Need help deciding on dust collection strategy

[David L Morse]

...On the other hand the 3500 FPM guidance may be conservative. I do not see any dust lingering in my 6" flex hose that I am using right now. Yet, I have not measured flow velocity greater than 3100 FPM in a 6" duct coming from any tool. The router table is the lowest flow. It measures only 1800 FPM, yet the dust moves through the system without accumulating. I am still processing this information and looking for others thoughts.

Yes, 3500 is conservative. I've seen numbers ranging from 2300 to 4000 for horizontal runs and 3000 to 4000 for drops. Those guidelines really are intended for industrial situations where dust loads are high and downtime is unacceptable. Milling wet timber for framing lumber makes lots of big, wet heavy chips and it takes a lot of velocity to keep that stuff moving. Your requirements are a lot lower if you're only processing dry material in a hobby shop and especially if you have segmented cutters on your jointer and planer. I've heard that turning wet bowl blanks can be a challenge for a DC but I don't do that.

In the shop right now, I am operating with a portable DC and moving it from machine to machine. I need to work on the pipe entrance to the dust collector where I measure flow. It is not straight. The flex hose is unsupported and just goes down to the floor.

I'm doing the same thing. Trying to measure flow directly with the hose connected to a tool doesn't really work that well. What I've done is carefully measure the flow versus motor current with a special test setup (photo in earlier post), not actual use. When the system is then doing something useful with a tool I can get a good estimate of the flow by measuring motor current.

Current.jpg

One other thought. Another reason you see 4000FPM used so often is that it corresponds to a velocity pressure of 1"wg. That's a really convenient number to use, it makes the arithmetic easier.

[Reggie Burnett]

Guys,

I just did a rough sketch of my workshop. The red hatch boxes are 6" main ducts and the green are 5" ducts. All overhead except at the tool where it will either be a 4" or 5" drop.

What do you guys think? What can I improve?

Once I get rid of some of the wood then I intend to move the DC to the center of the back wall and put more tools on the back wall nearer the DC. But for now this is what I have.

[David L Morse]

I'm puzzled by your mix of 6" and 5" for the horizontal runs. I hope you're planning to use blast gates, that DC would be nearly useless with all those ports open.

For your high flow requirement tools like the lathe, RAS and what looks like it could be a MS at the bottom I would consider 6" drops. Your main concern at those tools should be capturing as much fine dust a possible so 6" ports in your hoods with bell mouth entry. You really need maximum CFM here.

You have only a 4" pipe for your TS. Why not 6" under the slab? Will you be taking both cabinet and topside from this pipe or will you have a takeoff from the main for topside? If you're only using the buried pipe for the cabinet and the blade is shrouded then 4" is probably ok.

[Reggie Burnett]

I'm puzzled by your mix of 6" and 5" for the horizontal runs. I hope you're planning to use blast gates, that DC would be nearly useless with all those ports open.

For your high flow requirement tools like the lathe, RAS and what looks like it could be a MS at the bottom I would consider 6" drops. Your main concern at those tools should be capturing as much fine dust a possible so 6" ports in your hoods with bell mouth entry. You really need maximum CFM here.

You have only a 4" pipe for your TS. Why not 6" under the slab? Will you be taking both cabinet and topside from this pipe or will you have a takeoff from the main for topside? If you're only using the buried pipe for the cabinet and the blade is shrouded then 4" is probably ok.

Yes, blast gates at all tools. initially I think there will only be one tool used at a time. one man shop but my teenage boys might get involved at some point.

Good idea on the 6" drops.

Yea, the 4" pipe to the TS was a mistake. I did that way back when the slab was poured and I didn't know very much about dust collection. Trying to live with it since I don't really want a 5/6" drop hanging down from ceiling.

Do you like the idea of tapering the 6" down to 5" as it goes across the room? I saw an Oneida diagram that tapered 8" down to 6" partially across the room.

[Jim Becker]

I'm puzzled by your mix of 6" and 5" for the horizontal runs. I hope you're planning to use blast gates, that DC would be nearly useless with all those ports open.

For your high flow requirement tools like the lathe, RAS and what looks like it could be a MS at the bottom I would consider 6" drops. Your main concern at those tools should be capturing as much fine dust a possible so 6" ports in your hoods with bell mouth entry. You really need maximum CFM here.

You have only a 4" pipe for your TS. Why not 6" under the slab? Will you be taking both cabinet and topside from this pipe or will you have a takeoff from the main for topside? If you're only using the buried pipe for the cabinet and the blade is shrouded then 4" is probably ok.

He's using 6" main duct and 5" drops...something I mentioned earlier in the thread. The 4" in the slab is already in the slab. He's not installing it new...at least that's how I read things earlier.

As an aside, the lathe isn't a target for high flow since one cannot effectively collect from a lathe during cutting; only during sanding. That's also a good location for a floor sweep...once he has a cyclone, but not with a single stage setup.

[Jim Becker]

Do you like the idea of tapering the 6" down to 5" as it goes across the room? I saw an Oneida diagram that tapered 8" down to 6" partially across the room.

I think I mentioned it earlier, but "back in the day" most ductwork designs stepped down even for small shops because that's how the designers learned to do it for multiple concurrent machines and worker on larger systems. It's not necessary for a one-person setup to continually step down since all air flow is a single machine at a time. Some folks will do "all" 6" to the tools. I personally prefer 5" drops because that mates with almost any tool in a productive way...they either have 4" or 100mm or 120mm ports in most cases unless someone retrofits them.

[Reggie Burnett]

He's using 6" main duct and 5" drops...something I mentioned earlier in the thread. The 4" in the slab is already in the slab. He's not installing it new...at least that's how I read things earlier.

As an aside, the lathe isn't a target for high flow since one cannot effectively collect from a lathe during cutting; only during sanding. That's also a good location for a floor sweep...once he has a cyclone, but not with a single stage setup.

Thanks guys. One more question -- do you think I should take 6" all the way to the wall before tapering down to 5? I was thinking about tapering down to 5 a few feet before getting to the wall both going to the lathe and to the right side of the shop.

[Jim Becker]

I generally reduce at the branch using a 6x6x5 wye.

[David L Morse]

...Do you like the idea of tapering the 6" down to 5" as it goes across the room? I saw an Oneida diagram that tapered 8" down to 6" partially across the room.

With multiple flow paths there can be an advantage to adjusting pipe sizes to try to match velocities in the streams. For what will be primarily single path I don't see any advantage to different sizes. It's only a slight difference in pressure loss but seems like a lot more work to install.

...As an aside, the lathe isn't a target for high flow since one cannot effectively collect from a lathe during cutting; only during sanding. That's also a good location for a floor sweep...once he has a cyclone, but not with a single stage setup.

Actually it's the sanding operation I'm looking at here. Sanding on a lathe can spew out quite a bit of fine dust and lots of airflow can help control that. I agree, you can't do away with the broom.

[Reggie Burnett]

I generally reduce at the branch using a 6x6x5 wye.

WHere did you get 6x6x5 wyes? Or did you make them?

[Jim Becker]

WHere did you get 6x6x5 wyes? Or did you make them?

All my original fittings came from Oneida, but there are multiple sources for them.

[Steve Mathews]

All my original fittings came from Oneida, but there are multiple sources for them.

The wye fittings from Oneida for what they call standard pipe look like the ones I purchased locally. One end is crimped while the others are raw and require a crimped end from the pipe. I really like the fittings for spiral pipe from The Blastgate Co. All ends slip inside spiral pipe. My order from a local supplier hasn't arrived yet but I'm seriously thinking of scraping the fittings and replacing them with the ones from Blastgate. It might make for a cleaner installation. That is if I understand all of this correctly.

[Jim Becker]

Yes, my original fitters were for snaplock, but they are way heavier than HVAC fittings and have the crimps on the correct side. If I was going to do spiral (and I would if I ever move my shop, the proper slip fit version would be what I'd use.

[Steve Mathews]

Yes, my original fitters were for snaplock, but they are way heavier than HVAC fittings and have the crimps on the correct side. If I was going to do spiral (and I would if I ever move my shop, the proper slip fit version would be what I'd use.

Thanks for the nudge Jim. I'll probably lose about $300 in the change to Blastgate fittings but it should be worth it in the long run. BTW, are there other vendors for the type of fittings that slip into spiral pipe? Spiral pipe is used in a huge way in the industrial/commercial HVAC market. Just look up in the exposed ceiling of many restaurants (or try to remember what you saw when you were actually able to go to one. LOL)

[Jim Becker]

I can't answer your question specifically, but I don't believe that those fittings are something that Blastgate invented.