central vac hose for dust collection?

Pabs,
The biggest thing about DC is the CFM for the collection and little hoses, especially long little hoses will never really give you what you're expecting. It is not as sexy as upgrading a saw or another woodworking tool, BUT one of the best purchases I ever made was when I went from a shop-vac over to an actual dust collector, the amount of air actually moved and also a much quieter collector made a huge difference for me in my shop. I'm in a garage so I only have 1 run along a wall which has my miter saw, (in a hood), at the end and a couple of stationary sanders. The big tools use 10' 4" flex hose to connect with, and while that's not ideal, it is 100 X better than trying to make the shop vac work. The harbor freight DC is often used by many and I regularly see other DCs on craigslist market place etc. you may not be ready right now to do it, but I'd recommend to keep an eye out to jump on one when you see it, and once you've got it I'm fairly certain you'll feel the same as I did when I had to wonder why I kept futzing with a screaming shop vac.

so I'm a bit confused. ok, a lot confused

been reading on dust control over the weekend and confused about what is best for what application.
so I have my 4inch 1HP dust collector that I use for my table saw and planner mainly. From my understanding those DC units ae good for high volume machines. But if I want to use with say an orbital sander that has a 1 inch port I would need to use a reducer at some point and from what I understand that would greatly diminish the sucking power of the DC. So for orbital sander would be best to go with a shop vac type unit? and not the 4inch DC?

that being said, where does the mitre saw fit in? it also has a smaller port for dust collection requiring a reducer of some sort. Some have mentioned using the "big gulp" (I actually have one of those). if using that you would not use a hose directly connected to the machine right? basically have your 4" line hooked up to the bottom the big gulp and all the dust would just fall into that hole and then be sucked out (assuming the saw is in some sort of shroud )?

trying to figure out what to do but having a hard time understanding what is best.

any info on this would be greatly appreciated. learning learning learning..never ends does it!

Just a thought based on what I'm currently building that might provide an idea..
I have a 4" pipe from the DC drop into the corner of the miter station. After the blast gate, it changes to rectangular plastic drain pipe to better clear the turning radius. That rectangular pipe is mitered to a second piece that runs the width of the saw station. The bottom corner that faces the saw was removed, leaving a 1/2" gap - kind of like a floor sweep (bench-sweep?). A piece of Masonite (waxed) is attached at a slight angle from the back wall of the miter station to the front edge of the cross-pipe. Any dust hits the sloped Masonite and slides down to the deck and is sucked into the slot. I have the dust port connected to the DC just above the round to rectangle transition. I'm still putting this together, so don't have any pictures to share yet.

I used the Big Gulp overhead with the dust port being directed into the mouth of the port and was not happy with the results, when using a 2 HP dust collector. I even had EDPM rubber "drapes" hanging from the hood to allow flexibility when making angled cuts but still had to regularly vacuum the saw station area. Dust falls down, so you either need to collect it from that direction or have intense upward suction.

I briefly considered moving the Big Gulp to the bottom, but it takes too much real-estate for an against-the-wall miter station. It also isn't wide enough when making angle cuts and the dust is thrown into the corners. I think this full-width narrow port will collect what's thrown from any angle.

I have a 2hp DC for my large tools and run a central vac for everything else. This includes drill press, miter saw, router table, sanding and general clean up. It is ducted with blast gates and works far better and quieter than any shop vac I have owned. The ducting is also run into the garage part of the building for car/floor cleanup.

any info on this would be greatly appreciated. learning learning learning..never ends does it!

- Pabs

Click to expand...

Pabs-

This reply is long, but hopefully covers important info on dust collection in general, and you're specific need.
TL;DR- miter saw dust collection is hard, and inconsistent at best with traditional shop vacs or DCs.

Confusion about dust collection is nothing new…and everyone is still learning. The biggest issue is this: large impeller-type dust collectors (like you may think of as a classic DC) are designed to move large volumes of air, but at low pressure. This is great for clearing out dust in a larger area, like say under a cabinet saw. They excel at pulling dust out of the air, but may fall short of grabbing heavier debris like chips, especially if not properly sized or set up. ShopVac style units are designed for high pressure, but low volume. Their suction is most significant right near the end of the hose, and they do great at picking up chips….but since they don't move much volume, they're not so great at removing dust from the air in a larger space. Both machines have their place, but they need to be set up, ducted and deployed the way the manufacturer designed them to be used.

Where most dust collection falls short is exactly there: the system(s) aren't being used the way the manufacturer designed them, so they don't produce what you're expecting. Large dust collectors need to be able to move that large volume of air without impedance in order to keep the dust and heavier debris airborne. This mean smooth, straight runs of properly sized ducting with minimal disruptions. That's the only way to take advantage of the high volume and defeat the low pressure. So, using corrugated pipe or hose, sharp angles, reducing (or increasing!) duct diameter beyond what's recommended, too long a run of duct, clogged filters, etc will all render those big DCs fairly useless. When you reduce the required duct size too much, the DC simply can't move enough air to generate any pressure at all…so very little gets picked up: ie - necking 4" ducting from a traditional DC down to 1" for a palm sander.

On the other hand, shopvacs, with their much higher pressure, do a great job…at picking up what's directly in front of them. But, because of their low volume, if the focused vacuum pressure (end of the hose) moves even a couple inches away, the pressure reduction is so massive that the system fails to perform. For these systems to effectively collect dust, some sort of confinement has to be built to help focus the airflow and direct the light dust towards the hose. This could be the internal construction of the shop tool itself (as is seen in some benchtop tools), or through sealing up leaky tool casings or cabinets and allowing fresh air to enter through a small opening at a point that puts the dust production between that opening and the end of the hose…which isn't always an easy feat!

The easiest way to negate these pitfalls is to use the right sized ducting on the collector, and use it as it's intended. As a basic rule of thumb, any tool with dust ports 2" or less needs a shop vac-style collector, and anything with dust ports 4" or greater needs a larger volume DC. The manufacturer (probably) designed the interior of the tool to be in alignment with the dust port size, and the proper type of collection device takes advantage of that design. There are a couple collectors that bridge that dust port sizing gap, the Oneida Supercell being one of them. The Supercell essentially combines three shop vac motors together to generate really, really high vacuum pressure, and also move a relatively large volume of air. It's a somewhat niche machine aimed at the small shop with a single woodworker, using machines with dust ports 4" or smaller, but it does what it does incredibly well. Truly awesome when used correctly.

So, all this info leads us to your quandary about collecting for a miter saw. The issue is: large chips AND dust being thrown over a wider, unconfined area. Soooo…high pressure doesn't work great because the collection area is too wide, and high volume doesn't work great because the chips are heavy and the existing dust ports on the saw necks the opening down too much for the DC to be effective. Funnels like the Big Gulp try to address these by bypassing the saws dust port, allowing a 4" connection to function behind the saw at the end of the funnel which helps collect and consolidate the chips, and hopefully the high volume grabs the dust. But, it takes up a lot of room and requires a large volume of air to be moved…which isn't going to work with a shop vac. Another option is to add on a small homemade funnel (a lot of people just use duct tape to add some sidewalls and widen the funnel to the saw's existing dust port. This allows the blade to fling the chips into the duct tape walls, consolidating them down into the existing dust port where a high pressure (shop vac) style collector can effectively move them, while hopefully also directing the dust closer to the end of the hose where the system might grab that too.

Both models are incomplete for their own reasons, but both work better than the stock adaptation. IMO, the best option is using a high pressure, moderate volume system like the Supercell. This provides super high pressure to pull in the chips, but enough volume to gather dust as well. Absent that option, most of your options are going to either require some sort of an adaptor, or a different collection method. Building off what you already have may save money, but may (or may not) fix your problem. Whatever you decide, try to keep in mind the strengths (and weaknesses) of your system and design your solution around that.

I'd encourage you to look at your shop dust collection and mitigation as a whole. Look at what size and type of collector your machines were designed for and make decisions from there. Often, a small shop requires multiple, different dust collectors to be efficient which in itself is pretty inefficient. Dust collection is an often misunderstood and overlooked part of a woodshop, but the health, safety and efficacy of a properly laid out and used dust collecting system cannot be overstated. All that said, the miter saw is a challenge for many shops!

Hope this helps at least a little.