Few ideas and questions before I build...

[GregT]

I've read much of what's here, but OMG, there is so much!  I just have a few questions that I'm not sure about.  My intent is to keep my tiny shop neater.  The dust doesn't both me much (yet).

I want to build a Thien Baffle on a 55 gal poly barrel.  I will set it up for 4" for my old Craftsman 1 1/2 DC, but have adapters so I can connect my shop vac for sanding (ROS, Rigid Spindle). 

Will the same baffle set up work with 4" inlet/outlets if I just make adapters for 2 1/2" hose?  I keep seing 1 1/4" wide for the opening, but should it be bigger for 4"?  If so, I can always make an adapter plate to narrow it to use my shop vac.  I understand that the key is the baffle with 120 degrees of slot opening.

I have access to all sorts of 3 or 4" pvc sweeps.  Is it better for the chip inlet to be a 90 street ell, or will it perform better with a modified sweep? 

How far is the gap between the inlet and sidewall of the barrel for a 4" set up?

[phil (admin)]

Excellent question.

Using a 4" unit for both a DC and shop vac will work.  I will only mention that increasing the size of a can without an increase in CFM will reduce separation.  For optimum results make certain the inlet is as close to the edge of the can as possible, and use a shop vac that moves plenty of air.

[GregT]

Thanks, Phil.  BTW, I post as gjat on BT3.

I don't understand what you mean about increasing the can size decreases the separation.  I'm assuming the baffle works by shootiong the air/debris around the can perimiter which allows the velocity to drop and allows the fines and chips to fall down the slot to the can.  Wouldn't increasing the distance the air/debris travels allow better seperation?

[phil (admin)]

It is mostly the resistance at the surface of the can that does the slowing that allows debris to drop out.  The slower air speed reduces the "shove" against the outside of the can, and also makes it easier for the finer debris to wander over to the outlet tube.

[bennybmn]

So you think in general, a smaller diameter is better?

[phil (admin)]

So you think in general, a smaller diameter is better?

Speaking generally, you just have to make sure that your diameter is appropriate for your CFM.  The smaller the diameter, the better the separation but also the greater the static loss.