Miter saw DC port? Shop vac or DC?

[Jay Yoder]

Hi all, just wanted to get feedback on which route to go...

I have a Delta 12" CMS and wondered which is better at picking up the plume of dust off the blade...My Dust collector or a dedicated shop vac?

Is it a function of static or volume? The port is about 1.5"...I currently have it set up to collect from my dc. I have a wye under the saw and then a 2.5" leg to pull it off of the saw port but I have been less then impressed by the setup...

[Alan Lightstone]

I've been asking the same question on another board regarding the choice between a DC and a Festool CT22 on a Festool Kapex miter saw.

The shop-vac's provide much more SP, and the DC provide much more CFM.

I still haven't gotten a good answer as to which is more important with a CMS.

[Neil Brooks]

All I can do is muddy the waters a bit more.

My CMS station is the only thing my 28' DC hose won't reach, so ... I use my 6.5HP Craftsman ShopVac on it.

Does a mediocre job. Okay, but ... just not great.

From memory, though, so did the (2HP HF) DC, before I moved it.

It's been my personal impression that CMS's are just dust makers. Maybe a hood, of some sort, near the blade, would do better ... :confused:

[James Baker SD]

I would think that if you stick with only the small 2.5" dust port that the shop vac (with higher SP) would work best. If you upgrade the dust port (and hood) to a diameter more appropriate for a DC (4" to 6") then the DC would be the better choice.

James

[Jim O'Dell]

Not sure how you would modify the blade guard on a CMS or SCMS to get a 4" pick up there???
My plan is to make a hood to catch what the blade throws back that's hooked up to the cyclone, and hook up a whole vac system to the shroud port on my Hitachi 10" SCMS. Hope to have the best of both worlds when I can decide on a hood design. Lucky my Dad is as much a pack rat and scavenger as I am. He saved a whole house vac system that was being taken out of a house close to him and asked if I wanted it. ;) GOOD JOB POPS!!!! :D:D Jim.

[glenn bradley]

My Shop-Vac with a 25 foot, 2-1/2" hose adapted to a 6 foot 1-1/4" hose does a better job on the CMS than my DC with a 4 foot 4" hose off a 6" main adapted down just before the saw. That's just my experience, YMMV. ;-)

[Darin Higginbotham]

I have a catch box with my six inch hose from my 3 hp dust collector this catches the spray off the blade that doesn't go in the catch system with the 2.5 hose on it. That which goes in the hose instead of being sent to a shop vac goes instead into the mouth of the dust hose about six inches and provides the adequate suction needed to get 95 percent of everything, sorry not the best description.

[Alan Schaffter]

Ok, here's the deal. You really need both a DC and shopvac to collect from a mitersaw to do it right.

A DC has good CFM (800 up to maybe 2000 for a super sucker) but really poor static pressure at high CFM, and only slightly better at low CFM. See the typical fan curve at the link below- it goes from high SP/low CFM up to high CFM/low SP. The fan curve is the capability of the blower and based on the design of the impeller and housing. The point on the fan curve your DC operates depends on how long and size of ducting and what kind of ports you have connected- you can't get any higher specs out of a DC than what is shown on a fan curve.

Since DC's are designed to move large volumes of air- high CFM- they typically operate where the SP suction is low. Check out the fan curve Oneida publishes for their 3 hp Dust Gorilla (http://www.oneida-air.com/gorilla_3hp_curve.php). At the highest CFM the SP is only 1"!!! (Note: filters, cyclones, dusting, etc. add SP resistance and drive the point at which your system operates to the left. You use tables like those on Bill Pentz's site to calculate the SP resistance). When you add excessive ducting resistance or neck the ducting down to the size of a 2.5" standard shopvac or 1.5" ROS hose you reduce the CFM to an unusable level and the SP increases but to a level far below that of a shopvac. The highest SP achievable on that Dust Gorilla is only 12.5" but at ZERO CFM - ya gotta have some CFM. At 200 CFM you still have just a tad over 12" of SP. Bottom line a DC doesn't do anything well through a small hose or port!!!

On the other hand, while shopvacs typically move slightly less volume, 100 to 150 CFM, through their small hoses, their SP is a whopping 80" to 100" of water for the top of the line Fein or Festool- many fold better than a DC. Even a cheap Shopvac brand pulls 60" of water- 5 times that of the 3 hp DC. So use a shopvac with the size of hose it is designed for.

So, here is what you do- hook a shopvac to the blade discharge port but make a good box, shroud, etc. behind the saw and connect it to a 6" line connected to your DC.

If you don't have a shopvac, it is better than nothing to put a short hose on the blade discharge and put its outlet near the 6" dust port.

http://www.oneida-air.com/images/3hp-super-curve.jpg

[Eric DeSilva]

Ok, here's the deal. You really need both a DC and shopvac to collect from a mitersaw to do it right.

Two 4" ports around the back, and a small shopvac on an outlet trigger attached to the main output.

I still get sawdust (although small amounts) scattered on the floor in front of the machine.

[Matt Meiser]

My Makita has a rubber dust catcher that will collapse with the SP of the shop vac. A drop off the DC is just enough--with a big hood behind also connected to the DC.

[Peter Aeschliman]

I think Eric's approach is right- you need high static pressure if you're going with a small hose connected directly to the saw, and you need high CFM if you're trying to collect the dust cloud behind the saw. Both would be best.

[Jay Yoder]

Excellent replies everyone! So it sounds like I need to pull the 2-1/2" off of the DC and just dedicate a shop vac to it eh? That is easy enough. In fact when I designed the station I kinda kept that thought in mind just in case.

[Alan Lightstone]

Oh great. Something else to build.

Sounds like the combination is the way to go.

I'll try the CT22 directly to the Kapex with a 36mm hose and a 6" run from my DC to some sort of shroud I'll build. I think I'd rather a shroud than two 4" hoses like Eric, but who knows...

If that doesn't do it, I give.