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

$2 Router Table Clamps

This project is cheap fun assuming you have available scrap or scrounging skills.
The original idea was spotted on Thingiverse,  here's the link:
https://www.thingiverse.com/thing:776 

Materials used:
1/2" birch plywood https://www.menards.com/main/building-materials/panel-products/specialty-panels/hardwood-panels/1-2-x-20-23-x-20-23-c2-russian-birch-plywood/1254000/p-1452209920854.htm

3/4" hardwood dowel (to make the pivots)
1/4-20 threaded rod
1/4-20 nuts
1/8" hardwood plywood (to make the nut retainers)
1/8" HDPE sheet (to make the plastic washers)
A scrap piece of birch flooring (to make the knobs)
Woodglue

The knob in the centre of this image has a 1/4-20 nut embedded just slightly deeper than flush. The recess for the nut is a hexagon pocket cut with a 1/8" diameter bit which leaves a bit of material where there should 6 sharp corners, this provides a nice interference fit.  Barely visible leaning against the knob is a wooden washer,  this will be glued to the knob to act as a nut retainer.  To the right of the knob is a threaded rod and an "E-Z LOK" threaded insert.  The inserts have been installed from the underside of the table surface.  Every hole seen in the table above has a threaded insert installed.

 An exploded view.  The wooden washer is glued to the knob to act as a nut retainer.  In practice the nut may fit tight enough in the knob to make the retainer unnecessary.  If the knob is hardwood (I used birch hardwood) the knob itself could be tapped for threads eliminating the nut.  The pivot has been milled to provide a flat surface, this increases the holding power of the knob assembly.

WARNING: These clamps will collide with the router if you get too close.  For added clearance a bolt can replace the threaded rod and knob.