Questions before I build

[Zort]

Several years ago, I started to make a small top hat to sit on a 5-gallon bucket attached to my shop vac. When I talked with my brother about this project, he gave me a dust deputy he had, so I didn't make it. Fast forward several years and I have upgraded my table saw, bandsaw, etc. so I have several dust makers. To this end I am again planning to make a top hat collector.

I have read and re-read hundreds of posts over the years and gleaning from everyone's experiments and projects. My sincerest thanks to everyone that has added to my knowledge.

I think I have developed a plan but I have doubts about several parts of it.

I have a 2 HP Harbor Freight unit but with a larger impeller. I have a 35 gallon plastic drum (16 inch diameter, with 1/4"sides). I am planning a top hat with a 4" inlet and a 5" outlet.  The 4" inlet will transition to a rectangular opening 5.75" by 3". I am not planning a bellmouth at this time but I might add that in the future. (retired2's suggestions, but would a taller thinner opening be better)

So my questions:
Is a 16 inch diameter drum too small? I chose this drum because of the thick sides and light weight. (Question based on Post 369)
I think I would like to make an 8" tall top hat, with the inlet located towards the top as people have suggested the taller top deals with fine dust better.. Or, should I make it 6 inches tall and center the inlet?
How long should the transition from the 4" inlet to the rectangular opening be?
How far into the top hat should the outlet extend? I've read half the distance, but half of what distance, the top hat or the inlet?
Does it matter whether the inlet is on the right side or the left side?

My guess is that these questions have been asked and answered somewhere in the site but I haven't found them and would like to have input before I build.

[alan m]

Is a 16 inch diameter drum too small?

its tight but will  work. larger the better

I think I would like to make an 8" tall top hat, with the inlet located towards the top as people have suggested the taller top deals with fine dust better.. Or, should I make it 6 inches tall and center the inlet?

i would go 8 minimum. it give more time for the dust to move out to the side and ready to seperate out

How long should the transition from the 4" inlet to the rectangular opening be?

not sure but the longer the better. the more gentle the transition the better. remember to add 10% area to allow for the transition

How far into the top hat should the outlet extend? I've read half the distance, but half of what distance, the top hat or the inlet?

the way i do it is half the inlet size up from the baffel plate.

Does it matter whether the inlet is on the right side or the left side?


in theory yes but practically no. if the dust is spinning the same direction as the impeller the motor  should have less work to do and can move more air.   an air straightener will make it even better  build it whichever way suites your workshop

[Zort]

Thank you for your reply.

Would a taller top hat (for example 10-12 inches) help overcome the deficit of the small diameter of the drum?

I think i'll start with a 15 inch transition length.

[alan m]

i dont know. i doubt it. the smaller you go the more resistance there is by changing direction faster. i cant see having a higher seperater helping that. it would help with other areas though.

i wonder would angling the inlet increase the effective radius the dust is travelling in. not sure , it might cause other issues

[retired2]

The closer the swirling waste stream is to the edge of the outlet pipe, the more likely bypass will become a problem.  There is no magic formula or rule of thumb to determine where bypass becomes unacceptable.  You have three variables to tweak, the separator diameter, the width of the inlet port, and the diameter of the outlet pipe.  And keep in mind that adding a bell mouth will improve air flow, but it makes the effective diameter of the outlet pipe much larger.

I don't believe a deeper chamber will significantly reduce the amount of bypass from a small diameter separator.

[Zort]

Thank you for your input, retired2. When I started reading posts, it didn't take me long to realized that you are one of, if not the most respected contributor to this site; so I really appreciate you taking time to reply to my post.

I made the inlet this morning. The 4 inch circular inlet transitions to 2.5 by 6 inch rectangular entrance. The transition length is 12 inches. (Picture attached, hopefully)

So by my math, I have an 8 in radius, 2.5 inches for the inlet, 2.5 radius for the outlet. This leaves 3 inches of space, not very much in my opinion.

I think I have a couple of options--go for it with this drum or find something with a larger diameter.

[retired2]

I appreciate your compliments, but Phil is the real genius here.  He is not as active on the forum as he once was, but he knows more about what works and what doesn't than I ever will. 

I'm pretty sure your separator size will work, it is just a matter of how much more frequently you might have to clean your filter due to bypass.

It's a lot of work to build a separator so I would suggest build it as optimal as you can.  Go buy a large Brute garbage can at HD or some other retailer.  They are light, but sturdy, and they don't cost an arm and a leg.

[Zort]

It took a while but I have it made (almost). My dyslexia kicked in and I ended up with the inlet being opposite of what I intended. While alan m indicated that in practice it doesn't matter; it does matter in my shop so I'll have to do some modifications. I did hook this up to the blower just to see how it worked (not bad, considering all the air leaks)

Testing raised another question.

I understand it is important for the top hat to be "sealed" to the collecting drum. I plan to use foam window insulation material a a seal. Is the weight of the top hat enough to create a good seal or should I create a clamping system to hold the two parts firmly together?

[DustySanders]

I used window sealing foam from a big box store to help seal my top hat to a brute trashcan. It works well, but the foam isn't as stiff as I might like, and gets mushed down. I still think it seals ok, but I haven't gotten around to testing it. You can buy stiffer versions of the same self adhering foam from McMaster-Carr, a great website for supplies in general.