Top Hat vs "other way"

[Jack]

I have a DC very similar to a Woodtec DC (see attached), however mine is 1.5 HP.  Both have 4 inch hoses.  I want to build either a top hat like all those posted or just take a metal garbage can and install the baffle under a lid like in Phil's drawing, but then instead of running the inlet through the top cover where the outlet would be  connected, run the inlet through the side of the can at the point where the wide  part of the baffle starts ( where most people have their elbow start).  Wish I had a drawing for what I just wrote, but if you look at Phil's drawing you can see where the elbow is in relation to the drop slot.

On another matter, has anyone installed the Thein seperator and also a Wok type plate above the dust collection bag on the dust collector?   Seems like this idea might contain very fine dust which makes it past the separator.

Thanks for any opinions.

[jdon]

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 :)

[Jack]

Good points and thanks for the advise.  I have not started anything, but still reading.  I am now back to page 12 on this site and have found all of this very interesting, so I continue to read.  I found this pic somewhere on the site, and it looked very simple to build.  I guess I am not yet sure how to build the Top Hat walls and I also wonder  about a 90 degree connection for a 4 inch inlet.  Those two pipes need a lot of area within the top hat.  I guess I can get a 90 degree 4 inch elbow at Rockler.  On the other hand it probably would not do anything much to air flow if I converted everything to standard PVC 20 pipes internal to the separator and everywhere else stay with 4 inch ducting.  You seem to have convinced me towards doing the top hat.
As for the WOK,  I was just going off of Phil's comments that you cannot stop all the fines.  Seems to me that a WIDE WOK might collect more and thus reduce them even more in the filter.  I assume that if the separator is working that for the most part only fines would get by the separator.

[phil (admin)]

The thing with woks is that they leave a continuous gap.  And the continuous gap is really a killer when it comes to fines separation.  If you watch any videos of the Jet Vortex units, or any video of units modified with a wok, you will see the debris in the bottom bag spinning way to fast.  It will help with chips, but not fines.

If you've ever seen someone smoking a cigarette exhale the smoke through their mouth, you will see what is basically a horizontal mushroom cloud.  As the smoke gets further from the smoker's mouth, the stationary air in the room will peel the smoke particles off and carry them in all directions.  Close to the mouth, where the air is moving quickly, the smoke is quite directional.  Further from the mouth, the smoke is moving all over the place.

The larger D of the baffle decouples the air masses above and below so the relatively slow moving air BELOW the baffle can start to peel some of the fines out of the air ABOVE the baffle.

Put another way, the ability to separate fines depends on the speed differential above and below the baffle.  And the best way to increase that speed differential that I've found is closing the gap for approx. 120-degrees.

So if you want fines, skip the wok.

BTW, there was a build I once posted of a guy that made his own Vortex cone.  He basically discovered the same thing and added a 120-degree brim to the cone to improve fines separation.  He could have just made a baffle, but he at least learned something during the process.

[BernardNaish]

Hi, I have built a Thien separator into the top of a plastic trash can and I found that emptying the thing is very difficult. I suggest you use the top Hat design posted by Senior2 starting here:

http://www.jpthien.com/smf/index.php?topic=563.msg3024#msg3024

He used Perspex for the wall and had problems probably because it is not flexible enough for this application and tends to shatter. I have used polycarbonate sheet before and I know it can do this. It is easiest to bed the polycarbonate into the grooves in the top and bottom plates using silicon sealant. His design has the height of the separator the same as the height of the retangular inlet pipe and there is something to be said for making the chamber height twice the height of the inlet pipe. The inlet pipe still needs to hug the top plate.

Hope it goes well.

[retired2]

Hi, I have built a Thien separator into the top of a plastic trash can and I found that emptying the thing is very difficult. I suggest you use the top Hat design posted by Senior2 starting here:

http://www.jpthien.com/smf/index.php?topic=563.msg3024#msg3024

He used Perspex for the wall and had problems probably because it is not flexible enough for this application and tends to shatter. I have used polycarbonate sheet before and I know it can do this. It is easiest to bed the polycarbonate into the grooves in the top and bottom plates using silicon sealant. His design has the height of the separator the same as the height of the retangular inlet pipe and there is something to be said for making the chamber height twice the height of the inlet pipe. The inlet pipe still needs to hug the top plate.

Hope it goes well.

Hey Bernard!  I'm "retired", but what makes you think I'm senior?  ;D