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View Full Version : Hey Bob. what do you think of this for dust extraction ?



JDarvall
30th August 2008, 12:14 PM
Looking to use lathe without mask as much as possible when sanding....so

Been reading this stuff...
http://www.laymar-crafts.co.uk/tip15.htm

and his down draft idea sounds good. Just a little fan blowing down onto your work. You probably know all about it.

pic 1 - thats the basic principle I pinched from his site. just showing how most of the dust comes off the sandpaper with that fan blowing.

The problem he was saying, was, that if you widen the catchment area so that you can direct more of that dust down the pipe better, you drop the DE velocity, and it becomes hard to pull. Just volume extraction.

but what if you do this....

pic 2.... Have a wide catchment area, but have it very deep, so that its hard for the dust to reflect out of there and the DE can catch up despite low velocity. uno, the dust reflects about killing its own velocity. Maybe there's something special you could line the inside of that catchment area with. something to ruff it up so the dust doesn't reflect so well ??

Probably sounds really simple, but it makes sense to me. Thinking it work well with that down draft fan of his.

Whatya reackon ( or anyone else ) ?

BobL
30th August 2008, 12:29 PM
That downdraft fan might well direct the big chips and dust downwards and may even stop you sneezing from the fine dust but all it does to the very fine stuff you can't see, is spread it around the room ie is near useless for the fine stuff. The very fine stuff acts like a gas, it's very hard to push it all in a specific direction unless constricted but much easier to pull or suck. Remember when one lump of gas in an unconfined space goes one way some other lump has to go another way.

You are better off having a high speed high volume catchall behind the lathe. ie A large box and a 2 or 3 x 100 mm take offs connected to a 2 or 3 HP DC vented outside is the simplest solution.

JDarvall
30th August 2008, 12:40 PM
That downdraft fan might well direct the big chips and dust downwards and may even stop you sneezing from the fine dust but all it does to the very fine stuff you can't see, is spread it around the room ie is near useless for the fine stuff. The very fine stuff acts like a gas, it's very hard to push it all in a specific direction unless constricted but much easier to pull or suck. Remember when one lump of gas in an unconfined space goes one way some other lump has to go another way.

You are better off having a high speed high volume catchall behind the lathe. ie A large box and a 2 or 3 x 100 mm take offs connected to a 2 or 3 HP DC vented outside is the simplest solution.

gotcha. I think. so that really fine dust doesn't actually have velocity in that direction without the fan. just floats there.

How about 150mm instead of 100mm? .....From what I've been reading from that Bill Pentz stuff, dust extraction drops significantly when you go from 6" to 4".

hughie
30th August 2008, 01:16 PM
Jake,

I think some sort of directional fan is important with all the fine dust. The stuff that drifts in the air.
The fine dust is flung off the lathe during the turning and drifts around in the air. Unless you have some monster system ie like spray shop extraction and some super speeds, say around 25m per second for velocity......and a big budget :U it aint gonna happen.

Looks good to me :2tsup:

woodwork wally
30th August 2008, 05:51 PM
I reckon if I was 34 years old and had no other medical problems and some family I would be looking at every form of protection I could get and using it as often as possible. One thing you learn as you get older is that you DO NOT skimp money when it comes to your health cos if you do, you are gonna find it biting you on the bum before you are my age:(. This is a promise and I wish you no harm . I am told I look queer in some of my gear:oo: but even disabled I may be I have a wish to see a lot more birthdays yet and watch my grand kids grow up:).So take advise from a wounded old bugger buy it and wear it cos wood fibre is as bad as asbestous. enjoy your hobby safely and best wishes all Wally

JDarvall
30th August 2008, 10:27 PM
thanks Hugie and Wally.

RETIRED
1st September 2008, 07:47 PM
Jake you may be interested in this.

Our workshop gets full of dust as anyone who has been there can attest.

We did a series of tests on dust flow for most of the work we do. We ended up with a huge extractor fan and a 3hp dust extractor. Both vent outside.

The first pics are taken with the lathe going forward (normal rotation.)
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Side view. Roughing out. No extraction. Lathe forward.
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Roughing out. Extraction on. Lathe forward.
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Sanding. Side view. No extraction. Lathe forward.
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My view. No extraction. Lathe forward.
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Side view. Extraction on. Note the cigarette smoke.:)Lathe forward
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My view. Extraction on. Lathe forward.
That lot was using a "power sander":D
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My view. No extraction. Lathe reversed. Notice that there is more dust in the reverse rotation when using a "power sander". This is because of where you have to sand using it and the timber itself is acting as a fan as well.
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Extraction on. Lathe reversed. Dramatic difference.:cool::2tsup:
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Sandpaper. No extraction. Lathe reversed.
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No extraction. Lathe reversed. What you can't see is the dust that rotates with the timber and lands on the bed and your clothes.:D
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Extraction on. Lathe reversed.
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The hurricane maker.:wink:
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Dust extractor.
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The pick up behind the work. Formerly a hood off a 20" thicknesser.

We sand all big jobs in reverse because it is easier to apply pressure to the paper when something is moving away from you.
This setup has all but eliminated the dust from sanding and because a lot of our timber is bone dry, the dust from turning as well.

JDarvall
1st September 2008, 08:35 PM
Ta . :2tsup: Interesting stuff alright. noted the smoke :D

I'm thinking I mightn't have anything to worry about. I'm spoiling myself with a big DE unit. them pictures are giving me ideas. thankyou kindly.

Chris Parks
2nd September 2008, 12:14 AM
Velocity is the key to keeping dust suspended long enough to remove it from where your nostrils are. Keep the air moving and if you can't feel the breeze it ain't enough. Now to do that requires some serious fan sizes and power supply in a lot of cases and these tend to be hard to fit in an existing garage/workshop. If I ever build another workshop it is going to have big overhanging eaves and all the sides are going to open up when I am working leaving a roof and open sides. it is a fact of life that when we build garages/sheds we don't put any thought into what impact it will have on our health.

rsser
2nd September 2008, 06:40 PM
's pics aren't showing up for me.

Should I turn NetNanny off?

FWIW, I have an a/c behind me blowing over the work and a Big Gulp + 2hp DE on the offside; comes up OK on the snot test and the swollen sinus test.

PS, also use a box filter and when sanding a filtered visor.