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  1. #1
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    Default Table saw guards and dust extraction for "non-through" cuts?

    I have recently upgraded my table saw dust extraction. As part of that upgrade, I have installed a Felder overhead guard (taken from a K700S), which has a 3" inlet. I have put on a 4" flex as many Felder guys over the pond report that they get a little more airflow even though they are "not supposed to" as the 3" is the constricting point.

    This system works "well" for general ripping.* I can adjust the guard above the timber being ripped by a few mms and I cannot see any dust escape. In other words, the super-fast dust flying off the teeth is hitting the inside of the guard and being sucked away. Presumably all/most of the invisible dust is likewise being extracted? *Note, I have no instruments, so emphasis on the "presumably".

    But I have two observations:

    When I trim the width of something, where the blade is not trapped in a kerf, but is running along the side of the timber (say taking off 1mm), lots more dust escapes because the guard is not adjusted flat against the table, but only flat against the stock. Consequently, plenty of dust leaks out the side (left side, with the right sided fence). I've wondered whether it would be helpful to position a piece of timber or some kind of curtain on the side of the guard to try to trap this dust?

    Second, when make non through cuts, say grooving a piece of timber to take a panel, or working on tenons with the mitre guage, again plenty of dust is emmitted from the groove or from the underside of the tenon. Not sure what to do here?

    Consequently, I would say that my guard is dust "effective" only for "properly" through cuts. All the rest yield sub-optimal results.

    You guys must have come across this? Any solutions?

    Thanks.
    Warm Regards, Luckyduck

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  3. #2
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    Is this the guard?
    Table saw guards and dust extraction for "non-through" cuts?-fguard-jpg
    Attached Images Attached Images

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    Yes. (Please don't tell me it's s&*t because it took me ages to bolt the damn thing on my existing cabinet saw!)

    Incidentally, I just made a wooden insert to accommodate a 8" dado set, and there is plenty of space around the blade when cutting a 1/4" groove (like say 3/4"). This dealt with the dust issue much better than when cutting a groove with my normal blade and insert.

    Should I use the wooden insert (with wide mouth around the blade) for normal table saw work as long as I don't have little bits of offcuts? Come to think of it, little offcuts aren't going to be a problem anyway as the are sucked away by the bottom port and there is no fan to hit with my RL unit. ...

    I will get around to taking pictures of the whole dusty set up in a new thread -- one day (soon I hope!)
    Warm Regards, Luckyduck

  5. #4
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    Default TS dust extraction

    Ok, I'm supposed to be building some cabinet doors for a couple of small bookcases, but here I am!

    First shot, is the 150mm under table flex. The flex is actually 160mm, but I have used some 150mm PVC I had from my old dusty so it is restricted a bit.
    photo 1 copy.jpg

    Second shot, of the vent on the opposite side of the cabinet. I took the vent apart and removed half of the grill to open it up. Not sure if it is enough?
    photo 2 copy.jpg

    Third shot, the TS guard itself. It has quite nice adjustments in and out and up and down. So far I like it, but am willing to perform mods if necessary to make it better.
    photo 3 copy.jpg

    Fourth shot, shows the bulk of my ducting setup. There are three verticals on the right. The first one is 160mm for my thicknesser/planer. The second one is for my TS. The third one is for the BS, which sits directly behind my tablesaw wing. More on the BS in another post. You can see my SCMS in the background, and the 250mm mainline going off to the left doesn't travel more than another meter and then it goes down to the RL250, just out of the picture at left.
    photo 4 copy.jpg

    Thanks.
    Warm Regards, Luckyduck

  6. #5
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    Quote Originally Posted by LuckyDuck View Post
    Yes. (Please don't tell me it's s&*t because it took me ages to bolt the damn thing on my existing cabinet saw!)
    OK it's not "s&*t" it's just a really poor design for all round dust collection.
    Have a look at what John Samuel did.

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    Quote Originally Posted by BobL View Post
    OK it's not "s&*t" it's just a really poor design for all round dust collection.
    Have a look at what John Samuel did.
    Hi Bob:

    Hmm, ok, so short of ripping it out, what can be done?

    I have previously had a long look at John's setup which is very impressive. I just reviewed his design. Could you help me plan a mod for the "poor design" aspects of my guard? I primarily installed the Felder guard for its robust nature, and for the extremely easy way the guard assembly can be controlled for height, and telescoping in an out so that it can be moved entirely out of the way (to the right). These are very desirable for my situation and suits me very well.

    I do wish the internal ducting (i.e. rectangular vertical cross-section) was a full 4" but alas, it is only just larger than 3" from memory.

    So, unless I'm missing something obvious (which is a distinct possibility!), the biggest difference between John's guard and mine is the fact that John's fits around his 10" (or is it 12" John?) blade while the Felder guard is a ridiculous 700mm long (i.e. the depth of my entire saw top)! In terms of width, the Felder guard is pretty good, as it is about 30mm wide. But there is way too much space fore and aft of my 10" blade.

    Would you agree?

    If I am on the right track, I propose to modify this part of the guard by getting rid of it altogether and building something new. The lower part of the guard is made of plastic, and has clear side inserts, and white rollers front and back -- all this is attached with a couple of screws (see red rectangle in photo) to the bottom of the metal rectangular vertical arm.

    I could chuck this, and then make and attach (in a similar manner) anything I wanted, probably much closer to what John made, unless you, John, or others, have some advice on how to make his better?

    John, I saw you purchased some acrylic. Was it 6mm or a different thickness? I haven't really worked acrylic before, but I assume I can cut it on my TS and/or BS, and then glue it together?

    photo 5.jpg

    Appreciate your help.
    Warm Regards, Luckyduck

  8. #7
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    In partial answer to my previous questions about how to minimise dust escaping for non-through TS cuts, I have reduced the amount of dust escaping by turning my fence 90 degrees to the thin edge. This has allowed me to introduce the fence essentially underneath the TS guard, and use it as the stop block for establishing a shoulder when making tenons with a dado on the TS. The fence appears to be a solid stop which helps contain dust/chips.

    photo tenoning.jpg

    Assuming that making a new clear plastic "shroud" to attach to my TS guard arm will improve my dust collection (see previous post in this thread), I was wondering whether anyone has made a shroud with sides that can be dropped down, say with cam bolts or butterfly nuts?

    In instances where one is trimming the width of a piece of timber, say by 1 or 2mm, the appropriate side of the clear guard could be "dropped" down so that it actually rested on the table. If both sides could be dropped down independently, then these could be adjusted according to whether one is tenoning/dadoing from the left, or ripping to width from the right?

    Has anything tried this before, and would it work? I'm not sure if this design would require a double layer on either side of the shroud? That is, start with a rectangular shroud, and then have some slotted flat pieces on either side. Better yet, perhaps only have one of these flat pieces and somehow attach it (velco?) to the side as required? Just brainstorming here...

    Thanks.
    Warm Regards, Luckyduck

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    I was wondering if your 4" hose could be attached directly to the square tubing rather than through the plastic adapter? If possible, there should be a little better flow I think. Emphasis on I think.

    With respect to your thoughts on floating sides. Delta / Rockwell Unisaws used to come with a blade guard that allowed the left and right sides to move independently from each other. They didn't have any provision for dust collection, well the old ones didn't anyway, but if you were trimming off a little on one side that side would be against the table and the other was on top of the wood. If you didn't want one side down, like thin rips against the fence, that half could be flipped up and back out of the way. Do some searching for Unisaw guards to see what I mean. You could perhaps cut and shape a plastic side with a pivot at the back, bolted through the white wheel with a longer bolt. Another option is to attach brushes along side of the guard, maybe with magnets. BobL did a thread on that sort of thing.

    Pete

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    Quote Originally Posted by LuckyDuck View Post
    John, I saw you purchased some acrylic. Was it 6mm or a different thickness? I haven't really worked acrylic before, but I assume I can cut it on my TS and/or BS, and then glue it together?
    I used 10 mm machine guard grade polycarbonate to make the overhead guard/dust hood. It was cut on the TS. A few spots of superglue were used to hold it in place while it was screwed together. The screws provide all the strength on mine.

    If I were to make it again I would make the front piece of material seam free for the entire height, to improve visibility.

    Cheerio!

    John

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    Quote Originally Posted by QC Inspector View Post
    I was wondering if your 4" hose could be attached directly to the square tubing rather than through the plastic adapter? If possible, there should be a little better flow I think. Emphasis on I think.

    With respect to your thoughts on floating sides. Delta / Rockwell Unisaws used to come with a blade guard that allowed the left and right sides to move independently from each other. They didn't have any provision for dust collection, well the old ones didn't anyway, but if you were trimming off a little on one side that side would be against the table and the other was on top of the wood. If you didn't want one side down, like thin rips against the fence, that half could be flipped up and back out of the way. Do some searching for Unisaw guards to see what I mean. You could perhaps cut and shape a plastic side with a pivot at the back, bolted through the white wheel with a longer bolt. Another option is to attach brushes along side of the guard, maybe with magnets. BobL did a thread on that sort of thing.

    Pete
    Hi Pete:

    Thanks for your ideas. I'm definitely keen to make my dust collection as good as I can. Clearly, between my experience so far, and the feedback here, I've got a way to go.

    Thanks for reminding me about the old saw guards -- that's very similar to what I was thinking (ha ha, nothing new under the sun hey)! There is no doubt I need a new lower section on my guard; I've reviewed Bob's brushes idea which looks excellent. Will keep that in mind. I do worry about whether the brushes ever "brush" against the saw blade, or get caught under the timber being cut?
    Warm Regards, Luckyduck

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    Quote Originally Posted by John Samuel View Post
    I used 10 mm machine guard grade polycarbonate to make the overhead guard/dust hood. It was cut on the TS. A few spots of superglue were used to hold it in place while it was screwed together. The screws provide all the strength on mine.

    If I were to make it again I would make the front piece of material seam free for the entire height, to improve visibility.

    Cheerio!

    John
    Hi John:

    Thanks for your input. I've learned a lot from your dust extraction journey. Ta.

    I'm going to give your design a go and see if I can't attach it to my existing Felder arm. Where did you buy your polycarbonate? And do you have approx dimensions you could throw my way please?

    Finally, I'm still after your holy grail of having no residual dust lying on undisturbed surfaces. I'm making some headway, but I recognise that trimming timber to width (cutting say 1mm off) and general non-through cuts on the table saw yield more dust than I care for.

    Do you get enough airflow overhead to deal with these situations? Would an extra piece extending down one side improve the extraction?

    Thanks for your help!

    PS. Are you going to the show in May? If so, what day are you planning to attend? It might be good to meet!
    Warm Regards, Luckyduck

  13. #12
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    Quote Originally Posted by QC Inspector View Post
    I was wondering if your 4" hose could be attached directly to the square tubing rather than through the plastic adapter? If possible, there should be a little better flow I think. Emphasis on I think.
    Good point QCI.

    LD what are the internal dimensions of these cross sections?
    If the tubing is 4" the internal dimensions of the black plastic connector looks smaller than 3"
    The green rectangular tube only looks to be ~4" wide.
    Table saw guards and dust extraction for "non-through" cuts?-ldtsg-jpg

    Rectangular cross section ducting of the same cross sectional area as a round duct will have more resistance and hence lower flow.

    The best location for the duct on a TS guard is forward of centre - in fact as far forward as possible. So far forward that it would normally obstruct the operators view hence it needs to be transparent.
    Attached Images Attached Images

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    Quote Originally Posted by BobL View Post
    LD what are the internal dimensions of these cross sections?
    If the tubing is 4" the internal dimensions of the black plastic connector looks smaller than 3"
    The green rectangular tube only looks to be ~4" wide.
    Just disassembled ducting and measured everything up:
    - flex is genuine 100mm diameter = 7854mm2
    - black plastic port is genuine internal diameter of 75mm = 4418mm2
    - green steel tubing has internal dimensions of 112mm x 34mm, with slightly rounded corners = ~3808mm2, assuming my math is correct.

    So, I might like the boom arm itself, but the internals do add up to a poorly designed collector!

    Quote Originally Posted by BobL View Post
    Rectangular cross section ducting of the same cross sectional area as a round duct will have more resistance and hence lower flow.
    Noted.

    Quote Originally Posted by BobL View Post
    The best location for the duct on a TS guard is forward of centre - in fact as far forward as possible. So far forward that it would normally obstruct the operators view hence it needs to be transparent.
    Noted; I was (emphasis on the "was") pleased to see that the bottom of the green tubing is actually forward of the blade so that we have something of the "as far forward as possible" design requirement. However, considering that I am only working with 3808mm2 which is more than 2.5" but less than 3" in diameter, I'm now wondering whether I should bypass the green tubing altogether and dead head 4" flex straight onto a newly designed and built clear plastic shroud, along the lines of what John Samuel has done?
    Warm Regards, Luckyduck

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    Quote Originally Posted by LuckyDuck View Post
    Just disassembled ducting and measured everything up:
    - flex is genuine 100mm diameter = 7854mm2
    - black plastic port is genuine internal diameter of 75mm = 4418mm2
    - green steel tubing has internal dimensions of 112mm x 34mm, with slightly rounded corners = ~3808mm2, assuming my math is correct.
    So, I might like the boom arm itself, but the internals do add up to a poorly designed collector!
    Yep. Math looks right

    To illustrate the effect of the narrow rectangular tube versus a circular tube take a look at this calculation.

    The couple of mm close to the wall of a duct is where the air speed is the slowest so it can almost be removed from the cross sectional area calculation.

    So lets make the 100 mm (7854 mm2) duct a 98 mm (7543 mm2) duct and calculate the percentage loss in area : = 100 - (7543/7854 *100).
    This works out to be a ~4% loss in area
    For the 112 x 34 mm duct this becomes 110 x 32 mm and the %loss in area is 7.5%.

    This is another reason why narrow saw guards are also ineffective as inlets and further restrict flow.

    My guess is you are getting about 100 CFM through that guard.
    I wonder if it was designed for a vacuum cleaner, a good vacuum cleaner should pull 130 CFM through that guard, but a genuine 4" duct should pull 400+ CFM.


    Noted; I was (emphasis on the "was") pleased to see that the bottom of the green tubing is actually forward of the blade so that we have something of the "as far forward as possible" design requirement. However, considering that I am only working with 3808mm2 which is more than 2.5" but less than 3" in diameter, I'm now wondering whether I should bypass the green tubing altogether and dead head 4" flex straight onto a newly designed and built clear plastic shroud, along the lines of what John Samuel has done?
    Probably the best option

  16. #15
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    I see the math a little differently. Must be because of the cold. To fit the hose to the rectangular pipe you need to consider the circumference and not the area.

    !00 mm hose diameter times 3.14 (pi) is 314 mm.

    112 mm x 2 + 34 mm x 2 is 292 mm. Actual will be a little larger because you said that was the internal dimension.

    That means to me the plastic adapter gets set aside and the hose gets shoehorned on to the rectangular pipe. It doesn't do anything to improve airflow through rectangular pipe but it does eliminate the turbulence through the plastic adapter which counts for a little, I hope.

    Pete

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