Shop Vac vs. DC - Hard Evidence - maybe a ramble

[tom_murphy]

Okay, I can end the debate. I had originally plumbed my gara...shop to a Craftsman 6HP (yeah, right) shop vacuum to support one machine at time dust collection for router table, RAS, and contractor saw with dust panel underneath and makeshift closure of the back. It actually worked pretty well, but it was not catching the fine dust as well as I wanted.

So, I just upgraded to the the 2HP (at 20 amps? That math doesn't work) Harbor Freight unit. I had anticipated this move when I put in the plumbing and used 4" PVC for everything, including a convenience drop in the center of the garage ceiling to vacuum the floor and cars etc. All I had to do to install the new DC was to add a 4" port and hood it up with flex hose. Since I like having the availability of the vac, I left it plumbed in, but added a blast gate to both it and the DC so I can select which one to use.

It's a perfect set up for a side by side comparison of vac vs. DC.

The results:

- As mentioned above, the shop vac is okay as a DC for one machine, but not good enough for my wife, whose car was getting dussted regularly.

- The DC works MUCH BETTER on all machines. On the contractor saw, I could not see anything at all escaping while ripping some Spanish Cedar.

- The 2HP CD makes a lousy vacuum cleaner.

Okay, everyone already knew this, but it was interesting to see it first hand.

Tom

[CNT]

I am still using my shop-vac for all my "DC". But I want to add that the JET air-filtration does a beautiful job of cleaning the dusts flying around! I have the JET model (1000B).

Chuck

[Andy]

I, too, am still using my Ridgid shop-vac for DC, and a fan pointed out the window as an additional vent. I do have an ultra-fine filter for the shop vac, which helps. The shopvac works well when attached directly to my router table/bandsaw/RO sander, and I haven't had any problems with dust flying around or building up anywhere else in the basem... shop, as long as I have the shopvac attached directly to the tool. Interesting to read about them compared side-by-side, though! Andy

[toller]

How do you have it attached to your contractor's saw? I tried doing mine, but there are so many holes that it was pretty pointless.

What is spanish cedar?

[Patriarch]

"Andy" wrote in news:1120678938.260669.213570 @z14g2000cwz.googlegroups.com:

The Ridgid shop-vac I have screams like an F18 in full afterburner mode. It gets used when it is the only available option, and then only with hearing protection.

I'd rather use a broom.

Patriarch

[Larry Jaques]

Ay chihuahua! Eez $9.25 a board foot, señor. (16/4)

$7.92 b/f PICTURE

- Better Living Through Denial ------------

Dynamic Websites, PHP Apps, MySQL databases

[tom_murphy]

I just rigged some cardboard to close the back of the saw (have to remove it to move the blade off 90 degrees) and I have one of the "dust hoods" that closes up the bottom and provides a 4" dust port. With the vac I had that reduced down to 2.5" for the standard hose. It worked pretty well, but with the DC I don't get any noticeable dust off the blade coming out the top.

Spanish Cedar is pretty soft, but officially considered a hardwood according to the guys at the lumber yard. Why I'm using it is a long story, but it's commonly used raw for outdoor shutters because it has great moisture tolerance, i.e. it gets wet but dries very thouroughly wihtout disfigurement. It's also commonly used for humidors.

The shop smells wonderful!

[Bob G.]

================== Have to agree with the noise....But that can be fixed....!

My simply enclosing the shop vac in a box ...leaving a vent around the bottom for air flow... and cutting a hole in the top or side for the hose to enter... and adding a remote control X-10 device to turn it on and off...

Been using that method for years and never had any problems at all..noise reduction is very low...

I use the small 2 inch or so cheap clear plastic tubes and orange little blast gates sold as a Shop Vac system by The borg...

I HOWEVER DO NOT use it as a DC system....more of a central vaccum system for my sh I have 2 DC's in my shop ... a 2 Hp Griz which handles all my machines (1 at a time via Blast gates) and a 1 Hp little Penn State unit that handles both my Horizontal & regular Router tables, my spindle sander and my planner....also via regular 4 " PVC and blastgates... In addition I have a Delta air filter mounted up high on one end of the shop and a home made air filter sitting under my workbench on the other side of the shop....

By just using the shop vac as a DC ..without the 2 in pipe etc..hooking it up to each machine it honestly will pick up most of the chips...but hardly any of the small airborn dust .... Lets say it is a good CHIP VACCUM but a Pi$$ poor dust collector...

The real dust collectors on the oher hand will remove almost all the air born small dust particles but have a hell of a time picking up the larger chips... gets most of them but by no means all...

From My observations and simple tests...Dust Collectrors do a great job collecting dust but make darn poor vaccums...Shop Vac on the other had are extremely poor Dust collectors but suck up the larger chips better... Nothing new in this observation since DC move a heck of a lot of air with low velocity wheras a Shop vac moves much less air but moves it at a higher velocity...

With all these (2 air filters, 2 Dust Collectors and a central vacc system) in my shop you may think I really am a health nut ...but in truth I installed them ONLY to have a cleaner shop in which to relax...I honestly (at 61 years old & a smoker) was not in any way trying to protect my lungs etc...I just like my shop to be clean ...

Bob Griffiths

[alexy]

To summarize, you seem to have done an experiment to confirm that a dust collector is better at dust collection and a vacuum is better at vacuuming.

Startling results!

[tom_murphy]

Well...yeah. But since I did the plumbing for other reasons, the experiement only took about two minutes and I got to play with my toys and make sawdust in the process. Woohoo!!!!

[Clint]

So are you saying that you had your shop vac hooked up to the 4" PVC? Or was your shop vac hooked up directly to the machines? If it was hooked up to the 4" PVC, I think I can understand why that would suck (in a bad way).

Clint

[Tim Douglass]

It is also the wood of choice for the necks of classical guitars.

-- "We need to make a sacrifice to the gods, find me a young virgin... oh, and bring something to kill"

Tim Douglass

[tom_murphy]

I had a network of 4" PVC which was reduced back to 2.5 " where the vac was attached, and at each of the machines. So even though the RAS and table saw have 4" ports, they were connected to the network by the smaller hose. I had blast gates at all of the machines.

How it is now:

The vac is still hooked up through it's own 2.5" hose (very short run, hides in a cabinet) and a blast gate so it can be isolated from the system when I run the DC. The machine hookups are now 4" DC hose with

4" blast gates, i.e. 4" all the way to the DC. The DC also has a blast gate so I can switch in the vac for "central vac" use.

The "vac" port in the middle of the shop is still reduced to 2.5" so I can use standard hose and attachments (it hangs from the ceiling). At that point, there's about 20' of PVC run back to the vac. I left another vac port near the drill press for manual cleanup after drilling plus it can easily reach the work bench for general cleanup.

I'm not sure why you feel that the 4" PVC run would hurt the performance of the vac?

Tom

[Clint]

AFAIK, moving the dust depends on maintaining a air flow velocity (feet per minute). If the airflow falls too low, the dust can settle, all you end up with at the dust collector/shop vac end is a slow stream of clean air.

When you expand the size of the hose from the 2.5" diameter to 4" diameter hose, the velocity of the 4" section will about 40% of the velocity of the

2.5" section. Unless you've got enough airflow from the shop vac, it would be likely that it won't have the umph to get the dust all the way from the tool to the vac.

NOTE: This is all theoretical, as I'm using a shop vac for dust collection, and haven't played with larger hoses because of this. I thought about running some PVC or metal runs, but I don't want to do it twice (once for shop vac, once for the dust collector I know I need).

Clint

[tom_murphy]

In my situation, since the hose to the machine was down to 2.5" again, the air velocity at the tool was essentially unnaffected by the 4" pipe (air in = air out). That's why the vac sucks just about as well through the big pipe with normal 2.5" implements attached. It's actually a lot better than a long run of smaller pipe because there is less friction loss.

You're right about the slower velocity in the larger pipe, though, and it's possible that I was getting some accumulation of sawdust in the 4" sections. That's why I used a 5 gal. separator (2.5") right at the table saw before entering the PVC. The RAS port is actually very close to the vac tie-in which minimized the problem. It's a big vac, which still moves enough air such that the open hose would suck light sawdust in from at least 3" away. It's reasonable to assume that it could keep the same light sawdust moving through an enclosed 4" pipe. Larger chips would be a different matter. It's academic now because I have the DC.

If I was in a dedicated shop, I probably would have stayed with the vac because I was pretty happy with the results, but I really hated the fine dust all over the cars and my mechanics tools. (Like many others on the rec, I'm a car person too). Depending on how the new setup works, I still may end up getting an air filtration unit.

If I could just get these dang shutters finished I could bet back to car work...

[barry]

Very effective exhaust silencers have been available for Shop-vacs for years now. (Unfortunately not available for my Hitachi TS.) :') So I still use "ear-muffs" at times, but torture neighbors, and cat, much less.

HTH, J

[barry]

Details, details: GoreTex filter in vac is _much_ better (IMHO) at trapping fines than DC- those sub-micron fines are the stuff that gets down into your lungs. (USCG has investigated this for years re shipboard engineering repair safety.)

Crunchy-dust here and there? Scoop it up.

Nasty fines down in your lungs? See what develops.

HTH, J

[tom_murphy]

Yeah, but in order to get trapped by the filter or bag, the dust must first get pulled into the system. The vac was leaving the fine dust in the air around the machine (and me). BTW, I just ordered a one micron bag. Spec claims that it will filter sub micron stuff once a cake builds up on the felt. We'll see.

[Unquestionably Confused]

on 7/7/2005 2:00 PM tom [e-mail] said the following:

In a perfect world, perhaps... Think about it for a moment though. We are talking about a VACUUM. The more air that must be removed from a given vessel until the ultimate vacuum pressure (or lack thereof) is created, the less effective the vacuum device is. Granted, the difference may be small if we are considering a perfectly sealed 4" pipe which terminates at either end into a 2½" fitting. You still must consider the friction caused by the bends, etc. which will change the equation depending upon whether or the number of bends in the tube and the diameter. Ask a plumber how this affects water pressure.

Take it a step up to the point of ridiculous - just to demonstrate. How long do you think it would take to draw away all those chips coming from your planer if you had a 4" hose connected to the planer, which hose was then connected to an airtight box 10' square and 8' high, to which was then connected the intake on a 1100CFM DC? All that air can compress and expand in the box and that's going to be a factor in your efficiency.

[tom_murphy]

Or a 55 gallon drum that's used as a separator. I think the effect you're describing only really applies at startup. Once the steady state is achieved in the entire system, it should flow "about" the same and the efficiency should be about the same (ignoring the issues of turbulence for the sake of this discussion). Otherwise, I think the big separators would cause all kinds of problems.

My "network" consists of about 35' of 4" pipe which amounts to a pretty large "chamber" that the vac has to suck down to negative pressure before reaching that steady state. I can say for sure that the delay and any degradation in performance are negligible.

Back on to turbulence, this is greatly reduced by using bigger pipe.

I guess we're beating this to death, but it's an interesting discussion.=20

Tom