5", Rectangular Inlet, Bellmouth Outlet with Air Straightener, Top Hat Separator

[Lance]

I can't quite tell from the picture, are you using a solid material PVC pipe or the cellular core type?  I was going to make a wooden bell-shaped form on my lathe and push the pipe onto it using the tailstock while applying heat with a heat gun while slowly rotating.  When I went looking for pipe yesterday, all I could find was cellular core schedule 40.  I wanted the thinner DWV schedule 20 that looks like a more solid material.  I don't know if it really matters but, the solid material seemed more promising.

I used a solid core Sched 40.  At the 8" size I am using the stuff weighs a ton.  I had limited success.  I will get some pics and explanation up soon.

[Lance]

Here is what happened. 
I brought a pot of water to a boil and then I placed the PVC in the pot for about 10 min checking every so often for flexibility of the PVC.  (FYI... the heat only transfers a small way up the PVC so the only part that becomes flexible is the portion directly in the water.  After it was flexible I placed it on my press but I could not get it to flair much at all.  I placed it back into the water to heat it back up.  after leaving it in for longer periods of time and multiple attempts I decided the water was just not hot enough.  the second pic is the best flare I could accomplish:


I then decided to try using vegie oil as it should attain a higher temp.  I seemed to be working until I realized the PVC was melting an burning on the bottom of the pot.......oops.  Now I am going to owe my wife a new pot.  thankfully it was a cheepy. :P 

I then grabbed another pipe I had waiting.  This time we held it in the oil and kept it from touching the bottom.  This worked.  I put it on the mold and sure enough it was flaring nicely until it started bulging further up on the pipe.

I ran out of time and had to call it quits for the time being.  Here are some shots of what I was able to accomplish:


I am trying to decide if I am staying with that or if I want to attempt it again.  If I do it again I will heat up a smaller portion of the pipe so hopefully it does not flex and bulge further up the pipe.

[phil (admin)]

Excellent work Lance, this is going to be very helpful for others than may attempt the same some day.

[NCTinkerer]

Lance, It looks like the end of the pipe that first hits your form is cut square across with a pretty sharp edge.  Could it be trying to dig into the form?  I wonder if easing that edge might allow it to follow the form more easily.

[Lance]

Lance, It looks like the end of the pipe that first hits your form is cut square across with a pretty sharp edge.  Could it be trying to dig into the form?  I wonder if easing that edge might allow it to follow the form more easily.

I thought about that also.... after the fact.  I went back later and rounded those edges to help with airflow.  that's when I thought "I should have done this before hand".  The flip side was that using the veg oil to heat it worked well as lube.

[retired2]

Lance, It looks like the end of the pipe that first hits your form is cut square across with a pretty sharp edge.  Could it be trying to dig into the form?  I wonder if easing that edge might allow it to follow the form more easily.

I thought about that also.... after the fact.  I went back later and rounded those edges to help with airflow.  that's when I thought "I should have done this before hand".  The flip side was that using the veg oil to heat it worked well as lube.

Lance,

The wall thickness of that pipe is pretty heavy.  Did you consider tapering the wall thickness in the last few inches of pipe.  You could use a lathe or a large sander.

[kayak]

<snip>  There were two things I was trying to accomplish with my baffle design and both created construction problems.  The first was to avoid having a ledge along the outside wall of the drop slot.  Of course, that meant there couldn't be any dado to hold the bottom edge of the plexiglass. <snip>

Has having a ledge along the outside wall of the drop slot been shown to cause any problems?  It would seem that having a dado for mounting acrylic or poly both top and bottom (and inletting the two ends of the plastic) may alleviate the need to have any screws penetrating the plastic.  I'm slowly getting the stuff together to build my own tophat, and this is one of the aspects that is making my head hurt!

Got the HF dust collector, the Wynn filter is on order, as is the impeller from Rikon and the bellmouth from Spiral Mfg.

I'll be changing the inlet plate on the HF dust impeller housing to accept a 6" inlet.  My plate will be made from 3/4" MDO, and I hope to use a 3/4" roundover on the 6" inlet hole to give me a mini-bellmouth at that point.  In hindsight, I should have ordered two bellmouths, one for inside the tophat and one for the inlet to impeller housing.  Ordering two at once would have made the shipping cost a lot more reasonable per unit.  Maybe I'll get a second bellmouth someday, but more likely, once I get this thing working, I'll just leave well enough alone.

I have a 4"x10" to 6" Round End Register Box that I plan to use to transition from a ceiling drop from the 6" main trunk to the tophat.  Not as elegant or smooth a transition as R2's, but compact for my application (very small workshop).  Internal tophat hat height planned to be 10" to match the register box.

Regarding the bottom of the tophat, planning to layer it, top layer would be either 1/8" or 1/4" hardboard with the 1-1/8" drop slot. The next layer down would be another layer of the same thickness hardboard, but with a 2-1/4" drop slot.  The bottom layer would be 3/4" MDO plywood with a 3-3/8" drop slot.  All this layering is for the purpose of stiffening the baffle while maintaining a thin edge on the drop slot.

Would 6" flex hose work as a coupler for 6" duct pipe?  If so, anyone know where I can get short lengths? I only need to make two joints, tophat to impeller assembly, and trunk drop to tophat inlet.

Regarding air straighteners in the outlet of the tophat to the inlet of the impeller housing, I'm thinking of a very simple 3 vane (think of a Mercedes emblem) assembly.  Any info or thoughts on how long this would need to be to be effective?

Also, I believe it was somewhere in this thread someone mentioned polyester as an alternative to acrylic or polycarbonate, but I don't recall that comment being developed further.  Thoughts on whether this is a viable alternative, pros and cons?  Is it available as a clear product, cost comparison, etc?

Sorry for the random stream of consciousness in this post...
There's just so many details to look at!  And I'm trying to look at all of them before I make my first cut.

[NoBreyner]

I bought some PETG clear plastic from McMaster-Carr 5/64" 24"x48" sheet from Mcmaster-carr it's about $21.  There's a Youtube user "Marius Hornberger" a 20 year old who makes a segmented bucket and tophat thien baffle.  He used PETG and not only did it hold up to his collector's suction it also bends into tight corners.

5/64" is flexible, but I wish I bought the next smaller thickness.  I'm not sure when/if I'll build one of my own, but I have the plastic if I do.

copy and paste (Building a Thien-baffle Separator for the (Small Dust Collector #3) into youtube's search and you can see how he built his.

[JeffQ]

You might be thinking of PETG sheet goods, as it is in the polyester family. It is available in thin roll, or sheet from from the same plastics suppliers where one might buy acrylic and polycarb from. Property-wise it is between acrylic and polycarb... more flexible and shatter-resistant than acrylic, but better scratch-resistance than polycarb. In my book, just about the ideal material for the outer "skin" on a see-thru top hat design. If it has any disadvantage, it is that you can't run to your local hardware store or big box to pick it up... but a google or yellow pages search for "Plastics suppliers - sheet  goods", will get you a source.

[kayak]

JeffQ, what thickness would you recommend for the PETG?

[NoBreyner]

I was wondering if rounding over the inside edge of the Thien Baffle's drop slot would help at all.

[retired2]

I was wondering if rounding over the inside edge of the Thien Baffle's drop slot would help at all.

I don't think rounding over the inside edge of the drop slot would result in any appreciable difference in performance.  It might help if the baffle were thicker than recommended.  However, most of the waste is forced to the outside wall of the separator by centrifugal force, so it is the ouside edge of the drop slot that is far more important.  For that reason, I built my separator so there would not be a "ledge" along the outside wall and the baffle.

[JeffQ]

JeffQ, what thickness would you recommend for the PETG?

I think when I built my top hat I used something like an .080 or .100 thickness of the PETG. I was lucky enough to get what was pretty much an off-cut from one of the local plastics suppliers here for a great price. Anything around this thickness will allow easy forming around the plywood and top and bottom of the top hat, while still providing plenty of strength and vertical rigidity.

Vivak is one of the brand names for PETG, much like Plexiglas is a brand name for acrylic.

[Daniel3105]

Guys, I scrolled through all the pages and failed to discover the sketchup files. Are they available? Thanks.

[retired2]

Guys, I scrolled through all the pages and failed to discover the sketchup files. Are they available? Thanks.

http://www.jpthien.com/smf/index.php?topic=563.msg6317#msg6317