There has been a lot of discussion on extraction systems. Now mine is complete I thought I would document it and explain why I did things the way I did. I am always interested in constructive feedback too. My main goals were, clear the smoke, be quiet and be stealthy.
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The extraction begins with two 100mm PVC pipes going directly through the wall with a 5 degree down slope so any rain cannot run down the outside of the pipe into the house or laser machine. I also did this so the machine could be very close to wall which uses less space in my "full" workshop
I then made a custom adapter that joins the two 100mm pipes into a single 200mm rigid galv steel pipe. It is very smooth with little obstruction to airflow.
The 200mm pipe goes into the blower which turns the air 90 degrees. The 3 phase blower is rated at 1.1Kw when run at 50 Hz. It then runs off into some flex. The flex is there to handle any water that goes down the chimney, It has a small hole in the flex to let water out. The flex is the nosiest part of the system. If I wanted to drop the noise further I would need to replace it with rigid ducting.
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From there it goes straight up the side of the house and vents out at about 15 degrees off vertical. This blows the waist air away from the house and sends the air upwards which makes the smell at ground level non evident. I also painted the chimney and custom chimney brackets to match the house so it did not look "industrial" in appearance. The fasteners are inside the pipe too. The standard rigid brackets are really ugly.
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There is no cap on the chimney. Adding a cap increases the sound level a lot as the sound is turned horizontal. Also a cap would obstruct the air flow and stop it projecting upward. The system is designed to accept rain down the chimney with the integral drain before the blower.
By adding a VSD, the blower can be very quiet or very loud depending on how hard I run the motor. I did some airflow measurements "inside the cabinet" as shown in the picture, here they are.
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40Hz = 3.4 m/s 670 ft/min
50Hz = 4.2 m/s 827 ft/min
65Hz = 5.5 m/s 1083 ft/min
When cutting acrylic I typically run at at 40Hz. When running wood or thick acrylic I crank the speed up to 50Hz and if I get something extra smokey I set the motor for 65Hz. It is really noisy when I do this but the airflow is great. I still need to make a weather cover for the motor etc to complete things but I figure another winter like this will be okay.
This is how it looks from the road. Barely visible.
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Cheers
Keith
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