Z axis issues

[preso]

My Denford Compact 1000 has developed issues with the Z axis. During a machining programme it began to behave erractically and ended up breaking a router bit when it failed to move up to clear the spigot on the R type F1 jig.
It appears that I can home all the axes independantly but if I use the home all button the Z axis will stall and the Z display on the software will count slowly up towards home.
If I try to move the router motor manually it will click but not move. Usually this allows the Z to home and then everything appears to be normal. When I try to run a machining programme everything progresses normally until a large Z move is required. At this point the Z axis will often move the wrong way or "hunt" up and down until it eventually stops moving altogether. The X and Y moves appear to be normal. During this phase the Z motor will be making a very soft buzzing noise but otherwise will not move. Sometimes if I try to jog the Z it will move erratically or move in the opposite direction to the key press used on the keyboard. i.e. page up will cause the motor to move down and vice versa.
I was told that the cause could be a faulty Z axis brake. I was convinced this was the cause but I have since removed the Z brake altogether but the problem persists. So I can at least rule the Z brake out. I have also tried cleaning all the homing switches, the E stop and the door latch. I have not tried switching the X and Z axes on the board as I am not sure how to stretch the wires far enough to do this. I also am not keen to start pulling wires out of the terminal blocks.
I have verified that the nut and screw on the Z axis are free to turn and are not binding in any way. When the jog is working OK it runs up and down the slides quite freely and normally.
I am quickly running out of ideas and I need to get this machine up and running ASAP.
Please help.

[Denford Admin]

I think the next thing to try is swapping the X and Z wires from the Baldor orange connectors.
You should be able to pull enough wire out of the trunking but may have to snip some tie-wraps.
The orange connectors may also have a black coding pin on them which prevents the wrong axis being plugged in the wrong place - just remove them for the time being

If the problem persists on the Z axis then it's a faulty motor or wiring issue - otherwise it looks like a faulty drive.

[preso]

OK. I'll try this tomorrow. What happens if I try to run a machining programme though? Am I likely to damage anything and will the machine home normally? If I can swap the axes what is the normal way of testing to isolate the problem?

[Denford Admin]

No you won't be able to run a program really.

I thought you'd be able to reproduce it by jogging X axis (which will then move Z) by a large amount at a fast feedrate

[preso]

Ok, I have been able to swap the x and z axes and I have been able to jog the machine on all axes. The problem still seems to be in the Z axis motor. When I jog it with the X axis key on the keyboard it moves at random and eventually stops moving completely. The X axis movements are normal using the page up and page down keys. Just to be sure it was not a computer or driver problem I have installed VR Milling on a new laptop running Win 7, updated the 32 bit drivers and used a different USB cable. ( we were using a RS cable previously). None of these changes had any effect on the original problem. I have been in touch with Brent McCorkell at REA here in Australia and he has suggested that we probably need a new Z axis motor and wiring harness. Incidently our machine is really a Microrouter Compact. I inadvertently put this post on the wrong board.

[Martin]

Are you sure it is not a broken wire?

Check the resistance accross both windings of the motor. You should get around 1 to 2 ohms resistance. The wire can snap near the motor.

[Steve]

For a motor to run randomly like this it would suggest either a phase to the motor is broken as Martin suggests or that the machine is stalling for some mechanical reason. It could be that the brake on the Z motor is just snagging the axis and causing a stall. Thisa can be checked by removing a couple of bolts and lifting the brake off the top of the Z motor.

I would also inspect the coupling connecting the Z screw to the motor shaft for damage. Of you loosen one bolt on the coupling you will be able to turn the screw by hand and manually move the Z axis up and down which would prove if the problem is mechanical.

[preso]

OK,
I've checked the resistance across the motor and I'm getting 0 ohms across the red yellow pair. If I kink the wires near the motor I can get about 2.4 ohms. The brake is not currently on the motor and I have checked the freedom of the screw and the nut and they are OK. I am guessing the wires near the motor are fractured. What is the best fix for this?

[Denford Admin]

I think those older machines had stepper motors with short wires which we soldered longers ones onto (then heat shrinked/sleeved each of the connections)
Might be worth inspecting those connections and fixing the broken wire.
If the break is inside the motor,ie, you can't get into repair it then I'm sure Denford rep in Australia can supply a replacement motor with the longer wires

[preso]

I found a broken wire close to the motor which I was able to splice and cover with heat shrink tubing. I'll reinstall everthing today and see if I can continue machining. There were no added wires on the motor. I was just lucky it broke far enough away that I could rejoin it.
In the long term I will probably need to get a new motor as I am sure the soldered splice will eventually break again.

[hughhend@msn.com]

Did you ever solve this issue? I have the same problem and looking for some guidance. The z-axis makes a shutter noise and then the z-axis is off in the program which causes the bit to run into the F1 jig I am using. I have attached a picture showing burnt contacts in the Schrack SR6C4024 6 connection relay. Can this relay be the source of my problem? I will consistently have a z axis problem after less than a minute of running a program. I have ordered the relay but am wondering if my motor is the cause. I will measure resistance and check wires to make sure nothing else is at play.....