Stationary sawmill dust collection system

[stanmillnc]

I've got a 10HP cyclone dust collection system with rotary airlock that I'm in the process of hooking up in my shop. I'm pouring a concrete pad for my new LT50 electric mill, which will be located separate from my main wood shop. I'm wondering if it's worth tying the mill into my dust collection system (pretty sure it is), and if so, how do I go underground with it? I don't have a practical way, nor would I want to go above ground with the piping to the sawmill. 

My dust collector has a 12" inlet, which will be the main run size into the shop to branch off smaller runs to individual tools. If I connect the sawmill to this system, what size pipe should I use? It's about a 40' run from the dust collector to the sawmill. I assume PVC would not be a good option, due to static / explosive risk. What other kind of pipe would hold up underground? I will be traversing over it regularly with my Bobcat loading and unloading logs / lumber. I do have excess 12" diameter steel pipe, but I assume this is way overkill to reduce down to ~4" to connect to the sawmill and also that it would collapse due to the weight of gravel and traffic overhead.

Pictures here show general locations. You can see a little of my current Woodmizer mill in the background - this is where the new mill site will be as well. The opening pictured is for a silencer that hasn't been attached yet. The 12" inlet is on the opposite side facing the building. I'd have to tee off that in the opposite direction to get to the mill. 

And yes I did knock the dust collector over before I secured it to the concrete pad. Amazingly, it wasn't damaged and I wasn't hurt!
 

 

 

 

[barbender]

 You're an honest man, posting pictures of knocking that over😬

[stanmillnc]

Yep, pretty stupid mistake. Had been meaning to secure it with concrete anchors for awhile, and just didn't make it a priority. Knocked it over dragging a bunch of limbs over to the chipper. "Safety third."

The adage I've read here about no such thing as "Free Logs" sure rings true. If I didn't have to clean up a bunch of limbs and brush mixed in with a few decent saw logs from this free dump truck load of logs, I wouldn't have knocked it over! And I wouldn't have to spend hours running limbs through the chipper, paying for a crane service, etc.

The crane operator who came out to lift it back into place: "Didn't I already do this job...?"  :D

[rusticretreater]

Ah, the did something dumb today thread has competition.  Kinda like twitter and threads!  ;D :D

[Ljohnsaw]

There is NO risk of explosion or fire if you use PVC pipes, so use it. Watch CL and you should be able to get the super thick walled water main stuff pretty cheap or even free.

Going underground, I'd make provisions for easy access for when it gets clogged.

[barbender]

I'd think about leaving a small cable in it. It could be a ground, and you could pull some kind of plug with it when the pipe gets clogged.

[Southside]

ljohnsaw I am going to respectfully and strongly disagree with your statement there. I have seen static discharge off a 4' piece of PVC I had used to fill in a line one time, nice blue spark. Both my wife and I have been lifted by static discharge during dry weather on the outfeed of the planer when the skate rollers were supported by plastic saw horses. A simple piece of wire dropped from the roller to the ground fixed that issue. 

You definitely want to have a ground discharge system in place with PVC and wood chips.

[jpassardi]

If you decide to go plastic, double wall (smooth inside) HDPE is generally cheaper than PVC and comes in 20' lengths. It's normally designed to take an H20 loading with only a foot of cover and proper bedding. In PVC you'd likely need thick C-900 to carry wheel loading with a shallow bury.
BB's cable suggestion is a good one, maybe it could be grounded as well to help address static electricity.

[SawyerTed]

I'm thinking a concrete trough with your  4" piping laid inside and covered with steel plate.  You should be able to drive over it, access the pipe for repair and run the distance you need without extraordinary expense.  A steel grate on top could allow the trough to do double duty for drainage if needed and planned right. 

[Ljohnsaw]

ljohnsaw I am going to respectfully and strongly disagree with your statement there. I have seen static discharge off a 4' piece of PVC I had used to fill in a line one time, nice blue spark. Both my wife and I have been lifted by static discharge during dry weather on the outfeed of the planer when the skate rollers were supported by plastic saw horses. A simple piece of wire dropped from the roller to the ground fixed that issue.

You definitely want to have a ground discharge system in place with PVC and wood chips.

I never said there wouldn't be a whopper of a static charge. That's what makes life interesting 😂

I said you don't have to worry about a dust explosion. There is lots of talk about it in various woodworking forums but the fact is you'll never get the right mixture of a LOT of fine, dry dust to support combustion. Bet you can't find one real example of it happening.

[Erik A]

I think you already have the perfect sawdust collection system... its in your pictures, setting on tracks  

I would think pulling wet saw dust to a collection system is going to use to much power for what you get out of it.  I would assume the wet dust is not going to move well using air. If you go 4 to 12" pipe then back, the 12 will fill with dust. 

Although, you should be able to put a 12" pipe just under the ground and the bobcat would not hurt it at all. 

[Den-Den]

I agree with Erik, a 4" inlet will not allow enough air flow to sweep a 12" line clean.

The value of a ground wire in or on PVC is very low.  One inch away from the ground, PVC can hold a high static voltage that will result in a spark occasionally.  The risk of that spark igniting a dust explosion is very low but are you OK with that risk?  In my home hobby shop, I am comfortable with PVC dust collection piping. In a commercial cabinet shop??

[Larry]

Feeding a 12" pipe with a 4" could be a problem.  I think a simple solution is to open a couple other blast gates close to the intersection.

I bought some bare ground and built my shop with its own septic system.  The feed to the septic tank was 4" PVC which crossed my gravel driveway to my future house.  The county code calls for the 4" PVC to be encased in 6" PVC when crossing a driveway.  Can't remember if the 6" was schedule 40 or 80 but it worked.  Had many a concrete truck drive over it when I built the house.

I can't imagine any better ground on PVC than being buried in the ground.  I can't see sending coarse wet sawdust through the pipe ever being a problem but ya never know. 

[Southside]

ljohnsaw I am going to respectfully and strongly disagree with your statement there. I have seen static discharge off a 4' piece of PVC I had used to fill in a line one time, nice blue spark. Both my wife and I have been lifted by static discharge during dry weather on the outfeed of the planer when the skate rollers were supported by plastic saw horses. A simple piece of wire dropped from the roller to the ground fixed that issue.

You definitely want to have a ground discharge system in place with PVC and wood chips.

I never said there wouldn't be a whopper of a static charge. That's what makes life interesting 😂

I said you don't have to worry about a dust explosion. There is lots of talk about it in various woodworking forums but the fact is you'll never get the right mixture of a LOT of fine, dry dust to support combustion. Bet you can't find one real example of it happening.

I will see if I can dig it up but a pellet plant in Maine around '08 or '09 lost a concrete block wall to a static dust explosion, my wife was still with OSHA at the time and was one of the investigators so I got to see all the photos. 

[YellowHammer]

Southside is correct.  There are lots of examples of woodworking dust collector explosions and the information on the the internet is not wrong, but very misleading, because it doesn't mention that "homeowner" dust collectors are classed as 1500 CFM and under by the NFPA, and indeed, these are exempt from NFPA regulations and explosion free.  However, anything over 1500 may fall under NFPA codes because it is a fire hazard.  I personally know of two commercial woodworking dust collector explosions in the 20 and over hp range.  It is such an issue that my insurance required I have a professionally designed dust collector system and my local Fire Marshal inspects it annually.  As most people know, a NFPA non regulated "homeowner shop 1500 CFM dust collector" is very small, generally only 2 horsepower.  How much is the OP's flow rate?  Is it over 1500 CFM (2 horsepower)?  Is it a commercial operation?  If yes to both, then it falls under NFPA regs because it is big enough to be a fire hazard.  I'm not the dust collector police, but the information is available for all to read in the NFPA regulations and case histories.      

Quote from "Designing your dust collection system to meet NFPA standards — Part I, Gary Q. Johnson, Workplace Exposure Solutions" ---"About 40 percent of combustible dust explosions reported in the US and Europe over the last 25 years have involved dust collectors. Dust collection systems are now a primary focus of inspections required by OSHA's National Emphasis Program on safely handling combustible dusts."  If this document is read, it will immediately become apparent that a proper dust collector system is highly regulated in the larger systems, including flow losses, blast gate sizes, etc.  It is for this reason I had my system professionally designed.  The NFPA breakpoint is 1500 cfm.

Can a dust collector fire happen, either internally or externally? Yes.  Is it of concern in a small shop, with a dust collector rating or actual CFM of under 1500 CFM or about 2 hp?  No.  Is it a concern with a system with over 1500 CFM?  Yes, enough so that it falls under NFPA regulations if other site conditions are met.  Is it a concern in a commercial application with commercial insurance?  Yes.  Is it a myth?  No, the facts are out there and readily available.  

Get the codes, read the codes, follow the codes.  If you don't fall under the codes, read them anyway so you can follow "best practices."

Also, a person to object static discharge (drawing feet across carpet and touching metal) is NOT the same as generated from an insulator to fuel source, (PVC pipe to dust particle), which can be orders of magnitude higher voltage and current, and is dependent upon many things, including the two materials.  The magnitude of the charge is based on the science of "triboelectrification" and a simple electro static discharge across an insulator and a fuel almost started WWIII when the simple act of removing a Pershing nuclear capable missile from it shipping crate caused an ESD that ignited the missile propellant, killing several soldiers.  It's a very interesting part of history, made international news, and changed the direction of missile propellent research forever.  I personally helped in some of the investigation.  I also know of a trainee that was killed while unrolling some tape which caused a triboelectric spark of such magnitude that it sparked and fired a squib, which triggered a main charge, killing him.      

[barbender]

I always remind myself that lighting is basically static electricity😬

[customsawyer]

I also think you are going to struggle pulling wet sawdust 40'. Yet you will actually be pulling closer to 55' by the time you add your flex hose to go from the pipe to the mill.

[longtime lurker]

I would install a scraper chain under the mill and use the bobcat bucket, for a whole lot of reasons.

Wet sawdust is heavy and you're asking to move it through a big U shaped setup. It'll flow with a big enough blower but it won't be terribly efficient to run that size blower for that volume of sawdust.

When ducted, wet sawdust is traditionally put through a blower not a sucker, that is the fan is close to the source and blows the material through the ducting rather than at the discharge end sucking. I don't know the why of that but it's a thing and I figure they came up with that rule of thumb for a reason.

When it clogs - and they all clog sooner or later - that U shaped pipe will be a nightmare to clear.

Wet sawdust in bulk is a fire risk due to biothermal energy. It's best stored exposed rather than enclosed to help with heat loss to reduce the risk, and ideally not against your shed just in case

Mixing wet sawdust with dry shavings devalues the value of the shavings as a byproduct.

And ground out that PVC pipe if you do use it or your insurance company has just cause to refuse to pay out in the event of a problem. Proving a mill destroying fire didn't start in what's left of your ungrounded plastic pipe might not be easy. But more better to just use steel and save yourself the worry.

[stanmillnc]

Great feedback here - appreciate it everyone. Now I'm leaning the other way towards not hooking up my mill to the dust collection system. Seems that the installation complications and having to deal with the likely clog maintenance outweigh the potential convenience. 40' is a long run for wet sawdust, especially with multiple elbows and I tend to go heavy on the diesel blade lube, which adds risk. 

So before I pour this concrete pad - is there any kind of trough system I should consider? @longtime lurker what is this scraper chain mechanism you recommend? Or perhaps I should just mount a blower on the wall to shoot the sawdust just outside my mill shed?

[Ljohnsaw]

How about K.I.S.S.?  Lay out you mill so the sawdust is deposited like normal as a mound along the back side of the mill. Have enough room between the mill and your back wall or posts to drive the skid steer through and scoop it out.

[moodnacreek]

On my first mill I had a drag chain pulling sawdust from under the saw and dragging it over the bank. This is a great set up if you have room, no dust in the air and very low h.p.  But then we have an edger or worse a traveling head saw like most here so you need a blower of some sort and maybe a cyclone. Today I run 2 blowers to load a large box. I try to keep the blowers close to the pick up point. The noise of blowers is what I don't like, want to hear the saw working. I also have an augar under the floor for the mud saw chips pushing them into the head saw blower.

[rooster 58]

So on a similar note, I am currently installing a blower system on my lt50.i figured on 15' or so of 5" flex hose from mill to blower. At the blower exhaust,  need to go about 25' to a sawdust shed. I'm not sure if I should use solid 4" schedule 40, or use 4" flex hose.
      My other question is the edger. It looks like I might be around 40' from edger to blower and again nor certain of using schedule 40 or flex. Any thoughts?

[YellowHammer]

Blower and flex hose work fine if the flex is short and the blower has enough hp.  I like mine, and it serves both the mill and other secondary processing equipment, so works with both wet sawdust and dry chips.  Suction runs should be relatively short, I'm 30 to 40 feet in steel pipe.  Properly designed systems work well, and I've never had clog from my LT70.  Blowers are loud.

Chains and conveyors also work well, the big mill down the road uses them, and fills up dump trucks with sawdust.  

[rooster 58]

I'll be sucking from the mill only around 15 ft. Pushing it at most 25 ft. The culprit is the edger, which will be pulling around 30-35 ft. I'm not sure exactly because I don't have the edger yet. I have to pick that up this weekend or next 🤔 

[YellowHammer]

I do not run my edger through my good facility blower because an edger will throw big chunks of wood, knots, etc and will literally "blow out" a blower.  I am currently on disposable blower number 3 on my edger.  I've had hunks of wood dent the impeller housing so bad it blows paint off the outside, I've had hunks of wood puncture the flex hose, and more commonly, pieces of edgings will bend and fold over the impeller blades.

If the edger went through disposable cyclone pre filter it would protect the impeller.  That's what I'm doing now, running it through a cheap Vevor cyclone blower.