X and Y axis intermittent jamming

[GeoffW1]

Hi,

We have a CNC 3020, on which the X and Y axis intermittently jam or stutter. The machine has had perhaps 40 hrs operation since new. The fault does not occur at the same spots in travel each time.

I looked for posts on this and found several reporting a lack of lubricant in the linear bearings and ballscrews, so disassembled them. That was indeed the case as no lubricant at all was visible. I used a Nulon PTFE light grease to supply this and reassembled.

The problem was improved but still there. One thing I noticed was
that when jamming the axis screw could be turned by hand using the large knob on top of the axis motor, unlike the normal powered up condition when it is locked. This however would not clear the jam.

At that I began to wonder if the fault is electronic in nature, not mechanical. Has anyone struck this with a 3020?

Thanks

Geoff

[Sterob]

Hi Geoff,
I assume you have read all my posts regarding the problems I had with my X6-1500GT? ( 6040 )
I found it hard to diagnose mechanical problems unless a fair bit of disassembly was carried out. I had to check each linear bearing and I found TWO that were dodgy!
Is your machine using the parallel port interface? ( these come with their own set of problems, I have heard )
Have you check all the wiring terminations for tightness( inside control box)?
Ball screw bearings ok ( smooth) ? Shaft alignment with bearing mounts ok?

It should be VERY easy to turn the knob on the steppers along the WHOLE length of the ball screw. If not, you have a binding issue.

I considered PTFE spray but found better results using light machine oil ( sewing machine oil ) It drips a bit but it seemed to give smoother movement. You can buy it at any auto parts store .

If the ball screw were dry for a long period, they may be damaged. I could not see any visible damage to mine, but one was binding in one direction only....weird.

Steppers are strange fish. They loose torque the faster they are driven so binding shows up more at higher traversing speeds.

Your Z axis is immune to these problems? That might give you some clues.

Let us know what you find.

Steve

[rcaffin]

The problem was improved but still there. One thing I noticed was
that when jamming the axis screw could be turned by hand using the large knob on top of the axis motor, unlike the normal powered up condition when it is locked. This however would not clear the jam.

At that I began to wonder if the fault is electronic in nature,

Sounds like it. If it is easy to turn by hand, it is NOT jammed. Perhaps the motor driver faulted?

Cheers
Roger

[GeoffW1]

Thanks,

It has indeed turned out to be electronic, being a faulty or below par parallel interface in the PC. On swapping the PC around, the problem disappeared, and the little machine seems to appreciate its lubrication.

Cheers

Geoff

[rcaffin]

Hi Geoff

This is a KNOWN problem! Nothing is actually 'at fault'.

Older PP ports used 5 V logic, but more recent ones use 3.3 V logic. Many times it turns out that the 3.3 V logic output from the PC cannot drive the 5 V logic input on the peripheral interface board.
Sometimes you can solve this with a very cheap PP add-on board - provided it too uses 5 V! You would need to check that (before buying).

Cheers
Roger

[GeoffW1]

Hi Geoff

This is a KNOWN problem! Nothing is actually 'at fault'.

Older PP ports used 5 V logic, but more recent ones use 3.3 V logic. Many times it turns out that the 3.3 V logic output from the PC cannot drive the 5 V logic input on the peripheral interface board.
Sometimes you can solve this with a very cheap PP add-on board - provided it too uses 5 V! You would need to check that (before buying).

Cheers
Roger

Agreed,

On looking around, nearly all the parallel port cards seem to be universal-type, 2 notches, 5V/3.3V. Reckon that would work OK? They are quite cheap anyway.

Cheers

PS No, wait, wouldn't it be that the slot in the PC would be for 3.3V PCI only? I'll have a look.

[Sterob]

Wow...thats a trick for young players. I have not heard of that.
I skipped all that fun by buying a USB machine.
Glad you got it sorted and it won't get you again.:2tsup: