down draft table

[mark smith 20Participant @marksmith20]

Hi,

In my work im becoming increasing sensitive to the wood dust i make .

How would one go about making something like this (see link) out of plywood but with very efficient extraction of fine dust. I cant afford to buy one of these and i see centrugal fans on ebay for around £100. The work surface only needs to be around 1m x 0.5m . I don`t understand the ins and outs of extraction or how these fans work.

Any advice welcome.

Thanks

**LINK**

Example of fan

**LINK**

**LINK**

[mark smith 20Participant @marksmith20]

[vintagengineerParticipant @vintagengineer]

A vacuum cleaner would probably be better, You need a sheet of mdf and the rout slots in it that all terminate at the suction point and then you need to fit a worktop with suitable size holes in it. You need to control the air flow so that you dont get dead spots on the table. Another solution would be just to make a long tube with a slot in it connected to a vacuum and set on the edge of the bench.

[Martin KyteParticipant @martinkyte99762]

I take it you are talking about home operations.

You could consider one of these.

**LINK**

and there is some useful advise here

**LINK**

If you are using woodworking machinery you really do need to get set up with proper dust extraction. Hand tools you don't generate to much fine dust. You should also (perhaps you already are) be aware that some woods and materials are much worse than others. MDF is a point in question mainly because of the binders and chemical treatment and some African hardwoods are particularly bad. Wood is a biological and your immune system is designed to respond to biological molecules so you can get some fairly strong immune responses to some woods if you are careless.

Some more information here

**LINK**

If you really want answers to these questions you should try this forum

**LINK**

but by all means build your extractor table if you are set on it. However if all you are doing is hand work and sanding a household fan to the side of you creating a cross breeze and blowing the dust away from your face would be a start. Axminster and the like do air filters to clean up the whole workshop so they may be an idea.

What ever you do don't put too low a price on the health of your lungs.

regards Martin

[JasonBModerator @jasonb]

Basically just make a flat box with a series of holes in the top and a larger one in the side to poke the end of a shop vacuum cleaner into. One or two spacers to stop the top flexing may be usefull if your top is fairly thin. Coule easily be done with 6mm MDF and 25×50 softwood to make the box sides.

In both those photos taken off the net the user would acutally be better off putting an extractor hose into the outlet on the sander rather than use the downdraft and the little collector on the sander.

 

Edited By JasonB on 24/03/2017 12:27:54

Edited By JasonB on 24/03/2017 12:31:28

[Martin KyteParticipant @martinkyte99762]

Trouble with most cheapish vacs is the fine stuff is just going to pass straight through and get blown around the workshop. You need a good filter to trap the fine stuff. Also somewhat tongue in cheek if you are routing slots in mdf to make a down-draught table don't you need the down-draught table first to protect you against the dust of the slot routing?

Be nice to know what Mark actually does with wood.

regards Martin

[Martin KyteParticipant @martinkyte99762]

Ah just caught Jasons post. Is that not a vacuum hold down table rather than primarily for dust extraction?

Just a question.

regards Martin

[BazyleParticipant @bazyle]

I have a dust allergy problem so always do woodwork outside on a windy day and masked up to boot. I have a big woodturner's extractor for when I need to turn tufnol on the metal lathe. This fan has a cast aluminium fan designed to allow it to be hit by lumps of wood.
I think you need far more volume than a vacuum cleaner hence the big fans are a good idea but will need a good mesh in front – say 4mm. The table needs to be mostly hole like a grating as used on plasma cutters made out of plaster laths. Fine dust somehow moves even against a draft – like you can still smell a pig farm upwind.
Arrange the fan output outside and down the garden a bit, downwind. Make the shed air input not just an open window but a duct above your face or even better an air fed facemask instead of goggles.

[JasonBModerator @jasonb]

Martin, those tables will offer a degree of hold down but are meant as extractors. Most people who make these tables tend to add one of the non slip mats to help hold the work in place. You can use the same basic design for a hold down table but have less holes and apply a grid of self adhesive foam to teh top which seals the underside of teh work, lay something on teh uncovered holes to block them and get best hold.

Re routing the MDF, same as I said with teh sanders good extraction at source eg on the machine is always preferable to trying to pick up the dust/chips once it starts to spread out. As someone who makes a living creating sawdust thats how I do it, I have top and side extraction for when using the router handheld and better extraction when its in the router table.

My small extractors go down to 0.5micron which is quite good and would easiy work a table of the size the OP is asking about

Build of one here

[MuzzerParticipant @muzzer]

Some vacuum dust extractors have both a suction and blower connection. If you connect up the blower (outlet) to a tube that exhausts outside, you won't have the problem of fine dust recirculating in the workshop or the need for any fancy HEPA filter technology.

I did this in our Canadian house where the central vacuum system exhausted into the workshop, which wasn't ideal once I'd developed a house dust allergy. No, it wasn't the cause of my allergy – I only started to use it in place of the upright vacuum cleaner to alleviate the problem. Vacuuming the house with an upright causes a veritable dust storm of allergens – made worse by North American ducted air heating.

[Steven VineParticipant @stevenvine79904]

Get a filter, or be a filter.

You want to initially collect the dust at source, i.e. via an extraction hose on your tool. You then want an air cleaner, to knock out the airborne particles.

I use the Axminster NVD750 twin motor vacuum. It is not cheap, but it does a good job. The NVD750 does not get all the particles, so I back it up with the Axminster AFS500 air cleaner. Both of these filter out to 1 and 5 microns and manage to knock out virtually all of the airborne particles. I also always use a face mask FFP2/FFP3. A throat and nose full of MDF dust prompted me to shell out. What price is your health?

Mathius Wandel does stunning stuff with wood, and he does things on the cheap. Have a look at his home made dust extractor and workshop air cleaner. http://woodgears.ca/tools.html

Steve

[mark smith 20Participant @marksmith20]

Thanks for the suggestions, is there something wrong with the downdraft table in the link i posted. Are they not efficient ,design faults etc…???

I cant stand wearing masks if i can get away with it, and full face stuff is out of the question as i would be using it everyday for hours.

This is strictly for hand work not powertools.

Steven Vine i already have a Axminster twin motor dust extractor, attached to a large bandsaw. Its incredibly noisy .

Extracting to outside is an option i`d consider.

[Martin KyteParticipant @martinkyte99762]

Hi Jason. just asking on point one.

Totally agree on point 2. The first stage is not to let the majority of the dust escape into the workshop by extract on the machine. As you say catching the rest is secondary. You need to ensure clean air past your face either by mask or air ducting which I guess is the idea of the table. The dust does however need to get trapped by a good filter as you say. Blowing it outside is a bit of a bodge as it's not really containing the problem just giving it to someone else.

My point on vacs was that they are primarily designed to move air not to filter particulates and you are not necessarily going to know the filter spec on some old vac you picked up for a song.

Your point 3 is essentially what I was suggesting. Buy a commercial dust extractor with good filtration and arrange your own ducting/air table.

regards Martin

[JasonBModerator @jasonb]

Mark, nothing wrong with the one in your link which is a commercial size machine, won'r be much quieter than your existing extractor.

The fans you link to are ok for moving air with little resistance, if you were to use those with some form of filter that would quickly reduce the volume they will move. Would work if just blowing the air outside but I'm not keen on that as in winter it will blow all your warm air out of teh workshop and if as you say you are using it for several hours a day you will get dust build up outside which is not ideal if near other houses.

To make up a small one like I showed would not take much effort or cost and could be tested with your bandsaw extractor to see how it works.

J

[Martin KyteParticipant @martinkyte99762]

Posted by Steven Vine on 24/03/2017 14:50:11:

Get a filter, or be a filter.

Steve

Hadn't heard that one before but I couldn't agree more.

Hi Mark. When you say sensitive what exactly are the symptoms. If you are solely using hand tools then air flow control would seem to be useful. Maybe something at the back of the bench ensuring airflow past you over the work and then away into the extractor rather than underneath. More like the action of a fume hood but without the enclosure. It does sound like your issue is repeated low level exposure rather than high levels of dust. What woods do you use and maybe you could switch varieties for a while.

regards Martin

[densleighParticipant @densleigh]

Hi,

If you want info on home made dust extraction try here Billpentz.com

Lots of good ideas

[mark smith 20Participant @marksmith20]

Posted by JasonB on 24/03/2017 15:19:21:

Mark, nothing wrong with the one in your link which is a commercial size machine, won'r be much quieter than your existing extractor.

The fans you link to are ok for moving air with little resistance, if you were to use those with some form of filter that would quickly reduce the volume they will move. Would work if just blowing the air outside but I'm not keen on that as in winter it will blow all your warm air out of teh workshop and if as you say you are using it for several hours a day you will get dust build up outside which is not ideal if near other houses.

To make up a small one like I showed would not take much effort or cost and could be tested with your bandsaw extractor to see how it works.

J

From what i can see the downdraft table in the link i posted to use one of those fans and some sort of large filter ,the reason i want to make one is that they cost a fortune but are basically just a fancy box/bench with one of those centrafugal fans inside. Which should be cheap to make yourself . I cant find any parts manuals to see if theres anything else to them.

Blowing dust right onto the garden flower bed wouldnt be a problem for me.

I had actually considered one of those flat box jobs you point to but they dont seem too powerful.

[mark smith 20Participant @marksmith20]

Posted by Martin Kyte on 24/03/2017 15:25:04:

Posted by Steven Vine on 24/03/2017 14:50:11:

Get a filter, or be a filter.

Steve

Hadn't heard that one before but I couldn't agree more.

Hi Mark. When you say sensitive what exactly are the symptoms. If you are solely using hand tools then air flow control would seem to be useful. Maybe something at the back of the bench ensuring airflow past you over the work and then away into the extractor rather than underneath. More like the action of a fume hood but without the enclosure. It does sound like your issue is repeated low level exposure rather than high levels of dust. What woods do you use and maybe you could switch varieties for a while.

regards Martin

Hi martin, I have started getting severe sneezing fits and blocked nose . The wood i mainly use is this (extremely expensive stuff)

**LINK**

, i cant avoid it as its my job and the prefered only wood . I do use others such as ironwood species ,which also irritate to various degrees.

I would actually use a fumehood if i had the room and cash.

[mark smith 20Participant @marksmith20]

Posted by densleigh on 24/03/2017 16:01:50:

Hi,

If you want info on home made dust extraction try here Billpentz.com

Lots of good ideas

Thanks i did read that site a while back but ended up getting confused with all the talk of air volume etc…

[clogsParticipant @clogs]

Hi Mark,

sorry can't post the photo of a dust catcher I made, look on my album under wood shop, very simple and cheap……

I use these (3) as well as a large'ish shop vac, the motor /bag/trolley is out side when used…it's on a long 4"dia hose that I drag about the w/shop to where I need it………eventually it'll be under the floor, no trip hazard then…..

The dust catcher is made from two peices of 8mm ply, a bathroom extracter fan and an air filter of a 500hp Scania..

my photo show's it in pieces……

mine are connected to the over head flouresent light fittings (hooked up on chains) I also connected this electricaly, hard wired into the lamp feed and with a garden mower plug, 2 pin, male and female…

this is so I can unhook the chains, disconect with safety and take the whole thing down for cleaning…….I use a pull switch for the on-off….

It's suprising how much dust this thing takes out of the air………

good luck, if u wan't more details just ask….

Clogs

[mark smith 20Participant @marksmith20]

Hi Clogs , interesting.

Ive decided to make something slightly substantial  like this . I have a light steel framed bench on castors which could be boxed in all around. I watched the video and it is extremely quiet (not sure why) .

 

**LINK**

 

Im uncertain where the filters go in relation to the fan , i like the look of this fan ,though cant even see where the motor is???  Which is the inlet and which is the outlet?

**LINK**

Lots of filters on ebay such as **LINK**

Where does the fine dust go in these tables? Does it collect on the filters or drop in the bottom?

Edited By mark smith 20 on 24/03/2017 19:38:22

[Neil WyattModerator @neilwyatt]

Posted by Muzzer on 24/03/2017 14:22:34:

I did this in our Canadian house where the central vacuum system

You mean those things with vacuum cleaner sockets in each room are real!

You should get a Dyson, it's character building

Neil

[martin perman 1Participant @martinperman1]

Posted by mark smith 20 on 24/03/2017 15:02:39:

I cant stand wearing masks if i can get away with it, and full face stuff is out of the question as i would be using it everyday for hours.

Mark,

Because of the nature of my job I have to occasionally wear Hoods which are connected to battery powered fan units with HEPA filters fitted which are very efficient at removing dust etc down to very small particles so would work well for you, I dont find them uncomfortable plus I find a constant draft across my face refreshing.

Martin P

[vintagengineerParticipant @vintagengineer]

The main factor to make it work is to get a big as possible pressure differential either side of the table.

[clogsParticipant @clogs]

Hi Mark,

that dust extract table looks great, I'm sure it'll work fine but I found that however good the dust extraction is there is always stray airbourne dust……

I work a lot with Oak and it get's me every time……. lucky enough my workshop is quite long and I can get a thru draught running quite naturally which is handy as it gets a lot of the dust outside but still this airbourne dust just keeps falling down….

Hence the the overhead dust catcher, been using them for years……As they cost nothing really, give it a go u'll be surprised in the air quality…..actually all my fans came from bathroom upgrades and a skip…..they not so noisy and I think they move something like 10'ish cubic meter's of air per hour….

I also found that even when turning wood, making shavings u still get a lot of dust…….I have a dust/shavings funnel connected to a 4"in shop vac running when turning plus a dedicated dust catcher directly over the lathe……I have even tried an air fed mask but just can't get on with it so sold it, I think it was a "Trend" well certainly U.S. made, nice peice of kit but it was just me…….

Give it a try, u know u want to…..hahaha….

good luck……Clogs

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