Thread: Dust basics

Originally Posted by Chumley

1. What kind of machines is a dust extractor (eg Carbatec DC-3) suited to and what kind of machines is a shop-vac (eg Sturdee's cyclone bucket thing) suited to? I'm assuming the DC works best for things like a table saw and the shopvac for stuff like a sander, but what's the criterion that makes a machine suit one or the other?

A rule of thumb?

If it comes with a 4" dust port, it needs a DC. With a 2" dust port, a shop-vac.

The real criteria are the sheer volume of shavings generated per time and how fine the dust/shavings are. Fine dust is fine for a shop-vac, heavy shavings need the power of a DC to be properly collected. eg. a shop-vac would choke on a thicknesser or jointer due to both size and volume..

2. I just read that you shouldn't impede the flow to a DC, so if you drop a 4" pipe down to say 2" to fit a particular machine, you should open a blast gate to another machine or a dummy pipe that has a 2" pipe open - apparently this is to stop the DC overheating from trying to suck harder or not getting enough air? Is this correct? And does this apply to shop vacs as well?

Not quite. A 4" duct has about four times the cross section of a 2" duct. So, if you run a 2" adapter, to maintain the airflow you should either:

• open another blast gate with three 2" take-offs, or
• have four 2" lines running off the gate you're using, or
• open a 4" gate about 3/4 of the way.

Even better still, don't use a DC for 2" lines... use a shop-vac instead.

The reason is correct, sorta. It just don't work well. As for shop-vacs... I wouldn't bother hooking one to ductwork. They're small enough to move from machine to machine but if you must, then the same principles apply.

3. I recently read something about having to ground the plastic 4" DC pipes to stop fires caused by static electicity. Is this really a problem and if so, how do you do this?

Oooer! Can of worms that one. I believe it's no problem, haven't bothered earthing mine and never had a zap from it. Metal ducting should be earthed, but PVC? I don't think so.

FWIW, every fire I've had in my seperator can be attributed to human error - sucking up hot bits of metal, oily finishing rags or visitor's cigarette butts. But static electricity?

Wot Skew said.

Earthing schmerthing.

And shop vacs = High pressure low volume
Dust collectors, the reverse.

And in all this, shavings as opposed to dust ... is a different story.

Hi Chumley

I use this setup for big stuff with 4" ports.

http://www.woodworkforums.ubeaut.com...ighlight=dusty

and I use a triton dust bucket



Connected to a 1200 watt vaccuum cleaner for hand held machines.

This is what I would start with and maybe modify the triton to a cyclone if I ever got the time. The vaccuums collector never gets filled so it works fine.

If, big IF, I had a huge shed then I would look at building a cyclone, but at the moment I dont get fine dust over the place when I work so I am a very camper.

IMO try and not get caught up in air flow this/cyclone that. They go around in circles, so unless your an alien and get off on crop circles, best stick with the tried and true basics.

cheers

dazzler

In regard to possible overheating I believe that most DC's have a separate fan to cool the motor so reducing the airflow may only reduce their efficiency not over heat them (however I'm no electrical engineer!). I don't think their fans work well without enough airflow. I always run with a blast gate half open when I do use the 2" hose on the DC.

In regard to shop vacs the good ones should also have a motor cooled from an air supply separate to the vacuum (unlike most household vacuum cleaners). Festool's do and these can be used for high pressure uses eg: hold down table for sanding - although I'm still not sure I'd want to run my CT mini for too many hours like this!

Thanks guys,
Much appreciated.
Adam

I just went into the shed and tried it on my 1hp Carbatec Dust Extractor system.

With only the connection to my orbital sander open its 1inch diameter outlet hose would pick up a cabinet scraper laying on my bench from about 1cm. When I also opened a four inch gate the suction dropped off noticeably and it would only pick up the scraper from about 5mm.

With all gates shut the bag is still inflated, I'd say there is enough air leaking past the gates to prevent overheating.

I do not believe I have seen any extraction machine with a 4"or bigger inlet that could possibly overheat by having the airflow thru the pipe restricted.

forstly the motor and its cooling air is completly seperate from the functional airflow.

secondly
the load on the motor and the current drawn & therfore the heat produced will be lessend by restricting functional air flow.


earthing of plastic pipes is complete and utter BSfrom start to finsih in so many ways... this one has been dealt with very comprehensivly and vigourously..... but still continues the be a major recirculating stream of misinformation, half truths and superstision.

If anybod is silly enouigh to chalenge that.... I give the same reply I gave quite some months ago.
Show me one single documented case of a dangerous incident involving PVC pipe, static and a small worshop.......havn't heard or seen one yet.

as far as opening gate to keep air flow up.........not important in small situations unless you have large lengths of duct or you are running a cyclone where maintaining duct air velocity is important.
this is another case of getting less than half the facts.

I have several machines with duct reductions or restrictions, I run them with no other ducts open with no problems... and exprience reduced performance if I do open other gates.

most sataionary machines require high volume low preasure vacume as in a 4" pipe dust extractor.

most hand held powertools require high preasure lower volume vacume as supplied by a shop vac..... most of these will have 32mm or similar dust ports.

2" ports....... you'll have to figure out what they belong to

3" ports belong with the 4" machines.

Most commercial vacume cleaners & shop vac's have wht is known as bypass motors..... where the cooling air stream is seperate from the functional air stream....... lots of domestic machines do not have bypass motors..... they most certainly can overheat if the air flow is restricted.

For these check them out.
start the machine up..... bung up the hose.......does the machine still blow air freely somewhere...... yep... bypass motor..... no.... you can easily overheat that one.......its motor & bearings will probly die an early death too as they are eating fine dust all the time.

The first thing to look for in a new vac...... does it have a bypass motor.

cheers

Thanks - the answers to this have been printed and put in my ref book.
Cheers,
Adam

Originally Posted by soundman

I do not believe I have seen any extraction machine with a 4"or bigger inlet that could possibly overheat by having the airflow thru the pipe restricted.

Hmmm... I gotta disagree with this bit:

secondly the load on the motor and the current drawn & therfore the heat produced will be lessend by restricting functional air flow.

Then why is it that mine trips out on thermal overload if I "choke" the ducts for extended periods? And it does, indeed, overheat... too hot to lay bare hands on. I'm not even going to try to explain it, 'cos I don't know why and it doesn't make sense to me... but it does.

(Not looking for an argument here, just pointing out that it can make a major difference.)