Thinking outside of the box, really inside the box. "Sanding downdraft table"

[John Cooper2]

Picked up a pretty good sized squirrel cage blower today at a garage sale and later in the day did some sanding. Couple brain cells connected and I thought about making a Downdraft sanding table with the blower.

The thoughts have kind of evolved to something like this.

A rolling cart that is apx 3' x 5', part of the surface is a tempered hardboard that is used for pegboard and the rest would be a solid work surface. Below the surface I would have the blower sucking dust/air down through the pegboard.

The other part of this would include a shop vac attached to a Dust Deputy that would be inside the cabinet. This would provide dust collection to a lot of my mobile tools like, chopsaw, 6 x 48" sander, maybe my planer.

I expect to have a larger whole shop DC at some point but I am thinking that this portable solution may fit the bill for some time.

It looks like a lot of the downdraft tables use some form of furnace filter to filter out the dust. Would it be possible to reroute the air from the blower to the dust deputy? I think the blower would put out much more volume than the shopvac, but maybe if there was a way to direct the dust to the DD it would reduce the clogging of the furnace filters and extend there life.


Maybe just random crazy thoughts, but please tell me what you think

Thanks in advance.

[Chris Parks]

I am not a fan of DD tables unless you have a really big air flow and I doubt a furnace blower will provide enough flow for a lot of reasons. Fine dust when created tends to rise and it takes a lot of air going through the table to firstly stop it rising and then draw it down through the table. I also would think the area of holes to flat surface is nowhere near enough on a typical pegboard to make any sort of DD table work properly. Better a large grid of timber on edge (for strength) allowing unrestricted air flow to under the table. You could make the grid out of offcuts saving the material costs of the hardboard.

[Perry Holbrook]

About 25 years ago, Wood magazine had a plan for the table you describe. I built one. It does work OK, not perfect, better than nothing. One thing to keep in mind, the blower does move a good bit of air and the outlet end of the fan will be blowing air all over the shop. If it has dust laying on any surface, it will wind up in the air that you breath.

Perry

[John Lifer]

I think if you have the space, the need for a sanding table, and no other DC, then build it. There are good plans in at least two mags. I think a FWW in '10 or '11 had one that would be better for a filter. Kind of ignorant comment that you'll be spreading dust over the shop when you use this, if you don't use anything where else is the dust going but in the air? At the least build a filter box out of this thing. That would for sure help your air stay cleaner.

[Aaron Berk]

Is it safe to say that some DC is better than no DC?
Would that statement be shot down by the fact that if it's not GREAT dc, it would just perpetually recirculate the ultra fines?

I've been stockpiling squirrel cage fans and I now have 1 monster 3spd, and 2 smaller units. My plan is to mount them all into a single DD table. I would utilize the combined cfm to draw air through some 3 stage filtering.


Keep turning the gears John, you'll find the right combination....

[John Cooper2]

Thanks guys,

The gears are turning for sure

Keep it coming, will try to locate some of the existing plans

[Perry Holbrook]

I think if you have the space, the need for a sanding table, and no other DC, then build it. There are good plans in at least two mags. I think a FWW in '10 or '11 had one that would be better for a filter. Kind of ignorant comment that you'll be spreading dust over the shop when you use this, if you don't use anything where else is the dust going but in the air? At the least build a filter box out of this thing. That would for sure help your air stay cleaner.

Ouch, been a while since I was called ignorant, especially when it comes to the shop. I guess I didn't say that very well, let's try again. If you don't have an efficient dust collection system, dust will have settled on all surfaces, especially on the floor. When you fire up the down draft table, if the internal filters are working properly, the exhausted air will be cleaner. However, that exhausted air will sweep the settled dust back into the air, especially if the exhausted air is not directed away from the floor. Of course if you leave it running long enough or all the time and you figure out how to keep the filters working correctly, it will serve as a whole room air cleaner. Not the best design but (I'll try this again) better than nothing. Been there/done that.

Perry

[Jim Neeley]

Ouch indeed, Perry.. I think your question is a good one.

In my opinion (which, together with $10, will get you a cup of coffee ) a downdraft fan with the typical "rock catcher" (that's what the HVAC technicians call them because they're such lousy filters) furnace filter will do more harm than good. Those filters are too coarse to stop the fines we want to keep out of our lungs.

The *better* solution would be to watch Craigslist for a room air filter such as a Jet 1200 and get some good aftermarket filters for it (Wynn Environmental, etc.). If you really want to go with a downdraft and the furnace fan, consider the 3M Filtrete Allergen Reducing Filters (MPR 2200 which is ~ MERV 12.5), which start about $23. http://www.amazon.com/s/ref=nb_sb_no...elite+allergen

The down side to a good filter over the "rock catcher" is that it will decrease the air flow through the fan but at least what comes out will be somewhat better than what came it. In either case I would recommend using a respirator.

With your original concept the net effect would be to keep the fines swirling in the air as long as the fan was running. Some may argue that even the filtrete will leave some of that and I won't disagree. Is sanding outside until you get a DC a viable option? Outside you can use a fan to direct clean air towards you and blow virtually all of the dust away.

If you haven't visited Bill Pentz's site and read through it, I strongly recommend it. It is truly a wealth of practical information on staying healthy through better dust connection.

http://billpentz.com/woodworking/cyclone/index.cfm

Jim

[John Lifer]

Sorry for the OUCH. I was a bit harsh, but I still stand by the statement that if you filter the air circulating thru the box, you will have much cleaner air that if you do nothing. The first time you crank it up, you might raise dust that has settled, but so what? If there is that much settled out, it is being put back in the air by walking. And that is what John C. appears to be doing right now.(nothing) And I guess we can cut off and quit using the filter systems Jet, Delta et al are selling..... And Jim, who said anything about using a rock catcher filter? I'd put in a dual filter system with a low grade disposable and then one of the better home filters that would be near Hepa. If he runs it when working, it should clean a lot more than just a broom.... Guys, something, in this case is MUCH better than nothing...... All of us don't have deep pockets and unlimited funds. I just love the debate on which $1k router system to buy. Sorry for the rant, I'll just go back to reading.

[Chris Parks]

I stand by what I wrote earlier, pegboard won't do a good job in this as it is too restrictive. For a DD table to be effective you would have to feel a strong draught pulling the air into the table.

[Michael W. Clark]

Just my $.02, but if I had the squirell cage fan, I would build a room air cleaner. I like the concept for the sanding cart and installing the vac in it. You could probably wire it so you had add one of the iVac? outlets that turns on the shop vac with the sander. Personally, I'm not a big fan of the downdraft tables. Unless there is a lot of CFM and the openings are designed appropriatly, then you won't catch much. Mostly what you will catch is what falls into it. They have too low of a velocity to capture particles very far away from the surface, but may be acceptable for sanding flat panels. Even then, all you are going to get is what comes off the sides, the air won't go around the edge and suck the dust from the top of the panel.

When you said furnace filters earlier, I think of the coarse blue filters, others probably think of these too. That is the reason for the comments about spreading dust. The blue filters allow all the fine dust to go through, so it effectively gets all the big stuff and recirculates the fine stuff and keeps it airborn. Squirel cage fans are designed for high volume, low SP, and clean air. That is the reason they work better for room air filtration than dust collection.

Mike

[John Cooper2]

Mike,

I am starting to lean that direction of using the monster squiell cage fan for a room air cleaner. I have an extra 1hp dust collector that I think I am going to use for the "bench". Going to plum that into two dust deputy's and go from there. Got the dust deputy's last night so going to work out some connections today.

[Rick Potter]

For what it's worth, I have a Delta (Sand Trap) downdraft table, and while it works fairly well, I believe I get better results when my oscillating finish sander is hooked up to a shop vac.

Rick Potter

[John Cooper2]

I figure a two prong approach will be best, both a down draft and a vacuum hose on the sander.

Put a shopvac hose on the back of my oscillating sander today and even that made a world of difference.

starting to get a little more serious about this dust collecting thing.

[Jim Neeley]

"I figure a two prong approach will be best, both a down draft and a vacuum hose on the sander."

+1, except I add a room filter to grab what is missed.