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Ian is right that you can have a duct that is too large for proper chip transport, but again in my experience, 6" has not been a problem for my 1.5HP collector. I have 11 ft ceilings, so I think there is about 8 ft of vertical 6" pipe coming off my jointer. I have never measured CFM, so I cant quote a figure, but it has no problem lifting the largest chips from my jointer and transporting them to the cyclone, even if I leave a second blast gate open on a different trunk.
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It's very difficult to know in practice Scott the point at which lower air speeds will start to result in problems - and as before there's loads of DIY systems about running much lower numbers than the industry norm/standard without running into obvious if any issues. Quite a lot depends on the nature of the work done, the type and loading of chips and the types of machines. It's for that matter damn difficult to design a system that will precisely deliver a targeted airspeed with the sort of rule of thumb methods normally available to woodworkers.
It's likely the case that there's a significant cushion in the recommended airspeed numbers to allow for worst case situations involving all of the possible variables - like those above, leakage, dirty filters, extra gates being left open etc. It's also likely though that lots of DIY systems suffer blockages etc at times and are just quietly cleaned out. (based on reports, and on my own experience with a 1 1/2 hp bagger with a 4in flex hose) Especially those that are not highly optimised in layout terms, nor very carefully maintained.
Most fundamentally there's the question of what constitutes 'good' performance. Many regard picking up chips as 'job done'.
It's pretty much a given though that the air quality (as opposed to basic chip collection) delivered by low CFM systems isn't very good - certainly not unless hoods etc are very highly optimised. Even then there's machines, cuts and machine types that simply need lots of air flow to prevent fine dust escaping - sanders, chop saws, old iron etc
Last edited by ian maybury; 08-27-2015 at 9:46 PM.
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Hi Ian
If you were having lots of buildup in your ducting, I wonder if smoother ducting would have worked better for you. If you have a lot of pressure loss due to longer runs of flex hose, you might have had lowered CFM enough that you got lower velocities than if you had run a larger pipe with smooth walls that flows much easier. It is hard for me to know without measuring. I have thought it would be fun to replace the return grate on the room with the DC system with a baffle with a bunch of ASME nozzles so I could calculate CFM of the system under any operating conditions.
Agree with you on the machine variation. The jointer I use has baffles inside the collection hood that spreads the air and does a very good job of capturing everything that comes off the cutter. The 16 inch jointer leaks much less dust and chips than the 6 inch jointer it replaced.
My bandsaw on the other hand came with just one dust collection port for the lower cabinet, and had holes in the upper cabinet that sprayed dust straight up in the air. I have added baffles to the lower cabinet to direct more air to the blade, and ran a second hose to the upper cabinet and it is much better, but it still leaks some dust.
I enjoyed reading Bill Pentz's webpage, and read it before I put in my own system. Without trying to cause an argument, I thought there was a lot of good info there, but frankly thought his standards were very conservative, and for my purposes impractical. For instance, one of the recommendations for getting air quality to what he considered acceptable levels was to exhaust the DC air outside. For some, this will be fine, but venting outside would make it much more expensive for me to control temperature and humidity in the shop. Since I ingest way more dust every time I mow the lawn compared to working a day in my shop, it seems to be a reasonable tradeoff.
Thanks
Scott
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No doubt the situation i had back then could have been improved Scott, but back then (in the late 90s) i was in the situation most of us start out in where i just presumed that buying a mainstream 1 1/2 HP bagger from the manufacturer of my then combination machine and hooking it up would do the job. It didn't collect chips very well unless everything was squeaky clean, and i suffered all sorts of hoarseness and sinus issues as a result of the bag leaking fine dust back into the shop. These days i run a DIY variant of the Bill P/Clear Vue system with close to HEPA filtration, and it's been such a pleasure.
It's not about argument as we each have to make our own choices.
It's not however as though Bill P hocused up his stuff in isolation. It was initially very controversial in the US because he stuck his neck out and challenged the happy happy 'keep it cheap' status quo that i and many others ran into (that could exist only because hobby/DIY woodworking is unregulated - no air quality standards are applicable) - but the fact is that most western countries since (as a result of medical research findings regarding the health of woodworkers) have made mandatory the achievement of the highest of the then optional (but championed by various medical and occupation hygienist groups) levels of air quality requirement he describes for workplaces with employees. (or maybe a bit higher, my memory may be fuzzy - the recently adopted 1mg/m3 limit for airbone dust)
It's telling that most of the bigger hobby/DIY dust collection system suppliers these days are offering 5HP typically cyclone based units that run 6in ducts, HEPA like filtration and deliver around 1,000CFM depending on the detail of the situation - very much as he concluded (from the information that was then already out there) was required. Not only that, the packaged/rectangular/enclosed mobile dust collection units sold in Europe (especially in Germany) and around the world that are designed to achieve a legally required output air quality standard (and hence the 1mg/m3 shop air quality standard in use in appropriate conditions) typically start at the 160mm ducting/4Kw fan/high efficiency filtration level for single machine applications. The Felder RL series of dust collectors are a pretty typical example of the genre.
This isn't to say that very carefully designed and well maintained total installations in situations that permit high efficiency machine hooding running smaller fans can't sometimes get the job done, but it leaves them far more exposed to sharp peformance drops caused by the sort of issues previously described. For sure as i've also been trying to show there's a fair amount of necessary cushion built into the larger systems. The trouble is that most systems are not well designed or maintained. Many machines have restrictive hooding, or very little hooding - with the result that they need suction pressures that can't be achieved by smaller fans - or ditto very high air volumes.
Pardon my feeling the need to put this out, but it's hard to make good decisions without information...
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When I designed the DC system, I thought of using Nordfab ducting as a way to get enough performance out of a 1.5HP cyclone and cartridge system, not as a way to "keep it cheap". The stuff is pretty expensive, but it is smooth, conductive, and has relatively low pressure loss when you use their fittings (bends, contractions etc.). Others might be able to comment for the OP's benefit on the relative merits this type of ducting vs PVC or other materials, but I only have experience with this one product. The OP was asking about where to get 6" ducting for his cyclone with a 6" inlet, so I thought he should know that Grizzly has it, and that in my experience it has worked well with a 1.5hp system.
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Pardon my coming in again Scott. Nordfab i'd say is the Rolls Royce/Cadillac solution in terms of ducting. It has some major advantages in terms of re-usability, looks, convenience etc.
I went for spiral (which causes a bit more flow resistance) only because snap together is a very costly option here and i couldn't afford it. PVC/plastics seem to work well and be a proven solution, but there is the possibly only theoretical question of insurers might view it.
I agree. 26 gauge snap lock works fine and is economical. Sometimes you can find it at your BORG. Check with you local HVAC supplier or look for a local duct fabricator.Originally Posted by Bill Richardson
And as I have said many times, you should be looking at 800 cfm as a maximum single machine (TS top and bottom) requirement, and for that, 7" is the sweet spot for horizontal runs and works well for a 2 hp cyclone. 6" for vertical runs. But you can get by with 6" overall if you don't want to have a reducer at your cyclone inlet. My 2 hp Oneida came with a 7" inlet.
Last edited by Ole Anderson; 08-30-2015 at 1:06 AM.
NOW you tell me...
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