The agony of Upgrading to 5" or 6" tool ports

[Eric DeSilva]

The oneida blast gate I referenced will screw on just like a flange... And I bet it would be cheaper than getting a metal shop to fab one up.

[Scott Driemel]

Hey just for anybody's info. I just found at Oneida a piece of kit called "Angle Ring with Collar". For a 6" version it's a little over $20. Looks like the thing I'm looking for to convert the machines. Hopefully this might help others who have been on the "quest" as well.

[Chris Parks]

Ole, you can disagree all you want but all my customers who have tried it (references available) have found that the above approach works.

[Ole Anderson]

Ole, you can disagree all you want but all my customers who have tried it (references available) have found that the above approach works.

I am quite sure that it works well to keep the cabinet clean, but that was not the point that I was trying to make.

[Chris Parks]

No air velocity you can get will stop the ejection of chips from a cutter, it is not possible. What is possible and is the whole point of this problem is first you have to reduce the speed of the chip, that is trap it within the area of extraction and then you can remove it. In fact that is not the whole point either, the whole point is to trap and extract both the visible chips and the invisible dust that floats around us if not trapped. Of all the overhead collectors I have seen I still maintain that Alan Shaffer's is far and away the best at doing both and absolutely wins hands down.

[Ty Williams]

Sorry, but I disagree. I keep seeing this repeated and it just isn't correct. The flow of air in the system is dependent on the SUM of the restrictions upstream of the tool. You must add in the loss in each pipe, fitting and orifice to determine the total restriction upstream of the dust collector itself.

You're misunderstanding what I'm writing. My statements were ONLY related to the tool port, not the entire system. Youre absolutely right that the total flow through the system is determined by the sum of the losses in the system. However, you'll find this sum, at the very, very minimal pressures involved in home shop dust collection, are dominated by the narrowest point, regardless of length. So, effectively, you start out with whatever flow you can shove through the 4" port and then subtract the losses in the pipes all the way back to the impeller. If you're using 6" pipe, you'll find that the losses in the system are tiny compared to the restriction at the port. The system becomes dominated by the 4" port. If you increase the port to 6", you'll see a very significant increase in total flow because the 4" port was the most significant restriction.

In effect, if you're running 6" piping and terminating into a 4" port, you can safely ignore the contributions of the pipe and look solely at the port.

Of course, this is all physicist math where if it has the correct number of digits it's good enough.

Compressibility isn't particularly relevant.

It is at these very minimal pressures.

[Jim Andrew]

After considering the compression theory in dust collection I did some thinking about it. Appears that if you were going to try to compress air into a 4" port, the air would have to enter the port from a type of funnel shape, so that more air could be forced through the 4" opening. If you have a flat piece of metal, with a 4" hole in it, the flat shape of the opening would stop extra air from entering the port. Put some thought into that.

[Chris Parks]

There has been some work done in Oz after recognising that a bell mouth entry will increase the port flow.

[Ole Anderson]

After considering the compression theory in dust collection I did some thinking about it. Appears that if you were going to try to compress air into a 4" port, the air would have to enter the port from a type of funnel shape, so that more air could be forced through the 4" opening. If you have a flat piece of metal, with a 4" hole in it, the flat shape of the opening would stop extra air from entering the port. Put some thought into that.

You are on the right track. The efficiency of a square edge orifice is generally considered to be about 61% whereas a rounded entrance like a bell mouth is around 97%. http://www.buschusa.com/fileadmin/Co...An_Orifice.pdf

[Jeff Duncan]

Late to the party but you can have most hvac duct suppliers make any fittings you need….you just have to pay for them! I have mine made but they are a bit pricey. Now if I were doing a home shop I think I'd more likely buy some light gauge sheet metal and a rivet tool and get-er-done! No need to weld when pop rivets will do the trick just fine.

good luck,
JeffD

[Jim Andrew]

If you really want to spot weld, they sell spot welders at Harbor Freight. I make simple fittings, just a couple weeks ago made a 5" square to 6" round fitting. My wide belt sander was driving me nuts, having a 5" round flange on top of a 5" square duct inside the machine. So I used a dremel tool to cut the welds on the flange, and found the inside of the hole in the top of the sander was 4 1/2". Took my jigsaw with a metal cutting blade and trimmed out the hole square, matching the duct, had to file some to make it match evenly, then made a fitting from a piece of 8" pipe about 12" long. I used caulk and pop rivets to attach it to the top of the sander. When I figured the square inches of the 4 1/2" opening, which is 15.9, versus the square inches of a 5" square, which is 25, seemed I had no choice but to proceed with the change. The difference to 6" equals 28.269, so this is a big upgrade in the change. Just wish these machine companies would see fit to use 6" on as many machines as possible, especially sanders.

[Lee Schierer]

Don't forget that to get air out of a piece of equipment you also have to let air in. You need as many square inches of inlet as you have outlet, otherwise a larger diameter outlet is meaningless. You also have to have enough cfm capacity of your blower to overcome the losses and still maintain adequate linear feet per minute of airflow in the duct to keep particles suspended and moving along the pipe.