linlet for 1.5" duct

[Bruce Seidner]

I am building a Thien top that for 1.5" duct for 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. 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.

[tenfingers]

Bruce,

I haven't been here long but I've been creating dust in shops for around 40 years.

I'm not clear on your plan for a separator. Do you plan a garbage can size? For your application I would recommend scaling down the separator to use a five gallon bucket with hoses sized to fit your vacuum pump. The transition could be fabricated out of aluminum roof flashing. As small as the transition will be I doubt the vacuum could crush it.

Unless you vacuum pump can move more than 500 cfm. of air I don?t think enough centrifugal force would be generated in a garbage can sized separator to do much separation.

I would use a shop vac or even a house vac as a vacuum source. They are found cheap at garage sales and flea markets. They also have the advantage of built in filtering for whatever gets past the separator.

That way you don?t just blow what gets past the separator out into your space. Also you have a vacuum for sweeping your shop. To save space, you could build a cart to stack the separator under the vacuum to wheel it around the shop to where you need it or just to get it out of the way.

[tenfingers]

Bruce,

I just noticed your other thread. Before you use your H.F. blower for this project make a transition from the 1-1/2" hose to the 4" H.F. blower. I think you will find the 1-1/2" hose too restrictive to use with the H.F. blower.

Dust collector blower fans just aren't designed to suck air through a small hose.

IMO you should use a setup similar to the one pictured by Sub-Doood in your other thread. Only i'd use a "top hat" type separator to leave more room in the bucket and make the transition out of flashing.