Thread: Making 150mm DC ports for workshop machines

Thanks for posting the pics John.
Can I suggest that instead of creating new threads for all your posts it would be useful to have them grouped into one thread that way if anyone is looking to follow up what you have done on your system they can find it all within the one thread.

Took a few days off to take Fighter Command to NZ for a holiday. Brownie points are all topped up ... for now.

The bandsaw was the next job. Half the existing 100mm hole to the cabinet had a plate welded over it, for reasons that avoid me. The grinder soon had that off.

This pic shows the way I set up dust collection on the bandsaw. Essentially, it is three 90mm lines. One to the back of the cabinet, one immediately under the table and one over the table to pick up any very fine dust. I made up my own three way PVC fitting ... a bit fiddly, but really not that difficult a job.

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Then came the test. I cut ten 5mm strips from a piece of scrap MDF. The final photo shows the state of the table after this test ... clean as a whistle, and there are a couple of improvements yet to come.
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Very happy with the result.

I lied. Thought the drum sander was a finished project, but after using it a couple of times, two issues were found.

First, it was struggling to get enough air into the duct. Second, the big hole I cut to make the 150mm port weakened the already flimsy PVC shroud. A combination of the weight of the flexy and the suction produced by the cyclone resulted in the bottom edge of the outfeed side of the hood touching the outfeed roller. The sides of the shroud bowed in, a bit like a kid's cheeks as he sucked a thick shake through a straw.

Easy enough to fix (see pic). A strip of reinforcing ply was glued and screwed to the edge of the outfeed side of the shroud. One problem solved.

I experimented a bit to get good air flow combined with excellent dust collection. Then two small chocks were glued into place to cock open the infeed side of the shroud. This put the air where I wanted it, running in, up and over the drum in concert with the direction of rotation.
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It works like a bought one. I spent half an hour testing and producing dust this afternoon, and there were absolutely no traces of dust anywhere outside the shroud. At any edge of the shroud you can feel the air flowing in.

Fooled around with the vertical sander a bit. Air flow needed to be increased. After a bit of experimenting the shroud was moved 30mm further away from the wheel at the end of the belt, increasing the area through which air was drawn.

It worked well, but is not perfect. A couple of bits of scrap were reduced to dust during a test this morning. A few tiny specks of dust managed to find their way along the returning belt. The plan was to make a new shroud, but this one is very close. So, might just try extending the section of pipe that extends along the back of the belt, pulling air from the returning belt, unless any of you blokes has a better idea.

This beast used to be a wonderfully effective dust making machine. It was responsible for the dust gathering on windowsills and all other horizontal surfaces. In fact it was so effective, more than a few vertical surfaces were also well coated. The improvement is astonishing. Still need to upgrade the hose to the port used when sanding curved surfaces on the wheel, which is still using 100mm duct (although the much improved airflow has improved this remarkably).

The drill press now has a shroud to collect dust, especially when it is being used as a sander.
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I used a "Big Gulp" shroud from CT and converted it from 100 to 150 mm using a straight connector and some hot cooking oil. Not at all difficult.

It works like a bought one. Larger chips are not picked up well, but that is of little consequence because it does a great job of drawing away the fine dust, which was the primary objective.

Spindle moulder, jointer/thicknesser and drop saw yet to have new shrouds made up for connection to the new dust collection system, but we are getting there.

Have you seen my experiments on shrouds posted here?

A bell mouth shroud/ generates the lowest resistance (hence highest flow) and highest air speeds at a distance (and takes up slightly less room) from the mouth than the pyramidal shaped shrouds. Increasing the air speed is important for both chip and invisible dust collection points of view.

Yes, I saw that post.

Did some testing using the drill press to sand a cabriole leg. As I rolled the leg over the sanding drum the dust stream changed direction considerably. Seemed like I needed an inlet at least 300-400 across to be sure to capture all the fine dust. I thought about making a nice round shroud out of sheet metal or similar ... for about ten seconds. Then I bought the Big Gulp. It was a cheap and fast experiment, and it works just fine.

It is likely that a round shroud made from sheet metal would have been even better, but right now I was unwilling to allocate the time necessary. Also, because the angle of the sides of the Big Gulp is so steep, I doubt I am getting significant restriction, but let me know if I am barking up the wrong tree here.

I am halfway through a job and this is the last machine I wanted to connect up to the new dust collection system before resuming work on that job. I got the spindle moulder hooked up with a 150 mm port yesterday, so only have the drop saw and jointer/thicknesser to go.

For now I can wheel the drop saw outside if I want to use it. the jointer/thicknesser produces a bunch of shavings, but not a lot of fine dust. Both can wait until I clear the back log a little. besides ... they both need some thinking time. See next post.

One of the last machines I need to hook up to 150mm ducting is the drop saw. See pic.
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I am playing with designs for a port/hood for this machine. Seen a few designs on the web, but thought I'd ask you blokes for any bright ideas.

It seems that when I fitted the zero tolerance fence that I made dust collection more difficult.

Am thinking about either a semi-circular hood at the rear with the 150 mm pipe entering the hood squashed to about 90 mm high or something similar to this ... Chop Saw Dust Collection with a Clearvue Cyclone - YouTube

Any ideas gratefully accepted. It seems likely someone has already conquered this problem, but there seems to be a variety of different approaches. Some use a narrow slit in the port to increase velocity ... but does that capture the fine dust?

The last machine I will hook up to the new cyclone is an Elektra Beckhum combined jointer/thicknesser. I need to convert it from 100 mm to 150mm ports, and am assembling ideas.

Does anyone have any experience to share? Just trying to avoid reinventing the wheel.

One major concern is getting enough air into the machine and the 150 mm port. I can open the ports out to 150 mm, but unless I get more air flowing into them, I am likely wasting my time.

Originally Posted by John Samuel

Yes, I saw that post.

Did some testing using the drill press to sand a cabriole leg. As I rolled the leg over the sanding drum the dust stream changed direction considerably. Seemed like I needed an inlet at least 300-400 across to be sure to capture all the fine dust. I thought about making a nice round shroud out of sheet metal or similar ... for about ten seconds. Then I bought the Big Gulp. It was a cheap and fast experiment, and it works just fine.

It is likely that a round shroud made from sheet metal would have been even better, but right now I was unwilling to allocate the time necessary. Also, because the angle of the sides of the Big Gulp is so steep, I doubt I am getting significant restriction, but let me know if I am barking up the wrong tree here.

Good to hear it seems to be working OK for visual dust and can understand the need to get some things working as quickly as possible.

All flared inlets/hoods with tight radius edges produce some restriction. Unless the flare in the duct is very long (>10 diameters of the duct size) and eventual size of the opening large (ie >10 duct diameters) a steep angled flare doesn't improve flow much. What cause the restriction is the tight radius of the edges of the hood. Experiments have demonstrated that incorporating some sort of a flare before a bell mouth makes very little improvement to the flow indicating that its the bell mouth that makes all the difference.

While it is beneficial if the directionality of the dust stream being produced is covered by the width of a hood this is not necessary if enough suck can be created at the source of the dust. Bell mouth inlets project the same suck but about twice as far as regular hoods. This is ideal for something like sanding because they don't take up as much space as steep sided hoods.

Drop/mitre saws are one of the most difficult machines to deal with for fine dust in a workshop. In my travels around workshops to test dust I have not seen a single successful setup that captures the very fine dust. The focus on chip collection means that operators put all their efforts at collection at the back of the saw and leave the sides and top of the saw totally open. I measure lots of very fine dust billowing away from the sides and tops of these saws especially from saws that only use VCs. If I had a drop saw I would place the whole saw inside a cabinet with openings in the sides large enough for the wood to be poked through and a front door that allowed enough access to work the saw. The suck can still be at the back but being totally inside a cabinet at least some of the fine dust will be grabbed before it spills out into the room.

While I think you are overall in good shape, one concern I have is you still seem to think that the very fine dust will somehow follow the visible dust. Invisible dust does not always follow the flow of dust coming away from a cutting tool or surface. Sanding produces huge numbers of sub 10 micron particles and to find out what is going on with these, a particle detector is needed. If you do a lot of something specific (ie several hours of sanding) and you start off with a clean shed then wait a few days and look at what appears to settle out on undisturbed surfaces, if you can see anything then the fine dust is not being captured.

One very good analogy is rather distasteful but very accurate, and that it is when one goes to the toilet, the solids drop into the pan but the smell very quickly pervades the whole room - the very fine dust behaves much more like the smell than the solids - they quickly move from areas of high concentration to low. The japanese have it right when they place an extractor in the toilet seat (ie at source) and not in the ceiling which allows the smell to fill the room.

Thanks for your ideas Bob.

I am still something of a novice, but my reading of your stuff, and that of others like Bill Pentz et. al. has enlightened me about the difference in performance of fine and coarse dust particles.

The way I test all of my ports (in the absence of a particle detector) is with very fine particles I can see, smoke; a trick I learned many years ago in the army.

As I understand matters the reason we use high volume, low velocity systems is to capture the fine dust. The fine dust will generally follow air flow patterns. I detect the air flow with smoke. For the drill press, my current set up has the sanding drum 200 mm away from the leading edge of the port. A smoke source 300 mm further away from the port than the sanding drum still enters the port. There is a little swirling (only very minor) until the smoke gets within about 150 mm of the drum (350 mm from the leading edge of the port). After this point, the smoke travels in a quite straight line into the pipe.

The smoke source can be up to 300 mm left or right of the centreline of the pipe,and the smoke still travels very directly into the pipe. Much more than this and it begins to swirl about significantly, and some can escape the negative bubble. It can be 300 mm above the drum, and the smoke still travels into the pipe. However, if the table is close to the drum (it is right now), the airflow under the table is much more disturbed. So, to be sure of the airflow, the table must be lowered. If I do this, the smoke indicates that I seem to be creating a nice big negative pressure bubble.

All my ports are tested this way. The only port giving me a little concern is the vertical sander. It works very well, but not perfectly. My concern is that I am not getting as much airflow down the back of the belt as I would like. One day, when the pressure is off, I'll extend the section of the pipe running down the back of the belt in an attempt to create more airflow there.

I am sure you are right about the bell mouth; I just needed a some fast and cheap solutions for my commonly used machines so I could get back to making furniture. Nearly all of my recent free time has bee consumed by the new dust collection system. For now, I intend to use a reducer to hook up the thicknesser, and to crack an adjacent port to create more air flow through the line to the cyclone.

I don't use the drop saw a lot, but want as good a solution as I can get. When using less than perfect dust collection (especially almost any form of sanding) I turn of my big fan to create a draught through the shop. (Except for the drum sander ... the dust collection system works brilliantly there ... I am getting very good smoke flow all around the shroud (no dead spots that I can see) and no visible dust at all outside the shroud.)

The shop vac does a pretty good job of removing dust from the work when using hand held machines, but as you keep saying, they produce their own very fine dust. Mine has a cyclone and a filter, but the fact that I must clean the filter tells me that very fine particles must be escaping. When it is running, so is the fan, hopefully taking most of that fine dust exiting the vac out of the shop.

I suppose dust collection can never be perfect, but it can be pretty darned good, and that's where I would like to be.

Originally Posted by John Samuel

Thanks for your ideas Bob.
I am still something of a novice, but my reading of your stuff, and that of others like Bill Pentz et. al. has enlightened me about the difference in performance of fine and coarse dust particles.
The way I test all of my ports (in the absence of a particle detector) is with very fine particles I can see, smoke; a trick I learned many years ago in the army.

Smoke can be a very useful guide to air flow but not so good for invisible dust studies because not all of the smoke is visible and most smoke sources are poor analogs for fine dust production. Smoke sources themselves are not moving, at least not anywhere near the air speeds generated by tools. e.g. placing a cigarette, or something safer like a soldering iron and some rosin, at the location of a source of dust production is not the same as a the production of fine dust clouds swirled up by a dust making blade or tool. Being in the army I assume you know how to perform a smoke test but the main reason I don't advocate using smoke is because of the tendency for newbies to generate smoke by reaching for something combustible and setting it on fire. The next thing is the burning object is sucked into their DC and . . . . . . If anyone wants to try this please make sure your bags or chip collectors are empty.

All this reminds me of judging a high school science competition where some students set up a wind tunnel made of cardboard and a couple of pedestal fans inside the tunnels, their smoke source consisting of damp straw which they set on fire with a MAP torch. They were testing air flow over several different designs of roofs of model houses also made of cardboard. Their measurement method was via video - all very admirable. They successfully videoed the air flow over several designs but then their straw dried out and everything went up in smoke and they did a great job capturing the conflagration on video. Apart from the videos all they had to show was a pile of ash and a couple of melted down pedestal fans.

There are of course commercial smoke machines or fogs made without combustion such as placing dry ice into water but even these have the same limitations as mentioned above. Despite this they are useful guide and I plan to do something similar around moving blades. It would also be useful to see a video of one of your smoke tests.

Very funny! Wish I had seen that particular high school smoke test. I had a vision of smoking, smouldering straw being sucked into the ClearVue's duct work and meeting up with a bin full of wood dust. Not funny!

You are correct, of course, about a smoke test not being able to properly simulate fine dust being generated at the sanding drum or similar, if for no reason other than that dust has initial velocity.

Nevertheless, it does demonstrate the limits of my negative pressure bubble, and I am working well inside those limits. I am very pleased at the size of the bubble, it is bigger that I had thought, and it demonstrates the benefits of a low velocity, high volume system. Just for kicks I repeated the smoke test with the shop vac. The results were as you would predict ... terrible.

Tried to take a video, but the smoke is much more difficult to see than it is with the naked eye, and I don't feel like tracking down some potassium nitrate.

Originally Posted by John Samuel

. . . . .Tried to take a video, but the smoke is much more difficult to see than it is with the naked eye, and I don't feel like tracking down some potassium nitrate.