Some info about cfm calculations

Anything to do with air assist, vacuum tables, fume extraction and related...

Re: Some info about cfm calculations

Postby a542002 » Wed Feb 01, 2012 10:50 am

Hi guys
I have try pretty much every version of exaust fans but the only one who really works especially with cutting is the shop dustcollector from harborfreight
like this http://www.harborfreight.com/garage-sho ... 94029.html
without the bag direct connected to the machine and the outside. this thing pulles away everythings and mostly I dont need a air assist wher I use this one http://www.harborfreight.com/1-5-hp-58- ... 95630.html. this works perfect too
I will take a few picture here they are sofar my temporary setup.
greetings
walt
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Re: Some info about cfm calculations

Postby Liberty4Ever » Fri Dec 21, 2012 8:40 pm

I'm specifying an exhaust blower for my 2'X4' laser. I've read the posts in the laser exhaust threads a couple of times before, but I just read them again as I'm now making the purchase. My business has grown to the point that I'm bumming eight hours of laser time on my friend's laser every week, and I'll never be able to repay him for that, not to mention that it's a hassle to pack everything up to lase my parts across town.

One option I looked into was an air mover from a home central heating and air conditioning unit. Apparently, some of them are 120 VAC... maybe the air movers used for gas furnaces as opposed to heat pumps. My brother works in the HVAC industry, and might be able to snag me a used HVAC blower for free, but I have doubts that they'll be able to push enough air against the expected static pressure. I have another friend who has a good knowledge of this sort of stuff and he assures me that the performance would be weak. Apparently, even though HVAC air movers are designed to move a lot of air, they do that through a large cross section of air ducts at a relatively low velocity. An HVAC fan would probably move more air through a laser than some of the smaller fans that are being discussed, and may provide adequate exhaust for a laser, but would certainly be bigger and less efficient than a more suitable blower.

I plan on using make up air from outside so I don't pull all of the heated or air conditioned air from my shop. To avoid condensation, I'll only run my laser when it's not raining or very humid outside.

Based on my laser use, I know that I definitely don't want a marginal exhaust system. I don't want the smoke and debris hanging around and depositing on linear rails, timing belts, bearings, stepper motors, optics, etc.

The laser I'm using now has a nice Dayton industrial blower but the exhaust is weak. I think that blower is running with the blades mostly stalled - spinning but not moving much air because the back pressure is too high.

I guess I'll go with the 1 HP Hazard Fraught dust collector.

http://www.harborfreight.com/13-gallon- ... 31810.html

BTW - Search for "Harbor Freight coupons" and you can always find an online coupon to use. I just found a 20% off coupon. I'm taking it to my local store, although they may claim that the dust collector is already on sale for $10 off (less than 10%) so the 20% off coupon isn't valid. There's also a good chance that they won't have it in stock, and I'll need to try back later.

I have no doubt that the inline centrifugal blowers will work well, and they look like better quality at a comparable price to Harbor Freight, or maybe even slightly less expensive, but I've learned a few things using and maintaining my friend's laser for over six years. The materials that I cut produce black powdery debris that's a mess, or black oily gunk. Cutting acrylic and similar plastic sheets results in light gray-white powder that's very abrasive. I'm going to design my laser with the simplest exhaust path possible, and I'll make sure that the entire exhaust path is accessible for cleaning and maintenance. I'll be using my laser a lot and I cut some nasty stuff. I absolutely wouldn't want the exhaust motor in the exhaust path. I guess if the inline blower was inexpensive enough, I could replace it every year or so, but I'm trying to design my laser to require very little maintenance. If you're cutting cleaner materials and it's a hobby laser that you don't use very often, some form of inline exhaust may be your best option. If you will be creating a lot of greasy or gritty debris, I'd keep the exhaust motor out of the exhaust flow. I feel pretty good about the reliability of an exhaust that's designed to move air containing 50 gallons of sawdust and small chunks of wood per day. I might need to de-gunk the impeller blades and housing once or twice a year, but I could live with that.
Apparently, I didn't build that! :-)
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Re: Some info about cfm calculations

Postby a542002 » Fri Dec 21, 2012 8:48 pm

Hi there
you will be suprised with the HF exaust I have one and it drives you nuts from the noice and the craZY PART IS THAT IT DOES NOT MOVE MORE THEN THE INLINE WHAT i HAVE SHOWN . the noice on this is like what you hear from a good A/C house unit.
I can tell you my machine's running pretty much 8 to 10 Hr a day 6 days a week and the price with $ 80 on ebay is the best.
greetings
waltfl
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Re: Some info about cfm calculations

Postby Liberty4Ever » Fri Dec 21, 2012 9:30 pm

a542002 wrote:I can tell you my machine's running pretty much 8 to 10 Hr a day 6 days a week and the price with $ 80 on ebay is the best.

Do you have a rough estimate of the hours that your inline centrifugal fan has run since installed, presumably with no replacement and little or no maintenance? Also, what materials are you cutting? I cut some nasty stuff with a lot of gritty/greasy particle generation. It's pretty much six hours at a time, with an opaque cloud of smoke 1/2" thick and 6" wide at the exhaust on the edge of the laser bed. The exhaust port on the laser is filthy when I'm finished. I can only imagine what that'd do to the bearings in an inline exhaust motor. I assume the greenhouse blowers are designed for relatively clean air, but I guess it's possible that the dirty exhaust air might move around the motor instead of through it.

I definitely like the looks of the inline blower much more than the Harbor Freight dust collector, and it'd be easier to install, lower noise and the smaller inline blowers are cheaper, although I'd probably want the 6" or 8" inline blower.

It definitely has a lot going for it, if I could just overcome my fears of an early death from eating greasy gunk.

Considering that I usually pick up some takeout Chinese food and a large Mt Dew when I travel across town to use my friend's laser, I may also be at risk for an early death from eating greasy gunk. :o
Apparently, I didn't build that! :-)
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Re: Some info about cfm calculations

Postby a542002 » Fri Dec 21, 2012 9:49 pm

Hi there
I would say it runs since 14 month what means around 2500 hr now and I cleand them ones after 7month.
I got the 6 inch version with 500 cfm and reduced it to 4 inch on both sides.
greetings
waltfl
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Re: Some info about cfm calculations

Postby Liberty4Ever » Fri Dec 21, 2012 10:18 pm

Over 2000 hours with only one cleaning sounds great. That's probably 10 years at my current usage. I expect a lot more laser time for some future products, but most of that will be laser engraving black anodized aluminum or black oxide steel, which essentially produces no smoke at all.

The only reservation I have is that you might be cutting or engraving something that is fairly clean. Can you tell me what you're cutting, or how much smoke it produces and what type of debris collects in the exhaust system?


PS - This would be a good time to again state my appreciation for the great info shared in this forum, and my appreciation to Bart for providing this forum so we can share ideas, experiences, and inspiration.
Apparently, I didn't build that! :-)
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Re: Some info about cfm calculations

Postby a542002 » Fri Dec 21, 2012 10:35 pm

Hi there
I am cutting everythings from 5mm bamboo over 6mm acrylic to cardboard and painted stainless and aluminum. I also engrave all of this materials
the only what realy needs to be cleaned are the conector hose and the exit box from the laser there is pretty much nothing in the fan itself
greetings
waltfl
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Re: Some info about cfm calculations

Postby Liberty4Ever » Sat Dec 22, 2012 7:31 am

OK Walt. I bought an inline exhaust blower. If I don't like it, I'll sneak over to your house, break in, and leave a LEGO brick where you'll step on it barefoot. :)

I got an 8" inline blower. I'm building a 2' X 4'+ laser, and I want to make sure I get good ventilation. With make up air from outside instead of pumping out all of my heated or air conditioned room air, I don't guess there's any such thing as too much exhaust... unless it's picking up materials off the laser bed.

Here's the blower I just bought for $85.

http://www.ebay.com/itm/320912753715

Code: Select all
Features:

• Versatile - Suitable for use in various environments such as indoor growing rooms, clean-rooms, commercial filtration, cooling, air-scrubbing and ventilation, or anywhere a premium-grade inline fan is needed.

• Premium grade motor - Used precision wound motor and sealed bearing system; designed for continuous use.

• Superior air flow - body shape and ducted fan are designed for maximum efficiency, and to overcome long ducting or dense filtration. Body halves are sealed to eliminate loss.

• Squirrel-cage turbine - Contains 11 curved impeller blades, each measuring 3.25" x 2.5".  Blades are weighted and balanced within cage to ensure fan will operate vibration-free.

• Low noise - Impeller blades spin with convex side forward for whisper quiet operation

• Metal construction - Built-to last, sturdy metal housing and turbine impeller. Won't break or become brittle like plastic units. Powder coated frame to withstand high-humidity environments

• Easy Installation - Includes 2 removable legs / standoffs for easy mounting. 1" deep lips/collars for easy connection of ducts.


Specifications:

Input power: 120 Volts / 60 Hz
Connection size: 8"
Overall dimensions: 13" x 13" x 9"
Power: 198 watts
Motor: 1.72 amps
Speed: 2,530 RPM
CFM: 760 (true rated CFM, other dealers quote 1,200+ CFM for this blower)
Static pressure: 5.01 millibars
Noise: 55 decibels


My laser will be a few inches from an exterior wall. I'm going to cut an 8" hole in the exterior wall and run a piece of 8" stainless vent pipe through it. The entire run will be about 12", angled downward so any water tends to run out, not in. I don't expect much resistance in the short smooth pipe, so there shouldn't be much static pressure and I should get excellent air flow. I'm planning on having some sort of hinged plate sealing off the outlet on the outside wall, sort of like the louvered shutters on a dryer vent. I'll buy one for an 8" pipe if I can find it at a decent price. Otherwise, I'll build one.

I'll post more info and pictures on my build log once it's up and running.

Thanks for pointing me in the right direction.

I like buying hydroponics air blowers on eBay, where all of the sellers assure the buyers that the transaction will be discrete and the merchandise will be shipped in a discrete plain box. Discretion is good. :)
Apparently, I didn't build that! :-)
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Re: Some info about cfm calculations

Postby educa » Sat Dec 22, 2012 10:34 am

a542002 and others, I see you guys have quite a low of laser hours per week. Mind to share what you guys cut? You have a webshop or so ?

I would like to setup a webshop too in the nearby future. The laser allready works but I'm refining it right now.


Kind regards,

Bart
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Re: Some info about cfm calculations

Postby a542002 » Sat Dec 22, 2012 10:42 am

Hi bart
42Hr a week is not low. like I mentioned I am cutting lots of different materials like wood mainly bamboo and oak, acrylic, for boxes, figurine, special parts in acrylic for customer.
no I dont have a webshop anymore because I try this and the respond is not enough there are to many out there. I sell my overflow on crafts shows and farmers markets and this works better then i can do in a week.
the most sold items are engraved ones.
greetings
waltfl


educa wrote:a542002 and others, I see you guys have quite a low of laser hours per week. Mind to share what you guys cut? You have a webshop or so ?

I would like to setup a webshop too in the nearby future. The laser allready works but I'm refining it right now.


Kind regards,

Bart
a542002
 
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