How does sawdust get into a sealed electric motor?

[90cummins]

Picked up an old used motor to upgrade my Delta Unisaw from 1.5 to 3hp 208 3 phase.
The bearings sounded a bit noisy so I pulled it apart to give it a little pm.
I was surprised to see how much saw dust was in there being a sealed externally fan cooled motor.
I blew it out & removed the bearings & pulled the seals & gave them a good cleaning then re-greased & assembled and tested.
Can’t wait to install it with my power feed attached & do some ripping.View attachment IMG_0625.jpeg

 

[RayIN]

Perhaps it got in the same way smoke gets out???

 

[garry1p]

I would say that motor has been in a commercial operation for many years.

I'm still surprised at the amount, maybe it's dust resistant instead of dust proof.

 

[90cummins]

No doubt it’s old perhaps 60 plus years old!

 

[MAX-24-Dean]

Perhaps it got in the same way smoke gets out???

I like that as an answer! Air leaks as the seal has been lost due to vibration after years of service.
When the motor starts up it creates positive pressure and the rotating magnetic field expands enough to attract particles near the motor.
The particles then enter the motor due to negative pressure (suction) somewhere on the housing.
Sawdust in the right concentrations can be explosive with just a spark. Don't ask me how I know, and I was trained and forwarned.

 

[DarkBlack]

Very dirty! Might have come in through your junction box and where the stator wires pass through the motor housing.

 

[ponytug]

Like @DarkBlack I'd bet it came through the junction box.

As it is an induction motor, it is only going to possibly going to arc/spark when the windings fail, but I do think @MAX-24-Dean makes a great point about why it is worth cleaning the housing out and improving the sealing. I've seen the results of motor induced explosions and the results certainly make an impression. I would replace the felt seals on the shaft (just a guess. Many older motors had them. Did it have any / is there room for them?), sealing it up with some sealant when you reassemble the housing, and I would switch to water/dust tight cable glands / clamps.

Let us know how the saw is after the overhaul!

All the best,

Peter

 

[90cummins]

I removed the saw table top to make the motor swap easier and I found the s/n. According to the s/n the saw was built in 1953 which makes it 73 years old!
The mechanisms for blade raising & tilt were in excellent condition. The original motor with 4 brushes was very clean inside and the brushes showed little to no wear and zero wear on commutators.
This saw came out of a college many years ago so it may be all orginal. When I inspected the brushes I noticed the brush holder had index marks for timing purposes I’m guessing.
Ordered new belts because this motor runs at 3500 rpm with a smaller pulley.
Getting closer to the finish line.

 

[90cummins]

According to the s/n this saw was manufactured in 1953 which makes it 73 years old.

 

[DarkBlack]

My math comes up with 71 years. 72 if I change it to after new years 2025. Old , either way

 

[90cummins]

Won’t be working on this for awhile I’ve been admitted with Covid

 

[90cummins]

Like @DarkBlack I'd bet it came through the junction box.

As it is an induction motor, it is only going to possibly going to arc/spark when the windings fail, but I do think @MAX-24-Dean makes a great point about why it is worth cleaning the housing out and improving the sealing. I've seen the results of motor induced explosions and the results certainly make an impression. I would replace the felt seals on the shaft (just a guess. Many older motors had them. Did it have any / is there room for them?), sealing it up with some sealant when you reassemble the housing, and I would switch to water/dust tight cable glands / clamps.

Let us know how the saw is after the overhaul!

All the best,

Peter

No felt seals on shaft & bearings are sealed. Sawdust must have entered thru the junction box.

 

[90cummins]

My unisaw mod is finished!
The tilt/raise mechanism is cleaned & lubricated and operates very smooth. The gearing shows no wear despite its age so it may not have that many hours on it.
The re-wiring went smoothly & added an outlet for the power feed to plug into. New belts were installed & a closure plate made for a 4” dust collection port.
I cannot attach photos it says the file does not have an allowed extension.
Photos to follow hopefully

 

[90cummins]

Hopefully the photos are attached.

 

[ponytug]

That looks amazing! (Love the shop, too!)

All the best, Peter

 

[90cummins]

Thank you!
I certainly enjoy having space to tinker & do woodworking when the urge hits me.
Yesterday I was running oak thru the table saw using power feed and the saw did not disappoint me.

90cummins

 

[ponytug]

Thank you!
I certainly enjoy having space to tinker & do woodworking when the urge hits me.
Yesterday I was running oak thru the table saw using power feed and the saw did not disappoint me.

90cummins

That's great news!

 

[bmaverick]

This would be a great science fair project to find out how sawdust gets into a motor,

 

[90cummins]

Good one