need tips on improving air flow.

[Martin James]

Greetings. I am considering changing the flow pattern in my laser by chopping a hole in the top and hooking up my exhaust there. My table is large (900x1200) and there is a lot of smoke seepage on all the doors which is bothering me as I don't want to breath it. My exhaust system is based on a dayton 1/4-1hp two speed motor with dayton paddle wheel blower. This is the best motor/blower combo for high back pressure. The combo is rated for 1450cfm. @0. I don't remember the specs on the back pressure ratings, but it is the best that granger sells for the type of system. The blower sits inside against the wall and is hooked up to a plenum from which we normally have runs of flexible aluminized ducting. The run to the laser is about 20-25 feet of 8". I have purchased solid galvanized 8" pipe to replace the flex and I am planning to add several miles of weather stripping inside the laser box. These upgrades should increase the airflow. What I want advise on; is that the current factory exhaust it hooked up to draw from under the table, and I am considering moving it to the top of the box. I just figured that some of the smoke is being drawn out through the factory port, but and smoke that is left in the upper part of the laser box is rising and trying to exit through the cracks.

Normally I have to be careful when working with my system when using, for example. a polishing motor. If I were to be careless with a rag or light weight tool it might get sucked up into the flex hose. Even if I tape paper across the pass through blocking it off, we are definitely not seeing the top plexi pull in.

Thanks in advance for the comments
Cheers Marty

[Keith Winter]

If you have sufficient suction from your blower you don't need the upper flow. Granted all chinese machines vary but I use the downflow and it's golden on my 900x1400 machine. You mentioned stuff being sucked in? Is there no grate in the laser before the grate? If not then use chicken wire to add one.

Flex is aweful for air flow, you are are the right track there. How many turns and at what degrees are those turns? Have you measured your blower, is it putting out what it's rated? Is the 8" on both the in and out? You could also potentially be suffering from the opposite of what most people have happen when they use 4" pipe. 8" pipe might also be too big of a pipe for your blower....1-1/4 hp is pretty tiny. Bigger pipe is great for increased airflow but if you have a tiny motor trying to pull down a big pipe that can cause issues as well, the air doesn't move fast enough in that case. I would imagine it's plumbed with a 5" or 6" port at the blower, what is the port size actually on the blower? More more suggestion, I'm not familiar with your blower, but you could upgrade to the 2hp $200 cheap blower at harbor freight. I have that on 2 speedy 300 machines running 6" pipe to them it's good, it could handle your 1 machine, no problem.

[Kev Williams]

If your blower's got the pull, go to 4" pipe, at least for 6' from the machine to a reducer. I'm sure some will debate this, but the smaller tube will move the air faster, and faster moving air will find and draw your smoke more efficiently.

Where does the draw-air come IN to the machine? On my Triumph there's a 1-1/2" tall slot along the back of the machine where air comes in. The exhaust is a 6" hole towards the bottom in back. I have 2x4's blocking off all but about 10" of the slot on top. Just doing that creates more 'breeze' and the smoke moves away quicker. What I've been going to do (and you might try this) is to run some 4" dryer hose thru the exhaust hole to the FRONT of the machine and seal off the excess hole...This way the air has a path from back to front, and will get moving pretty quick, and should draw the smoke much better. I'm just using the smaller HF 'green' blower.

My LS900 isn't tiny by any means, it exhausts from the back (same HF blower) and draws air in from between the door space and the table. With the door wide open, it pulls exhaust back nicely, but shut the door and the velocity picks up big time, and smoke just flies straight back. Same should apply with our chinese machines, just need to fix the air pathway and speed. :)

[Martin James]

You mentioned stuff being sucked in? Is there no grate in the laser before the grate? If not then use chicken wire to add one.

. How many turns and at what degrees are those turns? .

Hi Keith thanks for the reply. You are right the flex has a very poor friction coefficient. We use the flex because you can move it to any location in the shop and hang it with string in several minutes.

Grainger does not sell the model blower we have any more, but it is similar to the least expensive high pressure model granger currently carries.
I have attached several screen shots of their current cheapest model. These blowers are all about static pressure.
Ours has a cfm of 1450 @ zero SP, and if I remember correctly it is rated down to 4 or 5 inches of static pressure. This is 8 to 10 times more than most radial fan blowers. I think with the metal work we spent $1200. I do have a delta dust collector in the woodshop and the granger is much more industrial.

The blade in the blower is 10 inches cast aluminum. Grainger sells different shaped blades for different static pressure requirements. Ours was rated on the less pressure more speed side. It is very helpful to have the 1/4 speed in the winter for jobs that don't require so much cdm, (like soldering electronics)

I don't have an issue with the blower sucking things out of the laser. I just mentioned that the system, which we use for all not hot exhaust stations, will suck hard enough, from the end of the 8 inch flex, to pull things in. Most of the run is up, so objects rarely go all the way to the blower, instead the hover half way up rattling till you shut the blower off.

One of the reasons I thought about moving the exhaust to the top is that this would avoid the 90 degrees of direction change we have currently with the exhaust coming out of the bottom of the laser in a downward direction.

It seems to me that the downdraft system probably pulls the soot away from the piece in a better fashion than if the suction was from the top. And also keeps more smoke away from the lenses.

I guess I can always cut the hole to try suction from the top and then plug the hole if I don't like the way it works.

thanks Marty
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[Rich Harman]

If your blower's got the pull, go to 4" pipe, at least for 6' from the machine to a reducer. I'm sure some will debate this, but the smaller tube will move the air faster, and faster moving air will find and draw your smoke more efficiently.

Yes, I will debate. A smaller pipe will increase velocity - inside the pipe. It will not increase the volume of air moved through the pipe and it will not evacuate air from the cabinet any faster. Changing from 6" to 4" will double the velocity of the air in the pipe. Friction losses will be greatly increased. It would be less effective and efficient.


Bigger pipe is great for increased airflow but if you have a tiny motor trying to pull down a big pipe that can cause issues as well, the air doesn't move fast enough in that case.
Oversized pipe should not be a problem for smoke evacuation. It can be a problem for dust and wood chips because you need an adequate velocity to keep them moving. But for moving air you could have a 10 ft diameter pipe and it would not reduce the volume of flow from the laser cabinet to the blower.

[Kim McIntosh]

Hi Martin,
With my 1200x900 machine I taped up the rear pass thru, put foam tape on the gap around the main door and cover up as much of the cutting bed as possible leaving a gap of about 25mmx1200mm at the rear of the cutting bed. I cut from the rear of the machine, which mean the front cutting area is covered. I mainly cut sheets of 1200mmx600mm MDF and have a sheet of 3mm MDF 1200x300 butted up against the cutting sheet. Made a heck of a difference.

Cheers
Kim

[Keith Winter]

It seems to me that the downdraft system probably pulls the soot away from the piece in a better fashion than if the suction was from the top. And also keeps more smoke away from the lenses.



Yes I just had this conversation with the Trotec rep monday. He confirmed what you just said, you don't want anything to be pulling above your lens. You would be pulling dust into the lens in that case, so if that slot is above it, I'd avoid it. If what you mean by "top" is higher on the machine but still below the lens then you could give that a try.

I'd cede to Rich's expertise on the velocity question, the 8" pipe sounds like a non-issue. BTW that blower looks much nicer than harbor freight :) Lets look at other potential causes. Big issue is the flex pipe, you already know that. What Kev was suggesting sounded like an open slot in the back of your laser. Mine had one which we covered, sounded like his had one that he covered too. Do you have an open slot in the back for pass-through? If so cover that, it's hurting the blower's ability to get the smoke out. If that's not covered then that's the issue very likely see photos of my vent out and pass through covered

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[Martin James]

Thanks for the replies. I have a bunch of weather stripping on order and i will replace my flex with the straight pipe and then report back. M