Union Tool Protractor Head

I found this protractor head for a combination square at a recent garage sale.  It had no rule with it, so I had to hope the rule on my Starrett combo square would fit it.  For a buck it was worth the risk.

UNION TOOL CO.
ORANGE, MASS. U.S.A.
Note that Orange, MA is right next to Athol, MA, home of Starrett (coincidence?)

I like taking things apart (to the extent of my limited abilities, anyway) to see how they work and to clean them up.

These thumb-screws lock the rotation ...

... and when completely removed, the inner part comes out

It didn't have to be apart to try this, but while it was apart, I tried the rule from my Starrett combo square in the head.  At first they didn't fit together at all - the rule couldn't get clamped tightly and I thought maybe it needed a different width rule.  But then I took the rule back out and removed the clamping mechanism.

Ruler is loose when fully tightened up

The clamping mechanism: Red arrow shows the part that fits in the ruler's groove.
Yellow arrow shows a raised "key" that only allows the clamp to work one way in the head.

After cleaning up these part and putting it back together, the ruler clamped tightly in the head.  It turned out that the clamp screw has a raised "key" that needs to be in the proper orientation in the head for it to fully clamp the ruler.

Protractor head reassembled with the Starrett combo square's rule

And showing it at a 30° angle

There was one last thing that I wanted to check out.  There's a bubble level on the back side of the protractor head.  I wanted to see if it was reading level accurately so I checked it against a couple of other levels.

Back side showing the bubble level

Set the protractor head to zero degrees and rested it on a four-foot level clamped
exactly level in the vise.  A small torpedo level is also there as another check.

Four foot level bubble perfectly centered ...

... but the protractor head bubble was off

At first I thought about sanding some off the base of the head.  It needed a little cleaning up anyway.

Cleaning up and flattening the base

It turned out that the bubble level has adjusting screws that make it a cinch to get the bubble just right.  It would have been a very bad idea to try to adjust it by grinding the base on sandpaper.

Loosen these two screws to adjust the bubble level.

And that's that.  For a buck I now have a protractor head for my combo square rule and it works great.  I've seen incomplete combination squares at garage sales - for example just the rule, but no head.  Maybe next time I'll pick up the parts - you never know when you'll find the missing part.