We currently run the Tormach-recommended Durakut 4010 synthetic coolant.  It is available from Tormach in 1 gallon jugs, part number 31750.

The stock coolant tank on the Tormach 1100 holds about 6 gallons.  The tank is located behind an access door on the left side of the gray base of the Tormach.  It is preferable to use distilled water to fill and top up the machine, though it has been initially done with Nashua tap water.  We currently run the coolant in a 5-6% mixture, which is within the manufacturers recommended range for the materials we most frequently machine.

A ratio of 0.3 gallons of coolant to 6 gallons of water yields a 5% strength mixture.
A ratio of 0.3 gallons of coolant to 5 gallons of water yields a 6% strength mixture.

Coolant to water ratio will change over time, primarily due to evaporation of the water.  If the coolant mixture is too lean (not enough coolant), machine rusting will be an issue.  If the coolant mixture is too rich (too much coolant), it is a waste of coolant and may potentially attack the paint on the machine. 

To maintain the proper ratio, the coolant must be periodically checked with a refractometer.  Many cheap refractometers measure in Brix units, which are specific to sugar content.  However, by performing a baseline comparison against a known mixture concentration, the concentration of the coolant in the machine tank can be checked.  This document from Tormach describes the process, and Steve R owns an inexpensive refractometer (specifically this one) and can check coolant concentrations until the space owns one

Based on initial tests, the Brix reading on Steve R's meter should be between 2.1 and 2.2 Brix for a 5-6% concentration of Durakut 4010.

Coolant levels and flow should be checked every time the machine is operated if coolant is to be used.
Coolant concentration should be measured and adjusted at least once per month (tbd).  Overall coolant level will diminish over time if the shop vac is used to clean up wet chips after a project, as some of the coolant mixture is carried away with the chips.  Additionally small amounts of coolant mixture are lost due to spray out of the machine enclosure.

The stock coolant system is very sensitive to tank level, and the pump will cease drawing coolant if the level in the tank drops even a couple gallons.  The pump inlet sits about 2 inches above the bottom of the tank, and thus it cannot draw from the last couple of gallons.  If the coolant output seems to drop off abruptly when the output is directed toward the table of the machine, then double check the level in the tank and adjust coolant/water mix accordingly.  When the coolant flow is aimed at a part, it will collect on the part/table/enclosure and drain back to the tank much more slowly than the pump supplies coolant from the tank.  It does not take long for the pump to get ahead in this case, draining the tank below the usable level.  Note that in this circumstance, the system will likely pump acceptably if the output is aimed directly into the drain screen, because the tank is replenished quickly. 

When the coolant/water mix dries on metal surfaces, the water should evaporate leaving the oily coolant mixture as a protectant for the metal.  Still, it is best to try to leave the machine, tools, work holding, etc., as dry as possible when finished to reduce the chance of rust forming.

Exposure to coolant is a known issue in commercial machine shops, and individual reaction to the coolant will vary from person to person.  Steve R. personally finds the Durakut 4010 to be a bit of a skin irritant, and notes some sinus/respiratory effects like sore/itchy throat when working around the machine for a lengthy period of time. The MSDS sheet is available here.