We do a lot of sanding. Probably 25% of our dust collection needs are sanding dust. I'm looking at dust collectors in the 5 hp range, priced at 3-4K or less. An Oneida Direct Drive system is the front runner right now. I've seen Belfab recommended a few times here, but they seem kind of low-tech. Is that a misconception?
(Dust Collection and Safety Equipment Forum)
From contributor I:
What do you consider a medium sized shop? We are a 3 man shop and I finally am happy with my dust collection after installing a used Torit 36" fan/cyclone and 30 HP direct drive motor. Our bag house has a total of 12 bags that are 15 ft long and 12 inches in diameter. We're still get sanding dust and fine dust around the shop so we run 2 Jet 1100CFM air filters. We had a Grizzly 10hp before that with added sister bags. As soon as the bags clogged with sander and fine resaw dust, we lost most of our CFM's and velocity. Properly engineered ducts with proper reductions at the branches are also crucial to getting the most out of a collector.
My 30HP cyclone and after filter was $7k used. I shopped a long time to get that sweet of a deal. If you plan on growth or adding machines such as moulders, multiple shapers, planers or jointers, I doubt 5HP will even be close to what you need. There are plenty of good used deals out there right now!
You really need to determine what your actual needs are in CFM. HP doesn't tell you what you need to know to buy a collector. Once you know what you need, you can make a better buying decision.
Good tip on starting with the CFM first. It only makes sense. Are cyclones all that necessary if the majority of dust collection is dealing with sanding dust? Too many years of reading Fine Woodworking has got me thinking that cyclones are the only way to go. However the majority of Torit and Belfab machines seem to be single stage.
Before I moved up from portable collectors to a single whole shop system, I experimented with a variety of different filter fabric bags and cartridges. I found nothing worked well on the drum sander. With the cyclone I run stock though all day without a problem, as almost all the dust goes directly into the collection bags, leaving the filters to breathe freely.