inlet size for a Thien top hat

[Bruce Seidner]

I am building a Thien top that for the 1.5" duct from my power hand tools. The top hat will be "powered" by a vacuum motor because it just seems redundant to have a separate shop vac and I don't need another one and have no space in my small shop. So, the plan is to run the 1.5" duct from the tool to the top hat and I am curious what the thinking would be in terms of the size of the inlet.

For instance, one option would be to create a 4" rectangle inlet and use a round to round transition ahead of the top hat to transition from 1.5" to 4" round duct which would then transition from 4" round to a rectangle of a larger volume to create a nice column of air to drop through the slot of the Thien baffle slot. The top hat will be powered by a vacuum motor typically used in commercial shop vac's. I will make the top and bottom so that I can fit different height sides and experiment with the volume of the top hat. I am interested in seeing how this works.

So what does the group consciousness suggest in terms of the size of the inlet. The choice is native 1.5" or a more typical 4" inlet that has the transition accomplished in the duct prior to entering the top hat.

[Bruce Wrenn]

I would use the 2 1/4" inlet / outlet, with a reducer to fit the smaller hose. This way, you can change sizes of hose later without loosing your original investment. As for the 4" inlet / outlet, you shop vac motor won't produce the required CFM for it to work, IMHO. You will still need a filter after shop vac motor to catch remaining fines (no system is 100% effective. Go over to Phil's web site (google "Phil Thien") and see what others have done. I enjoy my "Top Hat" Thien Baffle. Best of luck!

[Bruce Seidner]

I would use the 2 1/4" inlet / outlet, with a reducer to fit the smaller hose. This way, you can change sizes of hose later without loosing your original investment. As for the 4" inlet / outlet, you shop vac motor won't produce the required CFM for it to work, IMHO. You will still need a filter after shop vac motor to catch remaining fines (no system is 100% effective. Go over to Phil's web site (google "Phil Thien") and see what others have done. I enjoy my "Top Hat" Thien Baffle. Best of luck!

That makes good sense. Thanx.

[raul segura]

Id build for versatility of both size hoses and make the lid fit larger/smaller canisters to.You may be better of building the top end of a regular dust collector then adding the Baffle. 7 inch high x 6 inch diameter then the baffle. On small vacuums you don't want to very much at all on the hose sizes they are designed for. Redundant to what others have said.