Nearly free tramming bar

the black object protruding from the bar is a common dial test accessory

checking perpendicularity, more commonly known as tramming  

A very simple tool to check that a spindle is perpendicular to a surface.  Also used to find the centre of an object, especially useful  for round objects. The tools used here are a dial indicator and a dial test indicator.

Materials:
A piece of hardwood
A 1/4-20 bolt with the head removed
A 1/4-20 wing nut
A 1/4-20 nut & bolt to fasten the dial indicator

Why 1/4" bolts? It's a common router collet size and also fits the mounting hole on most cheap dial indicators.

finding the centre of a circular object

 

 

 

 

 

 

This tram bar was built without much effort towards being square or accurate.
It's for comparative measurement so as long as it's repeatable it's good enough. For the same reason the cheapest of indicators should work as well as pricey units.  In a pinch a bent piece of rod and feeler gauges can replace this whole apparatus