I’ve written before about the need for regular dust extractor maintenance. An extractor with a filter is not ‘fit and forget’. My extractor is a cyclone unit and since I removed the internal wire grid that avoids the low risk of accidental contact with the fan, it is less prone to blocking up. After considerable use, it still seemed to be working OK. But when I checked the filter recently I found a great deal of fine dust in it. After cleaning it, the extractor worked a great deal better. Not really a surprise!
The deterioration in performance had been so gradual that I had failed to notice it. I needed an objective measure of performance and a proper dust extractor maintenance schedule. Just putting my hand in front of the inlet now and again to see if there is still suction is not good enough.
Measuring air flow
Performance equates to air inlet velocity and filter effectiveness. Dust build up in the filter actually improves its effectiveness, but it cuts the air flow. The flow can be assessed by measuring the vacuum in the pipe. A vacuum gauge permanently installed as part of the system, with an easily visible readout, would be ideal. However, I opted to measure the speed directly with an anemometer. A digital anemometer can be got very cheaply. I bought this one from Amazon.
It was impossible to get a consistent reading from it just by holding it in my hand. I folded a bit of steel strapping to make a holder for it, with a hook that clips on the edge of the extractor inlet to secure it at a fixed short distance inside. I take it out again after each reading.
The reading itself is less important than changes in the reading over time. So I noted the indicated air speed just after I had cleaned the filter. I can take further readings at intervals as dust starts to build up again. This will tell me how long it takes for the speed to drop by, say, 20%. Then I can schedule a regular filter clean in my calendar.
It was interesting to see how far from the inlet the suction extends. The answer is not very far at all. A small diameter inlet is only effective when very close to the dust source, which is not easy to achieve at the lathe. The 7 inch inlet I have at the lathe does provide quite good air flow at the tool tip where the dust is generated.
Cleaning the filter
Cleaning the filter was straightforward. I took the cartridge outdoors and stood it on end. Tapping it with a wooden batten dislodged the dust cake and it fell to the bottom. In some places the pleats were close together, and those areas took more tapping. I also used compressed air. At first, the supply of dust coming from the filter seemed almost infinite, but eventually it slowed down.