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Post by reflector on Dec 31, 2017 0:23:28 GMT -5
Pardon the horribly drawn diagrams, but I'll go take some photos and whatnot to followup on this when I get a chance. Starting off: The typical portable table saw, including the Erikas from what I've seen seem to have a configuration like this. The general concept is that the saw dust generated by the cut is thrown downwards by the blade and the airflow induced by the spinning blade induces the dust to scream out the dust chute end. From what I can tell, most of the portable table saw designs don't really put much ductwork or airflow features in. If you stick your vacuum hose in and were to place your hand (saw off, unplugged) near the front where the blade would be cutting you generally don't really feel any airflow. Same thing said even if you were to have a conventional (Non Erika) style saw and were to reach inside to the shroud where the blade is at. The airflow is all the way at the back below where the riving is knife is approximately Attachments:
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Post by reflector on Dec 31, 2017 0:32:12 GMT -5
Compare and contrast as to what the MT55cc. The MT55cc has a little ridge on both sides of the housing, approximately where this drawing shows it. At whatever blade cut depth, any saw dust that is inside the housing tends to get trapped between the airflow induced by the blade and the ridge feature which acts like a duct. If you were to turn the vacuum on and move your finger (saw off and unpluged obviously) to near the front of the saw, you'd feel airflow from the vacuum all the way up at the front. The other thing is even if you don't have a vacuum, the amount of air blown out by the MT55cc configuration is a lot higher than than a comparably sized table saw when the blade is spinning. That's just from how the tips/gullets on the blade are able to efficiency move the air in that kind of ducted configuration since there's not a lot of turbulence that can occur inside due to where the air can go. You can kind of see the saw "suck" dust in if you pull the clear shoe down near the work. Speaking of the shoe, that's something the Erika is missing and most saws are. They generally have a huge gap between the table and the housing at some level. In the case of the Erika it has some cutouts on the blade shroud to accommodate for blade tilt. Attachments:
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Post by reflector on Dec 31, 2017 0:44:57 GMT -5
On the common portable tablesaw the easiest fix for under the table dust collection is to find some kind of soft, flexible material or even some kind of durable but relatively stiff cloth. I found some solid shelf liners work really well. In the case of some Dewalt and a Hitachi table saw they already build something like this in the design. Effectively what they do is use that piece of material to try to seal up the gap between the table and the duct, so none of the dust thrown down has that much of a chance to miss the shroud and end up all over the floor. Attachments:
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Post by reflector on Dec 31, 2017 0:46:45 GMT -5
As I don't own an Erika but I have looked at photos of the under table configuration, there's a huge improvement that looks like it could be made. Due to how the shroud has to move under the table, whatever "sealing" method has to effectively deal with movement and also seal. Perhaps some brushes or some kind of mildly stiff material (Again: I found some of that soft shelf liner material that works well) could be taped onto the side to form a funnel feature that redirects the dust into the cutouts on the side of the shroud that are intended to allow for the Erika to gather dust with the blade tilted. Attachments:
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Post by reflector on Dec 31, 2017 0:55:02 GMT -5
One feature I am currently testing out and have tested out an earlier design by using a piece of cut up tube is to pull all the suction from where the vacuum port is at the end of the shroud to emulate the MT55cc configuration. I've been using a 3D printed part that I use double sided tape to adhere onto the inside of the shroud. Before that I tried pieces of wood and aluminum foil duct tape on the motor side to reduce the gap between where the motor on most common table saws intrude to build features like this. Again, if you were to reach (saw off, unplugged) your hand towards the front of the blade after adding features like this, you would find that with the vacuum there's significant amounts of suction. Another thing is these ducts reduce the amount of recirculatory airflow that occurs inside the housing which causes the roostertail or dust to come out from the rear of the sawblade. It also captures some of the surface flow on the plate of the blade which flings air off in a centrifugal manner so there's less dust being thrown about. Attachments:
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Post by reflector on Dec 31, 2017 1:05:44 GMT -5
On a note regarding airflow: All of these modifications are about trying to assist in the efficiency of collection. If you have a dust collector or vacuum that has awesome airflow and suction then this will probably make most if not all of the dust disappear since the collection efficiency under table becomes >95%+ or some very high number since there's no where else for the airflow to go, so the dust has to go into the tube.
There's some modifications of the Bosch 4100 and other larger portable table saws with a solid base where the bottom is fitted with a piece of plywood and the vacuum port is sealed. What that's replaced by is a giant 4" port at the bottom with a conventional dust collection system which has a lot of CFM but terrible static pressure (=Heavy particles with lots of inertia still fly where they want) which means a lot of air is sucked into the saw overall by the negative pressure. Those work best if part of the saw shroud is removed since those low static pressure collectors suck at sucking to put it. They do replace a lot of air so any saw dust that gets under the table is quickly removed. A brute force method, but it "works."
When you're able to pull that high static suction right up to almost where the saw dust stream is generated under the table then the high static pressure will be able to capture everything effectively. Most of the internals of the saw shrouds are open and completely ineffectual in that regard. I've seen some "minor" design features that try to prevent less dust from escaping from the gaping hole on some saws between the shroud and motor and some of them could use improvement.
I'll add more stuff later. some regarding overhead collection. A lot of those overhead collectors are also brute force (high CFM) designs or at best capture the rooster tail of recirculating dust at the tail end of the saw but not necessarily the dust generated at the carbide tip and escaping dust from the gullets right up at the cut.
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Post by reflector on Dec 31, 2017 1:15:44 GMT -5
Regarding the big gaping hole where the motor is: One of the easiest fixes is to take some kind of flexible or soft material (See above about shelf liner) and just tape it onto the motor/gearbox assembly where the hole is. Bosch has a huge gaping hole where the motor and the arm bit that holds the riving knife protrudes through. On some Dewalt designs I found that Dewalt maintains a very small cutout. Hitachi does something kind of like that but they make the hole bigger than I think is necessary, they also throw a piece of material behind the motor like I mentioned before but it seems fractionally assed in terms of what they did. There is another feature on the Hitachi which is ridges on the housing which helps mitigate some airflow that can fly into the hole. Adding the splitters mentioned above also really helps this if you can stick them on the motor side. My initial tests were done with small (~5-10mm) square profiled short pieces of softwood that are aluminum foil taped on to add more of a rib to create a gap reducing feature between the disk of the sawblade and the area where the motor slot is at. If someone felt like they had the time they could probably design some way covers that stick onto the side and does a better job in terms of full sealing. In the case of the Hitachi I just used some aluminum foil tape over painters tape to tape up the area around where the overly large hole is at. Now the opening is much smaller, around 1" or more less on the slot width. The painters tape is used to just avoid letting the aluminum tape stick to the arbor/shaft. The aluminum tape goes over it to stiffen it. Aluminum foil tape I find very useful for taping inside the saws as it isn't very flexible and is fairly stiff so there's less of a chance it'll vibrate loose. The adhesive also seems very sticky, so you want to be careful as to where you put it since removing it is a pain if the surface is rough and metallic like the motor side shroud. Attachments:
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Post by holmz on Dec 31, 2017 13:39:51 GMT -5
Those look just like the pictures I left under the tree for Santa. Regarding the big gaping hole where the motor is: ... If someone felt like they had the time they could probably design some way covers that stick onto the side and does a better job in terms of full sealing. ... If someone has a plan then I could knock up a kit(s)...
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Post by reflector on Jan 2, 2018 11:09:15 GMT -5
Video shows my Bosch 4100 from two years (!) ago with the old modifications I had, inclusive of closing up the hole made by the motor and the side piece of shelf liner that seals the huge gap on the right side up. Attached photo shows the current state of the J shaped ducting and the piece of wood taped on to reduce the amount of space between the blade and side housing so there's even less dust that can get near that hole. Dado stacks still work since the 3D printed J shaped piece is beveled so I can actually remove the blade. It sits mostly very low so there's no real clearance issue unless you're putting in 10" dados and I think that's a wee bit much for a portable saw. I have also done a silly thing with my 0 degree ZCI in that I make them as shown in the other attachment to force the sawdust to come out much lower so it can't reach the gaps in the shelf liner material. I just glue on a piece of plywood using super glue and then raise the blade through the ZCI. The bevel on the plywood is just so the ZCI will sit flat when I drop it in instead of catching on the blade. The thing is your ZCIs won't stack together nicely afterwards since it has a protruding piece of plywood coming off the front. Attachments:
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