On to ventilation:
We use 2/3 of our 3 car garage for glass & jewelry and after settling on where to put things I revamped the old cross breeze ventilation.
I read everything, all the new and old threads and have seen plenty of vent hoods in biological and chemical labs where I do calibrations. I've even had experience with mapping the flow.
At the end of the day, I opted for funnels to keep things more open.
1 big problem to overcome is the layout:
No window, we have a back door and the 2 garage doors, bedroom above the garage and wall-wall, floor to ceiling cabinets on the side walls.
This pretty much required me to make a semi-portable system that me or the Mrs could put together quickly and easily plus be able to stow away neatly.
Vent size: I experimented with 4, 6 and 8 inch vent. 4 is worthless, 6 and 8 are very close as far as CFM, mainly limited by the size of the fan, but for a funnel I want increased velocity going into the opening, as well as adequate volume, so I went with 6 inch.
Fan: I know that radial fans are best for moving gas. I also needed to pull air thru 2 funnel openings and I had to decide on one big blower or 2 smaller ones.
I decided on a sawdust extractor from harbor freight to get the blower out of, plus I got a bunch of other re-purpose-able hardware.
http://www.harborfreight.com/2-hp-in...tor-97869.html
It claimed to have 1550 CFM which is more than double any other single 6 inch, and lots of 8 inch, axial blowers I could find.
The inlet is a tad over 5 inch, so I used a 5-6 inch adapter and a clamp to get it to 6 in.
I mounted it on a small dolly but sat it on another one to lower the inlet..this is temporary and the duster can is for scale.
Basic construction: I cut a hole in an old folding table and ran the duct down thru it, using 1 90 deg bend to turn and go straight back to a place to connect a 5 foot section with a 90 deg bend that connects to another 5 foot section that goes to the fan inlet. This puts the blower further away to hold down noise. The outlet runs down a long hose that gets shoved under a little trailer parked there.
The top of the duct turns with a 90 deg, then to a “Y” where I used flex duct and 6 to 8 inch adapters for the funnel inlet. The funnel inlet is 10 inches from the torch tip.
I used screws anywhere there was stress on the connection.
My thinking was that with the air column falling down and out, rather than up and out, it would reduce the pressure and pull more air.
For our surface we've always used 2x3 granite slabs we got at Home Depot with bent-just-right aluminum door flashing around the back and sides to stop the random glass skittles.
Here's pics of the whole thing:
Performance:
I used an Omega airflow meter to get velocity and CFM measurements.
Velocity is directly measured ( I looked for a sustained peak)
CFM is taken over a 60 second average all over the vent opening, which is set in the instrument to 8in dia. before the measurement.
For measuring the CFM and velocity away from the inlet, I used an imaginary 8 inch diameter “tube” coming straight out of the 8 inch funnel opening, extending to the torch tip.
I work well within an 8 inch diameter area around the flame and was interested in my actual work area.
Here's the results:
Notes:
The pull of the funnel changes the flame.
It tightens it a little bit if it's a strong flame, but a soft flame is slightly bushier. We both use Alpha's.
The extra air blowing over your work seems to cause striking glass to strike quicker and changes how reduction glass changes colors.
It's cooler at the end of the flame.
The intake noise makes talking to each other hard but headphones are nice too.
I set closest to the garage door and can't really hear the fan over the intake noise.
I added a good remote switch, to turn the blower on and off from the bench.
Plenty of real life suction. It can easily pull a big “yellow” flame in and can slightly “bend” a reduction flame.
When I was testing with incense, our son came out to look and mentioned you smell it outside but not in the garage.
We both feel slight air movement over our shoulders.
The funnel and all connections stay cold. The flame stops about 3-5 inches from the opening, depending on what I'm doing.
If you needed to move your torch up or down very much, the flex vent is adjustable.
Good Luck!
-Jim