shark guard port size

[David Hostetler]

Something to consider. The present model, the SG-K1 is offered with replaceable top pieces, so unlike earlier models, if you decide later on your port is too big, or too small, you can order a new port piece and just swap it out...

I have the 4" and a 4" belly pan on my BT3100. It works wonderfully. I used to have an OLD 2" model that worked great as a guard, not so hot as a dust hood. Not terrible, just not nearly as good as the 4"...

[Ryan Brucks]

I have a "2hp" HF DC, and a minimax CU300 combo machine. 5" port to the cabinet, and stock blade guard is around a 1.5" hole. Even with this very restrictive hole, I get better DC and noticeably more airflow using my HF DC to power both ports, than if I just use the HF DC for the cabinet, and shopvac for the blade guard.


I just finished making my own Lexan blade guard that is supported from the ceiling and is height adjustable (based on wood central plans). I made it for a 4" port, but I designed the sides at an angle so the opening at the bottom is only 1.5" wide to get higher velocity (mostly matters for when the blade is not surrounded by the workpiece). But I am also upgrading to a 5hp DC soon. If not, I would use a smaller port since my HarborFreight can't really feed a 5" and 4" well.

Someone mentioned something to the effect of "the fine dust doesn't need much velocity"... well the sawdust coming off the blade can be over 120mph, and even at the best case scenario 1000cfm, we are only talking 60mph wind in our DC pipes. So IMO nothing is overkill

Some people wrongly think you need to use a smaller fitting on the blade guard to get high velocity. This isn't really the case. It's about the air velocity as it passes the blade, so what really matters is the design and volume of the blade guard and volume of air moving through. A bigger port would always allow more airflow, but if the guard itself doesn't have the right taper, that velocity will be killed (the Shark guard has that internal separator you can tell is to keep volume down). I don't know how much the shark guard rises up and down with the cutting, but if it does, the area for airflow will be different at beginning and end of cut. That's another major reason I wanted mine suspended from above. I can control the height above the workpiece, and thus manage the air velocity a bit more.

[Michael W. Clark]

You could buy the 3" guard and put a reducer on top of it for 2.5" hose. This way if/when you upgrade to a cyclone, all you have to do is remove the reducer and install a 3" hose. ACGIH recommends 350 CFM on the blade (4" duct). I think this would get bulky, but maybe not, the user would need to make that decision. I would definitely recommend running a 5" or 6" duct over to the saw. The 4" is going to struggle to carry both branches adequately.

Mike

[Michael W. Clark]

Some people wrongly think you need to use a smaller fitting on the blade guard to get high velocity. This isn't really the case. It's about the air velocity as it passes the blade, so what really matters is the design and volume of the blade guard and volume of air moving through.

This is on point and also addresses the comment earlier about area and flow entering the cabinet. Its the velocity generated at the hood opening (or cabinet opening) that does the work of collecting and containing the dust. The velocity in the duct is just to keep the dust suspended and convey it to the collector. The starting point for any hood design is to know the minimum velocity required at the hood opening and the hood opening area. Multiplying these two together gives you the minimum CFM required at the hood. The duct is sized for the conveying velocity and CFM required. Sometimes the CFM is bumped up to get to a common duct size. The SP required to generate this flow depends on the hood arrangement, taper of the hood, and duct size/velocity.

The thing to take away is that the more open area (bigger gap around the hood), the more CFM required. The more CFM required, the larger the duct needs to be to maintain the conveying velocity without incurring extra SP losses due to duct friction.

Mike

[David Kumm]

What the OP should take away from this discussion is the difficulty in splitting air into multiple ports from a small collector. In Ryans case, the MM saw, although it has a 5" port, has a smaller flex hose internally to the blade shroud- if I'm not mistaken. My Knapp is the same way. That hose negates the full port size and allows for some additional flow into the overhead. Without that internal restriction you are likely to get inadequate flow at either port if not careful. The interchangeable port on the sharkguard is great and if you have a big enough collector, the 4" does not interfer and is slightly offset- good for slider- bad for ripping against a fence. A 10" guard with no scoring is fine with the 3" port now that the shark guard is narrower. The larger guard benefits from the larger port. Dave

[Ryan Brucks]

David you are right on the money. The reason I went 4" was mostly because my guard is insanely long, to cover the riving knife AND scoring blade. in fact the bottom opening on my guard is 19.5" long by 1.5" wide... or roughly the same area of a 6" port. But then account for the guard being only 1/4" above the workpiece, (instead, parimeter * space offset, so [19.5 + 19.5 + 1.5 + 1.5] * 0.25). With that, the area for airflow into my guard is actually around 10.5 square inches. The 4" port has 12.5" of area, so in practice, I am restricting airflow very slightly, and will have slightly faster airflow into the guard.

[Michael W. Clark]

David, yes the blade shroud inside the cabinet is a good example of a more "efficient" hood design that requires less flow (as compared to a connection to the cabinet). I thought this might be the case with Ryan's saw, but wasn't sure. Ryan, yes the offest area is what is doing the work (perimiter area under the guard) as you describe. However, I wouldn't think of it as being "restrictive" because some CFM is generated by the saw blade spinning. The exhaust from the guard would be the CFM induced by the saw blade + the CFM pulled through the slot below the guard. The slot velocity is equal to the CFM pulled from the guard divided by the slot area only when the blade is not spinning. When the blade is spinning, it is something less, hopefully the velocity is still inward if your guard volume exceeds the volume generated by the spinning blade.

Sorry for getting off-track/hijacking, it was not my intent, just thought Ryan made a good point when talking about port sizes and inlet area. One concern I would have about the large guard is how close you can get the fence to the blade. On my original guard, I can only get the fence within about 2-1/4" of the blade which becomes a problem on almost every project.

Mike

[Michael W. Clark]

Just re-read David's post, I would look at the 3" guard. If your collector is as Ian describes, you could go 6" hose, 5" for cabinet, and 3" for blade guard. It's a good idea to put a blast gate in both branches to adjust the flow as necessary. If you only want one gate, I would start with it in the cabinet branch.

Mike

[Cary Falk]

As a point of reference, My Excalibur over arm guard has a 3" port. The Arm is 4" at the base. I have a 4" hose connecting the base of the cabinet and the over arm guard. With the gate to the guard fully open, the guard sucks itself to the table pretty good. I am using a 3 hp dust colllector. In my opinion th3 3" guard is getting kind of bulky and gets in my way.

[Brad Gobble]

I have 4", works great.

[Van Huskey]

Get either a 3 or 4" port. Then use a true union ball valve or a blast gate on the run to the guard and you can adjust the flow to make it work best for your situation, you can't make a small port larger port easily but you can make a larger port effectively smaller easily. I like as much adjustability in the DC applications as possible, without a degree in fluid dynamics and a super computer to model the flow it really is a wild guess as to what will happen in the real world. Outside the scope of this thread the other side to that coin is to get as much flow as possible since dealing with too much flow is easy, dealing with not enough is hard.

[Steven Triggs]

Several have mentioned running 5" to the base cabinet of the saw. The port is 4" though. Does running a 5" hose with a reducer into a 4" port perform differently than running a 4" hose to the 4" port? I somewhat assumed that this was a weakest link situation, where the smallest opening between the DC and the tool was the effective size of the run. Perhaps I was mistaken?

Also, I actually have two identical dust collectors (picked them up for stupid cheap when Lowe's clearanced them). I keep one near the planer and the jointer, and the other near the table saw and the router table. I could connect both when using the table saw (one to the base, the other to the guard), but I'm hoping this isn't needed as it would be extremely less convenient.

Oh, and for whatever it may be worth to the conversation, this is the model DC that Fine Woodworking reviewed in 2006. Delta claimed I think 1200 CFM, but Fine Woodworking found it to have a true max flow of 925 CFM (quite high for this "class" of DC they said).

[David Kumm]

Steven, generally you will get more flow with the 5" flex entering into a 4" port than running all the way with 4" flex. Depends on a bunch of things but as pressure increases cfm decreases and the flex really adds resistance. You need enough velocity to keep the flow over 4000 fpm in the larger pipe but anything you can do to reduce resistance- fewer bends, greater diameter, more filter area, all help with the cfm. Dave

[Mike Goetzke]

My vote is for 2-1/2" - I have used the 4" also. I have a CV cyclone and need to move my TS into position when I use it. With the 4" port I found I had to use a gate or else there is soo much suction it can pick up sizable cut-offs. Also, a 2-1/2" hose is much more flexible and doesn't tend to make the Shark lean over like the 4" hose.

Mike

[Ole Anderson]

Several have mentioned running 5" to the base cabinet of the saw. The port is 4" though. Does running a 5" hose with a reducer into a 4" port perform differently than running a 4" hose to the 4" port? I somewhat assumed that this was a weakest link situation, where the smallest opening between the DC and the tool was the effective size of the run. Perhaps I was mistaken?

To answer your question, yes, that does become a weak link due to the friction losses of such an abrupt transition, but, no, the smallest opening doesn't make the effective size of the run the same as the smaller opening. So you are better off running a large hose to a small opening than running a long small hose to that same opening. Think 5/8" garden hose with a 1/4" nozzle. Same concept applies. You don't want a 1/4" hose feeding that nozzle. Of course, I wouldn't run a 6" hose to a 3" opening as your velocities in the hose are likely too small and will lead to a possible buildup of material in the larger corrugated hose. As I previously noted, I have no problems with my 3" top collector hose being picked up by a smooth 5" steel duct.

My Grizz 1023 had a 4" opening in the cleanout door for the DC. The door was easy to remove to enlarge the hole with a metal cutting blade in my jigsaw. I got a 5" bellmouth from PSI. The rounded transition from 5" to 7" reduces the friction losses due to an abrupt transition.