one indicator. Then I spun it around and zeroed the other indicator in the same spot (using a little mirror).
I think the skim cut at the lathe is the way to go. But if you miss the mark there, not to worry, just zero the indicators independently. The gizmo works great. I am retired so all I have got is time. (although I am retired, my wife says I work part time as a pain in the ass )