Thread: Know anything about making a down draft table ?

US Shopnotes has a 'free tip' drawing that they circulated a while ago, which I don't have a copy of.

It was basically a four walls of a shallow box with a floor sloping from near the top at one end to the base at the other end, where the extraction hose fitting was. The top was a naked sheet of pegboard. It wasn't dimmensioned as such, but probably ran to about 900 square by 150 deep.

Since the pegboard is substantially closed, a piece about that size should maintain the air velocity through the perforations to draw the dust down from the table top. However whether this large enough for your work, or what flow rates you can achieve from the dusty are for you to determine. I expect that the sloping floor and top 'drumming' from sander (hand or machine) would help clear the dust toward the outlet tube.

Hope this helps.

It does. thankyou.

sanding timber about 500x500.

At first been visualising something unrealistic I suppose. dust and crap being pulled away quick smart.

but DE suction doesn't ever seem to be enough. So worried the box will just be a pain in the ????. Just take up space.

anyone swear by them ?

Jake, I have made a number of downdraft tables out of HMWPE to use as a surface inside a cupboard in which to heat or distill acids. You can image that doing this in an open lab is a no-no but using a down draft table inside a cupboard was a cheap way of turning a cupboard into a fume hood and it worked very well. Thing is, if it can capture gas it should capture fine wood particles which are gas like but it really depends on what you are doing on the table. Hand sanding is a low velocity activity so the dust will be able to be captured by the flow speeds and rate. Using a power tool on the table is just going to spray your stuff all over your shed and then you end up relying on the table to act as a room scrubber.

The last table I made was the most successful and it consisted of two 600 x 600 mm boxes joined to a ducting and squirrel cage fan which drew up to 800 CFM. From memory we kept drilling holes in surface until the fan was drawing about 400 CFM. This might seem like a hard load on the motor but as discussed elsewhere it did not bother the motor as that table lasted until we demolished the lab 17 years later.

Now I have managed to keep one of these downdraft boxes but I have nowhere to put it in my shed!

Jake

ShopNotes had it as their woodworking tip a week or so ago- look here (I hope this works)

The unit in Jeremy's link is what I had seen, but I tried to describe it because I couldn't find it on the net. My sizes (guess) were out a bit though.

The best thing to make them out of is an old swampy aircon, they shift a lot more air than a DE and designed for a huge intake area... plus they only need 1/2~1hp compared to 2~3hp of a DE.
You could rig up some furnace filters on the inlet to scrub the air.

Thanks for the ideas.

I'll have to look out for a big aircon Harry.

Originally Posted by BobL

Jake, I have made a number of downdraft tables out of HMWPE to use as a surface inside a cupboard in which to heat or distill acids. You can image that doing this in an open lab is a no-no but using a down draft table inside a cupboard was a cheap way of turning a cupboard into a fume hood and it worked very well. Thing is, if it can capture gas it should capture fine wood particles which are gas like but it really depends on what you are doing on the table. Hand sanding is a low velocity activity so the dust will be able to be captured by the flow speeds and rate. Using a power tool on the table is just going to spray your stuff all over your shed and then you end up relying on the table to act as a room scrubber.

there you go. See I was hoping to use it for shaping chair seats. Hoping it suck everything away quick. Playing with the idea of clamping the seat to the top of the grid and rip into it at times. hand and power tools. An orbi for shore.

The last table I made was the most successful and it consisted of two 600 x 600 mm boxes joined to a ducting and squirrel cage fan which drew up to 800 CFM. From memory we kept drilling holes in surface until the fan was drawing about 400 CFM. This might seem like a hard load on the motor but as discussed elsewhere it did not bother the motor as that table lasted until we demolished the lab 17 years later.

sounds good. Wondering how were you able to measure the CFM ?

Somebody made on on here a couple of years ago.

SilentC has a pic of his here.
Auld Bassoon has some pics here.

Here are a link to another one that is worth a look.

http://www.woodworkersworkshop.com/p...ding_table.htm

I read some posts on this a few weeks ago. A few of the people who had built them ages ago said they were no substitute for a good sander and dust extraction combination.

The table will just remove the dust whilst a good combo will remove the dust and preserve the paper longer. I tend to agree, though I have not used a proper downdraft table my recent addition of a good sander and vacuum combo has made a significant difference to both the dust levels and paper life. I also do not really have room for another item in the shed, much better to re-use something I already have (shop-vac).

Originally Posted by apricotripper

Thanks for the ideas.

I'll have to look out for a big aircon Harry.
there you go. See I was hoping to use it for shaping chair seats. Hoping it suck everything away quick. Playing with the idea of clamping the seat to the top of the grid and rip into it at times. hand and power tools. An orbi for shore. sounds good. Wondering how were you able to measure the CFM ?

I used a Hot wire anemometer which measures the air speed. I inserted the hot wire probe into the box at the air exit point which was about 4" x 12" in area. Area x air speed in ft/min gives CFM.

For making something like chair seats you don't need a downdraft table what you need is just a fume hood/spray booth style of operation with three of the 4 sides and the top enclosed, that would reduce the amount spraying out into the room by ~80% (4 or the 5 sides). If you negatively pressure the box and there is a constant high air flow into the box even less will get out. So - plywood or mdf box and big old evap aircon fan. You could then also use it as a mini spray booth!

thanks.

Originally Posted by BobL

For making something like chair seats you don't need a downdraft table what you need is just a fume hood/spray booth style of operation with three of the 4 sides and the top enclosed, that would reduce the amount spraying out into the room by ~80% (4 or the 5 sides). If you negatively pressure the box and there is a constant high air flow into the box even less will get out. So - plywood or mdf box and big old evap aircon fan. You could then also use it as a mini spray booth!

brilliant........like the spray booth bit too......but how do you negitively pressurize the box ?

Originally Posted by apricotripper

thanks.



brilliant........like the spray booth bit too......but how do you negitively pressurize the box ?

Like this;

ok. so most machines that have dust extraction are being negitively pressurised I guess.

thanks Bob.

Originally Posted by apricotripper

ok. so most machines that have dust extraction are being negitively pressurised I guess.

thanks Bob.

Sure, but I can't think of one machine that is also normally enclosed on 5 of six sides while operating, even an router with a well vented cabinet and fence will spill invisible dust into a room when it stops and starts unless very high air flow rates are used.