Dust Collection on SCMS

[Andrew More]

So I've got the usual solution: build a box around the saw, then cover as much as possible of the front, add dust control port(s) in the rear. This seems to work okay, mostly because the saw is designed to throw saw dust backwards, into the box, and which point it either collects in the corners, or gets sucked down the dust collection port. The dust collection in the corners is annoying, but I can live with it.

Other useful information:
Ducting is a 6" which is reading the 20 m/s at the input, with is max for the DC I'm using.
Duct is at the bottom of the box.
SCMS is a 12" Bosch Axial Glide

Questions:
Is there another system than the basic box for SCMS? I'd like to be able to keep the ability to do miters with it. This rules out a system like Frank Howarth's for his RAS, which only allows for straight cuts.

The box is build pretty square, does anybody know if I would get better performance filling in the corners? In particular I'm debating add a curve to the back, which tracks with the arc made by the back of the saw. I'm also debating adding a slanting piece to the top, because the box is much taller than it needs to be to accommodate the saw fully open. Has anybody tried this, and if so what benefits did it provide?

Currently I'm blocking off the front using two pieces of plywood with a profile cut to allow the saw to move without interference. This creates a huge opening, and at the opening I'm seeing about 2 m/s air flow (down from 20 m/s at the duct opening) largely as a result. Does it make more sense to use a flexible curtain of plastic strips like you might see in a freezer doorway? Has anybody used this sort of system, and if so, what were the results?

EDIT: Added some pics of the current setup.
IMG_20190502_122142.jpgIMG_20190502_122152.jpgIMG_20190502_122157.jpg

[Malcolm McLeod]

I am contemplating using a box as well, but thinking of mounting the box on a pair of ball-bearing drawer guides. Guides would be mounted horizontally, 4"-6" apart, beginning just below table height, on the back of the stand for the SCMS. Box would have a 'flange' extending down to attach to the sliding portion of guides, and sit at mid-travel (left to right) of the guides when saw is set for 90deg cut.

As saw is moved to miter position(s), the box would slide L<>R to appropriate catch position. I need to mock something up to determine if a 'crank' mechanism could move the box to match the miter angle...?? If not, a simple manual bashing will have to do for positioning.

My plan is to have the box entry (profile as you call it) sized for good air velocity. Also to have the entry framed with angled pieces, such that the larger, high velocity chips should hit and deflect into the entry.

That's my concept, but no time to build it right now. Feel free to steal shamelessly and report how it works. Might save me some pain?

...anything beats my SCMS' current ability to broadcast dust over 3 acres.

Adder: Just saw your pics. I'd call your install a 'hood' (FWIW). I'm thinking of a relatively smaller box sliding along the back.

[Andrew More]

I am contemplating using a box as well, but thinking of mounting the box on a pair of ball-bearing drawer guides. Guides would be mounted horizontally, 4"-6" apart, beginning just below table height, on the back of the stand for the SCMS. Box would have a 'flange' extending down to attach to the sliding portion of guides, and sit at mid-travel (left to right) of the guides when saw is set for 90deg cut.

That's an interesting idea, but I think I would work on using the existing dust catcher on mine first, or attach the box to the saw directly. The guides would result in the shroud getting further and further away as you increased the miter angle.

[Frank Drackman]

I made the box & all of the appropriate dust collection stuff that everyone does. I close in the front with removable panels but they are held in space by small rare earth magnets. Quick to remove for miters and magnets index the panels in the correct location with no fuss.

Even after everything I did to help with dust collection it is still more of a containment box.

[Jim Becker]

What Frank said, other than I didn't do removable panels like he described. I previously tried a combination of under saw and blade guard collection, but miter saws are messy-messy beasts and hard to collect from efficiently. "The Box" seems to work the best for me...and as Frank eluded to, I still have to clean it out regularly even with an efficient drop to it.

[Andrew More]

I made the box & all of the appropriate dust collection stuff that everyone does. I close in the front with removable panels but they are held in space by small rare earth magnets. Quick to remove for miters and magnets index the panels in the correct location with no fuss.

Same, those panels are held on with rare earth magnets. I might be able to make the cut-outs a little more efficient, but that's about it.

@Jim - Agreed, I haven't seen any better solutions, but you never know. Honestly the SCMS really just highlights how foolish some people's fanaticism about dust collection is. On my saw that blade is moving at ~135 MPH, the dust collection 40 MPH, at the inlet, 4 MPH at the edge of the box!

[Frank Drackman]

I just use tempered hardboard for the panels with magnets glued to the back. I have small metal disks recesed into the frame of the box. It takes seconds to remove & replace. I find that it help keep the dust in the box.

What Frank said, other than I didn't do removable panels like he described. I previously tried a combination of under saw and blade guard collection, but miter saws are messy-messy beasts and hard to collect from efficiently. "The Box" seems to work the best for me...and as Frank eluded to, I still have to clean it out regularly even with an efficient drop to it.

[Tom M King]

Mine works great. This was a prototype, to see how it worked, and I never had to modify it at all. Maybe these pictures will be of some use. 6" port under a plenum below the slot along the inside lower edge. I don't care a bit that it accumulates some extraneous sawdust in it, here, and there. Different saw, but it does miters just fine. Total of 1" deeper than saw alone. I thought I might have to close up some more of the front, but no dust gets out onto anything, and we can even use it inside finished houses. 3hp 4-bagger on wheels, in this house also hooked up to jointer, and table saw, with no blast gates.