Duct size for Clear Vue 1800

[Joe O'Leary]

Try this: http://www.woodworkforums.com/f200

Tons of info (and Aussie humor!)

[Peter Christensen]

This PDF was brought up and discussed in that Aussie forum that shows the comparison between a pair of 45s and a single 90. If you look at page 54 you will see the values of how much straight duct each type of fitting creates. The three piece 90 is the worst for drag and it does resemble a pair of 45s and a short section of straight pipe. Even if you prefer the numbers from individual 45s added together with straight pipe they are still higher than the 90 with a 1 or 1 1/2 or more radius. Fewer direction changes are better.

I just found the Loren Cook Company have a number of design downloads including apps. It wouldn't let me download the desktop version, probably because I'm north of the border and I'll have to figure out my Apple password to get the apps. Thought it might interest some of you.

http://www.lorencook.com/downloads.asp

[Chris Parks]

I am no longer commercially involved with Clearvue due to retirement so anything I write is my view and should not reflect on them in any way.


To keep it simple and avoid confusion when I was selling Clearvues the way I explained it was as follows and keep in mind that we do not recirculate air through filters in Oz as it is not necessary. Very few workshops here have either AC or heating.

If you buy a CV1800 you can hook it up to 6" ducting to the machines and it is plug and play, no duct design, no need to get fancy with inlets etc because it has enough performance overhead to take care of the deficiencies that might be there in the installation. If using a Max, 9" main duct, 6" from that to the machines and if only using one machine at a time then leave an overhead blast gate open to scrub the air as the Max can extract from two 6" lines at the same time. In reality if you are using only one machine at a time and are not going to leave a blast gate open it is doubtful that a Max is a huge advantage at all IMO unless you have a very specific reason to use one. The reason the Max came into being was that if the 1800 was used outside the US/Canada?? it runs at 50hz and this results in an impeller speed of 2850 RPM which drops the air flow below the optimum requirement. The Max at 50hz matches the 1800 at 60hz in airflow through a 6" duct. It most probably slightly exceeds it but I have no evidence to prove that.

If using a generic a 14" impeller or less that is when you have to put your thinking cap on and minimise to the n'th degree all losses because to get anywhere near the performance often quoted as a minimum by the experts then you have to optimise everything from the initial inlet to the exhaust and absolutely avoid using less than 6" ducting. This means that every machine we use needs modifying as the ports on them are too small without exception. You need to do this on every installation in reality but on the less capable extractors it must be done.

Explaining DE that way generally made the lights come on for the customer, it was simple, did not add any more confusion and if they bought the machine they never had any performance issues. I have never had to do any duct design for an average workshop though I see people saying it is necessary all the time in this forum, most workshops are simply not big enough to need it and very few if any one has the knowledge or test equipment to do the necessary testing. The one criteria that must be used is the ducting has to be 6" to all the machines and the ports on the machines opened up to flow the maximum into the duct.

All cabinet machines such as table saws & bandsaws must have enough air inlet into the cabinet to allow the maximum flow out of the extraction port, air in must equal or exceed air out, pretty simple really. A lot of thicknessers do not have good air flow and the hood needs a lot of work to fix it.

[Joe O'Leary]

Very well said, Chris and exactly the same advice I got just today from the CV rep today. They have a sale on the 1800 equipped with the 16” impeller.

[Larry Frank]

Chris is correct about duct size with larger dust collectors. You can pull very good CFM and suction through 6" duct. I have a 5 hp Oneida Super Dust Gorilla and no issues with 6" duct. With smaller ones like the HF, you need to be super careful with duct design.

However, it is not always necessary to enlarge the dust ports on the machines. With a larger dust collector, you may be able to achieve adequate flow with a 4" port. For example, I get 670 cfm with the 4" port on my Sawstop. Would it be better with a 6" ? Yes, but is the improvement worth the effort...in my case probably not.

[Chris Parks]

Chris is correct about duct size with larger dust collectors. You can pull very good CFM and suction through 6" duct. I have a 5 hp Oneida Super Dust Gorilla and no issues with 6" duct. With smaller ones like the HF, you need to be super careful with duct design.

However, it is not always necessary to enlarge the dust ports on the machines. With a larger dust collector, you may be able to achieve adequate flow with a 4" port. For example, I get 670 cfm with the 4" port on my Sawstop. Would it be better with a 6" ? Yes, but is the improvement worth the effort...in my case probably not.

How did you measure the air flow?

What is adequate air flow and why is it not worth opening the dust port? Why wouldn't you want to maximise the air flow?

Larry, I think this is precisely the stuff that confuses people as it instantly raises questions that haven't been explained in your post. If I say to someone it is simply 6" all the way from machine to dust extractor that is as clear as it can get, enlarge the ports, hook up the dust extractor and press G for go. If the question is how to get a small impeller to pull 1000 CFM through a 6" duct then it gets harder, not in the duct design itself but in the ends, both entry including dust hoods and where the duct enters the DE and it will be a lot of work and usually more expense. I can't expand here on years of work that has been done in Oz, there is simply too much of it so it will require going there and reading what has been done. I am sure Peter C. will back me up on this as he has read it all.

[Joe O'Leary]

Chris, et. al.,
Fascinating reading on the Oz site about bell mouth entries. I need to drastically improve this on my General cabinet saw and SCM band saw. If I cut 6" holes, I assume it would benefit by having the inside of the entry be BM and let it act as inside flange. Does this make sense?

[Chris Parks]

Chris, et. al.,
Fascinating reading on the Oz site about bell mouth entries. I need to drastically improve this on my General cabinet saw and SCM band saw. If I cut 6" holes, I assume it would benefit by having the inside of the entry be BM and let it act as inside flange. Does this make sense?

A bell mouth will always increase entry air flow into a duct. We first started talking about this stuff a few years ago and I used bell mouths on car carburettors so dug out a few old books on it and things moved on from there. As I said in a previous post you must have air entry matching extraction in a cabinet machine.

[Larry Frank]

Chris...I posted how I did this and my results on SMC. However, the post got edited by a moderator for some reason and now is difficult to read. I used a hot wire anemometer and measured multiple positions across the duct. I used a digital meter to measure static pressure. I also checked the meter against a U-tube manometer. The performance curve that I developed was similar to the manufacturer curve but slightly lower. I believe that is as accurate as reasonably possible without going to rigorous testing and more expensive equipment.

Why wouldn't I want to enlarge the port? I do not want to spend the time to chop up my Sawstop and do not want to change the insides. To do a proper job means a lot of work on the inside ducts and such. It would mean changing the inside flex hose to a larger size and completely changing the area around the bottom of the blade. Unless you also do these things, it makes little sense to change the port size. Several of my machines would be extremely difficult to enlarge the port. To me the question is really how effective the current port works. I have a Supermax 16/32 sander with a 4" port and it works very well. I am not satisfied with the idea that one needs to change all the 4" ports on machines to 6". As I said before, the necessity is driven by the dust collector that you are using and how it works with your 4" ports.

Changing the port size is a ROI calculation . Is the cost in time and money going to make a big enough improvement? With my system and tools the answer is no. However, I have the advantage of knowing the real performance of my system. Many people with the HF or 1.5 - 2 HP dust collectors either do not know the true performance or think it is much better than it is.

[Jeff Bartley]

If 7" mains are better for a CV1800, and 7" pvc is not available, has anyone here mixed metal with pvc? Seems like using a 7" metal main with 6" pvc drops might be a good combo?

[Chris Parks]

Chris...I posted how I did this and my results on SMC. However, the post got edited by a moderator for some reason and now is difficult to read. I used a hot wire anemometer and measured multiple positions across the duct. I used a digital meter to measure static pressure. I also checked the meter against a U-tube manometer. The performance curve that I developed was similar to the manufacturer curve but slightly lower. I believe that is as accurate as reasonably possible without going to rigorous testing and more expensive equipment.

Why wouldn't I want to enlarge the port? I do not want to spend the time to chop up my Sawstop and do not want to change the insides. To do a proper job means a lot of work on the inside ducts and such. It would mean changing the inside flex hose to a larger size and completely changing the area around the bottom of the blade. Unless you also do these things, it makes little sense to change the port size. Several of my machines would be extremely difficult to enlarge the port. To me the question is really how effective the current port works. I have a Supermax 16/32 sander with a 4" port and it works very well. I am not satisfied with the idea that one needs to change all the 4" ports on machines to 6". As I said before, the necessity is driven by the dust collector that you are using and how it works with your 4" ports.

Changing the port size is a ROI calculation . Is the cost in time and money going to make a big enough improvement? With my system and tools the answer is no. However, I have the advantage of knowing the real performance of my system. Many people with the HF or 1.5 - 2 HP dust collectors either do not know the true performance or think it is much better than it is.

If the machine port is not enlarged why use 6" ducting, wouldn't that be a waste of money?

[Larry Frank]

No not a waste.... it allows me to deliver the best flow and static pressure to the machine cheaply and easily. If I ran 4" duct from the dust collector to the machine the static pressure loss would be significant.

[Peter Christensen]

What I plan on doing to the SawStop is cut out the 4" port and let the 4 inch hose sit in the opening of a 6" (or 7" tapering to 6", perhaps using a slightly longer 4" hose so it stays in place when tilting the blade. That will still clear the 4" and scavenge the rest of the cabinet of the dust getting by the blade shroud. The hose in the bigger port will also straighten out the excess hose that has the sharp bend in the existing design that allows tilting and adjusting blade height.

[Larry Frank]

That is an interesting concept of how to increase the size of the port on the SawStop. I took a look at my SawStop PCS and noted that there are a number of holes in the cabinet both ust up under the cast iron top and in the sides. This would allow a lot of air into the cabinet and reduce the sawdust in the cabinet. However, my thought has been that I want the dust collection as close to the source as possible. The current as purchased configuration directs all of the flow up around the saw blade. It works pretty well. I am wondering what will happen if you do as Peter suggested. I think a lot of the flow will come from other openings on the cabinet and not directly from around the blade. If you have a large dust collector, it probably will be fine but with a smaller one you may not have sufficient from around the blade. After looking at my Sawstop, it is not something that I would try. But, maybe you try it and it works great.

[Joe O'Leary]

Larry, Peter,
Do you guys have some pics. Hard to visualize what your referencing.
Thanks