Thread: Dusty Questions

Originally Posted by RobjG

. . . . I am thinking about Carbatec and their 2HP DC1200P but with the addition of a cyclone.
My question as I intend to install the DC outside in a covered annex and duct any of the dust fines through the opposite wall out into the yard do I really need to install the filter bag set up?.

A stock 2HP DC is well below par as a DC.
Adding a cyclone will result in significantly less flow and removing the filter bag will not make up for the loss of flow.
The only way a 2HP can come close to moving enough air is if it is modified along the lines show in the sticky at the top of the dust forum.

Ok another stupid question.....
Lets say all your duct work is 150mm min. a powerful extractor setup and vented to the outside, with duct gates where required.
What would be the effect of having small cyclones with small buckets, set up just after each machine........ rather than a large cyclone at the end of the duct work.
I'm thinking less large particle movement through the duct might compensate for pressure loss. Small cyclones seem to be inexpensive in comparison to large ones.
Any thoughts?

Originally Posted by RobjG

Ok another stupid question.....
Lets say all your duct work is 150mm min. a powerful extractor setup and vented to the outside, with duct gates where required.
What would be the effect of having small cyclones with small buckets, set up just after each machine........ rather than a large cyclone at the end of the duct work.
I'm thinking less large particle movement through the duct might compensate for pressure loss. Small cyclones seem to be inexpensive in comparison to large ones.
Any thoughts?

Yep - this would be a disaster.

Small cyclones are designed to be attached to "high pressure - low volume" suckers like vacuum cleaners.
The small high speed impellers used in vacuum cleaners generates pressures around 0.3PSI which draws about 100 CFM which will pick up chips but is considered inadequate for grabbing the large volumes of fine dust made by most WW activities which require a nominal 1000 CFM. Adding a small cyclone reduces the pressure by 10% (0.3 PSI) but seeing as there is stuff all flow to begin with it does not really matter.

Standard powerful dust extractors are "high volume - low pressure" suckers and generate <0.1 PSI but because the have large fans can move ~10 more air volume than a vacuum cleaner provided large pipes are used.
Adding even a large efficient cyclone with 6" inlets and outlets to these can reduce the flow by 25%. Adding a small cyclone with say 4" inlets and outlets will reduce the original 100 CFM flow by much more again.

A Large efficient cyclone like a Clearvue can be used but don't forget these use at least a 15"impeller and a 4HP motor partly of course to make up for the loss of pressure.

I'm thinking less large particle movement through the duct might compensate for pressure loss.

The extra friction/load imposed by the amount of the dust moving through the duct represents only a small added load to most large systems.
The impeller just sees the sawdust as a load like the air.
If an impeller is able to pull 1000 CFM through a machine that's equivalent to ~33.6 kg of air per minute
If a thicknesser is taking a 1mm pass of a 300 mm wide pine board that is 5m long in one minute thats around 0.75 kg or sawdust per minute - this means the sawdust adds only 2% to the load of the air already passing through that system.
In hardwood that would only be ~4%

The problem is the air still has to be pulled through the cyclone and the cyclone as a serious flow restrictor.

You would be placing a huge restriction between the machine and the dust extractor, dust removal would be virtually useless.

EDIT: Opps, posted at about the same time as BobL

Originally Posted by MandJ

You would be placing a huge restriction between the machine and the dust extractor, dust removal would be virtually useless.

EDIT: Opps, posted at about the same time as BobL

I was going to quote you as having tried this out so thanks for posting

thanks

It seems to me from all this information that the only way to keep your workshop dust free is either

1. have a dust extractor that's suction is so powerful that it could pull nails out of the wall

or

2. do all your wood working outside on the lawn.

Originally Posted by RobjG

It seems to me from all this information that the only way to keep your workshop dust free is either
1. have a dust extractor that's suction is so powerful that it could pull nails out of the wall

You will never keep your workshop dust free.
There is so much dust in ordinary air because whatever air you suck out of a shed is replaced by external air, if that external air is moving (i.e. a windy day) it will carry more dust so that when it enters your shed it slows down and is dust will drop out of suspension. That's another reason why houses get dusty.

The aim of wood dust extraction is to minimise the amount of "wood dust" in shed air.
To try and capture and retain all dust is like herding cats - that was one of my day jobs at Uni - it costs a ridiculous amount of money to do this.
OTOH for wood working all that is needed is to exchange woody shed air for far less woody outside air.
Unfortunately there are no plug and play devices to do this effectively and some planning.assembly/construction is required.

The ideal situation is to try and capture the dust at the source and this is where unfortunately there is no substitute for air flow.
Especially for a small shed/operation in which the DIYer does not spend a lot of time improving ventilation can assist.

The single best thing the DIYer can do is locate (or house and vent) their DC outside their shed.
Then if your DC is small e.g. 1-2 HP adding a couple of bathroom exhaust fans will help.
The next biggest improvement is to use a DC that can take advantage of at least 6" ducting.
To fully utilise the 6" ducting the machinery ports have to be made that size and opened up so they breathe.

For a small DIY shed it should not cost more than ~$1000 and much less than this if you can purchase used dust extractors etc.
For medium to bigger shed the costs do escalate quickly.

The most common setup I have seen in small DIY sheds is $10+k worth of gear in a $10+k shed and a $400 DC in the corner with a few metres of flexy on the floor and everything covered in dust.
For another few $100 and about 20 hours of work these dusty situations could be dramatically improved.

2. do all your wood working outside on the lawn.

FWIW I lost my sense of smell for 6 weeks making a 3.3 x 0.9 x 0.3 m cupboard out of MDF on the back lawn.
I should have at least worn a mask.