New HF/Thien/Wynn DC -- Expectations/Disappointments?

[Curt Harms]

A couple things. One, what kind of saw? I have a G1023 cabinet saw, nothing in the design to help with dust collection. I put a scrap of magnetic sign material over the 'smile' where the blade elevation mechanism moves and partially plugged the space between the cabinet and top with rolled up newspaper. I kept plugging until there was what I felt was reasonable air movement through the blade opening. You need a certain velocity to keep dust entrained in the air flow. A stock saw, either contractor or cabinet style won't produce that without a honkin' big dust collector and appropriate ducting, there's too many leaks. Plug some of the leaks and velocity should improve. You don't want to starve the system of air but that seems unlikely with a '2 h.p.' collector. It also seems easier to 'steer' the dust into the ducting while it's airborne. Once it settles it doesn't want to move. I also made the 4" dust collector hole into a 6" hole. This is with a '2 h.p.' Penn State collector w/ Thien baffle in the funnel.

[Danny Thompson]

The innertube solution Ryan mentioned completely solved the fine particle chimney issue.

With a closet organization project deadline looming, two sheets worth of MDF went through the system, before I could make the other adjustements. Everyone knows, MDF is about as bad as it gets. I am glad to report, although some dust continued to settle in the back of the cabinet, the airborne dust level was nearly eliminated. The only untrapped dust came off of the blade (no blade guard dc, yet, so a respirator is still in play). Even so, after two days of dust-making and a few days of settle-time, there is no noticable dust layer in my shop! This is is a major step up in performance from the ShopVac/Hepa Filter/DustRight Vortex pre-separator setup.

Rounding over the edges of the MDF at the router table could have made a mess, as well, but no. The DC mounted to the Bench Dog fence with a 4"-to-2 1/2" adapter made the dust completely disappear.

Conclusion: Totally worth it!

Opportunities for improvement remain. My saw is a Jet JTAS-10RL. It contains many alternate channels for inbound air, including the smile you referenced, Curt. I'll work on plugging those. Plus there are the stovepipe and shorter flex hose. Above table DC. We'll see if those make a difference.

[Ryan Mooney]

Well that's fantastic news. The contribution of air leaks to bypass is still pretty amazing to me, such small amounts of air change the dynamics so much.

I'm really curious about how much the in ring baffle costs airflow wise. I have a pre-separator, but had to open up the gap overly wide to support separating planer shavings and that hurt my fine dust separation some so have considered doubling down and adding a baffle to the ring as well to pickup the fines on the second pass.

[Danny Thompson]

I'm really curious about how much the in ring baffle costs airflow wise.

Not sure how to measure that, although, the FWW article measured CFM for the internal baffle. I believe it was around 520 CFM with no baffle or pre-separator (quickly declining to 250 CFM after 30 lbs of dust)
520 CFM with an internal baffle (declining slowly to 500 at 30 lbs)
430 CFM with a cyclone pre-separator (stable)
360 CFM with a trash can pre-separator (stable)

This suggests no real incremental hit from an internal baffle and you may be better off replacing the pre-separator with an internal baffle. Something to consider.

[Ryan Mooney]

520 CFM with an internal baffle (declining slowly to 500 at 30 lbs)
430 CFM with a cyclone pre-separator (stable)
360 CFM with a trash can pre-separator (stable)

This suggests no real incremental hit from an internal baffle and you may be better off replacing the pre-separator with an internal baffle. Something to consider.

That's encouraging, I may well add a baffle! My filter on the last cleaning was a bit on the grungy side (this was after ~5 30 gallon barrel dumps so I'm not complaining as I believe that it isn't a whole lot worse than a meh cyclone and I know how/why I compromised the separator design).

I really like the pre-separator from a convenience perspective, pulling the drum and dumping it is a lot easier than pulling the bag off and I'm afraid I'd still have the same long stringy shavings problem with a baffle as I had with the pre-separator and would need to open up the slot overly wide obviating some of the fines capabilities so .. yeah some compromises.

[Curt Harms]

I remember one bit from Bill Pentz' site re blower. The subject was using a marginal capacity blower with a cyclone. There was less of an airflow penalty if the cyclone was after than blower than if the cyclone was before the blower. The downside of course is all the 'stuff' goes through the fan with a 'push through' system. A single stage dust collector has a fan that can take some crap hitting it, something like an airfoil blower can't even tolerate dust buildup on the blades.

[David L Morse]

I added a Thien baffle to my HF DC last weekend and have been trying to measure the difference in flow it makes for the last few days. I have four pressure ports on the DC and have been trying to infer relative flow from pressure data. After learning more about centrifugal fans than I really wanted to know and doing way too much review of fluid dynamics I finally today put together a test pipe with a pitot tube. Should have done that Sunday!

Here's what I measured today:

With both 4" ports on the DC open it pulls a total of 630CFM without the baffle. Adding the baffle drops the flow 17% to 520CFM.

With one 4" port open it's a 15% hit, going from 550CFM to 470CFM

Add 10' of flex hose to each port and total goes from 400CFM to 350 CFM for a 12% drop

With the flex connected to my table saw the total flow top and bottom is 300CFM without and 270CFM with the baffle. (I think I should do something about that flex tubing!)