CNC made Coolant Tank

Sooner or later the home machinist comes across the thorny question of using coolant when cutting, and it doesn't take much looking to come to the conclusion that coolant kits are bloody expensive.

But they don't need to be, there isn't anything precision or high tech about it.

For this project the pump goes in the left hand end of the tank you see pictured on the right, (which in the illustration has the side missing) any old aquarium pump such as a fluval, provided it fits inside a 100 x 100 x 300 mm envelope.

It doesn't even have to be a new pump, all we really need is the pump head. You will (depending on the pump you select) be limited to a certain maximum head, but 1.5 metres is easily obtainable so just avoid looping the coolant hose up to the ceiling and back down again.

This design has a tank with exterior dimensions of 400 mm long by 320 mm high by 120 mm wide.

This project is made out of acrylic, acrylic doesn't rust, and doesn't react to most things you find in and around a machine tool, plus it has the benefit of being clear. The downside to acrylic is it is a better thermal insulator than metal, but in our hobby application this won't be an issue, we simply aren't going to have the spindle power available to overheat this volume of coolant.

First, let's discuss the parts and construction.
 The sides, when slotted, will tend to be bowed outwards due to the stress relief of the slotting process, so the cross brace is glued and clamped in place to prevent this.

The lower base, base, all four sides and cross brace thus form one solid structure, every joint glued properly. Look at my other projects for tips on using acrylic, it is wonderful stuff, it can be cut, drilled, tapped, solvent welded, bent, all quite simply, just use the right techniques and the right solvents.

The primary and secondary filters can be slid out, this is a periodic, coolant change event thing, not needed every day.

Particularly note the 10 mm gap between the secondary filter and cross brace, this is there for you to insert some washable filter medium (eg open cell foam)

The lid should be screwed onto the main unit, not glued, you need to remove the lid to access the filters.
The lid also needs to carry one grommet for the electrical power cable for the (submersible) aquarium pump, one outlet (bulkhead) nipple to go from the pump discharge to the machine tool, and one inlet (bulkhead) nipple to return coolant from the machine tool.

The larger compartment in the plans is for the pump, the smaller compartment is for the return coolant.

This is a dead simple project, about 25 quids worth of acrylic and an aquarium pump, this is dead easy to clean periodically, doesn't hurt (corrode) if it sits unused for weeks, and it is a sight glass, the only thing to watch is coolant itself.

I'd suggest you put your pump about half way down the reservoir, and fill the reservoir to two thirds full, you want enough coolant to go up the pipes and around the work and through the table and back down to the tank, and allow for some losses to splashing and evaporation, without scavenging the pump, and you want to allow some expansion room for swarf and crap getting carried back down to the reservoir without overflowing the tank.

I am assuming, given that this is basically a plastic tank, and the comments I have been making here, that when we say "coolant" you are not one of those people who believe "coolant" = neat oil.

I am assuming you are one of those people who believe that "coolant" =  oil + water, emulsified into a non-combustible thing reminiscent of tea or coffee.

Selection of coolant I'll leave up to you, you could start with the cheapest supermarket motor oil you can find and dilute it 5:1 with potable water, whatever you choose, you MUST learn what every professional machinist already knows, that using liquid coolant has a lot in common with using a hosepipe in the workshop.
  1. It is bloody dangerous around electricity
  2. Rust never sleeps
So from the safety aspect we have a sealed, designed to be immersed aquarium pump, inside a plastic tank, good so far, then, on the machine work table we will get splashing, and the operator will get wet hands, very bad, so pay attention first, not later, lying on the floor.

We also have to remember that the water component of our coolant, not just in liquid form but also as vapour from the cutting tool work surfaces, is going to get everywhere, so we have to allow a minimum of 30 minutes to THOROUGHLY clean and wipe down and oil the machine after use, this includes the cutting tools and up the spindle, not just the table and work vice.

In the morning direct the coolant straight back down the return hole and run the pump for ten minutes before machining, you want that emulsion smoothed out.

FYI I mainly use Rhino for CAD, MeshCAM for CAM and Mach3 for CNC.

If you need me you can try https://surfbaud.dyndns.org/ (self signed cert)

December 2008