Cut Motor Brushes failed at 298 Hours

[Digitalwoodshop]

When I started my machine this morning after I installed the bit and the machine went through it's homing I noticed that the cut motor did not start prior to moving. With the second bit I took the shaft out and spun the cut motor. This time it spun up as part of homing. The 3rd bit did not.... Then it tried to cut without the cut motor on. I stopped it and spun the shaft again and this time the cut motor stuttered. I stopped it and checked the right cover switch and it looked good.

I then removed the top Motor Brush holder and found the problem. The brush was worn too short to make contact. I had a spare cut motor I got from someone who had a bad motor. I took out the brushes and they were much longer. I then went to work on the bottom brush holder cap and stripped the flat slot. Ended up removing the motor with 3 screws and went to work removing the bottom cap. No luck... Ended up drilling a slot out so I could get it out. My suggestion is to remove the motor for better access to the bottom and inspection of the communicator through the hole.

SO with my spare parts I was back up and running and used a new brush cap to replace the one I drilled.

So on the phone I go to LHR and got Chris. Again he was Very Professional and knowledgeable as notated in the past. The Brush was not a separate item but he went to the TOP and had it added to the system while I waited.

The part number for the Cut Motor Brush is P007-00020 @ $2.50 EACH. Be sure to order 2.

I recommend replacing the brushes at 250 cut motor hours. If the spring gets to the communicator it could cause damage to the copper communicator.

I asked if the Cut Motor Bearings could be offered like Porter Cable offers them for replacement if so inclined. He said at this time it was not going to be offered and it is a unit only replacement of the whole motor.

I wonder if the cut motor speed magnet on the armature would prevent removal of the bearings? I bet it is welded on after Assembly?

Would like to see the brush cap offered too.

I asked about the price of the cut motor MWM A2 011 and they said they would get back to me.

Here are some pictures.

AL

[Kenm810]

Thanks Al, Good info to know and to hang on to.


The photos also help me know what I'll be looking for. http://www.carvewright.com/forum/images/smilies/icon_smile.gif

[Digitalwoodshop]

Just a side note to the CCM or Check Cut Motor error.... I now get it when the project first starts to cut. Not with the 2nd or 3 bit change. Never had CCM error on either machine before this. Something I did note after changing the brushes was the cut motor did not turn as smooth. I think the extra length of the brushes are pushing against the commutator and when the motor first try's to start up it takes a bit longer to get to speed then faults out. I am half tempted to sand the brushes down about 1/4 inch and see if it goes away. I have 2 sets on order. Turning it manually it turn harder.

It also takes a bit longer to spin up when I change bits. I have been checking for heat around the cut motor but I an not finding anything like a hot bearing.

AL

[HerbO]

Hi Al,
Maybe the brushes need to wear in a little. I had problems with the brushes on a pipe threader last week. I had the old motor and swapped brushes from it. I noticed that they were sparking a little to much but after an hour they smoothed out. Just a thought.

HerbO

[Digitalwoodshop]

Thanks, Yes I was watching the sparking as the brushes seated for the first 50 min project. I believe the brushes are seated now after 6 hours of carving. The motor still turns hard. If I pull the drive cable out of the motor the cable alone turns easy, so it is the motor.

I notice just before the CCM the motor speeds up past normal RPM, might me the PWM (Pulse Width Modulator) kicking out and the motor going with full voltage. Then I get CCM.

AL

[Jeff_Birt]

Al, I think you stumbled on to something here. When you changed brushes, the new brushes were not seated, that is not formed to the shape of the commutator. Not to mention that after 300 hours on the motor the commutator will we worn down, have arc burns, etc. The new brushes not being seated, created a lot of sparks, erratic running and most importantly, LOTS of electrical noise. I'm guessing that maybe the cut-motor RPM sensor is picking up the noise and that is what is causing the CCM error.

Now the question is how to filter the noise out.

[Digitalwoodshop]

Jeff, your take on this could be right on.... Yes there is still arcing in the commutator. For the benefit of everyone, I believe the first radio transmission between the US and Europe was done on a spark gap transmitter... Sparks from the commutator are flashing but at the same time they are generating EMI or Electro Magnetic Interference or Radio Waves.

A quick check tomorrow will be setting up both machines, 50 hours and 300 plus hours and turn on a AM radio..... a Basic EMI Detector. The sparks emit a Broad Band signal like the spark plugs on a AM radio in a car.

A simple fix for LHR could be a a EMI Filter on the wires going to the processor or shielded wires.

I did not even pick up on the EMI issue.... And I should have.... I worked at a Antenna Company doing Calibration for 2 years that makes the QualComm Omni Trak Trucker white dome antennas.

AL

http://www.microwavespecialty.com/majorprojects.html

[rpringle]

Al,

When I worked for NCR (National Cash Register) we would get many hours on the cash regesters motors and the brushes would wear down.
We would replace the old brushes with new and then use a fine polishing stone on the comutaor as the motor ran. In a short time the brushes had a clean/smooth serface to seat to.
Probably this will help.

Russ

[cajunpen]

My hat is off to all of you electronic tech savvy guys. I'm really happy I've got a Fresh Warranty on my machine. I would not even begin to know where to start troubleshooting this machine. Sounds almost like we are still Beta Testers - machines on the market before all of the bugs are even close to being fixed. Oh well, I see improvement over this time last year - not nearly as many problems. Hopefully you guys (on this Thread) will finally get this machine figured out - PLEASE keep up the good work, and if you ever need somebody put in jail - give me a call, that's where I can shine :-)).

[bobi]

Thanks, Yes I was watching the sparking as the brushes seated for the first 50 min project. I believe the brushes are seated now after 6 hours of carving. The motor still turns hard. If I pull the drive cable out of the motor the cable alone turns easy, so it is the motor.

I notice just before the CCM the motor speeds up past normal RPM, might me the PWM (Pulse Width Modulator) kicking out and the motor going with full voltage. Then I get CCM.

AL

A few years ago, before we had alternators, we would use emery paper between the generators commutator and the new brushes to pre-fit them. Put the emery around the commutator, grit side out, put one brush in the holder and turn the armature back and forth. That will put a matching arc in the brush real quick. After doing both, blow the graphite dust out, and install the brushes. The break-in will be a lot quicker.

[dpowli]

The postings on seating the brushes are right on. I have worked on and around industrial motors of all sizes for 36 years. The arcing that your seeing is a big problem! You are burning the commutator on the cut motor. The Rf being generated would be my secondary concern.

[Digitalwoodshop]

I did glue a piece of very fine sand paper to a 1 inch dowel to pre seat the brushes for next time. I had thought of it too.

Thanks,

AL

[Digitalwoodshop]

Bump...... For ease of finding.

[m439798765432]

My two cents? Working in the industry of DC motors and I think this is what is being discussed. When we change brush maybe sixteen or more at a time, after surfacing the comutator with a very fine stone I use a chalk compound to brake in the brushes. This chaulk is shaped like the chaulk used by welders to mark steel, but is supplied by the company Idea they supply many items for the electric field. Yes I use emery cloth that is silaca only, aluminum oxide conducts electricty. The key word is aluminum. And many other parts of this to protect that $40,000 plus motor.