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Chris Wright
04-20-2015, 1:29 PM
Hello all!

I have just purchased a 80w Trotec Speedy 400 and am in the process of figuring out the best way to vent the exhaust from the machine. We rented an office space that will allow us to blow it outside the building but have read about concerns with noise to neighboring businesses and filtering the exhaust because of the smell.

I was recommended a Penn State 2hp blower and was wondering if anyone else could shed light on if a noise suppressing box for the blower might be needed or how you vent your exhaust out. I read that aluminum or galvanized metal is recommended for hosing and was also wondering where you guys might have purchased any other accessories needed.

Thanks so much for your help. Excited to join the laser engraving community!

Bruce Clumpner
04-20-2015, 1:37 PM
I run a muffler made for hydroponic farming, it just clamps on to my 4" flex tubing exhaust out under my garage door. It cut down the fan noise considerably, and is fairly cheap. My neighbors certainly appreciate it too...

Bert Kemp
04-20-2015, 3:47 PM
My neighbors put an electric fence 40 feet from their house to keep their 3 horse's down on my property line 15 feet from my back door. they poop everywhere and the flys will pick you up and carry you off, never had flys till they moved in and the stink they never clean it up just leave it there, so I really don't care about the noise as if they could hear it anyway.Wish I could get the wind to blow towards their house when I'm cutting leather.:eek:

Tim Bateson
04-21-2015, 10:09 AM
I have mine in another room to help me - it's up against the outside wall. Until I told a neighbor last year he thought it was just our cloths dryer. However I rarely do much that smells bad. It's been 7.5 years, so far no complaints & I live in a very strict HOA community (subdivision).

Mark Sipes
04-22-2015, 1:20 PM
The requirment of the Trotec 400 for exhaust is 177 cfm minimum the 2hp blower you are looking at is rated at 1360 cfm the 1 hp is 660 cfm . more than enough unless you are pushing the air a fair distance noise factors are 72 and 62 db.... the noise created when 2 people are talking. The smell of the material is your major factor as I see it. You did not mention the items you would be cutting/rastering. Rubber stamps (worst) ----- aluminum (least)


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Scott Shepherd
04-22-2015, 1:29 PM
The requirment of the Trotec 400 for exhaust is 177 cfm minimum the 2hp blower you are looking at is rated at 1360 cfm the 1 hp is 660 cfm . more than enough unless you are pushing the air a fair distance noise factors are 72 and 62 db.... the noise created when 2 people are talking. The smell of the material is your major factor as I see it. You did not mention the items you would be cutting/rastering. Rubber stamps (worst) ----- aluminum (least)


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I don't think that number is accurate. My belief, from extensive testing with some very high dollar equipment, is that when laser manufacturers spec something in CFM, they mean INSIDE their cabinet, meaning you want 177 cfm INSIDE the cabinet. That's VERY different than 177 CFM. If I owned a Speedy 400, I'd be looking at a 1200 CFM blower, which, in my testing, gives about the right amount of suction inside the cabinet.

Keith Colson
04-22-2015, 4:17 PM
Scott is right 177cfm in the vent pipe would do nothing.

I have a 3 phase 1.1kw blower and it is perfect for me. With a VSD I can dial in the amount of air flow and noise I want to make. Typically I run it at 80% power but for those smokey jobs I can crank it up to 120%. The noise is not the motor but the air going through. I found that rigid ducting is so much quieter. Flexible plastic ducting lets a lot of the noise out.

Running at 80% speed I get less than 70db but if I crank it up to 120% i can make a terrible racket around 90+db. This is where the VSD is awesome, you can tune it to be quiet so you don't bother people around you.

Cheers
Keith

Mark Sipes
04-22-2015, 4:30 PM
Maybe Trotec Corp. will add to the comments for their system... they state 300 m3/hr is a minimum

Scott..Please explain how 177 cfm going in and 177 CFM going out is different in volume calculations. If your statement is correct in the abstract.... then 3000-4000 cfm in should get you 1300 CFM out ?



My table is 17" x 29" x 6" for plastic that is 1.4' x 2.4' x .5' = 1.68 ft3 . at 177 cfm I should get 105.4 air exchanges/min or 1.75 x/per sec. at 1300 I am vent the room/house.

Scott Shepherd
04-22-2015, 6:38 PM
Maybe Trotec Corp. will add to the comments for their system... they state 300 m3/hr is a minimum

Scott..Please explain how 177 cfm going in and 177 CFM going out is different in volume calculations. If your statement is correct in the abstract.... then 3000-4000 cfm in should get you 1300 CFM out ?



My table is 17" x 29" x 6" for plastic that is 1.4' x 2.4' x .5' = 1.68 ft3 . at 177 cfm I should get 105.4 air exchanges/min or 1.75 x/per sec. at 1300 I am vent the room/house.

Mark, you lost me on that calculation there. If I were to try and explain it, I would botch the technical terms horribly and confuse the issue even greater. I spoke at length with a number of higher ups at Trotec about it, I spoke to a number of people at other manufacturers as well. I came to the conclusion no one knows much about air flow and they don't want to.

We had an issue where we were helping someone with an airflow issue (lack of airflow in certain parts of the table). We brought in an airflow engineer that had measuring devices that costs $1000's of dollars. We started with a 1200 CFM blower, then went to 1,800, then to 2,300 CFM, even had a 300 CFM machine that had really high static pressure (18-19 if I recall correctly). While all that was going on, we were taking measurements inside the cabinet. The problem is, with all the changes, it didn't change the air speed coming through the cabinet.

We heard all the "you're pushing the exhaust too far" (it had to go up 2 stories) and "you have too many bends in it", "You need smooth pipe, not rippled". In the end, everything that all the experts said would solve the issue didn't move the needle. We were told things along the lines of smooth wall tubing would get you a 20-30% increase, when, in fact, measured, it got us less than 3%.

In the end, in my opinion, all that is non sense. It means nothing. Want to know what means something? Air speed. If you hit 180 fps (I think it's fps, not ips, I'd have to look at my notes from when it was happening), then the smoke cleared the cabinet really well. Didn't matter if it was a 45W single port laser or a 100 w double port laser. If you were down in the 150 fps range, you'd start seeing smoke drift up to the lens opening in the head, which was bad. Any time you got to 180 fps, then the smoke pulled through excellent.

It was in extensive talks with the air flow engineer where he said that the specs were not for the blower, they were from inside the cabinet. He explained why that would be the case, and it made sense at the time. Unfortunately, I'm not smart enough to recap what he told me :)

Scott Shepherd
04-22-2015, 6:57 PM
That might be fpm, not fps. I'll see if I can dig out my reference material and find it to clarify.

Bill George
04-22-2015, 8:05 PM
That might be fpm, not fps. I'll see if I can dig out my reference material and find it to clarify.

fpm feet per minute = air speed cfm cubic feet per minute = volume of air being moved
air has weight and it varies as to relative humidity.
I probably could find all my air flow books someplace, but I think we found out last time, as you pointed out none of the factory engineers really had a clue.

Mark Sipes
04-22-2015, 8:11 PM
I pull my air 3 ft and push it 1ft. 4 foot run from table to outside.


Scott - "you're pushing the exhaust too far" (it had to go up 2 stories) and "you have too many bends in it", now we are talk resistance to air flow. that's a whole different issue. isp, fpm, fps is not a measue of volume but rather resistance to flow.


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Scott Shepherd
04-22-2015, 8:37 PM
Scott - "you're pushing the exhaust too far" (it had to go up 2 stories) and "you have too many bends in it", now we are talk resistance to air flow. that's a whole different issue. isp, fpm, fps is not a measue of volume but rather resistance to flow.


Mark, I only mentioned those things to illustrate that all the things we were told would correct the issues didn't make any measurable difference. In the end, air speed was king and without it, no matter what the configuration, it wouldn't clear the cabinet.

Mark Sipes
04-22-2015, 9:07 PM
How does this help Chris...... Chris... how far do you need to move the exhaust to vent to the out side?. how many turns will the pipes be making? what is the height difference from machine to vent?



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Mike Lysov
04-22-2015, 10:58 PM
My blower makes up to 70db noise but it produces this level of noise when it is connected to a laser with plastic hoses.
It was much louder(about 80-85db) when I took it out brand new of its box and tested its noise level disconnected.

Tim Bateson
04-23-2015, 8:51 AM
For what it's worth - My in-box air flow increased when I switched from metal piping to PVC. I might add, when I switched to PVC, I also increased the run 2x.

My unscientific test - Start smoky job, then turn on the blower:
Short run with metal piping - smoke would be pulled out, but at a lingering pace.
Long PVC run - smoke is yanked out.

Scott Shepherd
04-23-2015, 9:17 AM
How does this help Chris...... Chris... how far do you need to move the exhaust to vent to the out side?. how many turns will the pipes be making? what is the height difference from machine to vent?

None of that matters Mark, that's my point. The number of turns and the height different to machine made no difference.

We had a 2,300 CFM blower hooked up, running over 2 stories of metal pipe, measured it, unhooked the metal pipe so there was no run of exhaust pipe, other than 5 feet from the machine to the blower, and it didn't change any numbers at all inside the cabinet.

My point in raising any of this was merely based on the information that was provided telling him that 300CFM was all that was required. Yes, that's all that's required INSIDE the cabinet, not on the spec of the blower motor hooked to it. Two VERY different things.You won't get 300CFM inside the cabinet with a 300CFM rated blower.

Mike Lassiter
04-23-2015, 9:23 AM
something else to consider is if you are using a cutting table and the air is being pulled through it then you lay a full size sheet of material on top of it. You have the proper sized blower and ductwork, but you just choked the airflow by covering the cutting table. It is like having a dirty plugged filter on your central heat & air unit. How can it breath?
Having the potential to move 1500 cfm but restricting the inlet (cutting table covered) will not let 1500 cfm flow.

Bill George
04-23-2015, 11:56 AM
something else to consider is if you are using a cutting table and the air is being pulled through it then you lay a full size sheet of material on top of it. You have the proper sized blower and ductwork, but you just choked the airflow by covering the cutting table. It is like having a dirty plugged filter on your central heat & air unit. How can it breath?
Having the potential to move 1500 cfm but restricting the inlet (cutting table covered) will not let 1500 cfm flow.
Amen.
The design of the machine air intake is very important. You are in effect designing.... in Reverse a supply air diffuser or register. They are designed for face velocity and throw to cover the wall or window or whatever you want to cool or heat with air. In the case of a air intake only under the cutting table, you need a way to bring in air from other areas of the machine, and a way to open and close those air intakes is needed. The more you restrict the air intake the higher negative static pressure and there is a limit as to how as to much air (cfm) a forward curve fan can move. Most if not all published fan ratings are in "free air", you need the fan curve to see what happens in a real world situation.

There is "friction loss" in pipe, fittings and anything else in the air flow path. That was proved by Tim when he replaced the metal pipe and fittings in his system with PVC.

Scott Shepherd
04-23-2015, 12:16 PM
There is "friction loss" in pipe, fittings and anything else in the air flow path. That was proved by Tim when he replaced the metal pipe and fittings in his system with PVC.

I'm not sure I agree with that totally Bill. I agree there is friction loss in pipe, but going from metal to PVC, I can't imagine it's a noticeable difference. In fact, I saw less than 3% difference in any style pipe. That was going from a ribbed pipe to a smooth pipe. We took elbows out, smoothed out the entire intake side of things. Didn't make a difference. I suspect there's a point in which no matter what you do, not much changes, and that's because you're pulling such a high CFM through a system. I suspect at lower CFM's, you'd probably see more noticeable results, but that's just my gut feeling.

I have a number of youtube videos that are private from when we did some of the testing. I'll watch through them when I get some time.

I don't disagree with the theory, but I think you can pull so much on a system that changes start to become very minor. A 2300 CFM system on a laser with a 4" duct, that's then necked down to 19 sq. inches of intake inside the cabinet and 18 sq. inches from the front of the cabinet (letting fresh air in) is going to struggle to show any improvements, I think, because you're maxing out the system, so to speak (although not technically maxing it out, but rather pushing past the top of the bell curve).

Scott Shepherd
04-23-2015, 12:43 PM
I think the number is 580 fpm inside the cabinet. That's where we saw smoke clear on various machines. Forget any numbers I stated earlier, they were from memory (or lack there of). I just watched a video again.

Bill George
04-23-2015, 12:51 PM
You can't push or pull 2300 cfm (cubic feet per Minute) normally thru a single 4 inch pipe. It would need to be a special (expensive more Hp) blower designed for high static pressure. Why not just go to a larger pipe to more air with a standard blower?

Scott 600 fpm is not a un-realistic number for a standard blower system.

High static, high velocity HVAC systems do use flexible and hard PVC piping. OK it might not be PVC because of the fire hazard, but it is plastic.

Scott Shepherd
04-23-2015, 1:16 PM
Bill, their system is lower CFM, but it pulls 5,800 PA, or about 24 inches of water (if I said that right). They said that high static pressure would solve the problem. It didn't. It got worse. The high CFM, low static pressure out performed the low CFM high static pressure system by a significant amount.

That's when I came up with measuring the air velocity and determining what actually worked in real life, rather than on a computer sitting in an engineering lab. What I did learn is that 580 fpm, smoke clears properly from all the systems I tested. Below that, not so much. Didn't matter what was pulling the air through it, high or low static pressure, it just mattered that it was hitting that magic sweet spot of 580 fpm.

I'm sure someone way smarter than me can tell me why it works and map it all out, but for me, I just needed to try and get it working and that's where we ended up.

Bill George
04-23-2015, 3:52 PM
Scott it does not surprise me that a person in the field doing what you did, solved the problem. I will take someone who tries it out and makes changes until it works over someone who just has the book learning like some engineers I had to work with. Maybe next time they need to come and ask you what to do!

Static pressure is the air pressure pushing outward on the duct walls and out any openings. On the intake side of the fan, its the opposite.

SP is measured as Inches of Water Column. Most commercial HVAC systems have 5 IWC or less, residential usually less than 2, exhaust systems.. well I have never seen them at 24 but...

Kev Williams
04-23-2015, 4:32 PM
I'm sure I'm in the minority here, but it seems like way too much rocket science for sucking some
smoke out of a metal box... ;)

I have a sure fire method that works great for me-
If the blower I'm using sucks out all the smoke, I'm golden :)

Scott Shepherd
04-23-2015, 4:57 PM
I'm sure I'm in the minority here, but it seems like way too much rocket science for sucking some
smoke out of a metal box... ;)

It is until it's your box it won't suck smoke out of ;)

Bill George
04-23-2015, 5:18 PM
You know Kev, that's kind of the way I look at it. I hooked the blower up... the one I had on hand to the new to me ULS and the smoke went outside. True its a little noisy but working is the key word. I need to get back to work, had a large order come in and the promise of another Monday.

Mark Sipes
04-23-2015, 6:34 PM
With all said....... I hooked up a 2 hp blower to my machine and ran it the 4 feet to the vent and the material on the table keep getting sucked into the exhaust. Solution was to run 87 feet of pipe around the room from the table and then out the vent. That worked......then I woke up from this nightmare and went to my laser that runs a 300 cfm inline fan and went to makin' money.



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