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Message |
    
Brian_B
Registered
Username: Allegheny
Post Number: 6
Registered: 07-2006
| | Posted on Tuesday, November 28, 2006 - 03:06 pm: | 
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I wasn't quite sure where to put this post ....
In trying to plan out a dust collection system to handle both my ShobBot as well as my non-CNC tools, I was shocked at the prices of preformed steel tubes and fittings. Accordingly, I went web-searching for other options.
The first URL I found was Bill Pentz's excellent site on dust collector theory and design:
http://billpentz.com/woodworking/cyclone/index.cfm
In addition to an in depth discussion of the theory of airflow and such, he has Excel spreadsheets to calculate the size and power of cyclone separators for a given purpose (i.e., to collect wood chips vs fine MDF dust) - very enlightening stuff. He even has several very extensive pages on how to build your own cyclone with plans, etc.
I already have a cyclone, and I was looking for a way to build a duct system using readily available PVC pipe - unfortunately, fittings for such a system would be limited to those for typical water plumbing systems. So a 5" feeder line coming from a 15" surface planer and going into a 6" trunk line at a 53 degree angle would be impossible to find.
However, I found an amazing piece of online software that allows you to create virtually any "T" or "Y" fitting. You enter the parameters of the particular fitting you need and it generates templates to be taped to the two sizes of pipe. You then follow the templates with a saw, tweak the cuts a bit with sandpaper and glue the two pieces together.
It even has an online tutorial. It is located at:
http://harderwoods.com/pipe.html
Brian
Walpole, MA |
Greg Waggy
Registered
Username: Gawnca
Post Number: 106
Registered: 11-2006
| | Posted on Tuesday, November 28, 2006 - 05:24 pm: |
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Brian, Those seem to be very good links. I'll know more as I delve ito them a little deeper. Thanks for the contribution.
Greg |
vadeem
Registered
Username: Vid1900
Post Number: 18
Registered: 10-2006
| | Posted on Tuesday, November 28, 2006 - 06:32 pm: |
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Looks like I have been doing everything wrong with my dust collection for years.
Thanks for the link. |
Greg Waggy
Registered
Username: Gawnca
Post Number: 108
Registered: 11-2006
| | Posted on Tuesday, November 28, 2006 - 06:46 pm: |
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What I am wondering is, I have the blower fan and motor unit from when I replaced me centeral heating and airconditioning unit, why couldn't I build a new housing for it and use it for dust colleting? With the unit wide open it won't max out its speed but once the intake sides are restricted, it does come up to speed and moves a lot of air. |
Brian_B
Registered
Username: Allegheny
Post Number: 7
Registered: 07-2006
| | Posted on Tuesday, November 28, 2006 - 08:20 pm: |
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Greg,
The problem with using a HVAC blower unit is that is designed to produce relatively high CFM at a very low pressure - a 5 ton (60,000 btu) A/C will need 2,000 cfm but at only 0.1" water pressure - a shop vac can typically generate a minimum of 35-40" of water pressure. Consider that an HVAC blower may only be using a 1/2 or 3/4 hp motor while the smallest dust collector uses at least 1 hp - for a decent sized shop you need at least 2-3 hp, and 5 hp would be better.
Digging into Pentz's site, you'll see that you need tremendous airflow to handle the really fine dust (as from cutting MDF) - something like 800-1000 cfm but at air speeds of over 4,500 - 5,000 sfm (standard feet per minute) - your HVAC blower would DIE!
I've heard of people utilizing one of the cheaper, i.e. non-cylcone, motor/blower units as the basis for a home-built cyclone. But this has problems as well.
The non-cyclone units are also known as single stage machines, since all the air and debris pass directly through the impeller and into collection bags or cannisters. Because of this, the impeller has to be strong enough to handle wood chips slamming into it at 2000 ft/min on a continuous basis. A second design criteria is that the fit between the impeller and its housing needs to be "looser" than for a cyclone - you have to have enough room so that chips don't get caught and wedge between the impeller and housing. At best you would blow a circuit breaker - at worst the motor would get fried, the housing would burst, etc.
Because the blower on a cyclone only ever sees dust, and little of that if designed properly, the tolerances can be much tighter, making for a much more efficient blower with higher volumes, air speeds, and pressures with the same or even less hp. Pentz's site is enormous, but it's all there if you want to read about it.
Brian
Walpole, MA |
Greg Waggy
Registered
Username: Gawnca
Post Number: 112
Registered: 11-2006
| | Posted on Tuesday, November 28, 2006 - 08:29 pm: |
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Hi Brian, I just wrote Bill Pantz and he told me just about the same thing. I do have an advantage though, he only lives about 12 or 15 miles from me. So you can bet I'll be gleaning all I can from his expertise. He does have a great web site covering many topics including dust collecting. I will be able to spend many hours looking through there.
Bill did mention that I might use this fan unit as an air cleaner, whatever that means. LOL
Sure glad you found and shared that web site. Thanks! |
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