Hi Matt. The issues on wood dust/chip collection seem to be that (a) the system needs to draw in enough air to the machine inlet (the machine hood, guard, collector etc plays a big part in this) to create a fast enough (they say 50 feet/sec) flow into the system across a large enough bubble/volume/sphere around the point of work to prevent the spray of fine dust flung away by the blade from escaping into the shop.
It (b) needs enough air velocity inside the duct to carry dust and chips along without it settling out and leading to a blockage/fire risk. This is where the 4000 ft/min number comes in - there's a max duct size for which a given volume of air (cubic feet per minute) delivers this velocity, or something above it.
The other key bit of information is that it takes much less volume to do a good job of collecting visible sawdust and chips (around 350 cfm is the figure quoted for most machines) than it does to trap the finer invisible sub micron dust that it truly dangerous. (our lungs can't clear it out)
The likes of Bill Pentz (he has some excellent web pages on dust collection and systems - he comes up easily by name on Google) suggests that you need around 6 - 700 cfm to meet the US OSHA air cleanliness standards, and around 1,000cfm to meet what's medically known to be safe. This latter needs a duct size of around 6 inches to keep the pressure drop reasonable in a small shop.
He suggests that you need a much finer 99.99% efficient at 0.3 micron filter to deliver safely filtered air, and that you need a cyclone to drop out the dust and ships before filters this fine to stop them blocking far too quickly.
He's done an enormous amount of testing, and argues that most DIY/hobby level dust systems (a) don't have a big enough motor or fan impeller to shift the required air volumes - but that many fake it for advertising numbers by testing against an unrestricted fan inlet (no ducting) and probably with no filters; and (b) use filters so coarse (to avoid overly frequent cleaning, and to maximise flow) that they just recirculate the fine dust back into the room.
They then use small ducting (100mm and similar) to maintain a high enough air speed to prevent blocking with a low enough air volume not to overload the fan motor.
We tend to find these systems to work OK (even if they need very frequent filter cleaning) because so far as we know they do a decent job on the coarse chips and dust we can see.
The problem of course is that while you can have lots of suction/pressure drop (which enables smaller/longer duct runs) or quite decent volume (which gives good collection) alone with smaller motors and duct sizes you can't have both. It takes around a 4hp fan and 6 in ducting for example to deliver around 1000cfm and 4000fpm in a small shop.
Bill's testing is the background i was drawing on in commenting on the 106 L/sec/225cfm volume of the DX 5000. I can't say for sure, but it's hard by his data to see it doing more than lifting the visible dust and chips.
The problem with adding more ducting is that for every metre of duct you get a given amount more pressure drop. The nature of fans is such that as you increase the restriction on the suction side the volume of air moved is reduced. (so is the HP drawn - so it doesn't cause overloading)
On positive side the 2KW of the DX5000 is a lot more motor than your average bag and filter system, so the chances are (but i've seen no info on the ads i checked) it delivers a lot of suction/pressure drop at its 106 L/sec/225cfm. (i.e. that it will tolerate quite a long run of ducting, or a restrictive filter with relatively little reduction in volume flow) This if actually the case means it should perform much better with more hose length, and on the restrictive dust collection arrangements on many machines than the typical radial impeller 1 hp basic bag and filter dust systems sold to us hobbyists. By the ads it also has a 0.5 micron filter which should be much finer than the typical DIY bag system too - the extra suction probably makes it feasible to use this.
Hope this helps...
ian
) Are there similar machines at this sort of price with the specs that you describe that are capable of running a centralised system or are they are masquerading as suitable when they're not?
