For a long time I didn't own a shop vacuum because all the ones I had been around hurt my ears. Then quieter ones started coming out, and eventually I bought a used one. The design was still... sub-optimal, because with a little more plastic, they could have designed it so it wouldn't use up filters so fast... but then Shop-Vac wouldn't do a brisk business in replacement filters, now would they?
This irked me for a long time.
Then I discovered A) big filter bags designed specifically for shop vacuums and B) HEPA(ish) filters. The HEPA-like filters tended to clog fast, but not when used with the bags. Two stage filtration got me a system with good suction that doesn't fade until the bag is full, a noise level I can live with without having to don hearing protection, and relatively low cost on the disposable bags; the "HEPA" filter didn't get changed at all.
I could have used this system as an air cleaner or filter except the vacuum motor isn't THAT quiet. It's just quiet for a shop vacuum - meaning, it doesn't cause immediate hearing damage. >_> You still don't want it running if you don't have to.
But even so, I was still buying filter bags every so often. And some of them sucked better than others, and someties it was hard to find the good ones, and-and-and-
This irked me for a long time.
Last year, I started half-heartedly investigating cyclonic separators, but virtually all of the solutions I found - be they commercial or home-brewed - involved some kind of outboard separator + tank. For that reason, most people are building special (large, occupying a lot of precious floor space I do not have to spare) carts to hold both their shop vac and the separator together, although a few clever folk have made their carts so the two pieces stack one above the other, which is more-or-less what I wanted...
Even those look clunky and, well, if you've been reading this blog for any length of time, you know by now what's coming.
They weren't good enough, dammit! They weren't clean enough, elegant enough... etc.
So I let these thoughts marinate a while and occasionally, when working with the shop vac (last week I made a funnel for capturing chips on the mill which attaches to the shop vac hose, but I've yet to come up with a good way to hold it in position) I gave it some more thought.
The more I thought about it, the more I suspected that the thin, flimsy (because material cost) stainless steel drum which makes up the tank of my Shop-Vac was a standard-ish size and shape drum of SOME sort, made on standard drum-making machinery somewhere because that's how _I_ would keep costs down if _I_ were asked to set it up.
Why this matters, is that if the dimensions of the lip / opening of the tank can be matched up with an existing drum or drum-lid, it would make creating an integral Thien-baffle cyclonic separator right into my existing shop-vac -- into a trivial task!
I took careful measurements of the rim and went looking / shopping for odd drums. And I was right, and I found drums and drum lids which are exactly the same.
Even stainless, if I'm prepared to pay over two hundred US dollars which I sure as hell am not. Note, that is not a flimsy drum however. It's a lot of stainless, and stainless is expensive 'cuz iron is cheap... but there is hardly any iron in stainless: it's made of nothing BUT the expensive alloying elements that go into regular steel, without most of the iron. But I digress.
I found a plain, painted steel, five gallon drum which is about nine inches high and the exact same lip size and diameter as my shop vacuum's tank (!!) so it can be made to stack neatly onto my tank, and the existing motor head will fit perfectly onto it in turn, and latch onto it, just like the stock tank.
Tidy AF. No footprint increase. Ten inch increase in height over stock. Same intake port for the hose as the stock vac. Compact. Elegant. Ooohhhh yeah. Mmm baby. †
That tank provides the space for the filter and a baffle to protect it from incoming dust before it has a chance to be separated.
The Thien baffle is supported off the bottom of the new tank by a few rods. It uses the wall of the original Shop Vac as the outer wall of the peripheral slot. So the "slot" is just an area of diminished diameter on the baffle*, which is otherwise a simple disk. A cylindrical baffle around the exit port in the center is a powerful tweak found on commercial cyclonic units which improves separation so I'll include that as well. It's just a plastic drain pipe fitting hot-glued into place.
The whole thing drops into place without modification of any kind to the motor head or original tank, or hose - nothing. It can be removed to revert the unit to wet vac mode as quickly as opening the head and changing the filter over to the foam sleeve.
It's going to cost me about $50 at least (plus shipping!) to do this my way, but it's going to be oh so elegant and will almost look like it was stock. Money is tight right now, especially since I just took three days off from being sick last week, so this might not happen for a long time.
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* J. Phil Thien's design relies on boundary layer drag and a baffle to significantly reduce the height of the traditional, funnel-shaped cyclonic separator, but the essential concept is the same: because of the entry and exit air flow locations, air inside the separator rotates vigorously, like a cyclone, thus the name. Due to conservation of momentum (kinetic energy) the air rotates at a higher RPM in the center near the exit, and at its slowest at the outside, near the surface of the tank. This causes dust and physical matter (which has more mass than the air) to stay to the outside. As the dirt reaches the nearly-motionless boundary layer of air near the surface of the tank, it slows down so much that it simply drops out of the air from gravity and falls into the bottom of the tank. That is the concept, however there are many different physical configurations which can be used to make this happen.
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† I'm so excited by this rig that I think it might be a product idea. I could sell it. I would need to find out how many tanks are the same diameter. The filter height and diameter is common across multiple brands and models. Because I would only be interested in making one size/type/model because the cost of the extra tank dominates, and economies of scale say the only way to do it is with one tank size so maximum quantities on purchases of that tank size. If it fits more than a few makes and models, it could be a thing. O_O Even if it only fits several models of one brand it could still be a thing - this brand is popular as hell. And of course, I haven't yet built and tested it, to make sure it doesn't suck... or that it does suck... you know what I mean.
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