Fan recommendation

[John Pletcher]

I recently upgraded from the Epilog Mini-24 to the Helix and I believe I need to get a larger exhaust fan due to engraved images drifting left or right. I've cleaned the encoder strip and all is well for a short while, then the image drifting occurs again. When I remove the x-axis cover, there is noticeable dust build up present.

I'm working in a rather confined space, therefore the decibel level of the fan came into the mix. For the Mini-24 I chose a forward incline squirrel cage style fan that was rated at 400 cfm, but only 0.5" static pressure. It worked fine for the mini, but I don't think it has enough guts for the larger Helix.....apparently.

I'm considering the 1 hp unit from Penn State Industries that's rated at 660 cfm @ 5" static pressure. The reason I'm considering this one is the sound level is rated at 62 decibels, which is about what the Helix is. The other reason is, it's in stock. The larger 1.5 HP unit from Penn State Industries is out of stock. The one from laserbits is rated at 72 decibles, much louder. Does anyone have experience with the fans from Penn State Industries. I definitely need a larger fan, but want to be sure I get one that will meet my laser's needs and one I can live with.

Mounting the fan outside is probably not an option due to neighbors may complain about noise.

John

[Glen Monaghan]

First, I know practically nothing about the practical issues of cfm vs static pressure for laser exhaust purposes, so take the following with a large grain of salt.

I've been contemplating a new exhaust system to recirculate within the room rather than dumping conditioned air outside and your noise concerns mirror my own. Two lines of thought that I've been pondering but haven't seen any discussion on are regarding input and output of the exhaust.

For openers, watching the swirling, sometimes back-to-front-to-middle-to-exhaust port sort of smoke patterns inside the machine makes me think that the air flow patterns in the machine leave much to be desired. The volume inside of the machine is rectilinear and much, much wider than the machine's round exhaust port. For inside recirculation, the exhaust will be fed to a filter, typically rectangular and, again, much larger cross section than the laser's exhaust port. Then to the fan, which typically has a circular intake port. So you have to go from rectangular to circular to rectangular to circular, which seems pretty inefficient. The two circular sections (laser exhaust port and fan's port) are the smallest areas of constriction. Typically, going to higher cfm fans, you have larger ports (often 6" or even 8") but most of our lasers have a single 4" port on back. So that little 4" round port on the machine is a major bottleneck. My first ponderous pondering, then, is about the merits of removing the typical round exhaust port from the back of the machine and replacing it with a larger, rectangular port that spans most of the back of the machine. The new port could be about as wide as both the machine and the rectangular filter, possibly greatly improving air flow/extraction inside the laser and eliminating the inefficiency and bottleneck of funneling into and out of a 4" round port. Might also knock off a tiny bit of noise by reducing air velocity through that choke point.

The second pondering is whether any reasonably simple treatment of the fan's output can make a decent reduction in noise. The fan impeller is usually a major source of exhaust system noise because of the many sharp edges moving very fast. You definitely don't want a direct path (or even a decently reflective path) from impeller to eardrums. A baffle/muffler might be possible, but I'm of the impression that they typically produce a lot of back-pressure that would probably be detrimental to our exhaust system. I'm not versed in the tradeoffs of baffler/muffler operation, but don't want to constrict airflow or introduce turbulent noise, and so that's why it's just a pondering on my part... I'm more curious whether a simple expansion chamber on the output would make a useful reduction in perceived noise. Sort of like a "handgun silencer", providing a place where high speed air coming out of a (relatively) small opening (the fan's output hole) could expand and slow down before emerging into the room at large and assaulting our eardrums.

And of course, there's also things like minimizing large resonating flat panels in construction, using heavy sound-deadening pads on panels, eliminating sharp mechanical transitions, using the larger and slower impellers to move given volume of air at lower speeds through the largest ducting practical, etc.

[Joe Pelonio]

Try Grainger. Mine is an 8" but reduced to 4" and it's strong enough to suck out small waste pieces. They have a large assortment, and this one is quieter than the laser itself. About 2005 version of this, but was under $200 back then. My local store had it on the shelf.


http://www.grainger.com/Grainger/FANTECH-Inline-Centrifugal-Duct-Fan-4YM45

[John Pletcher]

Glen, Joe;

Thanks for you input. I come from the forest products industry and have worked many wood products companies. One in particular had an engineer on staff who's sole job was dust collection design. He even said that dust collection / vacuum systems are part science and "black magic". I know it comes to trade offs and the first system worked fine for my smaller system. I knew that forward incline fans are not really suited for dirty air streams, so I had no problem periodically cleaning the fan. However with the larger Helix, the fan just doesn't have enough cfm to adequately remove smoke and particulates from the cabinet, which have been causing problems with dibris accumulation on the encoder strip. I wound up ordering the fan system from Penn State Industries as it's rated at 660 CFM @ 8.5" static pressure and an acceptable 62 decibels. It's supposed to arrive sometime this week.

[Craig Matheny]

Try Grainger. Mine is an 8" but reduced to 4" and it's strong enough to suck out small waste pieces. They have a large assortment, and this one is quieter than the laser itself. About 2005 version of this, but was under $200 back then. My local store had it on the shelf.


http://www.grainger.com/Grainger/FANTECH-Inline-Centrifugal-Duct-Fan-4YM45

Joe I have looked at these fans before and I have wondered how much lose is there when you size down by 50% I looked at a fan made by the same company but 6" duct and it is only 20cfm less. What my thought is would that one lose less by stepping down to the 4" or is it irrelevent? Have to replace 2 units this summer. Plus how long have you had yours and do you clean the units?