Re: Porter Cable Belt Sander Problem (LONG)
Thanks to both of you. When I pull the brushes out, how do I tell if they are shot? Also, where can I buy replacements?
It helps if you first know what healthy brushes look like, so that is what I will tackle in this post.
Although brush assemblies come in many styles, if you analyze the two I focus on below you will notice certain commonalities present in all brushes: 1) the actual carbon/graphite brush, 2) a spring assembly that keeps the brush mated against the motor commutator as the brush wears, 3) a housing that retains the brush and allows it to be referenced againsg the motor housing and 4) an electrical connection to provide power to the brush.
NOTE: When you remove your brushes (or brush assemblies), you should make note of the orientation of the brush. Although the curvature is obvious when aligning brushes, you should also try to keep the brushes in the same orientation to ensure they maintain an optimal seating. This only applies to used brushes since they have already seated themselves to perfectly match the curvature of your motor's commutator relative to how their housing aligns with the commutator. I usually use a pencil or marker to mark a 'C' on the side that is closest to the power cord and I work ONE brush at a time so that I don't get brushes mixed up. When you reseat, or if you install new brushes, run the device at full speed under no load for several minutes to allow the brushes to fully reseat. Do not use the device under load until you have done this since freshly installed brushes may not be fully seated until the dervice has run for several minutes.
First an exaggerated outline of what an intact brush should look like. The curvature is exaggerated for clarity, in reality the curvature will be mor subtle.
The following examples are from a Porter Cable 690 Router. I chose this motor as a starting point simply because it is a rather large motor with large brushes, which I felt would provide some good photos. This motor has very robust brush assemblies compared to many motors and is more indicative of better-quality higher-end universal motors.
This is the servicable portion of the brush assembly. The unit consists of a graphite brush and integral spring assembly. Observe the curvature of the brush where it mates with the motor's commutator. Also notice there is plenty of length remaining in this bush, so many more years of service may be expected from this brush.
Notice the smooth face where the brush mates with the motor's commutator. I little bit of wear along the trailing edge can be seen, but this is typical of normal wear. A brush in good condition will look much like this brush -- smooth faces, plenty of length, and no signs of abnormal wear, arcing or pitting.
This photo shows the brush housing (brass housing at left), the graphite brush (center, just visible between brush housing and motor commutator), and the motor commutator (the circular array of copper conduction strips). Notice how intimately the brush and commutator mate with one another, indicative of a well seated brush. Also notice no obvious damage, pitting, or overheating in the commutator (the copper strips). The blackening is normal and is reside from the graphite brush -- it also provides lubrication between the brush and commutator. (Note: near the brush a small bit of dust -- likely Purpleheart -- is visible, this is not a defect in the commutator.)
A view from another angle of brush housing, brush, and commutator. Also visible in the background are the motor windings.
This is the brush housing and is where you insert the serviceable brush/spring assembly. Not shown is the brush/service cap which screws in place to lock down and secures the brush and spring assembly.
The following photos come from an old Ryobi 1/4-sheet Palm Sander. This is more indicative of the type of brush assembly found in many smaller as well as lower-end universal motor products.
This is an overview of the rear end of the motor... Note the two brushes assemblies, left and right, in the brass housings. For this motor, each brush assembly is a compete assembly and must be replaced in whole (that is, the brush, spring, and housing are a single integral unit). You can also see the rear bearing and to motor commutator (copper strips in center).
This closeup shows the curvature of the graphite brush. Notice the smooth face of the brush where it mates with the commutator. Also notice that, as is common in cheaper motors, this brush sits offset slightly so the left most portion of the brush has not yet seated to the commutator. Fortunately good contact is made with the portion that has seated. As this motor is used more in the future this brush will wear down some more and ultimately fully seat as a consequence of normal wear.
Also notice that there is still a good bit of travel left in this brush (this brush housing traps the brush, so additional length is located inside the housing -- the portion you can see is the wearable portion of the brush). We only need about 3/64" travel with this brush to ensure good contact. Also note that there is a spring internal to the housing which keeps the brush securely mated with the commutator.
This is an overview of the complete serviceable brush assembly for this motor. Since the brush is an integral part of the housing, the entire assembly must be replaced when the brushes become worn. As noted earlier, as is common on cheaper motors you can see that this brush seats slightly off center relative to the commutator. As such, the curvature you would expect to see is shifted upward slightly with the lower portion of the brush not yet worn sufficiently to mate with the commutator at present.
To replace this assembly, disconnect the power cable via the quick disconnect. You then press the new assembly's brush against the motor's commutator, then press fit the entire assembly into the manufacturer-provided receiver for this brush assembly. Then reconnect the power cable. Afterwards you will want to run the motor no-load for about 5 minutes to allow the new brush assembly to seat with your motor. If possible, running the motor for 15-20 minutes before load is applied allows ever better seating. If you expect to need to run the motor at considerable load after installing new brushes, the longer you can allow it to run no-load to seat the new brushes the better (up to 30-minutes). The extra time allows the brushes to more completely mate with the commutator.
This photo shows the brush mated with the commutator. Also inspect the commutator for any signd of pitting, arcing, melting, or other signs of damage. Especially inspect the commutator if your brushes disentigrated during use since they may have suffered extensive damage during the event.
Another view of the brush assembly and commutator. Notice there are no signs of obvious damage to the commutator contacts -- no pitting, scratches, burning, or other signs of abnormal wear.
Of course, while you have the motor disassembled, go ahead and turn it through multiple revolutions manually. Exert lateral pressure on the motor assemblies. Look for any signs of wearing, rubbing, abnormal contact or friction with non-moving parts. Make sure there are no signs of excess runout in your bearings and that your bearings are spinning freely. These checks are especially important if you have noticed excessive vibration when in use since bearing (or sleeve) runout is typically the cause -- especially bearings subject to extensive lateral forces as is common with routers. Also check how the bearing seats into the motor housing, large lateral forces can distort the housing around the bearing allowing an otherwise good bearing to vibrate within its seat. This sort of repear involves some sort of shimming to restore a tight fit around the bearing (plastic, brass or copper foil, etc. work well for this).
With respect to where to obtain replacement brushes (as well as other parts)...
The best source is nearly always the manufacture of your tool. Porter Cable is still in business. Visit their website or call their service number with your model number, type or revision code (if present) and serial number and ask them what part you need to order to replace the brushes, etc.
In the case of brushes, always order them in pairs and replace both pairs at the same time.
Good luck restoring your sander. I hope this information proves helpful.