Designing a dust-collection system for my shop: any problem using 6" pipe? - Contractor Talk - Professional Construction and Remodeling Forum

Panzer5 · 05-18-2009, 09:30 AM

I'm buying a 1250 CFM 1.5 HP dust collector for my (garage) wood shop.

Would there be any downside to using 5" or 6" pipe to transport sawdust (rather than 4" pipe)? The dust collector uses 4" tubing at the tool & impeller.

Because I have to run at least one length of pipe through the rafters to keep the floor clear, I'm designing the system with one run against the wall of the garage (where there will be two tool ports) and another run up and over the rafters (where there will be another two drops for additional tools). The rafter run will likely be about 30' long. The termination of each run (at the tool side) will have a gate to allow me to shut off airflow to tools I'm not using.

My dad suggested I use a 5" or 6" pipe - rather than 4" pvc for the rafter run.

So the question is: do I lose any efficacy of the system by using a wider pipe?

naptown CR · 05-18-2009, 09:51 AM

What will happen is the velocity of the airflow will decrease by at least 50% in the sections where the pipe has been enlarged. This may lead to a build up of dust in the duct work in these sections and you will lose efficiency. There will also be issues where you transition back to the 4" port on the collection unit. My first reaction is this is not a good idea unless you have a dust collection machine that is much more powerful and has a 6" inlet then you could have more blast gates open without affecting performance but this is a very small machine.

naptown CR · 05-18-2009, 09:56 AM

Just looked at the machine If you use the 6" coming out of the machine ahd branch off with 4" for the other run you will be ok. The start up blast gates are cool I would get as many of them as you need will make your life soooo much easier and keep system performance up as you can't forget to close the gate on the last machine you just used.

Anti-wingnut · 05-18-2009, 10:05 AM

Two issues here
1) As you increase cross sectional area, your air velocity will decrease. So while it seems counter intuitive, a larger diameter ( too large) will not carry as much dust to your collector as a smaller pipe. This is because as velocity decreases, the tendency for the debris to fall out of the airstream and to settle at the bottom of the pipe increases. Whether this is the case with your system I do not know.

2) Many feel that using PVC pipe can increase the likelihood of a static induced dust fire. For this reason round metal duct is recommended by many.

The particulars of this occurrence are this: A moving mass of air can and will produce static electricity, this is what causes lightning. If the dust stream is in a properly grounded metal duct, this charge will be dissipated constantly. A non-conductive duct can allow a charge to build up, and initiate an internal spark which could ignite the dust.

From what I know, I would recommend the majority of your system be composed of 4" metal duct which has been grounded. Whips and connections can be composed of shorter sections of flexible plastic duct
Taunton Press's Finewoodworking web site "Knots" is a good source for more info, as is this book http://www.amazon.com/Woodshop-Dust-Control-Sandor-Nagyszalanczy/dp/156158116X (which I have not read)

Anti-wingnut · 05-18-2009, 10:13 AM

I just read the spec sheet for you machine, and I see that it does have one 6" port. It may be alright to use 6" duct, but your velocity sure will be higher with 4"

naptown CR · 05-18-2009, 11:00 AM

Quote:

Originally Posted by Anti-wingnut

Two issues here
1) As you increase cross sectional area, your air velocity will decrease. So while it seems counter intuitive, a larger diameter ( too large) will not carry as much dust to your collector as a smaller pipe. This is because as velocity decreases, the tendency for the debris to fall out of the airstream and to settle at the bottom of the pipe increases. Whether this is the case with your system I do not know.

2) Many feel that using PVC pipe can increase the likelihood of a static induced dust fire. For this reason round metal duct is recommended by many.

The particulars of this occurrence are this: A moving mass of air can and will produce static electricity, this is what causes lightning. If the dust stream is in a properly grounded metal duct, this charge will be dissipated constantly. A non-conductive duct can allow a charge to build up, and initiate an internal spark which could ignite the dust.

From what I know, I would recommend the majority of your system be composed of 4" metal duct which has been grounded. Whips and connections can be composed of shorter sections of flexible plastic duct
Taunton Press's Finewoodworking web site "Knots" is a good source for more info, as is this book http://www.amazon.com/Woodshop-Dust-Control-Sandor-Nagyszalanczy/dp/156158116X (which I have not read)

Quote:

Originally Posted by Anti-wingnut

I just read the spec sheet for you machine, and I see that it does have one 6" port. It may be alright to use 6" duct, but your velocity sure will be higher with 4"

That's what I just said I also agree with 2 separate metal runs as anti suggested for both grounding and velocity. The length of the runs are less problematic than the increase of pipe size. On the long run if you want top performance don't use 90 elbows but use 2 45's to turn the 90 as the static pressure will be lower and you won't lose as much velocity.

Panzer5 · 05-18-2009, 12:47 PM

Thank you all for the excellent (and timely) suggestions. I'll look into the metal pipe & the automatic gates.

Will any metal ducting (aluminum or galvanized) work - or should I prefer / avoid one or the other?

Also - any thoughts on the trash-can lid cyclone?

naptown CR · 05-18-2009, 01:04 PM

Quote:

Originally Posted by Panzer5

Thank you all for the excellent (and timely) suggestions. I'll look into the metal pipe & the automatic gates.

Will any metal ducting (aluminum or galvanized) work - or should I prefer / avoid one or the other?

Also - any thoughts on the trash-can lid cyclone?

Galvanized will be more readily available and cost less.
I have heard but no experience good things about the cyclone separator it will certainly catch the big chunks.

**Leo G** · 05-18-2009, 01:18 PM

Use this Excel spread sheet that Bill Pentz designed for approx dust collector pipe sizing. It is the one I used to get mine started.

http://www.billpentz.com/woodworking...staticcalc.xls

Panzer5 · 05-18-2009, 02:06 PM

The Bill Pentz article - if I'm reading it correctly, suggests I use 6" pipe & tubing to all of my tools. But all of the blast gates I see on line are 4".

That seems a bit confusing (he obviously put a lot of work into that piece) - but I'm still not sure how useful it is considering all the tools are ported for 4" & most off the shelf parts are also 4"...

**Leo G** · 05-18-2009, 02:25 PM

On my system I have a 7" main truck that quickly drops down to 6". All of my down leads are 5". That is as small as I suggest you go for any ducting. The down leads go to your gate and after the gate you put your flex tube and reducer (as close to the machine as physically possible). This way you will be able to maintain a higher speed in the vertical drop to pull the chips against gravity. When it gets into the main trunk it should try to maintain a velocity of 4000 ft/m or the larger chips will drop out. As you approach the end of the line the trunk gets bigger to slow the velocity of the chips (more important in a cyclone system).

If you go to Oneida's site you will find all the tubing, ducting and gates you require. They aren't cheap at that site, but they will have what you need.

And of course the ever important picture of my system. Come on boyz, you knew it was going to show up in this thread. Why are you acting so surprised.

Panzer5 · 05-18-2009, 02:29 PM

Alright, I'm jealous.

But... How much are you paying in rent?!?

I own my garage (alas, from the looks of things, I am a much smaller fish than you!) and can only dream of the day I get big enough to have a full sized shop!

FWIW, most of my tools are of the portable "contractor" type tools - which have 4" standard dust / chip collector out-feed manifolds. Will it matter much if I drop a 6 or 5" flex hose down to a 4" manifold - if it's only the length of the adaptor?

**Leo G** · 05-18-2009, 02:36 PM

Paying more than you, and probably more than your mortgage. This is only half the shop. On the other side of the right partition wall is a space that is slighlty bigger than the shop. I use it for storage and have my 435sq ft spray room. This is what I do for a living. And believe it or not when I get a large kitchen going in here it can get cramped when the boxes start going together.

Panzer5 · 05-18-2009, 02:40 PM

Grin!

I can only dream (at this point).

What are the tools against the back wall in the second photo? A shaper, joiner & router set up to serve as out-feed tables for each other?

naptown CR · 05-18-2009, 03:40 PM

Quote:

Originally Posted by Leo G

And of course the ever important picture of my system. Come on boyz, you knew it was going to show up in this thread. Why are you acting so surprised.

I'm surprised that we haven't seen a picture of Gus's shop here yet.

**Leo G** · 05-18-2009, 04:00 PM

3 Shapers. Delta 3HP, the one on the left is the newer version with the bigger table and better fence system. This is my door setup. The left shaper has my stick cutter, the center has the panel cutter and the right has the cope setup. When you want to use a shaper you just pull it out about 2' from the wall, all the shapers are on wheels. To the far left is the 3HP oscillating sander, 6 x 108 belt.

Railman · 05-18-2009, 05:24 PM

Panzer,
If you haven't bought the collector yet, you might want ot look at Penn State's collectors.
http://www.pennstateind.com/store/TE...cid=4382919670
They have nice features at very reasonable prices. I use the one above one for one of my saw, & drilling stations. I use two small collectors for light saw & drill work, & a bigger Torrit unit over a 4cu yd dumpster for my heavy work.

Definately go with a cyclone. It's much easier to get rid of the dust.
If you opt for the one you posted above, add a cyclone prior to the unit. Since cyclones typically filter out about 98% of the dust, the filter cartridge won't have to filter out much. There's a guy on ebay that fabricates, & sells them for under $100. That's for the cyclone only. I bought a couple, but only ended up using one. I put one on a similar unit to the one your buying over a trash can, for my 3 assembly saws station, & never have to clean the bag. The trash can is a breeze to empty.

Run a 6" Galv trunk line. From there you can get by with short 4" pvc drops, or flex pipe. If you do run pvc lines, run a bare copper ground wire through the pipe, & ground at end.
Joe

Railman · 05-18-2009, 05:32 PM

Gus,
It sure helps to have the extra head room for noise control doesn't it!
Your shop is way less cluttered than mine.

I made my original cyclone from two 55 gal drums, using Oneida specs. It used a 3hp Cincinnati cyclone with an 8" trunk line. It worked perfectly for my first shop setup, for 4 yrs or so, & then had to upsize.
Joe

Panzer5 · 05-18-2009, 06:55 PM

Railman - that Penn State looks very interesting - thanks for the tip.

I talked to a rep at JDS who told me the collector I was looking at probably wasn't the best solution for my needs. He suggested I step up to the 3 hp version - which gets 2500 CFM and which has an 8" inlet, and is currently on sale.

I guess I'll continue to do some more comparing & thinking about this before I rush out & buy my parts!

**Leo G** · 05-18-2009, 07:10 PM

I was going to mention that 1 1/2HP is kinda wimpy to be suing on a system of ductwork. I have 2 1/2HP and it is adequate but I could have used a 5HP unit.