Static line for dust line

[Bill Weaver]

I just bought a new dust collector and in the assembly instructions it recommends a static wire run thru the inside connecting to the machine and to dust collector grounding area. I was curious to see how many of you fellows have used this and if so how difficult it was to string this inside the flex tube. I will be running the tubing to both of my lathes.

Thanks Bill

 

[John King]

Bill Pentz

Checkout out Bill Pentz, Cyclone Dust Collection Research at http://billpentz.com/woodworking/cyclone/index.cfm and make your own decision. - John

 

[Mark Mandell]

Two suggestions:

Forget the wire. BTDT. . . . useless; you can't "ground" plastic, and the damn wire contributes to clogs.

Next - "86" the flex hose for as much of the system as you can. The interior flex ridges impede the flow and rob you of system efficiency. For plastic, use 4-6" PVC S&D (sewer & drain) pipe. The smooth surface will do much better.

Other alternative is metal piping. This does get expensive, however, because it's heavier gauge that your ordinary snap-joint smoke/HVAC stuff. Other advantage is that it's self grounding.

 

[Steve Worcester]

Run metal, no static line

 

[Rob Wallace]

Bill:

You may want to review some design theory about ductwork before you begin spending time and money on your dust collection system.

As has been said, internal grounding wires are useless and more of a pain than anything else. The efficiency of your system will be dictated more by ductwork size (diameter), length, and fitting design (wye's, ell's, drops, blast gates, etc.) than anything else. How well your system will work is very much influenced in the installation of ductwork, regardless whether you have a one-stage, a two-stage, or a cyclone system for generating the vacuum and providing filtering.

You might take the time to have a quick perusal of the following tutorial on ductwork:

http://www.oneida-air.com/static.asp?htmltemplate=static/ductwork_tutorial01.html

Whatever you do, DO NOT use those ridiculous corrugated inexpensive plastic pipes as major duct runs..... they have so much inherent static pressure loss that you will be losing half or more of your air flow in straight runs of pipe! This kind of "ductwork" is useless. The best systems will be of metal duct, with fittings that are designed for good air flow. Unfortunately the weakness of PVC-based duct systems is that the available fittings (although relatively inexpensive) are designed for plumbing (waste and vent) applications, NOT for optimal air flow, which is what you want/need. The worst of these PVC DWV fittings are the ELL's with a tiny curve radius compared to the 1.5X pipe diameter minimum curve radius that is recommended for air systems (you can simulate correct ELL radii using 45's and some pipe in between). There are a few plastic fitting manufacturers that recognize this incompatibility between air systems vs. DWV plumbing applications, and some make air-flow designed fittings that are compatible with PVC pipe sizes (Schedule 40 and/or Schedule 10) - these are the ones you should seek out if you are going with a PVC ductwork system.

I'll say I have never built a PVC system (mine is totally metal except for the flex drops to machines), but have helped troubleshoot 5 or 6 all-PVC systems of friends that were really under-performing as far as system efficiency. Use as as large a pipe diameter as possible from the collector to any inlet, and minimize turns whenever possible. Never use T's in your system. There's lots of information on dust collection system design on the internet..... Just realize that what you read in the "instruction" manual of your new dust collector may be a far cry from what should be done to install an efficient system to get the best airflow volumes possible with your collector.

Good luck setting up your system and turn safely!

Rob

 

[Bill Boehme]

It is one of those urban myths that has taken on a life of its own. As everybody has said, forget about the silly wire because it is worse than useless. It costs extra money and it creates places for trash to hang up.

Let's see -- plastic is an insulator -- that is why it is used to insulate wires. So the myth is that if you get a bare wire and then put it inside a plastic tube, somehow the plastic will become a conductor. It doesn't work with insulated wire and it doesn't work with wire in plastic pipe either. With regard to the equally silly idea that the wire grounds the two pieces of equipment, the DC and the machine it is connected to, may I point out that both pieces of equipment are already grounded in a proper electrical installation.

Concerning the use of PVC sewer pipe for ductwork, wire or no wire, they can build up quite a static charge since they are basically a Van de Graaff generator. Use metal ductwork.

 

[MichaelMouse]

I just bought a new dust collector and in the assembly instructions it recommends a static wire run thru the inside connecting to the machine and to dust collector grounding area. I was curious to see how many of you fellows have used this and if so how difficult it was to string this inside the flex tube. I will be running the tubing to both of my lathes.

Thanks Bill

What you want is a grounded wire to touch the exterior of a non-conducting material before you lay a hand on it to keep yourself from getting a static poke. Dry conditions favor static buildup, but you can get them in relatively high humidity as well. Make it a practice to touch, and the rest of the time you can use the static to collect dust that might remain airborne. Vacuum it off once in a while to keep your precipitator working. Since I only use it for sanding, I'm not too concerned that I have ten feet of flex hose. Slows things down at the planer, occasionally, so a shorter one is at the ready for swap out with my roll around one-tool setup. Might make a much difference in draw as using a drop hose and working against gravity. I let mine drape, so gravity is my friend, or at least not my enemy.

 

[Bill Weaver]

Thanks for all the info fellows, I'll take this in stride and see what I get.
Thanks again.

 

[Bill Boehme]

..... Use as as large a pipe diameter as possible from the collector to any inlet, ....

Forty something years ago I, along with all the other students in a thermodynamics class learned a valuable lesson. The only problem is that it was on one of the two exams given that semester. The question was, "what is the optimum thickness insulation for a cylindrical six inch diameter steam pipe?" Temperatures and thermal conductivity values were stated. This was sort of mind boggling, but it was effective, if not a harsh way of teaching an important point. Up to that point, we mistakenly assumed that the more the better when it comes to insulation. Nobody got the right answer, but we did learn afterwards. While the exterior temperature decreases with greater thicknesses of insulation, the thermal flow INCREASES due to the greater surface area of the of the exterior. The answer lies in solving a boundary value calculus problem that showed that there was indeed an optimal thickness. Any greater thickness resulted in more heat loss just as in the case of the insulation being too thin. I think that the thickness was somewhere in the neighborhood of 1.5 inches for that particular problem.

There is a similar principle in sizing air ducts. There are two opposing principles involved -- velocity and pressure loss. Increasing the diameter of the ductwork certainly does reduce the pressure loss, but at the same time, it reduces velocity. Velocity is important to keep dust and shavings flowing sufficiently that there is no buildup in the ducts. Any buildup of dust and shavings results is excessive pressure loss without any significant increase in velocity. Since we generally have insufficient data about our individual DC systems and no inclination to solve a calculus problem with suspect results, it is a good idea to use design guidelines provided by the manufacturer (hopefully they provide that) in sizing the ductwork. Don't make the mistake of assuming that bigger is always better.

 

[Greg Keddy]

Increasing the diameter of the ductwork certainly does reduce the pressure loss, but at the same time, it reduces velocity.

As a good rule of thumb, for a shop that uses one machine at a time a 6" main with 6" drops to each machine balances pressure loss while maintaining sufficient velocity to keep chips suspended. Move up to an 8" main with 6" drops if running two machines at a time. All of this assumes that you have a DC capable of keeping up with your duct runs.
I'll second, or third (wherever we are at) the notion of reducing flex hose lengths whenever possible. I ran a 10ft length of hose bent at 90 degrees to one of my machines and it cut my airflow in half (1200cfm to 600 as measured by an anemometer). Apparently, each foot of hose is equal to about 3 ft of HVAC pipe.

 

[MartyL]

DC duct

Hi all, I had Oneida engineer a DC system for their 5hp cyclone . . . you would not believe the accuracy of the duct sizing 4 different diameters to achieve fantastic suction at the tool end! This is not a do it yourself project!
Marty

 

[Gerald Lawrence]

Pvc

Rob gave you good advise. I will have to differ with him on PVC . I use it and there a fittings you can make yourself that work fine in the home shop. I have made blast gates ,central distribution boxes and all work well. I do Wish I had larger central lines.
On the PVC you can join by glue (pvc) , Caulk joints, or use a screw to hold the joint in place. I do not claim my system to be highly efficient, but it works. I think this pressure values or over-touted. The question is does it work for you? Also be sure to empty regularly as this will reduce vacuum pressure greatly.
Also you will rework this several times before you are happy and allowing versatility in setup will make this easier. Or remember it is not set in concrete.

 

[Patrick Miller]

Fittings

I installed a collection network in my small shop using 4" drain PVC for the main runs with 4" flex for the drops from the ceiling. I installed a microswitched blast gate on each drop and ran the low voltage lines from each back to a relay that turns on the blower. The entire cost for the switching was only $110.00 and that included 4 aluminum blast gates. I extended a 1/4" rod as pull handle down from each gate. It's right there at the tool and I can turn on the blower for the specific tool standing at the tool. I can tell you that I am much more apt to use the extractor now that is so handy to operate. Another hint- none of the darn fittings seem to fit each other! I used my lathe to turn the needed sleeves and bushings from scraps of pvc/abs pipe to mate the connectors.

 

[Ron Rutter]

A 6" line is probably optimal. The advantage of a larger line is that it reduces the velocity & increases the volume of air which gives you better fines pick-up. ( the bad stuff)
By the same token you have to have a large enough DC in line with the length of your runs to provide the static pressure needed.
The best source of info on systems & cyclones is the Bill Pentz website. A cyclone keeps all the course stuff from going through your fan & in conjunction with a drop box also saves you from having to empty the bags. The Pentz units require a lot of headroom. There was a short cyclone in Wood Magazine some years ago that works fairly well. (I have built both)
If you ever build a cyclone make the outlet pipe as large a you can. This reduces the outlet velocity & leaves the fines behind better!!
Ron.

 

[Ron Rutter]

Hi all, I had Oneida engineer a DC system for their 5hp cyclone . . . you would not believe the accuracy of the duct sizing 4 different diameters to achieve fantastic suction at the tool end! This is not a do it yourself project!
Marty

Marty. You might find that your fantastic suction tunnels & leaves stuff behind that is not in line with the tornado!