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Allan Wright
05-25-2007, 3:36 PM
Has anyone rigged up a rheostat to their exhaust fan motor to be able to dial back the exhaust when cutting small or fragile parts? I'm going to be lasering some paper and cardstock and thought being able to control my airflow would help.

Or should I just use my blast gates to do that?

James Stokes
05-25-2007, 4:14 PM
I use my blast gates.

Joe Pelonio
05-25-2007, 4:17 PM
What I have done for paper is cut a piece of screen and velcro it over the exhaust outlets inside the machine. It is wide enough to also curve onto the x ruler on the vector grid, so any escaping pieces are caught. I did that after a piece of cardstock got stuck in the fan and the noise droive me nuts so I had to take it apart.

Pete Simmons
05-25-2007, 4:46 PM
Yes - I use an inline blower and I installed a speed controller such that maybe I could slow it down and not pull all the cool air out of my house (live in Florida).

Guess what....I never slow it down. Sometimes with a long time between laser work I turn it off. If I ever get around to rewireing or replacement I will remove the speed controller.

Gary Hair
05-26-2007, 5:09 PM
Has anyone rigged up a rheostat to their exhaust fan motor to be able to dial back the exhaust when cutting small or fragile parts? I'm going to be lasering some paper and cardstock and thought being able to control my airflow would help.

Or should I just use my blast gates to do that?

I wouldn't just close down the flow from your laser without opening up flow from somewhere else. If you restrict the flow too much you could create a lot of drag on the motor and potentially damage it. I have a dust collector in my shop and when I am using the smaller, shop vac size connectors, I open another gate somewhere to let the air flow more freely. It won't diminish the draw on the smaller line and I think it will increase the life of the motor.
If you need to, just put in a "Y" connector and a blast gate on two sides. Connect one to the laser and leave the other open (maybe a screen so you don't suck up the dog...).

Gary

Gary

Bob Keyes
05-26-2007, 7:23 PM
Dear Gary,

I hate to contradict you, but the load on the motor will actually go down when you damper. If you starve a fan for air then it has to do less work and the amp load goes down. So dampering a fan makes it easier on the motor. That's why a vacuum cleaner or shop vac will sound higher pitched or faster if you put your hand over the nozzle.

The only problem I see, is that apparently some lasers use this air to cool the laser. I would think that restricting this flow in any way, on that type of machine, would be detrimental.


I wouldn't just close down the flow from your laser without opening up flow from somewhere else. If you restrict the flow too much you could create a lot of drag on the motor and potentially damage it. I have a dust collector in my shop and when I am using the smaller, shop vac size connectors, I open another gate somewhere to let the air flow more freely. It won't diminish the draw on the smaller line and I think it will increase the life of the motor.
If you need to, just put in a "Y" connector and a blast gate on two sides. Connect one to the laser and leave the other open (maybe a screen so you don't suck up the dog...).

Gary

Gary

Dave Fifield
05-26-2007, 11:18 PM
Allan, I use one of those ($29) router speed controllers on my exhaust blower. It works very well indeed. I don't bother with a blast gate as the weather around here never gets cold enough.

HTH,

Gary Hair
05-27-2007, 1:53 AM
Dear Gary,

I hate to contradict you, but the load on the motor will actually go down when you damper. If you starve a fan for air then it has to do less work and the amp load goes down. So dampering a fan makes it easier on the motor. That's why a vacuum cleaner or shop vac will sound higher pitched or faster if you put your hand over the nozzle.

The only problem I see, is that apparently some lasers use this air to cool the laser. I would think that restricting this flow in any way, on that type of machine, would be detrimental.

I was worried this afternoon as I hadn't learned anything yet and I really believe in the saying "you learn something new every day". Thanks for taking care of that! I'll have to trust that you have verified this with an amp meter, right?

Gary

Curt Harms
05-27-2007, 3:35 AM
Dear Gary,

I hate to contradict you, but the load on the motor will actually go down when you damper. If you starve a fan for air then it has to do less work and the amp load goes down. So dampering a fan makes it easier on the motor. That's why a vacuum cleaner or shop vac will sound higher pitched or faster if you put your hand over the nozzle.

The only problem I see, is that apparently some lasers use this air to cool the laser. I would think that restricting this flow in any way, on that type of machine, would be detrimental.

I'm not a laser dude, I'm not familiar with laser equipment so take this for what it's worth. What Bob says is correct for a dust collector setup with an external motor-less air moved-less work being done-less amp draw. Many shop vac-type setups use the air flow for motor cooling after it's filtered so by restricting flow the vacuum will be moving less air but will also be have less air flowing through or over the motor for cooling. Something to consider.

HTH

Curt

Bill Cunningham
05-27-2007, 7:50 PM
A speed controller/rheostat/Variac/Etc. Will work fine if your motor has a commutator and brushes. If your motor is a more modern induction type, you will only burn up your motor. A blower is just a low level compressor of sorts, if you clamp off or restrict the intake, the load goes off the motor.. Many piston and vane type compressors from 100 to 6000 psi use this method to unload them, rather than shut them off between high and low pressure cycles. It much easier on the system, and requires less electricity/fuel than stopping and starting the motor, gas or electric.

Allan Wright
05-29-2007, 10:55 AM
Thanks everyone!

Nancy Laird
05-29-2007, 10:59 AM
Allan, if you have a downdraft cutting table on your laser you shouldn't have any problems with losing small pieces of anything, as the downdraft will hold those pieces on the table. That said, we just rigged up a piece of screen over the exhaust before we got our downdraft table, and the screen caught everything before it went through the blower.

Nancy