Poor Man's Downdraft Table?

I'd be a little concerned about incenerating the bag. But if you used a small cyclone unit I don't see any reason why it shouldn't work.

You could also build your own, using a similar design. I would exhaust the air to the outside, since it is hard to filter out all the fine particles. Typically one oversizes the fan and then uses a gate or some other way to reduce the airflow to an appropriate level. There are plenty of handbooks that show how to design industrial exhaust systems.

I would worry about the fabric filter igniting due to hot sparks from grinding, probably would need a high temperature non-flammable fabric or put a metal filter in front of any fabric filter. The McMaster Carr catalog on page 597 shows some metal filters. A cyclone filter would probably take out the larger pieces, perhaps including the incandescent ones.

Richard

alderotes wrote:

We have a small Torit dust collector on our wide belt sander and if we use it more then a few minutes at a time the filter bags do catch on fire. I'd suggest a dust collector with an all glass filter such as a furnace filter. They don't have to collect exactly all the dust as you should exhaust it outside anyway. Leigh @ MarMachine

I'll check out McMaster-Carr. I hadn't seen metal filters before, would be nice if I didn't have to invent them :)

Thanks,

George

When you say grinder, do you mean a handheld angle grinder? If so, Bosch and some other companies make dust collection hoods which allow you to attach a vacuum hose to the grinder and collect the dust at the source. But there is still the problem of the vacuum filter catching on fire.

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George, I had a look at the link you included. There are a couple of thoughts apart from the obvious burning filter ones. The downdraught table you listed is meant for finish sanding of wood. You are suggesting a metal grinder. This sends the debris a long way whereas a finishing sander doesn't. You will need taller side skirts and possibly a top to the unit. You are now almost into a full cabinet build. Do you have a blast cabinet? That might do the job. On the subject of exhaust, if you extract your dirty air from the workshop, it will be replaced by nice warm air from outside. Your shop will soon be as warm as outside so why not work out there to begin with.

John

Distance is the solution to hot metal bits lighting the bag off - make the downdraft welding table of all metal, and run a long sheet-metal suction duct outside to where the dust collector fan unit is. Any hot metal that has to travel 20' or more through the ducts should have enough time to cool down before hitting the filter bag.

You can get sheet-metal ducting and fittings at any good home center. And be sure to seal the joints and gaps between the ducts with paint-on duct sealer, or you'll lose half the vacuum between the fan and table. Duct Tape dries up and falls off, Glencoat with embedded fabric tape for reinforcement is almost permanent.

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Richard's leading you the right way, a metal filter has been around for many years, most of the residential are aluminum. Think a filter for an kitchen stove exhaust, they are usually small/thin maybe 3/8" thick furnace a/c types are 3/4"(they say 1", but like wood it ain't or I could call John Holmes shorty) the spray on material to make the filter more efficient is an oil based so I don't think that would be a good idea. also having a baffle to keep sparks/ hot metal hitting the filter material would make it last. tt

There's been various plans published lately for small cyclone separators for woodworking, there's no reason these wouldn't work for catching grinding dust. All it takes is a little tin-whacking. There's usually a bag unit/filter on the outlet side of the separator for catching the fines, but by that time all the heat should be gone. The one unit I saw in a magazine sat on a 55 gal barrel for a catcher and was about that diameter by about 7' or 8' tall when mounted. I don't remember where they got their blower, it was more substantial than a shop vac, though.

Stan

I recently bought a used 10" baldor grinder with a dust collector. The dust collector sucks the sparks and dust off the grinding wheel, through the blower and into a cloth bag. Apparently going through metal tubes with several corners and through the blower cools the sparks enough. The original bag was still reasonably intact with a few tears etc. chuck

I was looking at a larger Torit Dust collector and it had what the dealer called a spark trap. It was a box with the air ducted past several sharp bends with a dead end corner for the heavier particals, the one likly to be glowing red to get caught in. I don't recall but there must have been a cleanout door to remove this dust. Steve Peterson

I'm thinking of a bench grinder. I don't want to exhaust to the outside of the shop, I'm hoping to filter the air through the cabinet.

George

Hmmm. . . maybe the Grizzly would work with some baffles like you describe above a metal filter.

George

I have a very nice dust collector/vac head that fits on the top of a

If anyone is interested, let me know and Ill give you the details. I also have new hoses for it.

Gunner

"This device is provided without warranty of any kind as to reliability, accuracy, existence or otherwise or fitness for any particular purpose and Bioalchemic Products specifically does not warrant, guarantee, imply or make any representations as to its merchantability for any particular purpose and furthermore shall have no liability for or responsibility to you or any other person, entity or deity with respect to any loss or damage whatsoever caused by this device or object or by any attempts to destroy it by hammering it against a wall or dropping it into a deep well or any other means whatsoever and moreover asserts that you indicate your acceptance of this agreement or any other agreement that may he substituted at any time by coming within five miles of the product or observing it through large telescopes or by any other means because you are such an easily cowed moron who will happily accept arrogant and unilateral conditions on a piece of highly priced garbage that you would not dream of accepting on a bag of dog biscuits and is used solely at your own risk.'

The supplier isn't much use to you as they are in UK but one of our wood work shops has an extraction fan adaptor that fits onto a standard dustbin (trash can). That may work for you especially if you arrange the inlet to point down through the top and the exhaust to draw from the top with a baffle between them. The reduction in air speed should allow the sparks to settle out. Try this link to see what I mean.

John

Hand grinding with a portable grinder should be done in an isolated area. That doesn't neccessarily mean farther away, but in a space that has barriers to stop the airborne debris from circulating. This could be a curtain, wall, booth or cabinet-type area. The handheld grindr will spew crap in an infinite number of directions, so it shouldn't be included in the area of the other machinery.

Hot sparks and grit can be directed to a pool of water (don't know what that sweeper is named.. oh, Rainbow), and most of the crap will stick to the water. Real air cleaners force the airstream into (under the suface) of the water, so the debris collection is very thorough. Hand grinding isn't always as easy to tame because of the directional slinging of the crap. The use of curtains or something else for containment is almost mandatory. If a suitable blower intake is piped from the wet box (downstream from the collection container/vessel), the debris is effectively shot into the pool with baffles or some other means. If the vessel isn't prone to combustion, there shouldn't be any problems when the outlet of the blower is vented outdoors.

This is gonna suck in the winter in cold climates because this system will evacuate the heated air from the shop. That would indicate the use of filters for the exaust, or an air makeup supply for a system that's vented outdoors.

WB ..............

Outstanding suggestion, and much cheaper than a cyclone.

||On Tue, 20 Jul 2004 14:49:19 -0700, alderotes wrote: || ||> A downdraft table would be a real boon so I could use my grinder ||> inside the shop. I don't want the grinding dust on my machines so I ||> do it outdoors, but its nasty on those 112 degrees days.

Steel tubing frame, or use existing bench. Expanded metal top, grinder mounted thereon. Side skirts as need. Squirrel-cage blower pulling air through the expanded metal mesh. Baffling directing air through a water trough to catch particles and quench sparks Change water as needed. Texas Parts Guy