I am new to dust collection. I just bought a 2-stage Jet collector (the one that sits on a garbage can).
What’s the conventional wisdom when connecting a 4″ dust collector to tools with smaller dust ports? Specifically, I am going to connect my Ryobi BT3000 table saw which has a 2.50″ dust port. do I run 4″ flexible pipe all the way to the table saw and then use a reducer to attach to the 2.5″ dust port, or can I reduce it near the wall and run smaller hosing to the machine? Same question with smaller tools (belt sander, biscuit joiner). You obviously can’t run a 4″ hose to a biscuit joiner, but what’s the optimal design? Do you want to minimize the length of smaller (ie 2.5″ hosing), or are there other considerations?
Thanks
Replies
I looked into this a few years ago when designing my own central collection system. You'll want to run the 4 in duct to the machine then reduce. But be careful..... the key to good dust collection is airflow. You should be ok with your connection, however. You might look into some of the articles published on the subject in Fine Woodworking or "Dust collection Basics" a book published and available at many of the woodworking stores.
Bobby D from Tennessee.
The port that the dust pick-up has on the machine (2 1/2", 4", etc) will determine the amount of cubic feet per minute (CFM) of suction that it can generate. You can put your 4" hose to a smaller machine, but you will only get the amount of cfm that the port will allow. Now that the technical stuff is over.....
I use my dust collector on any machine that I can efficiently use it on. On the smaller machines, oscillating sander, jig saw, etc., I use a shop vac.
If you plan on hooking up a permanent piping system, I recommend a spiral, metal pipe. It will pick up less static electricity, and is more durable.
Len (Len's Custom Woodworking)
> .....What's the conventional wisdom when connecting a 4" dust collector to tools with smaller dust ports?
Most comments I've seen relative to dust collection systems only mention CFM. While it's true that CFM is a major factor, air velocity is another. You can have all the CFM in the world but if it's traveling through a 3' diameter duct (exaggeration for emphasis), the actual air velocity may not be sufficient to carry heavier material through the system.
Conversely, a lower CFM through a smaller duct (consider the standard shop vac) will suck up about anything but an anvil, but not many shop vacs have hoses big enough to let an anvil pass (grin)
So, not being what you would term an expert on the subject of dust collection, (I'll be working on that issue when I get into construction of my new shop) it seems 'intuitive' to me that for things like sanders and the type of machines or equipment that create fine powder-like dust, smaller conduit would be appropriate. Bigger equipment such as jointers, planers, drill presses, the kind of machines that create chips and larger waste particles, require correspondingly larger duct sizes along with correspondingly higher CFM.
None of which answers your question(s) I suspect, but perhaps give some food for thought.
[email protected]
It seems like there is some confusion between CFM (air volume), and static pressure.
Static pressure is essentially suction, and everything you attach to your dust collector reduces it. Unfortunately, static pressure is not constant - it changes with CFM. Every blower has a SP vs. CFM curve - your goal is to hit the place on that curve that gives you adequate air velocity (based on the CFM and the size of your pipe) as well as acceptable SP. Remember, SP needs to be positive or you won't suck up anything, and everything between your blower an the location of the dust reduces SP.
The tradeoffs are such that: larger pipe has lower static pressure loss, but also lowers air velocity. Smaller pipe, by contrast, has higher static pressure loss, but raises air velocity. Elbows, joints, ribbed piping all increase static pressure loss.
In practice, for short runs to a single machine, this means using pipe as large as possible for as much of the run as you can - so use the 4" all the way to the tool if possible, but if you need to step down to something smaller, you should do it as close to the dust source and as gradually as possible.
Hope that helped...
Doug
Looks like there is some confusion about terms. Maybe I can clarify some.
CFM or cubic feet per minute is the rate of flow of air thru the system.
SP or static pressure generally expressed in inches of water column iwc is the driving force generated by the fan to induce (suck) the air and dust thru the system. It will be lowest (larger negative number) at the fan inlet and near zero at the inlet collector or machine. Remember that for a dust collection system the numbers will all be negative relative to atmospheric pressure.
V or velocity is the speed of the air in the duct generally expressed in fpm. Generally for dust collection you want 3 to 4 thousand feet per minute for reliable transport of larger particles/
Your fan is rated in CFM at a certain static pressure and performance curves are generally provided by the manufacturer. Remember CFM at a certain static pressure, at any other pressure the cfm will be different.
First you should determine the cfm requirements of each machine. This is generally given in your dust collector's manual or in many reference works Taunton's book on dust collection is one. Then size the pipe to that machine to provide the 3-4000 fpm velocity. i.e.,
diam = 12 *2*((CFM/vel)/pi)^1/2) or for 350 cfm at 3500 fpm
diam =12* 2*((350/3500)/3.1416^1/2 = 4.28 inches
Use either 4 or 5 inch pipe.
After junctions use the sum of all machines likely to be on simultaneously, in a home shop this is probably one machine. For smaller machines provide a second partially choked opening. This will insure adequate transport velocities in the larger pipe close to the fan.
Maybe off topic, but what does the specification "SCFM" refer to?
Thanks.
Rich
SCFM is Standard Cubic Feet per Minute. The "Standard" typically referenced (unless otherwise specified) is the ASME (American Society of Mechanical Engineers) standard of 14.7 PSIA, 68Deg. F and 36% relative humidity.
CFM is also known as ICFM (Inlet CFM) or ACFM (Actual CFM) - essentially the volume of air at the inlet to the blower.
Doug
Thanks Doug.
Rich
I have set mine up with 6" plastic pipe around the perimeter of my shop. There are gates located around the various machines and 4" hose attached to the gates. (BTW the 4" hose I use is for RV sewage systems. It is blue colored and has metal wire in it that rpovides good static protection. I then use reducers as needed to attach to the various stations. The 6" white piping is wrapped, on the outside, with stranded copper wire. This system has worked for many years without any problems at all. If you try to use really small hose, like vacuum cleaner size, the efficiency is reduced and it is also loud.
Where did you find your connectors to reduce the 6" to 4" when connecting to the ducts on the machines?
It turns out that I have 4" white plastic pipe to begin with so the normal collector hose fitting work as-is. I have cadged together some custom shapes by cutting the white plastic and heating it with a heatgun and forming while it is soft. I have also sawed wooden discs to fit inside the collector gate and sized a hole in the wood for smaller hose connections. I bekieve all the fittings were bought at Rockler.
while on the subject. Does anybody have any info on that "DustBoy" system you always see in FWW. Is it any good? Thinking about buying one.
Anything info would be appreciated
Finky
The stuff above will get you off on the right track in terms of dust collection, however I would think that rather than using a DC for your smaller tools you'd be better off hooking up a shop vac with its more flexible hose.
FWIW
Don
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