Uncontrolable varying depth??

[gumbo]

My newest problem with this machine is, while carving the lincoln cent face (this would be my fourth of the same carve in three days) the carve started what I thought was fine but actually was leaving lines all thrrough the carve region which were hard to see through the sawdust. Walked away fron the machine and came back some time later to see the machine running but hardly touching the surface at all. So basically the carve started at the right depth and then started to rise to where it was almost off the board. Tried cleaning the chuck, reformatting the card , reuploading the program etc. with no avail. All carves afterwards were the same, lines and decreasing depth, but none of the problems happened at the same place on any carve, seems to be random. Actually on one attempt on the same line it carve to a depth raised up as it traveled left or right and plunged back down on the other end of the board. (I hope I explained this so everyone can understand. At this point I am extremely frustrated, as I just replaced the power suply about a two weeks ago.

I hope someone can help, and Thanks to everyone in advance.

[Icutone2]

Lose bit? Z belt tension to loose?

[DocWheeler]

Gumbo,

I would suspect your Z encoder on the back of your Z-motor. There are many posts on this. Be careful not to lose the two small nuts when taking the three screws out (don't ask!).

Carefully remove the dust from the inside and on the small disk.

[gumbo]

I am not at home right now but I will try it when I get home. How do you suggest cleaning it? vaccume, brush or air(low psi)?

Thank You

[DocWheeler]

How do you suggest cleaning it? vacuum, brush or air(low psi)?

All the above including Q-tips. Be careful not to scratch or bend the disk.

[Digitalwoodshop]

Gumbo,

It could be a loose bit in the bit holder if you are still using a QC.

It could be a bad or dirty encoder like said above. Careful of the vacuum so you don't kill your machine with static.

Could be a lump of sawdust on a Z Roller or Z Rail. I hold my finger to the bearing and move the head up and down once a week catching the film of dust from the wheel. I also wipe the rails once a week especially the area between the upper and lower roller.

I blow out my Z Belt at every bit change. It could be a chip impacted into your Z Belt or Roller Cogs.

Some have had the plastic encoder wheel spin on the shaft of the Z Motor.

The Z Encoder can develop bad solder joints.

To test the system I would draw a square and use carve region and carve the whole square to .05 deep. This will show things like the head not being level and the Z in operation. It tells you the health of your machine.

And if the wood is staying under the rollers correct? Not popping up only being held by one roller?

Good Luck,

AL

[RayTrek]

Hello

Doc is most likely on the money with encoder being the problem. I have made it a habit to clean both Y and Z encoders about 7 to 10 hours of carve time depending on what material I am carving. After seeing this post this morning I went out and cleaned and took pictures, this is 7 hours of carve with select pine, I turn the motor while blowing to make sure that the dust gets out of the infer receiver (the black box).
Note, the gorilla glue on the encoder window at the motor shaft, this was my fix for when the window encoder (disk) was slipping on the motor shaft of the Z motor.

While I was doing this AL has posted also with some great info
He and Doc are a great asset to all of us thanks Guys.
Ray

[liquidguitars]

Just my 2 cents if it works for you cool, BUT..

I am not to keen on removing the encoder housing if i was a newbie. If the encoder is dirty its likely if from a failure of the motor.
so cleaning it would not accomplish anything if that was the case.


LG

[gumbo]

60% through the carve and it looks great, you guys were spot on (Sofar we'll see at the end). When I removed the cover there was no sawdust in there but it was covered with a grey carbon looking dust, I am assumeing that the piece that rides on the disk is like a brush on a motor and that is where the grey dust is comming from. If anything changes in the carve I will be sure to let you know.

Again I want to thank everyone the forum comes through again.:-D

[DocWheeler]

Gumbo,

I think it is optical as in counting the thin lines on the disk, nothing should be touching the disk. I do not know where gray dust would come from, but appreciate the information.

Also, Ray, thanks for the vote of confidence, you don't do bad yourself!

[liquidguitars]

I think the gray dust is from the motor. could bea good idea to get a new one..

[Digitalwoodshop]

I have not opened one of the motors but it is on my list of things to do.... Yes, I had gray dust too and I believe Jeff is right and the Servo Motors have Brushes. Ken is right, it is a optical encoder that counts pulses or black lines. A dirty disk can make the black lines run together. See picture 1 showing the sun shining through the disk showing the lines.

Picture 2 I have posted before but that is me and my first computer in 1977 on a Tin Can homeported in Yokosuka, Japan. Every hand crank and dial is hooked to Servos, Synchro, 10 Turn Pots, Ball Integrators and lots and lots of GEARS... This thing calculated the aiming of the 5 inch Gun with a 12 mile range.

I remember hearing about Magnetic Keepers, tools used to disassemble Servo Motors in the Navy Training... As a result....

I have not been in a hurry to take a motor apart as some servo motors will destroy itself if dissembled.... Yes... This comes from 20 years of Navy Training and I was a Analog Gun Fire Control Computer Tech.... So I searched on line and quickly found this....

http://www.servorepair.com/servo_talk_sample.htm


Next, do not take your motors apart. It is easy to cause a great deal of damage by simply "looking" into a motor. Here at A-1 Servomotor Repair we see thousands of dollars in damage each month caused by well meaning but uninformed customers. We see even more damage caused by electric motor repair shops that lack the knowledge, training and equipment to work on servomotors. Often inexperienced people damage or brake parts that can not be replaced. This can cause a motor to be non-repairable and convert an otherwise good motor into scrap.For more information contact A-1 Servomotor Repair at (888) 336-8430 or visit our web site www.servorepair.com (http://www.servorepair.com).


"Why does my servomotor or stepper motor have low torque?" This is perhaps the most commonly ask question of A-1-Servo Motor Repair's Technical Support Staff. The answer is usually simple - low magnetism!

Generally, low torque is a direct result of low magnetism. servo motors and stepper motors utilize very powerful permanent magnets to create torque. If the magnets in the motor are not fully charged it will be impossible for the motor to generate full torque.
The term "permanent" magnet is, to some extent, misleading. For a motor to develop full torque, it is necessary for the magnets to be saturated, or fully charged. While the permanent magnet remains "permanent", the strength of the magnet does not. In fact, there are a number of ways a magnet's strength can be reduced. No matter how a magnet's strength is lost, it's just a matter of time before you'll notice the warning signs and ultimately be forced to resolve the problem or discard the motor.

So how does a magnet loose its "full charge"? Two of the biggest contributors are overloading or disassembling a motor.

First, any time a motor is disassembled, there is a high probability that the magnets will be discharged to a point where the torque will be diminished. The results vary and may or may not initially be noticeable. With some motors, the results will be immediate. In fact, disassembly of a stepper motor will typically demagnetize the magnets to a point that the motor is useless until it has been properly remagnetized. With a few motors, the reduced energy will have little effect until the motor is under full load. At that time the drive / controller will indicate an error.

Overloading a motor is another way motors can be demagnetized. This could be caused by many factors: excessive feed/speed rates, crashes, mechanical binds, parameters that are not set correctly, as well as many other electrical or mechanical problems.

Overloading a motor results in excessive current. Excessive current demagnetizes motor magnets regardless of the cause. What makes things worse is that high current is only required for a short period of time, less than a second in some cases!

Typical scenario: A device is driven past a limit switch and crashes into a stop causing a momentary over current condition which causes the motor to be partially demagnetized. The motor now requires slightly more current to operate normally. The drive provides the extra current. However, more current equates to more heat generation. Heat reduces the magnetism even more. As the magnetism is decreased, the process continues to deteriorate: more heat = less magnetism = less torque = more current for normal operations = more heat... get the point? This goes on until the drive reaches its maximum current limit and alarms out, or the motor can't meet acceleration demands, or the motor self-destructs, etc... It is easy to see how this process occurs over a period of time. By the time the motor totally "fails", the original crash / overload has often been forgotten.

So what is the solution? First, avoid overloading your servomotors. Pay particular attention to the daily demands you place on your system. You might be able to get parts out more quickly by pushing your machines, but that quickness comes at a cost. Second, be observant to any potential mechanical binds and follow your manufacturer's recommended maintenance schedule. Finally, check your parameters. Don't set the maximum current limit too high. You will find other limits related to current in the parameters. Check these settings to be sure they are correct for your specific motor. In many cases this will prevent a motor from being damaged and add years to its life.


Once a motor is demagnetized the ONLY WAY it will ever work properly again is to have it rebuilt. The rebuild MUST include remagnetization by a facility having the experience and the specialized equipment necessary to do the job right.
If you have a motor rebuilt, ask the following questions BEFORE you turn your motor over to any repair shop: (1) Do they have a substantial amount of servomotor repair experience? (2) Do they have the ability and the equipment to properly magnetize your motor and bring it up to the original specifications? If you don't get a strong, believable response, don't let them touch your motor. Keep looking for a shop you can trust.

[fwharris]

Al,

You have stepped up to the plate once again and hit it out of the park!!

Great info for us un knowing ones here. Thanks,,

Rockies 1 - Phillies 1, Going to the Mile High City to play some snow ball now!! BRRRRRRRRR