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  1. #1
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    Default SCMS extraction.

    Playing around with dust extraction on my new Bosch Glide saw.

    I don't have room to locate it permanently on a bench so its going on a hydraulic lift trolley, and shoehorned under the RH wing of the TS and I'll pull it out when needed.

    This means there is limited room for any sort of a dust shield/surround. I started to make a large curved surround out of polycarbonate sheet but after many hours of work I determined that though the glide saw has no rails and takes up less space behind the saw than conventional SCMS, the range of movements that cover all the various angles means any surround still cannot cannot sit close to the saw and and takes up considerable room. Any surround that covered all the saw angles would not allow the saw to fit in its allocated space

    So I decided to test out a few things.

    The first thing was I wanted to see how effective my shop vac was using the standard dust collecting port on the saw. The Vac a is a Ryobi wet and dry so I was able to direct its outlet air outside the shed.

    The sawdust on the bench is the result of 5 cuts of a 100 x 25 piece of pine with the only thing collecting dust being the shop vac..
    I was impressed at how relatively little mess there was - there's some sawdust that escapes the rubber shroud behind the saw but its not that much although making lots of cuts means that its going to build up over time.

    ShopVac.jpg

    More importantly, the particle counter (shed background was around PM10 of 2 µg/m^3) showed no more than about 10µg/m^3.
    OK lots of cuts may see this build up over time but even that is could be taken care of by ventilation.

    The next step was to try a single 4" BMH (no vac) on just one side of the saw. Same 5 cuts
    The photo below shows that the BMH is only catching the stuff on one side - what it really shows is that with the shop vac intake directly in line with the sawdust stream the shop vac is catching most of the visible dust. The BMH is to the side and further back so cannot capture the dust at source.

    BTW for this test I removed the small rubber sheet/scoop around the inlet of the shop vac collection point near teh saw blade because when that was on and no vac was running a significant amount of sawdust was forward scattered - ie a real mess.

    Now even though there's a lot of visible dust deposited on the right hand side, the fine dust levels were lower that using the shop vac alone ie ~5 µg/m^3).
    The particle counter was tried at position P2 - same result as P1.
    At position P0 the counts were a bit higher and briefly during one cut went to 50 µg/m^3 but that lasted <30 s before the BMH was able to clear it back to shed background. I was not game to try the particle counter out at position PX.
    This suggests the single BMH is doing good job on the fine dust, but poorly at chip collection on the RHS although a second BMH on that side should easily clean that up.
    I4inchBMHGS.jpg

    Next I tried both the shop vac and BMH same 5 cuts
    Least mess and similar fine dust levels to using the BMH by itself.
    BMHplusShopVac.jpg

    I'm going to experiment with this a bit more including trying 2 x 4" BMHs and a 6" BMH. Meanwhile I'm pleased to be able to start using the saw for small numbers of cuts with just the shop vac, or shop vac plus a BMH positioned just to the side of the blade.
    Attached Images Attached Images
    Last edited by BobL; 6th July 2022 at 10:59 AM.

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  3. #2
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    Thanks Bob, I'm looking on with interest - I'll be tackling SCMS dust collection too at some stage.

  4. #3
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    Love you Bobl, just when Ive finished fitting a 150 BLM to the rear of my SCMS you come up with another idea. oh happy day..
    I would love to grow my own food, but I can not find bacon seeds

  5. #4
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    Setup looks very similar to one I posted about some tine ago - Post #20

    New Dust Extraction setup

  6. #5
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    I'll follow this with interest Bob, as I'm in the process of putting together a simple solution for mine too.

    One thing I noted with my Makita is that without any extraction fitted it is amazing how much of the dust is caught by the "catcher" behind the blade and directed up and out the vacuum attachment point. It certainly make a mess if left open.

    If your saw is similar, it would be interesting to see how you would go with the BMH to one side as you have it, and a piece of hose from the vacuum port running into the BMH.

  7. #6
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    Bob are you going to test any pickup configurations with compound cuts?

    Pete

  8. #7
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    Quote Originally Posted by QC Inspector View Post
    Bob are you going to test any pickup configurations with compound cuts?
    Pete
    Yes.
    Quote Originally Posted by Lappa View Post
    Setup looks very similar to one I posted about some tine ago - Post #20
    New Dust Extraction setup
    Yep - very similar and it may have even been subconsciously where I got the idea. the only difference are my BMHs are attached to and so move with the saw.
    Did you end up adding the cloth shrouds you mention in that post?
    Quote Originally Posted by Tonyz View Post
    Love you Bobl, just when Ive finished fitting a 150 BLM to the rear of my SCMS you come up with another idea. oh happy day..
    Oh don't worry I have other ideas.
    Quote Originally Posted by LanceC View Post
    One thing I noted with my Makita is that without any extraction fitted it is amazing how much of the dust is caught by the "catcher" behind the blade and directed up and out the vacuum attachment point. It certainly make a mess if left open.
    Yep it does make a mess.
    If your saw is similar, it would be interesting to see how you would go with the BMH to one side as you have it, and a piece of hose from the vacuum port running into the BMH.
    Yes I will try that.

    The size and shape of the rubber pickup shroud on the saw is designed to cope with the extreme compound cuts but as it is easily removable on this saw I wonder if anyone has experimented with larger - different shaped shrouds?

  9. #8
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    See you finally pulled the trigger on a new SCMS.

    Am definitely interested in this as i'm eying off the same saw.

  10. #9
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    Yeah did the deed last week. So far I’m pretty happy with it. Spent all morning doing more testing and have a heap of interesting results to put up but just b4 lunch was called away for babysitting duties. Will post wheN I get home later this evening.

  11. #10
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    Because my Makita has the rails that slide, its hard to fix the BMH to the saw itself. My BMH is mounted on a sheet of ply that slides into a groove at the back of the table. I just slide it along to align with the saw when I cut at angles and have vertical panels that also move.

    I did not go ahead with the cloth as the amount of chips/dust not captured is minimal and easily vacuumed up after a session.

  12. #11
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    Hey Bob,

    I sort of assume you may have seen this but just in case Dust RICOCHETS back down! (Easy Fix w/ a FLAP) - Bosch Axial Glide Miter Saw - YouTube the clip has some great video of how dust comes off the blade on the Bosch for various timber thickness. it was one of those videos i spotted looking at dust collection options.

    I found it intriguing the path the fine dust was taking off the blade.

    Cheers
    Phil

  13. #12
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    Quote Originally Posted by Aussiephil View Post
    Hey Bob,

    I sort of assume you may have seen this but just in case Dust RICOCHETS back down! (Easy Fix w/ a FLAP) - Bosch Axial Glide Miter Saw - YouTube the clip has some great video of how dust comes off the blade on the Bosch for various timber thickness. it was one of those videos i spotted looking at dust collection options.

    I found it intriguing the path the fine dust was taking off the blade.
    Thanks Phil - very interesting indeed, I had not seen that Vid till just now.

    It sounds a bit pompous but initially I avoid looking at youtube for new ideas etc as
    a) I don't want my mind clouded/influenced by what others have done
    b) A lot of youtube stuff, especially about dust, is misleading.

    Despite what it looks like that video is really only looking at visible dust. The sort of dust that mainly interests me is the invisible stuff which can move differently to the visible stuff and can only be detected by a particle counter. However, I will definitely include in future trials some of the suggestions in that video which I think will be very useful especially for sliding and compound cuts.

    I will shortly follow up with a post about the results of a number of experiments (using the saw as a chop saw) that I did this morning before I saw that video.

  14. #13
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    This morning I did a series of dust extraction experiments on the glide saw.

    I also need to state that the results in my previous post are somewhat unreliable as I was not certain of a bunch of things.
    - position of the particle counter, always in the same place.
    - consistent location of the BMH
    - whether the ventilator was on or off.
    - not checking back ground dust levels often enough.

    Here are the results of the 10 experiments - all in chop saw only mode - 5 cuts of 90 x 35mm pine (~25% more sawdust that yesterdays cuts)
    The particle counter is about 1m slightly to the left behind the saw position unchanged during the testing.
    BG = background before the measurement - as you can see it was pretty low so good for making these measurements.
    P1, P2 and P3 are different positions for the BMH - P1 is slightly back through to P3 being teh closest I could get the BMH.
    chopsawdata.jpg


    Experiment 1
    This is using the standard saw extraction, ie shop vac only. The ~20µg/m^3 is about double yesterdays result. One of the reasons for this is when I did this test yesterday I left the 4" BMH (no extraction) in place which happened to be blocking the air path to the particle counter. The 20µg/m^3 seems low but remember this was only 5 cuts and subsequent cuts would accumulate inside the shed fast than any vac could clear the air. This setup certainly picks up a good deal of the chips as overall chip scatter was low.

    Experiment 2
    Same as 1 but this time with ~800 CFM of ventilation 2.7m above the particle counter. 5.2µg/m^3 is very acceptable especially as the ventilator should keep the dust at or below this level for all subsequent cuts. This really shows the value of general ventilation.

    Last night (before looking at any vids this afternoon) I had an idea for a larger scoop just behind the blade.
    The black one is the original, while the grey one is cut out of a wheelbarrow wheel inner tube.
    The scoop is easily removed/replaced so even though a longer scoop would get in the way of a thicker workpiece in saw slide mode in chop mode this doe not matter.
    Scoop.jpg

    When I put the first large scoop on the saw and fired up the vac this is what happened.
    The scoop just collapsed under the suction.
    This was due to 2 problems - one was the size and the other was that I had cut the scoop from the very outside of the tube and it was flexing too easily in the middle as it had been folded that way for storage.
    Squishedscoop.jpg

    When I cut the scoop from the sidewall of the tube and a touch smaller
    Here it is with vac suction on.
    OKscoop.jpg

    Experiment 3
    Is the same as experiment 1 but now using the longer scoop.
    So just using a longer scoop halves the PM10 (10µg/m^3) at the test location.

    Experiment 4
    Uses large scoop and the 4" BMH shown in the photo above. The saw vac extraction port was blocked. The chip scatter was definitely worse but the PM10 was down to 6.7µg/m^3

    Experiment 5
    Similar to experiment 4 (ie blocked vac tube) but BMH 1cm closer to dust source
    One thing I noticed was the side of long scoop nearest the BMH seem to block chips from getting into the BMH so I unhooked that side of the scoop and generate what I call a lopsided scoop like this.
    Lopsidedscoop.jpg

    It didn't noticeably change the ship scatter but it marginally dropped the PM10 at the particle counter. (5.1 µg/m^3)

    Experiment 6
    Same as experiment 5 but this time with BMH even closer to the dust source - this reduced the chip scatter and dropped the PM10 to the second lowest reading (2.2 µg/m^3)

    Experiment 7
    Same as experiment 6 but this time with the vac running - again low chip scatter but marginally greater PM10 (3.5 µg/m^3)

    Experiment 8
    4" BMH was removed and Lopside long scoop leaning towards a naked 6" flex located ~150 mm from the dust source.
    No vac (2.5 µg/m^3) Also low chip scatter.

    Experiment 9
    Same as 8 (6" naked flex) but this time adding a 2" flex (sucked on by the DC) connected to the saws vac port (1.8 µg/m^3)
    This is equivalent to shoving the saws vac port up the jacxi of a 6" DC duct. Also low chip scatter.

    Experiment 10
    No BMH or naked flex opening, just the 2" flex (sucked on by the DC) connected to the saws vac port (5.2 µg/m^3) and the ventilator on. Interestingly this is the same as for the vac with the ventilator on (experiment 2)

    The results for 6 - 9 are all basically the same as PM10 values below about 5µg/m^3 are pretty difficult to distinguish. I would call all these about the same.

    The longer scoop seems like its definitely worthwhile, at least in chop saw mode, as it is really easy to take off and put on,
    The simplest reasonable solution seems to be a shop vac or 2" DC hose with a ventilator although the vac has less chip scatter.

    OK Loads more tests to do.
    6" BMH and adding in some solutions-ideas from Phils' vid link - thanks Phil.
    I may combine these tests with sliding and compound angle modes.

  15. #14
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    Quote Originally Posted by BobL View Post
    Thanks Phil - very interesting indeed, I had not seen that Vid till just now.


    Despite what it looks like that video is really only looking at visible dust. The sort of dust that mainly interests me is the invisible stuff which can move differently to the visible stuff and can only be detected by a particle counter.
    Some thoughts overnight, probable not in order as i'll just dump them from the brain.

    I would expect both visible and non visible particles to behave and travel in similar paths in the presence of a high speed air stream which is certainly the case with a spinning saw blade. The more disturbed that air flow becomes as it moves away from the blade then yes the non visible particles could be easier to disturb though this is offset by them being stuck better to the primary air flow path. The more laminar that flow is the harder it would be to disturb them.

    It's this thought about laminar flow of the air that makes me question the validity of placing a suction input at a near right angle in this case to the primary air flow when the saw is running, when the saw stops then obviously the suction input (the BMH) becomes the primary flow but has to fight initially to establish itself leaving some on the invisible particles to float away.

    I wonder from a single user perspective if your shouldn't have a measurement point at about where your head would be. I understand the current points give you an understanding of what is happening behind the saw but ultimately it's the point your breathing the air from that is important i would have thought.

    Having watch the slow motion and normal speed of that visible dust coming off the blade there seems to be any number of obstructions that make it hard to keep the air stream as laminar as possible but Bosch seem to have got vaguely in the ball park.

    The mods that seem to work all seem to be working with that high speed air stream from the blade.

    To wrap my thoughts:
    there are two key considerations.
    The high speed air stream generated by the blade spinning and how that behaves when actually cutting wood.
    The disturbed air that circulates around saw body both during the cut and especially after the cat is completed and the blade has spun down.

    be interested to run a small smoke machine to film the surrounding air volume flow patterns.

    anyway this is longer than i thought it was going to be...
    Cheers
    Phil

  16. #15
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    Quote Originally Posted by Aussiephil View Post
    Some thoughts overnight, probable not in order as i'll just dump them from the brain.
    I would expect both visible and non visible particles to behave and travel in similar paths in the presence of a high speed air stream which is certainly the case with a spinning saw blade. The more disturbed that air flow becomes as it moves away from the blade then yes the non visible particles could be easier to disturb though this is offset by them being stuck better to the primary air flow path. The more laminar that flow is the harder it would be to disturb them.
    Yep in general I agree, but after testing many high speed dust flow streams over the years I've found lots of instances where this is not the case. The issue is usually the flow is not laminar as it is a high speed, open stream. flow. Laminar flow can only occur at slower speeds in a constrained volume. The first particles to deviate from the flow will be the finer ones as they behave like a gas and rapidly diffuse out of the visible dust /air stream, same way as a fart can still spreads around a room even when there's an exhaust fan in action.

    This is why the detector can easily see fine dust 1m+ away from the source within about 10s seconds of starting the cut yet no visible dust seems to immediately reache this distance. Over time of course a layer of dust does accumulate/appear on surfaces which is when that fine dust settles and clumps together. After a series of cut that take seconds, the fine dust levels take about 30s or so to peak at that distance and then (provided no more cuts are made) it drops, to shed background in about 3-4 minutes. With a ventilator running its less than half that. If more cuts are made the shed back ground accumulates and takes much longer to settle down.

    It's this thought about laminar flow of the air that makes me question the validity of placing a suction input at a near right angle in this case to the primary air flow when the saw is running, when the saw stops then obviously the suction input (the BMH) becomes the primary flow but has to fight initially to establish itself leaving some on the invisible particles to float away.
    A 4" BMH should extract about 4x more air from the vicinity of the saw than the vac so the role of the BMH is to capture the fine dust that escapes the saw/vac high speed flow. For a few cuts this is not important but as soon as more cuts are made it is this that accumulates and hangs around for hours. You are right about one dust port fighting the other for air and dust but if it ends up capturing the dust does it really matter?

    I wonder from a single user perspective if your shouldn't have a measurement point at about where your head would be. I understand the current points give you an understanding of what is happening behind the saw but ultimately it's the point your breathing the air from that is important i would have thought.
    Absolutely correct Phil. Last night I charged up my wearable detector and will be using that for future experiments. The reason I started out with a particle detector at that distance away behind the saw was to reduce the chances of damaging the detector. I will still run the bench top detector but more of a way to check general shed background.

    When a SCMS is placed up against a wall or poorly vented enclosure, fine dust that escapes the vac/saws has nowhere to go except to bounce off the wall and back towards the operator. Likewise parts of the vac/saw airstream heading away from the operator that strikes various parts of the saw. This testing I am doing is in an open shed and I'm not going to use an enclosure or locate the saw up against the wall so my results may have limited application for others.

    Having watch the slow motion and normal speed of that visible dust coming off the blade there seems to be any number of obstructions that make it hard to keep the air stream as laminar as possible but Bosch seem to have got vaguely in the ball park.
    I think its more than "vaguely" - I'd rate it as one of the better SCMS in terms of dust collection. It's certainly better than the Makita at the men's shed and my mates Ryobi.

    Anyway thanks for you considered thoughts - much appreciated.
    Now I'll have to leave this for a while as I have a couple of BMHs orders to fill and a couple of honey-do items to attend to.

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