What I did today - Thien seperator lid

[Bill Stock]

Has anyone had success with doing this with 4" size lines? I just have a small portable DC (the little ones with the side bag, similar to what Rockler's been promoting lately) but it gets decent airflow if you use 4" lines... Also doesn't have that much suction so I woud't have to worry about crushing cans. Plus it's much quieter

I had a little King DC that I bought when I sanded the basement floor. I used it to blow the cement dust out the window. (Ever seen a white cedar hedge. The neighbours had one before I put a water baffle on my contraption.)

Anyway, I took the wheels and bag off mine, routed a slot in a piece of MDF to fit over a rubbermaid GC, cut a 4" hole in the MDF for the sucky side of the DC. Laid the DC on top of the MDF (bolted through) and siliconed between the dust port and the MDF. The fit between the GC and MDF is friction (it's that tight). I put an sucky port on the side of the GC and the output from the DC goes to a GC with a one micron bag on top. When I upgraded to the better bag I did manage to suck the GC flat , but some threaded rod between the MDF and base solved that.

All the big stuff stays in the first GC and only the finer stiff gets to the second GC. It's amazing how quick the planer will fill that first GC.

[docrowan]

I've been following this thread with interest. I've checked my shop and the best fit for me would be a 20 gallon trash can. In that size do y'all think a Rubbermaid plastic trash can work or would I need a metal one?

Oops, just saw the previous post. I guess it will work.

[pelligrini]

With a shop vac, I doubt it. I collapsed a green rubber one and a harder but thinner plastic tan one easily with my vac.

[Garasaki]

Yeah, but...

What trash can's HAVEN'T you imploded!?!!?

[docrowan]

I have a Ridgid shop vac, I think it's a 14 gallon and has a lot of suction. Maybe I'd better bite the bullet and get the metal 30 gallon can.

Thanks for the info.

[pelligrini]

Yeah, but...
What trash can's HAVEN'T you imploded!?!!?

That has yet to be determined, so far im 0 for 3. Luckily, the plastic/rubber ones will go right back into shape.

I've got a Rigid vac too, it's the 16 gal model with the detachable motor for use as a blower.

[docrowan]

Hmmm, I'm thinking a relief valve could be made:

Cut a 2" hole in the top with a hole saw.

Make a 2-1/2" diameter cover plate of 1/4" hardboard that goes inside the lid and seals to the underside of the lid.

Glue a 5" stove bolt through the center of the cover plate.

On the top side of the lid, glue a 2" long piece of 2-1/2" diameter PVC pipe, through which you've drilled several 1/2" holes to allow air to pass through.

On top of the PVC pipe, glue a 2-1/2" diameter disk of 3/4 plywood.

Drill a hole in the center of the disk large enough for the stove bolt to freely pass through, but not a compression spring.

Thread a 2" long compression spring over the stove bolt.

Thread a wingnut on the stove bolt that will bear on the compression spring.

Adjust the wingnut so that the cover remains closed during normal suction, but allows the cover to override the spring tension when intake hose is blocked.

You would probably have to try a couple different springs to get the right amount of tension.

Some additional air intake holes could probably be drilled in the plywood disk as well.

What do y'all think?

[pelligrini]

That's a neat idea! I was just going to leave an adjustable opening hole.

[dbhost]

I've been following this thread with interest. I've checked my shop and the best fit for me would be a 20 gallon trash can. In that size do y'all think a Rubbermaid plastic trash can work or would I need a metal one?

Oops, just saw the previous post. I guess it will work.

Seriously doubt it. With a DC and far less static lift, not to mention some bracing of the can sidewalls sure, but with a shop vac, no dice. Too much static lift will suck the thing in almost instantly I would bet... Try it and video that thing. Probably good for a laugh...

[jkristia]

just curious - can somone explain what 'static lift' is, and why this is higher with a vacuum?

[LCHIEN]

just curious - can somone explain what 'static lift' is, and why this is higher with a vacuum?

Static lift and vacuum are more or less the same.
Vacuum is usually expressed for more complete vacuum, which is negative pressure. Oftem expressed in PSI, also in mmHG and sometimes in inches of water.

Static lft is the amount of water column a vacuum can pull, as in a long tube dipped into water and a vacuum applied at the top - the number of inches the water rises in the column is the static lift in inches of water.
The relation ship is approximately (rule of thumb)
32 feet of water lift = 380 inches of water lift = 15 PSI vacuum = -15 PSI pressure = -1 atmosphere = 30 mm Hg vacuum = -30mm Hg pressure

As you can see, vacuum is negative pressure. But you can't get lower than -1 atmosphere (of vacuum) but there's no upper limit on positive pressure.

DC's have large impellors and vanes to move lots of air but they are not well "sealed" to prevent back leakage so they can't put up a lot of vaccum. Typically they will have several inches of water static lift before they run out of air flow. (which is why they need large hoses or ducts of very low resistance (measured in inches of water) to work well.

Shop vacs have much smaller impellors but they are more positive in moving the air (a harder push with no way to leak back) so they can put up much more impressive vacuum pressure when dead-ended but much less air flow when open ended compared to a DC which puts out enormous airflow when open ended but not a lot of pressure when the airflow is blocked off (closed ended).

[pelligrini]

Somehow, I knew loring would come through with an excellent answer.

[jkristia]

I almost regret I asked .
Thank you for the detailed explanation, at least now I (kind of) understand the different between static lift (vacuum) and air flow .... I think