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I've got a portable DC with a 6" hose but am planning to upgrade to a larger stationary unit with a minimum of 6" pipe.
I've been looking for some of the best sources of 6" DC hoods and machine fittings. It doesn't make sense to me to bring a 6" line to my TS, jointer, etc., and neck it down to 4" at the tool.
Jim
I agree that machine hoods are lacking but even with a 4" port at the machine you will be much better off bringing a 6" line right to the port. You gain velocity by not using runs of 4". On a 5 hp 15+" system the same concern is valid when using 6" mains. The pressure increase of 6 vs 7 translates to a large loss of cfm with the fan configurations used on hobby systems. You may have to have the machine ports made. Dave
What tools are you trying to collect from ??? Often times, you'll probably need to fabricate your own collection hoods in order to keep the cost reasonable. About the only tools I can imagine that would require such shrouds would be drill presses .. miter saws .. radial arm saws. Of these, a 4" hood with a reducer at the point of use should be more than sufficient for the amount of dust/chips produced, with the possible exception of the RAS.
It's not entirely about air flow ... it's also considering the size and volume of waste that you are trying to move.
Most that I have seen at the machine (if not stock at 6") have been self-fabricated. Apparently, except for us, not enough people need these things to pay for marketing them ;-)
What Glenn Bradley said...
My company orders custom fabricated sch40 PVC fittings from a company called CM distributors in Escondido, CA. They use what appears to be a plastic welder to meld two pieces of pipe together to form nice sweeping WYE's. The interior is very smooth and it's air/water tight. One WYE costs about $30 though.
Attachment 229929
I read some papers and I came to a conclusion that if I design a reducer, the angle at which the pipe reduces is optimal at 7 degrees considering friction and turbulence. Does that jive? Or will that make my reducer fittings too long and I'll need to increase that angle?
Chris, this would be considered an expansion if you are going from a small port on a piece of equipment to a larger duct. I know it may seem like semantics, but the losses are calculated differently for expansions vs. contractions. You will actually get a static pressure regain due to the duct enlargement. The amount of regain is dependant on the velocity difference in the two ducts, ratio of the diameters, and taper angle. What realy hurts is that a CFM necessary for 6" is attempting to be drawn through the 4" duct, resulting in a high hood loss.Quote:
Originally Posted by Chris Tsutsui
For example, consider an open end 6" duct at 800 CFM. The hood loss (static pressure a couple of duct diamters back from the end of the duct) is about 2"wg. If we change this to a 4" inlet with a 4"x6" expansion that is 6" long, the hood static pressure is about 7"wg (including the SP regain). If you don't have enough fan to overcome this SP at 800 CFM, then the CFM drops until the CFM and SP can be develloped by the fan. If you can enlarge it to 6", it will be a much better solution.
Mike
Yeah I guess it isn't a reducer, but an expansion or enlarger...
So do you know if 7 degrees is the optimal taper angle? The inlet and outlet is given for me but the taper angle is what I want to make a logical decision on.
My geometry is a bit rusty but I have a 4" machine outlet and i'm going to a 6" duct. Then the custom taper should have a centerline length of 8.14 lineal inches for the tapered section.
Thanks
I'm thinking practical instead of mathematical, but anyway, if I were to make a Y using 2 pieces of pipe, couldn't I just 45 the end of the pipe on my miter saw, then take my edge sander that has a 6" flat pulley on the
end, and just put the 45 degree square pipe against the pully and sand it till it fits against a 6" pipe? Then just draw inside the pipe with a marker and saw it out with my jig saw, and glue the pipe on over the hole. Seems pretty simple if you have an edge sander with 6" pulleys. For making Y's out of plastic pipe.
Chris, I am not sure about an optimal taper angle. What I have done in designing systems is to evalute the length of run that I have available and the SP available from the fan. Most of the time, I end up at 10 degrees or less. If you use 8" of length, then you have a hood SP of about 6.7" as opposed to 7" for the 6" length.Quote:
Originally Posted by Chris Tsutsui
Its not very common to do this on a machine or hood connection. Usualy the machine connection is maintained or there is a hood that has a larger face area than the duct area. The most common place for contractions and expansions are at connections to a filter, cyclones, fans, etc. I plan to make a new hood for my machines with a larger connection on the hood. For example, on my TS, I have a 4" port, 90 EL toward the back of the saw, then another 90EL to run the duct uner the outfeed portion of the saw (my DC port is on the LH side of the saw). I can make a new hood out of plywood or plasitc that has a 5" port facing the back of the saw. I saw a picture of one on here, but I can't remember where. I plan to put a 3" connection to the blade guard then bring both the 5" and 3" to a 6" duct to the collector.
This leads back to the OP's question. I still have to figure out how to attach the 5" duct/hose to the hood. What fittings/methods are recommended?
Mike