J. Phil Thien's Projects

Okay, since nobody else has responded yet, I'll jump in. But beware, I'm a newbie myself, and just getting into my own top hat build, so buyer beware!

Nonetheless, IMHO while you could certainly have a side entry through the wall of a garbage can, it seems like a lot of work, with little benefit. First, getting a clean cut hole with a good seal around the inlet port seems difficult, especially if the can is corrugated or ribbed- the geometry defies my limited mind. However, if there's no vertical corrugation near the top, it would be easier to configure an opening. Most metal cans I've seen have one or more horizontal corrugations near the top (i.e., not a perfectly smooth cylinder), which might cause turbulence in the downward spiral flow of debris, and impair efficient collection.

Building the separator inside the can would reduce the volume available for waste, and would require more frequent emptying. With respect to emptying, unless the inlet tube is perfectly flush with the inside of the can, you might have trouble with having the baffle trapped below, so getting the baffle out to empty the can could be a real challenge!

With a top hat sitting on top of the can, you have more flexibility in design, and easier access to the components, so it would be easier to make tight seals, esp. at inlet and outlet ports. The only added seal is with the top lip of the can, which is pretty straightforward with a circular groove and maybe weatherstripping on the underside of the top hat. Finally, a separate top hat makes emptying a lot easier.

Whether a wok in the collector might help with fine dust collection (presumably what was missed by the Thien separator), I think it would have a slight benefit, if any. As far as I can tell, the principle of separation with a wok is essentially the same as with a Thien separator. I've never read anything suggesting that a wok is better, so fine dust that got past the Thien would also get past the wok. the only way it theoretically might help is if the width of the gap in the baffle is so large that more fine particles get by than normal (the narrower the baffle opening width, the better for small particles, but more clogging with chips and shavings; larger gap means less clogging, but more fine dust gets by). However, most wok designs I've seen have pretty big gaps, anyway, so I figure they'd have the same limitations as does the Thien design. So, if your collector already has a wok, I'd leave it it (probably can't hurt), but I wouldn't put one in as an addition to an external Thien separator; get a better filter canister instead!

Again, consider the above the opinions of a non-expert. Good luck :)

In all respect, might I suggest an alternative approach. Your power tools are limited to band saw, drill press, and spindle sander, so the volume of dust and shavings is pretty low, compared to table saw, planer, and jointer.

I'd think that a shop vac with an attached cyclone would be sufficient for these tools (assuming you use one tool at a time). It would cost a lot less than a big dust collector, and you could use the savings to buy a shop air filtration system (air cleaner).

I don't have a spindle sander myself, so can't speak to built in dust collection capabilities, but in my experience, FWIW, it's pretty hard to get efficient dust collection in most band saws and drill presses, anyway. So "uncollected" dust produced, which could be airborne and picked up by an ir cleaner. Just my .02  :)

I can't speak from experience about metal cans collapsing, but I had a 5 gallon plastic (polyethylene (or polythene, I think you say), I think)
collapse when the vacuum hose was obstructed. I solved it by nesting it inside an identical plastic pail. The double thickness does the trick for me. You might want to try rounding out your pail, and jamming it into a new pail (or vice-versa).

I'm curious about Bulldog8's design- did you keep the same orientation of the baffle slot and the inlet- that is, did you leave the 120 degree solid section in front of the inlet?

My impression is that the orientation of the slot is important, at least when the inlet is just above the baffle.

In Bulldog8's video, it looks like the air path takes about two full 360's above the baffle. I can't tell whether: a) Bulldog8 carefully designed the geometry (inlet angle, height, etc.) to get good separation; b) he was just real lucky that the slot just happened to line up well with airflow by the time it hit the baffle; or c) maybe the orientation of the slot isn't all that important, at least with a tall separation chamber.

Still trying to sort out the complexities :P 

First, some caveats: I'm new to the site myself, and I'm not a physicist or engineer, so buyer beware. With that in mind, from my readings, regardless of the size of your vacuum hose, ideally you want as large a diameter as possible, particularly if you have a long run.

It's not the suction (vacuum?) you need to be concerned about. Rather, it's the airflow (cfm) you can wring out of your setup. The enemy of airflow is turbulence and "friction" (for lack of a better word), so all the advice about smooth linings, minimal and large diameter bends, etc., and large diameter runs.

I picture the diameter effect as similar to an electrical run from your breaker box to an outlet. You get a lower voltage drop at the outlet with larger gauge wire, even though the appliance/tool plugged into the outlet has smaller gauge wire. Likewise, you'd get better airflow with, say, 4 inch pipe with 1-7/8 inch connections at either end, than with 1-7/8 (or 2 inch) all the way.

The only things affecting suction are the power of your vacuum, and the opening area at the open (far) end of the system- the diameter (volume) of the pipe in between have no bearing on the suction (vacuum).

Just my .02

Snagging of shavings on the baffle support never occurred to me. Doh!  :-[  There's clearly a lot of experience abd wisdom on this site, and I've come to the conclusion that I should start with the tried and true designs, and tweak after I have a working system. Thanks to all- it's a great site!

I'm in the process of planning/designing a top hat separator, and have found all the information on this site very helpful, esp. retired2's detailed assembly documentation.

I have a couple of questions:
1. I assume that a rectangular inlet is preferred, in that it provides for better laminar flow as air circulates in the separator. Also, the cross sectional area of the rectangle should be no less than that of the entering hose, to prevent air flow restriction.

That being the case, is there an optimal height to width ratio of the inlet? It seems to me that the narrower (and higher) rectangle would result in better laminar flow. So, for example, a 2 inch wide, 12 inch tall inlet would provide better laminar flow than a 4 by 6 inch inlet, and a 1 by 24 inch would be even better. Are there diminishing returns as the separator volume increases (to account for the taller rectangle)? This is all theoretical, since building 12 or 24 inch tall separator would get pretty involved. My gut instinct is to go with what appear to be practical dimensions (a la retired2's design).

2. I've been thinking about how to support the baffle, and rather than using threaded rods, I thought I might try using a couple of thin strips (3/8" to 1/2" wide) of sheet metal, hung from the top of the separator, with a right angle bend at the bottom of each strip to support the baffle. The wide dimension of the strip would be parallel to air flow, so I figure that it would produce less turbulence than a rod, but haven't seen anybody trying that. Any reason why it wouldn't work?

This is a great site with terrific information- all feedback will be appreciated!