CNC Coolant Filter (0.2)

Four months ago I made a couple changes to my CNC coolant filter to improve operations; I added a slider shelf for easier chip basket access, changed to a lower mesh count (100µm / 140 mesh count) for quicker coolant draining in the chip basket, changed the catch basin to a smaller container with a sealable lid to prevent coolant evaporation when not in use, and made the coolant reservoir more accessibility for checking coolant levels and PH.

Drawbacks of v0.1 Setup

The v0.1 setup filtered chips from the coolant with no spills, so that alone was a huge improvement over the prototype, but beyond that, it left a lot to be desired for ease of use. It was a major pain to empty chips after a job was complete, because there wasn't enough room to remove the chip basket — the entire assembly (reservoir + filter catch basin) had to be pulled-out, from under the CNC table, in order to empty the chip basket. My original plans for v0.1 was to cut the front off of the laundry basin and add sliders so the filter could be pulled out, but I couldn't bring myself to make the cut.

The awkward coupling of the reservoir and catch basin (laundry tub) also meant it was difficult to check coolant levels and measure PH in the reservoir. The filter mesh (50µm / 270 mesh count) I was using started to clog after 2-3 jobs, and then eventually during a single job. Even after a thorough cleaning of the mesh, it was clogging consistently, and I was feeling anxious about high coolant levels in the chip basket, again.

Updates

The changes are minor, but they have been a real delight during operation. These minor iterations have made life more enjoyable when using the machine.

Ditch the Laundry Tub

Decoupling the laundry tub (see v0.1 post) from the reservoir was the first step in tackling the updates. No matter where I moved the laundry tub it took up too much space and I kept bumping into constraints. Due to it's height and vertical location, I'd have to add a small pump at the drain to get coolant back into the reservoir, which meant adding a float switch for coolant height in the catch basin, or changing the coolant return to be located on the side of the reservoir. All of which I didn't want to do. Very quickly I decided that I had to ditch the laundry tub — it felt messy trying to move forward with it.

The simplest idea at the time was to put the chip basket inside a smaller plastic bin and as long as that bin was located higher than the reservoir, it would drain.

I found a plastic container by Sterlite called a Gasket Box with dimensions of 47cm x 37.8cm x 28.3cm / 18.5" x 17.875" x 11.125" and 30L capacity. This had a nice foam gasket around the perimeter and four snap latches to seal the lid, to prevent evaporation when not in use. The latches weren't necessary, but the design and shape of the container worked well for me, and most importantly it fit the chip basket nicely.

Where to buy: Home Hardware

Hanging Chip Basket

The chip basket hangs just slightly below the top interior edge of the catch basin (gasket box). I used scrap pieces 5052 aluminum sheet and bent wide S-shaped hangers for each edge of the container.

I kept the chip basket (seedling plant trays) from v0.1 because they worked very well. I still need to better secure the filter mesh to the tray, but it's a minor asthetic issue.

Where to buy: Amazon

Bulkhead Fitting

I added a bulkhead fitting (drain) to the back of the filter catch basin (gasket box) so coolant would flow back to the reservoir.

Unfortunately I couldn't put the fitting for the drain on the bottom of the container due to height restrictions and the coolant return slope. I positioned the drain as low as possible on the side to minimize the coolant remaining in the bottom of the filter catch basin. Not ideal in my mind to have a small amount of coolant always in the bottom of the container, but it would allow me to visually inspect the colour of the coolant easily. I entertained the idea of having a small pump in the bottom of the container to circulate the coolant, but in the end I abandoned that idea.

I also added a ball valve to the reservoir return drain, so the flow could be shut off if I had to move the filter catch basin, or the reservoir.

Where to buy: Home Hardware

Slider Shelf

The slider shelf allows me to pull-out the filter catch basin and chip basket for easy access. Being able to conveniently empty the chip basket has been the best change by far. There's not much to the slider shelf, it's just a couple 2x4s, plywood and heavy-duty drawer sliders.

Where to buy: Rona - drawer sliders

Filter Mesh

Lastly, I changed the filter mesh count from 50µm (270 mesh count) to 100µm / 140 mesh count for better coolant flow. Previously a shallow pool of coolant was starting to form and not drain through the basket fast enough, as shown below. After an hour of operation, this pool of coolant would be near the top of the chip basket.

The 100µm / 140 mesh count works much better. It filters chips and the coolant drains through immediately. I might try 70µm filter mesh in the future to compare the filtration qualities, but at this time I'm very happy with 100µm.

Where to buy: Amazon

I've only used this new filter setup for 4 months, but it is a significant improvement over the v0.1 setup. These minor updates have made life very enjoyable when using the machine. I'm really glad I took the plunge and ripped out that massive laundry tub.

Wish List

There's only a couple items I would change to improve operations further.

• Dual filter baskets for quick change during operation. I would love the ability to easily empty the filter basket without stopping operations. I currently have to shut off the coolant pump, shut off the CNC table drain, slide out the filter chip drawer, pull out the full chip basket, swap in an empty chip basket, and try to not drip coolant on the floor from the full chip basket. Once swapped, then I open the CNC table drain and turn the pump back on. It's not as smooth and efficient as it could be. Having two baskets with a way to automatically divert the drain flow direction would be lovely.

• Coolant level indicator. This is a wish list item that has carried over from v0.1. Having the ability to see coolant levels during operation is really helpful. I had attached a fuel sending unit on the reservoir, but never got around to hooking up a circuit for it. Having an analog and digital read out would be ideal. Digital to signal a stop if levels are too low, and analog for a quick casual glance.

• A rigid filter catch basin drain pipe. The flexible hose I currently have attached to the filter catch basin and reservoir allows the drawer to be pulled out. The flexible hose is excessively long to accommodate the full extension of the drawer, and therefore takes up a lot of room, and also has to be supported so the hose doesn't sag and stop draining. It works, but it's a failure point that I'd like to make more robust.

• Inline filter with high mesh count. In the original prototype I used an inline filter, and I'd like to bring that back but with a different setup, possibly on a separate filter circuit that's independent of CNC operations. Then I can run the inline filter to clean the coolant a bit better.