Attaching the sides of a top hat

[revwarguy]

I've just spent a frustrating hour with the search function here and I am letting it go with no joy.

Can some one tell me what method they used to attach some Lexan sides (or hardboard, or anything else, for that matter) to the bottom slot and the uprights on a top hat? I am using MDF top and bottoms, pine uprights, and Lexan sides.

Just glue?  If so, what kind works with Lexan?  Nails?  Screws?

TIA,

[alan m]

iv seen a few use threaded bar at 5 or 6 locations around the seperater. put a pipe over the threaded bar and tighten it down to hold the sandwitch together
im sure glue and dowels would work well too

[revwarguy]

I guess I didn't make myself clear, sorry. I am talking about the sides of the separator, not a sandwich layer that makes a surface for the top or bottom.  The sides of the separator are what the airstream and dust ride against until gravity pulls the heavier than air dust down into the drop slot.  How are these sides attached?  Are they just fitted into place and then a sealant applied on the outside. or are they usually glued and or naile/screwed in place before the top is put on?

[alan m]

sorry,
the plastic is usually glued into a slot.
because the sides have to be flush with the drop slot , there will only be a rebate for the side to sit in. that material is so thin it would be hard to get any mechanical fixing in there

[retired2]

This is how I did it, and there is a fair amount of discussion from others in th thread.
http://www.jpthien.com/smf/index.php?topic=563.30

This is an idea I had after my build was complete.  As far as I know, no one ever used the concept.  There is a video of a short tet I did to explore the concept.
http://www.jpthien.com/smf/index.php?topic=573.0

[revwarguy]

Thanks, alanm and retired2 for the links.  I don't know why, but after spending many hours on this site, I still managed to miss that.  :-[

You did a very good looking job on yours and the video is proof of function.  I am using Lexan, and I think I'll just caulk around the outside where the Lexan meets the wood.  You don't mention how the top was sealed - can you remove your top to experiment (Like with different bellmouths or such) or is it closed up permanently?  Also, do you now think the threaded rod to stabilize the baffle is needed?  I am using a 3/4 MDF bottom that is also the baffle with the bottom inside of the "C" chamfered at a 45 degree angle, so I wasn't planning any other support for it.

This reminds me, I once saw a claim for an aircraft engine manufacturer about improved performance of an updraft manifold.  It had a similar arrangement as the bellmouth, but also provided a "swept" conical shape under it, I guess the purpose being to fill in a dead air zone.  I've included a quick sketch here to show a side cross section of what I mean.  Anyone try something like this?  Perhaps it looks inconsequential, but the bellmouth didn't seem all that important once either!  Don't know how this might affect the "height=1/2 the diameter" rule, perhaps not at all, but maybe I'll try and do something like that on the lathe - looks easy enough, but I'll just have to guess about the size it should be.  Any reason to think this would adversely affect performance? No idea how to report any meaningful results though.   :-\

[retired2]

Thanks, alanm and retired2 for the links.  I don't know why, but after spending many hours on this site, I still managed to miss that.  :-[

You did a very good looking job on yours and the video is proof of function.  I am using Lexan, and I think I'll just caulk around the outside where the Lexan meets the wood.  You don't mention how the top was sealed - can you remove your top to experiment (Like with different bellmouths or such) or is it closed up permanently?  Also, do you now think the threaded rod to stabilize the baffle is needed?  I am using a 3/4 MDF bottom that is also the baffle with the bottom inside of the "C" chamfered at a 45 degree angle, so I wasn't planning any other support for it.

This reminds me, I once saw a claim for an aircraft engine manufacturer about improved performance of an updraft manifold.  It had a similar arrangement as the bellmouth, but also provided a "swept" conical shape under it, I guess the purpose being to fill in a dead air zone.  I've included a quick sketch here to show a side cross section of what I mean.  Anyone try something like this?  Perhaps it looks inconsequential, but the bellmouth didn't seem all that important once either!  Don't know how this might affect the "height=1/2 the diameter" rule, perhaps not at all, but maybe I'll try and do something like that on the lathe, but I'll just have to guess about the size it should be.  No idea how report any meaningful results though.   :-\

I doubt you would need the support rod with a heavier baffle - I'm not even sure it is necessary for mine.

If you read the entire thread on my build (yes, it is long and tedious), you will see that I have a removable piece on the top so that I could test straight pipe to bell mouth, as well as different positions.  Clearly, the bell mouth improves air flow, but one question I have never posed but have wondered about; is it possible that air flow can be improved inside the separator chamber to the point that separation suffers?  That is something you should be alert to if you begin altering the proven outlet configurations.

[revwarguy]

but one question I have never posed but have wondered about; is it possible that air flow can be improved inside the separator chamber to the point that separation suffers?  That is something you should be alert to if you begin altering the proven outlet configurations.

Agreed.  I have a thought - since you have a way to enter the sep chamber, as well as a way to measure airflow, however indirectly, as well as already having "before" data captured, if I sent you a "swept conical shape" commensurate with your bellmouth size, you want to give her a go?  :)  I would think that double stick tape would work. 

Assuming airflow is increased, how do we measure if the separation suffers?  How was it determined when the bellmouth was adopted?

P.S.  I will spend some quality time with the rest of your thread.

[retired2]

but one question I have never posed but have wondered about; is it possible that air flow can be improved inside the separator chamber to the point that separation suffers?  That is something you should be alert to if you begin altering the proven outlet configurations.

Agreed.  I have a thought - since you have a way to enter the sep chamber, as well as a way to measure airflow, however indirectly, as well as already having "before" data captured, if I sent you a "swept conical shape" commensurate with your bellmouth size, you want to give her a go?  :)  I would think that double stick tape would work. 

Assuming airflow is increased, how do we measure if the separation suffers?  How was it determined when the bellmouth was adopted?

P.S.  I will spend some quality time with the rest of your thread.

The change in airflow was measured with an anemometer.  Efficiency of separation is very hard to measure especially if the difference is subtle.  And separation is dramatically affected by the waste material.  The shavings I used separate easily, but there could be quite different results if the test were being run with fines, i.e. mdf or sanding dust.

I would like to help you with testing, but unfortunately I just don't have the time right now, and it is quite a bit of work pulling my separator out of the frame where it is now mounted.

[alan m]

the way i think the bell mouth works is by reducing the tubulance by smoothing out the entry to the pipe.
having that conical shape there should help smooth out the air entering the pipe. it will also stop the moving air creating any kind of venturi type pressure diferentials in that area.

[revwarguy]

Well, it was just a thought.  Perhaps retired2 is right - since we know only that the bell mouth increases airflow but do not know if that adversely affects separation performance of fines I guess I should just leave well enough alone.  I do remember that the conical shape was there only to fill a dead air space, though.

[alan m]

dont be put off by that. it might reduce seperation but it could also improve it. trying it is the only way to know. proving it will be dificult if the change is small

[guy48065]

I'm a little late to the party but I'll post just to add a materials option.  I made the chamber sides from a 12" long piece of a 22" diameter concrete form.  A local concrete & stone supply sold it to me for about $6, it's nearly 1/4" thick and easy to work with.  I had to slit it up the side and remove about 1/2" in order to reduce the diameter just a tad.  A different drum or a different brand of form might result in a slip fit--YMMV.
Top & bottom are 1/2" ply, top glued & sealed with OSI Quad caulk, 3/4" screws every few inches around the perimeter.  I used threaded rod spacers--I didn't trust the bottom only held along 1/3 of its circumference.

I initially wanted the "cool" factor of a clear poly chamber but in the end didn't want to deal with the hassles of taking something thin & flat & forming it round.