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Dust control at the lathe. What works best?

Dust control is an important issue for woodturners. We work in an environment where hazardous levels of dust are in the air we breathe. Turning generates dust, and breathing dust is harmful to our health. It can cause breathing problems or cancer. Dust on the skin can lead to dermatitis. All types of wood dust are hazardous, including softwood dust, though some are more likely than others to cause allergy.

The best dust control is not to make dust. Keeping tools sharp, using the less dusty timber species, and wet sanding with water, oil or wax instead of dry sanding, will help reduce dust levels. But most turners make dust and need a way to protect themselves. There are several options for dust control.

Breathing mask

This is the easiest, and at its most basic, the least expensive dust control option. A mask can be effective for low levels of exposure. It may be appropriate for people who do not turn often or for long periods of time, where the cost of dust extraction is not justified. But it is not the best primary protection for most turners. There are several reasons for this.

A mask must seal to the face to prevent unfiltered air flowing under the edge, so a beard is a problem. The filter may impede air flow. The mask may be uncomfortable to wear. Some may cause spectacles to fog. If it doesn’t seal properly, or you take it off when the job is done, you will breathe dusty air. Hazardous dust is so fine that it remains suspended in the air for a long time after work stops. Although a well-fitting mask can protect the wearer, it can only do so while it is being worn.

For many, the best kind of mask is a powered unit that filters the air before blowing it over your face. These can be comfortable, or at least acceptable for hours of use, as the positive fan pressure means that the mask doesn’t have to seal to your face. In addition, the visor and helmet may be impact resistant. If you wear spectacles the air flow will help stop them fogging. But you will still breathe dust when you take the unit off, and a mask will not prevent dust from contacting your skin.

Air cleaners

These filter the workshop air to remove background dust. But they aren’t a complete answer. Most importantly, you work closer to the dust source than the air cleaner does, so the air you breathe carries the heaviest load of dust. A cleaner takes a significant time to remove all the suspended dust in the shop. It’s not just a matter of comparing its rated airflow with the volume of the workspace. The filtered air mixes with the unfiltered, diluting the dust concentration, which goes down slowly as the air passes through the cleaner multiple times. You should put the air cleaner where it will set up a circulation of filtered air around the shop, but there are always likely to be dead spots where dust removal is slower.

Air cleaners are a supplement to dust extraction at source, not primary protection.

Fans

Some people suggest a fan to blow the dust away from the turner. In the right conditions this could work. It will cut the concentration in the inhaled air even if the dust remains in the workshop. If there is enough general ventilation in the shop, the concentration may not build up to harmful levels. But it is not normally a reliable method. The ventilation and the direction of airflow from the fan may vary, and dust may reach harmful levels without you knowing.

Dust extractors

A dust extractor catches the dust at source, before it gets into the general air circulation of the workshop. This is in principle the best solution. It’s the reason workplace health legislation prioritises extraction over the other options.

But not all extractors are suitable. The lathe is a difficult machine to extract dust from. The dust source may be anywhere along the lathe bed or across a spinning disc. The work throws the dust in all directions, including towards you and away from the extraction inlet. Meanwhile, you are bending over the work and breathing in the highest concentration of dust.

The suction has to overcome the speed of the air movement generated by the spinning work. Dust from the tool or from sanding will go with this moving air, which may be quite rapid. You can feel the wind coming off the edge of a spinning disc. This means that a powerful extractor is necessary.

Unfortunately, the suction from any extractor falls off very rapidly with distance from the inlet. At a distance equal to the diameter of the inlet, the air speed is only about 10% of what it is in the mouth of the inlet. This is because the air enters the inlet from all directions, including from behind it. Therefore, to capture the dust effectively the inlet diameter needs to be large, so the dust source can be within its effective zone; it must be adjustable so it can be positioned close to the dust source;  and the extractor must be powerful enough to provide sufficient airflow through the large inlet. Although any extractor is better than none, it’s not enough just to use a large collecting hood if the extractor is too small for it.

It is important that the extractor has a fine filter, or exhausts outdoors. If it doesn’t, much of the dust will return to the workshop. Although a layer of dust inside the filter will itself act as a fine filter, it will also reduce the airflow. With a fine filter, an extractor left running will act as an air cleaner.

Types of extractor

There are two kinds of extractor – high volume, low vacuum; and low volume, high vacuum, which are similar to domestic vacuum cleaners. Lathe dust control needs a high volume air flow to capture the dust, and not high vacuum. There is an overlap between these types of machine, and some powerful high vacuum machines are able to move more air than a small and inefficient low vacuum one.

It is important to check the cubic feet per minute specification. Don’t mistake the high suction that you feel when you put your hand over the inlet for high airflow. The vacuum will pull hard when you block the inlet. But comparatively little air is moving through the pipe when it is open. The amount of airflow needed depends on the turning being done – larger diameter items and higher lathe speeds need more airflow. As a general principle, more is better.

High vacuum machines are very good when the pipe connects directly to the source. But at the lathe, the inlet must move as the source moves, which is not always practicable.

Other dust control issues to take into account are noise levels, ease of emptying, and the quality of the ducting. Ductwork should be as short and straight as possible, as bends and even straight sections increase friction and reduce airflow. Smooth bore ducting causes less friction than corrugated flexible pipe. Leaks at the joints and at blast gates reduce airflow at the inlet. The ducting should be large diameter to reduce friction, but not so large that air moves slowly through it and deposits chips.

Whatever kind of extractor is used, it will often fail to get all the dust. A dust mask can then be used to supplement the extractor.

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