Breathing Room for Motor...

Re: Breathing Room for Motor...

Barry Irby

>I looked at Enclosing my Rockwell saw. I don't know the answer to your question, but you should leave openings for air FLOW around the motor and throguh the enclosure. And study your saw with the blade tilted and verticle. I was surprised to find out that my (replacement) motor came within about a quarter inch of the top height of the table when the saw was fully tilted. Would have had to "thin" the top of the enclosure to allow for it.

As long as the motor can draw fresh air

Forrest Addy

>As long as the motor can draw fresh cooling air without recycling warm air you're good.

Forrest, a qustion about this....

Bryan in Broad Ripple, IN

>I have a question about this issue that has been bugging me for awhile. Intuitively, I agree with you that motors shouldn't recirculate warm air. It just makes sense.

However, I have seen otherwise. For example, older unisaws (pre-dust port days) and many lathes with enclosed stands don't allow much, if any, fresh air into the case around the motor. These are units designed to run all day, and they don't experience over-heating issues. For example, I have a PM 45 lathe with a standard TEFC motor, and there is only about 2 to 3 cubic feet or air around the motor in the enclosed stand. How come units such as these don't over-heat?

I've been told that the motors just don't put enough heat into the air to cause problems. What I surmise is this: the motor does not put enough heat into the air as long as the fan can properly circulate air (albeit warm air) around it. I suspect that problems occur when the fan impeller is damaged or if the air passages around the motor become plugged and air cannot be circulated around the motor case. Further, I suspect that there is a balance between motor size, and enclosure size, so that a minimum volume of air is present to ensure that the air temp does not rise above certain temp. Obviously, a 3/4 hp motor in a 3 cubic ft enclosure will live a happier life than a 10 hp motor in the same enclosure.

Any thoughts?

-Bryan

Forrest, a qustion about this....

Bryan in Broad Ripple, IN

>I have a question about this issue that has been bugging me for awhile. Intuitively, I agree with you that motors shouldn't recirculate warm air. It just makes sense.

However, I have seen otherwise. For example, older unisaws (pre-dust port days) and many lathes with enclosed stands don't allow much, if any, fresh air into the case around the motor. These are units designed to run all day, and they don't experience over-heating issues. For example, I have a PM 45 lathe with a standard TEFC motor, and there is only about 2 to 3 cubic feet or air around the motor in the enclosed stand. How come units such as these don't over-heat?

I've been told that the motors just don't put enough heat into the air to cause problems. What I surmise is this: the motor does not put enough heat into the air as long as the fan can properly circulate air (albeit warm air) around it. I suspect that problems occur when the fan impeller is damaged or if the air passages around the motor become plugged and air cannot be circulated around the motor case. Further, I suspect that there is a balance between motor size, and enclosure size, so that a minimum volume of air is present to ensure that the air temp does not rise above certain temp. Obviously, a 3/4 hp motor in a 3 cubic ft enclosure will live a happier life than a 10 hp motor in the same enclosure.

Any thoughts?

-Bryan

A motor enclosed in a volume

Forrest Addy

>A motor enclosed in a volume isolated from the outside air will perform well if the captive air is free to circulate, the enclosure is sheet metal and conducts heat to the ambient air, and the surface area is large enough to transmit heat to the ambient air. There are even books on this topic if you care to scrounge for them.

Many of those older saws you refered to were supplied with louvres or had dust collectros connected to them.

Just because a motor is running for some time in a captive air environment doesn't mean it's a candidate for burnout. Most woodworking, and metal working tools loaf along at a small percentage the available HP. Long rips in hard wood may challenge the motor but unless the rips are one right after the other for several minutes the motor can rest between cuts to dissipate its built up heat.

I've seen saw motors that have been entirely clogged with sawdust or running in a mass of sawdust and go on for generations that way. If a motor is run to a heat build-up to less than destructive temperatures and sufficient time to cool it may never need fresh air.

That said and the advent of a need to rip a thousand feet of sticks to make maple moldings from you should be concerned for cooling air for the motor. Whether its fresh or captive, it needs to be cool enough to extract the heat from the motor.