Thread: SCMS dust extraction

Pics will be useful.

Also what is the DC your are using?

Hi Bob

Pics tomorrow, the camera is otherwise engaged ATM.

Still using the DC7 (reckon I'll end up with a clear vue max when we get settled in the new digs), going to put a manometer on the DC7 tomorow as well.

Hi ozhunter:

I look forward to the pics too, as I'm currently reassessing the dust extraction to my SCMS. I currently have a vacuum cleaner dedicated to the saw, which works fairly well for chip collection, but oh not so good for dust extraction!

Righto. In amongst other annoying stuff like work, I made some mods to the dust extraction set up. I didn't go down the road of the slot across the back of the enclosure (although I will probably investigate sometime.

Here are some pics of the enclosure when I first made it.

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This is a view inside the enclosure now. There is only about 4mm clearance between swivel head and the port. The "doors" on either side will be hinged so they can fold out of the way if I need the full swing of the saw, but I reckon 90%+ of my cuts are 90 degres anyway.

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This is a closeup of the back of the enclosure, it will be relevant in minute

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Left and right side of the table after vacuuming prior to the test cuts.

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The close up of the rear of the enclosure after 20 cuts through a piece of MDF 140x16

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Left and right view of the table after the 20 cuts. I found if you where a bit vigourous when entering the blade into the MDF at the start of the cut it would throw these bigger chips out.

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These twp pieces of scrap are what makes a huge difference to how much saw dust ends up not being collected. I notice when I had a torch in the enclosure to try and see what the chips where doing, that a large proportion of the saw dust was hitting the column and being deflected sideways. This saw dust was not being collected. These two wings catch it as it bounces off the column and direct it toward the outlet.

Very pleased with the result, not sure how much invisible dust this set up catches, but it would have to be catching some I would think.

Now onto the table saw.

That looks pretty good to me and I personally would not be worrying about those visible chips that remain behind in those corners.

The sawdust is collecting in those spaces because the air speed in that space is not high enough and they represent a sort of "dead space".

If you want to get rid of those chips you have a couple of options;

1) Vent that area (i.e. a PITA to set up and all you do is lose suction from elsewhere)
2) Fill in those spaces with triangular pieces of timber - this effectively eliminates the dead space.
3) When you have finished fire up your compressor and with the dusty running give everything a good blow down - this will clean up the corners plus you can also use a a brush and the compressed air to clean off all the stuff that sticks to the machine and later comes off and invades the shed.
Don't worry about the fine stuff spraying around, the CFM of the compressor will be WAY LESS than the DC, just leave the DC running for a couple of minutes after the blow down.

One of the reasons I installed compressed air in my shed was that I prefer and use method 3) .

Thanks Bob. I have done the compressor thing a couple of times. Works well.

I'm not concerned about the piles in the corners. They don't get any bigger than that and the dusty keeps the piles at a constant level.

Very pleased with the way it works. If you put your fingers in the oulet and relax your hand, it feels like your hand is getting pulled down.

Lots less mess than before.

I'm trying to determine the "best" way to extract invisible dust generated by my scms and note that your large port comes up from under the table. With a large airflow it appears that you're getting a lot of the invisible dust as well as gravity assistance for the chips. Nice!!

My extraction pipe will be coming from above, so I won't have the gravity assist. This doesn't matter too much for me as I really want the finest dust captured.

I'm also concerned about the dust generated at the beginning of a wider cut, when the blade is pulled forward and therefore away from the dust port. Trying to think of a way of moving extraction points closer.

Do you think a 6 or 8 inch port directly overhead rather than underneath will be effective? What about ditching the shroud idea altogether and locating two large (say 140mm dia) bell mouths on either side of the saw, nested right behind the fence (which should be opened) and held in place on movable stands of some kind? Or is this a bad idea and I should go the shroud route with one single large port?

Many thoughts anyone?
Thanks!

Originally Posted by LuckyDuck

My extraction pipe will be coming from above, so I won't have the gravity assist. This doesn't matter too much for me as I really want the finest dust captured.

Provided you have enough volume (an in your case you will) it should work just as for fine dust when captured from below - however this often means a 180º reversal of ducting because ducting usually comes in from above.
Table saws, routers and SCMS are some of the machines that would benefit from some ducting coming in under the floor.
I would watch where the visible dust impacts behind the SCMS and put the inlet right there - usually it's directly behind the saw but this is a big problem for most of these types of saws as they are usually operated right up against a wall.

I'm also concerned about the dust generated at the beginning of a wider cut, when the blade is pulled forward and therefore away from the dust port. Trying to think of a way of moving extraction points closer.

Blade sprays most of the dust backwards so it doesn't really matter

Do you think a 6 or 8 inch port directly overhead rather than underneath will be effective? What about ditching the shroud idea altogether and locating two large (say 140mm dia) bell mouths on either side of the saw, nested right behind the fence (which should be opened) and held in place on movable stands of some kind? Or is this a bad idea and I should go the shroud route with one single large port?!

The shroud is I think worth having as it constrains both fine and coarse dust.

I'm far from an expert, but after playing with mine I think a shroud is a good thing to have. The visible dust is launched at a fair clip out of the kerf, so I'm assumimg the invisible dust is too. The enclosed shroud gives you some chance of capturing the dust.

If I could have I would have put the port right behind the saw, but the pivot column on the back of the saw arrests the rearward movement of the dust and shoots it in all directions.

I'm pleased with the way my shroud/set up works. There seems to be a lot of air movement and, as the photos show there is very little visible dust left from the 20 mdf cuts so I must have acheived something.

Thanks Ozhunter and BobL,
Yeah, a shroud is probably best -- could you tell I was trying to get out of the extra work?

I see now that perhaps I should actually do the whole 180 degree bend and get one port coming from underneath.

I've read a couple of places on this forum about interference, or a dead space with regard to having two different ports service the same area. I know you've said putting a port directly behind the SCMS is desirable, but aside from the space issues (I don't have space either as the saw is too close to the wall for a decent sized port), what about the fact that some chips/dust are spewed out either side. Like you said, it does come out at quite a clip!

So, let's assume that the dust shroud is the way to go, and that I don't have the space directly behind the saw for a port, should I put one really big port on one side or the other of the saw, directly behind the fence?

Or should I put two lesser sized ports but both coming up from the bottom, directly behind the fence?

Or, and this probably depends on what you guys think about that interference and "dead" space issue, could I put two ports asymmetrically, say one on the left hand side, coming up from the bench, directly behind the fence, and the other coming into the dust shroud, on the right hand side, either from the top or the right hand side of the shroud.

Sorry, I'm probably making it more complicated than it needs to be.

Thanks for your thoughts!

Lucky Duck, I have recently finished making a mobile SCMS work station with a dust shroud at the rear, not small but then again not that far rearwards either. Effectively you will require about 20mm more rearward space than your SCMS can slide rearwards, so it isn’t that much bigger than the absolute minimum rear space requirement. Width could and sometimes is an issue if built in somewhere and later on I wish to change something, so I built a mobile unit with 8 x 600mm deep drawers underneath

I will post some pictures later as I don’t have any of the finished product, I do have a couple I took during the build. After talking to a staff member about what I was trying to do at the Melbourne Carba-Tech store then being shown this big gulp thing; part number DBGULP, currently $26.00, I immediately knew I had a workable solution at a reasonable price.

I recessed this into the floor, so I have nothing rear of the cabinet, but below there is a 100mm flexible 3m hose running to an Oneida cyclone. My unit works a treat, yep it could be better, but I now have a virtually clean workshop whenever using my SCMS. I get pretty much the same spatter of dust particles as shown in the previous pictures from Ozhunter’s build.

Even with ear muffs on I can hear the rumble of the air running into the big gulp, this coupled with the fact I have two big roller doors for a flow through air situation makes the whole place nice to work in. My SCMS would have to be the biggest mess-making machine to make dust that is hard to almost impossible to collect without building a shroud.

Mick.

Thanks Mick for your ideas. I'm currently running a vacuum hose onto the built-in rubbery dust shroud that came with the SCMS. This system probably collects perhaps 80% of the chips, but must extract virtually none of the fine dust. I know this must be the case because most of the chips do as you say, and splatter straight back from the blade (and mostly into the vacuum port), and yet there is a fine mist of sawdust settled all over the top of the machine and on the brick wall directly behind. It's the fine stuff I want to get.

I would love to see pictures of your dust shroud. One of the issues we all face is that SCMS machines, by virtue of their design, require a lot of space above (for blade to move up and down) and sideways (for mitre cuts, etc.). Like Ozhunter, I do a lot of 90 degree cuts, but I also do plenty of angled cuts too, so I need a shroud that will cater for both. I like the simple solution of having hinged sections which can be moved back out of the way. I'm also keen for some kind of shroud over the top, perhaps with a second port, to try to eliminate the plume of fine dust escaping upwards. Don't know, grasping (is that gasping) for dust solutions at the moment.

Thanks.

Lucky Duck, I have attached a few pictures of my SCMS rolling stand, complete with dust shroud. Quite fortuitously, due to a prolific amount of stuff being deposited on nature strips these days, the total build came it at about $88.00.

This was for a set of wheels from Aldi $10.00, screws from Aldi $0.50, square drive screws from Screw-it $1.00, big gulp, 3 metre flexible hose and offset reducer 100mm down to 63.5mm from Carba-Tech $76.50.

Mick.

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Mark, the blue hose is not going to do anything useful for overall dust capture and is very likely to reduce the over flow rate from the hood. The reason for this is that a DC cannot generate enough of a pressure drop within the throat of the big gulp to drag much air through the blue hose and all the blue hose ends up doing doing is block the flow in the 4" flexy. I have tested a similar setup and we were getting less than 20CFM through the equivalent of your blue hose and losing about 50 cfm of flow through the 4"flexy. It is really important to keep the throat on the big gulp as clear as possible.

Hoses attached direct to saws like that are designed to work with vacuum cleaners that generate ablaut 3-4 times the pressure of a DC so they can pull some air though these narrow hoses.

I guess you also know the limitations of 4" ducting?

Instead of a big gulp I would also recommend a bell mouth inlet that can be located within the back of the enclosure. It's not that intuitive but inlets that do not have appropriately curved intake edges have higher resistance to air flow and will reduce a systems CFM draw.