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Dust extraction upgrade

I have recently improved my dust extraction system. For a long time I have used a 2HP cyclone system with four felt tube filters hanging from a homemade plywood distribution box. I had a 7 inch pipe running across the ceiling with smaller branches to the lathes, bandsaw and drill press. The branches to the two lathes were 5 inches in diameter.

Filters

This system worked quite well, but had some problems. The cyclone and fan unit were OK, but the filters took up a lot of space, and the distribution box leaked. Leaks before the fan reduce the suction. They cut efficiency, but are harmless. But the pressure after the fan is positive, so leaks in the box result in dusty air blowing out unfiltered. There isn’t much point in having a dust extraction system if it does that!

I therefore dismantled the box and replaced the filters with a new cartridge filter, smaller but just as effective. While doing this I found the remains of a plastic carrier bag that had been sucked in, gone through the cyclone and fan and stopped at the fan outlet where there is a grid to prevent people putting their hands into the fan. It had created a partial blockage.

The new arrangement gave me more badly needed floor space. Rather than put the cartridge filter next to the cyclone, the normal arrangement, I extended the cyclone outlet with about 5 feet of 7 inch pipe so it could go in a corner of the workshop which was otherwise dead space.

Ducting

The next issue was the branch line to the lathe (I am now using one lathe instead of two). By reducing the duct diameter from 7 inches to 5, I had been unnecessarily reducing the air flow. Dust extraction is difficult at the lathe, so the more air flow the better. As the extractor has a 7 inch inlet, I decided to extend the full size duct right to the lathe. I was also able to shorten the duct and eliminate some bends which were reducing the air flow. The ducting is smooth bore metal, with the last 3 or 4 feet in 7 inch flexible hose. I put a metal blast gate at the point where the hose starts. The suction now feels stronger.

I tidied up the branch line to the drill press and improved the dust extraction from my Startrite 352 bandsaw. This saw, being an older model, had no proper provision for connecting to the extractor. I cut a hole in the sheet metal of the lower stand and bolted on a flanged adaptor for a 5 inch hose.

I fitted a dust level sensor to the lid of the collection bin. This turns on a flashing light when the bin is full. I have only once allowed it to overflow and fill up the filters, but now I no longer have to keep opening the bin to check. (Update – I have found this sensor unit unreliable and very prone to showing the bin full when it isn’t. I no longer use it.)

Adjustable inlet

The last job was to make a new adjustable dust extraction inlet for the lathe. The inlet has to be as close as possible to the point where the dust is generated. The suction falls off very rapidly with distance, and has to compete with air movement caused by the spinning wood or sander. It’s easy to get the inlet close enough for small spindles. But for faceplate work and larger spindles it can be difficult. To put the inlet where it needs to be, it has to move in and out to accommodate different diameters of work. It also has to move along the bed to cope with different lengths. If the headstock swivels, the inlet must move with it.

Movable stand

I made a movable wooden stand for the inlet (see sketch below). A wooden post is held upright by standing it in a bucket of loose gravel on the floor behind the headstock. I fixed two boards to the post in a V formation, buried in the gravel to anchor it. The post has a projecting arm at about the height of the lathe spindle, at the end of which is a wooden cradle to support the hose, which hangs down from above.

I made the cradle to fit the hose, and strapped the hose to it with bungee cord. The cradle swivels on a bolt and locks to  keep the end of the hose turned to the workpiece. I can pull the arm to turn the bucket to any position, or slide the bucket to move the inlet along the lathe bed. The weight of the gravel keeps the bucket and post firmly in position but it is not heavy enough to make adjustment difficult. It would be harder if I did not have access to the back of the lathe.

So far, this arrangement is very satisfactory. The hose and bucket are out of the way and the inlet can move close to the job. The hose is long enough to move freely, but not longer than it has to be. The stand is stable, very easy to adjust in and out, and cost next to nothing. The only slight problem is that because of the better suction, more of the chips are going up the pipe along with the dust. This makes the bin fill more quickly than before. Possible improvements might be to make the arm telescopic and adjustable for height. That would avoid having to move the bucket. But now it seems fine as it is.

dust inlet stand

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