The 'Blokebox' drop-box

[woodbloke]

Here's my finished drop-box, apart from the input and output ports that have yet to be cut (awaiting 'ose :wink: )
The interior is as on Mike G's thread:

except that the main vertical baffle has now been moved to within about 75mm of the input port

The front has been fixed using 10 toggle clips made from some 6mm ply and screwed under a little pressure (applied with cramps) to get the seal. A window has been cut and fixed with some hot glue on the internal rebate.

A close up of the toggle fixing is shown:

All internals have been sealed with copious quantities of silicone so it ought to be pretty airtight - Rob

 

[MikeG.]

Power it up Rob, and report!

Mike

 

[woodbloke]

Power it up Rob, and report!

Mike

No 0's yet. I'm hoping that this is going to work (I can't see any reason why it ought not to [-o<) and if it does, then I plan to build a ginormous one for the 'shop extraction system later on, with the sucker as the Camvac 386 - Rob

 

[TrimTheKing]

I'm still not sure I understand these. I am not doubting they do their job, and I will be making one myself, but can either of you explain to me whether you lose any suction from the original source?

I read in one of the posts that the baffles disturb the airflow, slowing it down so that the dust drops in the box (which makes sense and I am fine with), but do you ultimately lose any 'suck' from your extractor?

Looking good btw Rob, interested to see it in action...

 

[wizer]

The thing I can't get my head around is the loss of space. With one of these, you double the footprint of your extractor. Ok, I understand if you build a small vac above the drop box. But on chip collectors or something like my RSDE2, you double the footprint by using one of these. :-k dunno, maybe I'm looking at it through wizer tinted glasses....

 

[mickthetree]

I find it hard to get my head round as well Mark, but my basic understanding of it is that it shouldn't matter the size of the box (in theory??) as long as there are no leaks, you are still moving the same amount of air through it.

Is this right??

I'm guessing that for a very large box there might be a lag when it starts up as it creates the initial vacuum within the box?? But I'm just guessing.

 

[TrimTheKing]

I find it hard to get my head round as well Mark, but my basic understanding of it is that it shouldn't matter the size of the box (in theory??) as long as there are no leaks, you are still moving the same amount of air through it.

Is this right??

I'm guessing that for a very large box there might be a lag when it starts up as it creates the initial vacuum within the box?? But I'm just guessing.

That's kind of how I understand it too mick, but it's the 'slowing down the air' part that I don't get.

If you slow down the air inside the box, but are still sucking it out at the rate the extractor can manage, then surely you run out of air to suck at some point...

Please excuse my dumbassery, I am learning sketchup at the moment so anything else I know has fallen out of my brain :shock:

 

[MikeG.]

but can either of you explain to me whether you lose any suction from the original source?

No Mark, I couldn't detect any drop in suction. I did a simple test.......holding the biggest sheet of ply that the vacuum could suck up without the box, then seeing if it managed the same with the box attached. Not a perfect test.....but no discernible drop.

Mike

 

[woodbloke]

I'm still not sure I understand these. I am not doubting they do their job, and I will be making one myself, but can either of you explain to me whether you lose any suction from the original source?

I read in one of the posts that the baffles disturb the airflow, slowing it down so that the dust drops in the box (which makes sense and I am fine with), but do you ultimately lose any 'suck' from your extractor?

Looking good btw Rob, interested to see it in action...

Mark - I'm puzzled with that one as well, but I'm trying very hard not to understand the physics of the thing as it'll give me prolonged brain ache. I'm going with Mike's guidance on this as the dropbox guru and future world grand supremo (and abolitionist of decent hand planes :lol: ) that the thing will work - Rob

 

[MikeG.]

(and abolitionist of decent hand planes Rob

No, I shan't abolish them Rob, I'll just set a limit per person.

Mike

 

[BMac]

This 'slowing down air' business got me too until I compared it to sediment tanks in a sewage treatment plant. The water rushes in and out but the body of water hardly moves at all to allow particles to drop. Maybe the air acts the same way - rushes into the box, slows when the volume increases and then gets sucked out at the same speed at the other end?

Brendan

 

[TrimTheKing]

This 'slowing down air' business got me too until I compared it to sediment tanks in a sewage treatment plant. The water rushes in and out but the body of water hardly moves at all to allow particles to drop. Maybe the air acts the same way - rushes into the box, slows when the volume increases and then gets sucked out at the same speed at the other end?

Brendan

Makes sense, cheers Brendan.

 

[Mr Ed]

(and abolitionist of decent hand planes Rob

No, I shan't abolish them Rob, I'll just set a limit per person.

Mike

So long as that limits about 10 I'm with you comrade. Come the revolution...

Ed

 

[woodbloke]

This 'slowing down air' business got me too until I compared it to sediment tanks in a sewage treatment plant. The water rushes in and out but the body of water hardly moves at all to allow particles to drop. Maybe the air acts the same way - rushes into the box, slows when the volume increases and then gets sucked out at the same speed at the other end?

Brendan

That makes sense...easier to visualize :shock: So if the input port and output port are approx the same size, there ought not to be too much of a difference in the amount of air passing through the box...it just gets slowed down in the middle to drop the sawdust or chippings - Rob

 

[DavidE]

This 'slowing down air' business got me too until I compared it to sediment tanks in a sewage treatment plant. The water rushes in and out but the body of water hardly moves at all to allow particles to drop. Maybe the air acts the same way - rushes into the box, slows when the volume increases and then gets sucked out at the same speed at the other end?

Brendan

Makes sense, cheers Brendan.

Good example Brendan - a similar way of thinking about it is rivers.. where the river is wide you get a slow flow etc and also on the corners the rocks and stuff build up on the inside (think of a car differential).

There will be some loss - as one of the laws of Thermodynamics tells us "You can't get something for nothing". However, if you try to maintain the minimum area available the same as the input/output pipe it should be minimised. You'll get losses in energy from the flow travelling over a longer path, from making it change direction and from throttling it (what the baffles do). The magic is getting the scale right so that when you cause the dust to drop out the affect on the flow is minimal.

This is why I mentioned in the other thread using a Cyclone off a vacuum cleaner with a larger extractor may be problematic is it will create quite a constriction and thus will be lossy.

Hope this helps
Cheers
David

PS Rob - good looking box you need to get those holes sorted and it working!

 

[Ironballs]

Laminar flow is what you're talking about in sewage plants, you're trying to achieve the same effect here but in a much smaller space, hence the baffles.

As long as you have no holes/leaks then the old rule of every action has an equal and opposite reaction should apply, in other words, what goes in must come out

 

[woodbloke]

The 63mm tubing was ordered from Axminster last night so should be here on Monday. With any luck and a following wind I ought to have it up and running on Monday evening - Rob

 

[Qwibble]

Davids advice sounds good. Keeping the scale appropriate, minimising use of baffles and sharp changes in direction. These cause turbulence and result in air friction. The extractor will have to work hard against this friction and this will reduce the amount of air it can pull though the box.
Mike seems to have got it pretty much spot on with his box, with minimal losses and good dust droppage.

Once I get my workshop up and running (working on moving house first!) I'll have a go at making a dust collector. Design wise I'm thinking of a round dustbin with a traffic cone on top (think Wizer and his dunces hat).
Dusty air inlet will be in the middle of the bin, facing downwards. The large increase in volume should cause the velocity (and the dust) to drop dramatically. Air will be extracted from top of the cone. The gradual increase in velocity up to the clean air outlet might just result in lovely laminar flow and minimal loss of sucking power. Fine dust will still get through, but that'll be fed to Henry.

I could be very wrong about all of this. But once I sart building it I'll sort out a WIP and keep you posted. Qwibble BEng (Hons)

EDIT: And nice looking box Rob, it'll be interesting to see how it performs. I'll stake a pound that it'll eat all visible dust, but it you might loose a little sucking power with that long path.

 

[TheTiddles]

Not that it makes much difference, but you won't have laminar flow (where all the air is moving parallel to the pipe sides) anywhere in any dust extraction system. The summary of how the particles are dropped from the air flow is right but the energy loss in doing it is huge comparred to a cyclone system. Whilst these box thingys look like a nifty way to spend a few hours, is emptying your extractor so hard?

Aidan

 

[woodbloke]

Not that it makes much difference, but you won't have laminar flow (where all the air is moving parallel to the pipe sides) anywhere in any dust extraction system. The summary of how the particles are dropped from the air flow is right but the energy loss in doing it is huge comparred to a cyclone system. Whilst these box thingys look like a nifty way to spend a few hours, is emptying your extractor so hard?

Aidan

Agreed Aidan, it's not hard to empty the extractor. The main benefit though is that the filters in the vac won't get clogged as all the dust will be in the box, not caked on the outside of the paper filter, in which case losses will be just as high...I think - Rob