Z Axis suddenly drops during board measuring

[hobbycentral]

I was trying to do some simple cut-outs tonight and broke my first bit. When I start a project the machine makes it through measuring the width, it then started to measured the length. After the head went back to the left end of the board (facing control panel) and before it said to select the bit, the z-axis dropped until the bit hit the board. I stopped the machine, removed the board and looked for any issues - I didn't see any. I powered the machine off and back on and ran the z,x and y tests and then restarted the project. The machine did basically the same thing but this time the Z Axis slammed it hard enough into the board to snap the 1/8 cutting bit. I'm guessing the Z amp is failing? Any ideas would be appreciated.

Thanks
Bill

[badbert]

Check the encoder!

[bergerud]

Could also be the FFC wire. The flat ribbon wire that connects to the carriage. Check it for broken wires or bad end connections.

[Digitalwoodshop]

Joined in 2009 so like posted above, FFC Cable is #1 in my book.... Then a dirty Encoder, then a Frozen Z Roller Bearing.

2009 so I am guessing a 14 pin FSC Cable... But be sure to count the pins... IF you get a 14 pin cable from LHR and your machine has the older 18 pin cable and sockets and plug in that new 14 pin FSC Cable the wider pins will short out the computer.

AL

[hobbycentral]

Thanks, I will take a look at both the cable and the encoder.

[hobbycentral]

I reseated the cable with no change, I removed the back cover of the encoder. It looks like there may be some smudges on the edges ( i didn't touch it), I bew it off and replaced the cover - now I get a constant Z stall. Before I removed the cover the proplem was tht the Z carriage would travel to the far side of the machine with no issues and then travel back to the center of the board and slam the z carriage into the board with no errors given. Is there a safe way to clean the encoder? What are the readings for a good Z test? It is a 14 pin cable and I wil order one, but I' surprised that it would be bad if the Z test moves the Z carriage up and down. I've had this machine for over 3 years and it is only used cut out 1/16 balsa most of the time with very little actual carving - I'm surprised at how much maintenance it requires (several X gears, removing and cleaning the board sensor etc.). I have 3 other CNC machines and I've only ever had to replace a drive belt.

Bill

[Digitalwoodshop]

Bill,

The Encoders just make pulses as the clear disk has black lines and a LED and Sensor... On off pulses....

To test... Pull head to the top stop pin. On LCD and Keypad, Options, Sensor Data, and Z Data. I tell you to place the head to the top pin FIRST as when you call it up it will start at 0000. Move the head down and up looking for it to keep counting as you move it.... End up back at the top pin and it should be 0000 again, the starting place.... If NOT.... Problems like a LOOSE Clear disk on the Shaft, a drop of glue will fix that. OR a broken Circuit Board Connection from the Round Pads that the Pins are soldered into. The pins can cause the round copper pad to push away from the board snapping the connection.... A EARLY 2007 problem... not common now.

A second test... Same 0000 at the top... BUT while moving the head UP and Down Gently FLEX the FSC Cable.... Looking for it to OPEN the Connection.... The FSC Cable may have a break in the wire and since the thin copper touches then does NOT Touch, the Computer will keep moving the head waiting for the correct number of pulses... Hence Driving into the board....

Most likely a bad FSC Cable....

As for cleaning the Disk... Cotton Swab, light pressure, and gentle air.... Check for loose disk... Common..

AL

[hobbycentral]

Thanks AL, I will do the tests. I wasn't sure, but I thought I had read in the past not to try and clean the encoder disk, so I thought I would ask first LOL.

Thanks
Bill

[hobbycentral]

I completed the sensor check: full up read -1.039, fully down 1.89. I cleaned the wheel with a swab and it still reads the same but it works fine now. Now if only Sears still sold the cutting bits LOL. The funny part about all of this is that I was cutting Z plates for another CNC machine when it quit working.

Bill