Improving dust collection from Kapex SCMS - Need help with overkill method

[Chris Parks]

George, the Kapex is no different to any other SCMS, chop saw, mitre saw, call it what you will and they all require a lot of work to minimise the fine dust problem. 4" ducting unfortunately will not flow enough air and any impeller under 15" is in the same boat in fact I overdrive my Clearvue CV1800/15" with a VFD but that is somewhat defeated by only being able to source 6" PVC in Oz where 7" would be far better and the air flow would increase by a lot. It is simply not practical to capture all the fine dust at source and all we can do is maximise fine dust capture on a SCMS.

[Alan Lightstone]

So, been real busy building this. I think I'm done, although I'm already thinking of a modification.

Here are some pictures of the shroud:
Shroud with front covers installed.jpgShroud without front covers.jpgMiter Saw Station Grit Modules.jpg

DustRIGHT Dust Collector Installed.jpg

I'm seriously thinking of making two removable magnetically attached covers for the front openings for the two holddowns, so that if I'm not using them (which I usually do) I can close off that opening to help with suction.

Joel at Grit Automation was great in helping me connect a trigger module to the Kapex, and two collector modules - one for the Festool vac, and one for the DustRIGHT dust collector. The reason for this, I think, is pretty cool, and should help with dust collection. I have it programmed so that the Festool vac turns off 30 seconds after the Kapex completes its cut, and the DustRIGHT collector turns off 1 minute after the cut is completed. These delays, I think, should significantly improve dust collection. Yes, I could have plugged the Kapex directly into the Festool vac as I have for years, but it always struck me as a mistake that the vacuum turns off immediately after the Kapex stops cutting. That prevents removal of a bunch of wood dust from the shoot and around. My Grit Automation system, hopefully, will improve that by adding the delays.

Haven't had a chance to test it yet. And I'm not going to weigh sawdust like one of the Youtube videos, but I'll get a subjective test.

[Jim Becker]

That's a good implementation that will really help a lot with capturing the fines while using the miter saw and it still gives you the ability to do those non 90º cuts when necessary. I'll go as far as saying that if you have another angle that you "frequently use", it wouldn't be a "yuge" effort to make a couple of alternative pieces that match that saw position, too.

[Alan Lightstone]

45° comes to mind, but that might be in both directions, and it really wasn't terribly fun to make those front pieces. I did space the left and right walls so that the Kapex has room for those cuts. I'll likely just cut without one of the front pieces if I choose to do that. But, who knows...

[Chris Parks]

It would be neat if GRIT could tie in a dust monitor that turned on the extractor and opened at least one BG when the fine dust levels rise over a set level. A major problem we found when training users is that someone can walk up to a mitre saw, do a cut and walk away before the DE has reached anywhere near full speed, in fact I sometimes do it myself when not thinking about what I am doing. GRIT are the first company to put some real R&D into the dust issue but I shudder to think what it has cost and hopefully they have some real success in the market place.

Some photos of my mitre saw hood.

Glide Saw Installed.JPGTop View of Hood.jpgAir Entry at Bottom of Hood.JPGShowing Incra Fences.JPGBlast Gate Installed in Top Plenum.JPG

This works opposite to every other shroud by pulling air into the bottom of the plenum and then drawing the dust and air up through the curved plenum into the 6" duct which if I had my way would be 7" but that size does not exist in Oz. Since these were taken I have removed the manual blast gate at the top and added one of our automatic blast gates instead. Like all other shrouds it does not collect all the fines even though I can faintly detect the air flow on my body and the difference between having the DE at full speed or not can be seen by how the visible dust behaves along with the smell of the dust which is floating in the air.

[Alan Lightstone]

That's a really interesting design, Chris. As I said in a previous post, I couldn't run ducting from the bottom (sigh) but I do see its advantages in causing the dust particles to move that way. I didn't mention it, but I did heighten the floor behind the miter saw so that the duct is closer to the floor. The movement of the saw limited that further, though you had an interesting solution to that.

Actually, with the time delays, my Grit Automation system will keep the dust collector and vacuum running after the miter saw is turned off, so solving the issue you mentioned. Just having the Festool vac hooked up to the miter saw would have it turn off instantly, which I agree is certainly suboptimal.

My Grit Automation system has two air quality modules that turn on my two Jet air cleaners if the particle count exceeds the level I set, so it does accomplish what you said.

[Scott Winners]

May I please ask a stupid question?

I live in Fairbanks, Alaska. My shop is a single car garage @ nominal 12x24 feet. I too found a miter saw to be the gateway drug better woodworking in the mid 1980s. A miter saw is an impressive tool, and they have come a long way since 1986. But in my mind this is a construction tool to use on jobsites, an outdoor tool, like a frisbee or a soccer ball or any of the hockey stuff.

I have a $300 folding cart/dolly doohickey under my miter saw. If I really need it that bad I am happy to shovel off my driveway and drag my mitersaw outdoors at -20, -30 Fahrenheit for whatever rough cuts I want to do that bad. I got sharp handsaws in my shop, I've got good filtration in my shop, I have good particle counts on my instruments while using my hand saws. Don't tell me a miter saw is a joinery tool, I got better sense than that.

I know some of you guys (statistically) are under HOA oppression, but there is a bunch of power tool users from the heavy hitting group in this thread.

The stupid question I have is why are y'all working so hard to use an outdoor tool, like cleated sneakers or a football helmet, inside your shop space? Dad wants to know. You are not my kids and you don't have to answer me. But if you were my kids you are already looking at one raised eyebrow and I got an itchy trigger finger over my belt buckle trying to understand why you think it is a good idea to make this big of a mess inside the house when I already spent good money on your outdoor clothing that is suitable for the weather we have.

Thanks.

[Jim Becker]

Scott, everyone works differently. I rarely use my miter saw and it's been that way for years. So it's on a compact portable stand and, at least when it's "nice" outside, I can open the "big door" and park the saw so it spews forth outside. But if I was going to invest in a highly accurate miter saw with intent to use it frequently, I'd likely opt for a workstation not unlike what's being discussed here because I do try to pay attention to dust control and the only tool harder to do that with than the miter saw is a lathe.

[Alan Lightstone]

So ran my first test today. No question that the setup reduces dust. Not totally, as I still see some small woodchips/dust in the openings in the front of the Kapex, an area I knew would be an issue. So far, not sure anything has reached the floor, which always was an issue in the past.

Here's an after picture:
Kapex Dust Collection After Picture 1.jpg

I can feel suction coming through the holes for the clamps, and this is probably wasted suction, so I think I will make magnetic inserts to close those holes when not used, though they will be a little inconvenient.

Also, I'm wondering if I should enlarge the gap on the sides of the dust shoot. I think some sawdust is shooting off on an angle towards the back and maybe not being captured there. Any thoughts as to the wisdom of this? Here's a picture of the front with the small gap to the sides of the native dust chute:
Shroud with front covers installed.jpg

[Chris Parks]

It might be that the shrouding has reduced the air flow, this sort of stuff is always suck and see.

[Jim Becker]

I can feel suction coming through the holes for the clamps, and this is probably wasted suction, so I think I will make magnetic inserts to close those holes when not used, though they will be a little inconvenient.

Alan, the dust collector works by moving a large quantity of air at high velocity but low static pressure. That in turn moves the dust. It's not "suction" like a vac extractor which moves a small amount of air, but with very high static pressure. If there is no airflow into the enclosure, dust collection will be reduced. So you have to balance things so you have air coming into the box that at least gets close to the geometric size of the dust collection port to get maximum performance. You can, however, control "where" that air comes in from and use that to benefit and influence the direction that the dust is moved...towards the DC port.

Folks used to try and seal up their cabinet saws to get "better dust collection" and in turn got worse performance. That got fixed by finding ways to increase air flow, both at the collection side by larger ports and by making sure that the cabinet wasn't closed off too much such that it inhibited air coming in to allow for the volume necessary to carry the dust. The same thing applies here.

[Alan Lightstone]

Alan, the dust collector works by moving a large quantity of air at high velocity but low static pressure. That in turn moves the dust. It's not "suction" like a vac extractor which moves a small amount of air, but with very high static pressure. If there is no airflow into the enclosure, dust collection will be reduced. So you have to balance things so you have air coming into the box that at least gets close to the geometric size of the dust collection port to get maximum performance. You can, however, control "where" that air comes in from and use that to benefit and influence the direction that the dust is moved...towards the DC port.

Folks used to try and seal up their cabinet saws to get "better dust collection" and in turn got worse performance. That got fixed by finding ways to increase air flow, both at the collection side by larger ports and by making sure that the cabinet wasn't closed off too much such that it inhibited air coming in to allow for the volume necessary to carry the dust. The same thing applies here.

Good points, Jim. I was really thinking that the air flow into the shroud then dust collector should be closer to where the cut is being made, which those cutouts for the clamps really don't fit that paradigm. Especially the one on the right which is closer to the dust collector hose inlet.

I'm making two pieces of wood to cover those now. Of course I screwed up the first one, so repairs being made now. Once those are done, I really probably have to increase the open area of the shroud near the blade so that it is roughly equal to the area of the 6" dust collector duct (28 sq in). Have to do some rough measurements to see what that is.

[Jim Becker]

Absolutely target the air low "into" the hood as best as you can. It will truly make things as optimal as it can be. There's no perfect solution 'cause the tool throws stuff a whole bunch, but keeping the air flow as high as possible will help capture more of the fines which are the truly dangerous particles.

[Chris Parks]

Alan, you could use a blast gate as an air inlet to control & adjust the inlet flow.

[Alan Lightstone]

Alan, you could use a blast gate as an air inlet to control & adjust the inlet flow.

Shouldn't I want the inlet flow from the dust collector, and by extension the front of the shroud to be as much as the dust collector can produce?

I finished the two pieces of wood with magnets to place on the front holes when not using the clamps. Just waiting for the paint to dry.

Unfortunately I can't remove those front bottom pieces. Didn't think of this and inside is a reinforcing piece that glues to them. So probably going to hand saw two diagonal cuts in front to increase the open area around the Kapex shroud.