My CNC has gone CRAZY please help

Hi All!

I am new to this site but I have already learned a lot about CNC milling by looking around.
I am just starting off with CNC machining so apologies in advance if I use the wrong terminology if I talk total nonsense.

So here is my situation.
I bought a small Chinese CNC router. This one except that mine is 3020 not 3040 otherwise the same thing:
https://www.ebay.co.uk/itm/4Axis-304....c100009.m1982

I use it with a laptop and Mach 3 licensed v3.041
I generate the G-code in Fusion 360

I only machine out of various wood materials and only very small parts. No bigger than 50mmx50mmx10mm

The issue is, when I try to do any operation with multiple passes (when the machine does a new path around the part at a lower depth) every new pass will shift to the left around 0.5 mm or around that much. Each pass in itself is the correct size but they are all shifted to the left on the X axis so I end up with a stairs effect as I have 5-6 passes each shifting to the left.
What I don't understand is that the machine is accurate as the first pass is perfect size on each axis, and every other pass is perfectly accurate, but they are all shifted to the left.

Here is what I have done so far to investigate:
I have turned by part 90 degrees then generated a new G-CODE to see if its the code, but the same thing happened, each pass was shifted to the left on the X axis but in this case the shifting occurred from top of the object to its bottom due to the 90 degree rotation, but from a machine perspective it was on the same axis(X)

I have also run an axis calibration in Mach 3 on the Settings tab where I told Mach 3 to move on the X axis 100mm left and right then measured the actual travel of on the machine with a caliper and it perfectly accurate. i have done this a number of times and it was always the same distance traveled what I have set it Mach 3.

I have also tried to run some G-Code that is a 2d trace where the machine has to lift the tool on the X axis several times to travel to a new starting point in the Code which is similar to a new pass in a 3D pocket processing and the machined part turned out to be perfect.

I have also checked all the screws around the X axis on the machine, tightened them, oiled up parts where it was needed, and could not see and loose movement anywhere.

I swapped the USB cable to a new USB slot on the Laptop, which had no effect on the outcome.


Can somebody please help me as I have no idea what is going on. Why is my machine 100% accurate in some operations consistently and inaccurate in some others? It makes no sense to me at all.

Please see image attached.

Any help is much appreciated. Have a nice day!

You are losing the position of your X axis. Now you need to find out where and why.

You said you did check "all the screws" - including the coupler between the motor and the lead screw, right? That probably means it is the motor itself losing steps.

There are three main reasons for losing steps:
1. The motor tries to run too fast or accelerate too hard during rapid moves. Decrease speed and/or acceleration in Mach3 settings.
2. The cutting load is too high. Decrease feed speed or depth of cut in your CAM program.
3. The axis has too much friction. Remove the motor, rotate the lead screw by hand and check if the axis moves freely.

Try running the same program "dry", without a tool in the spindle. Does the machine still lose position?

As you have checked and found no mechanical problems

you need to test X axis the stepper driver

if your control box is like this in the advert you linked to

Attachment 429956

The use of the multi pin centronics connector for the connections to the 3 stepper motors

makes it difficult to swap the X axis motor over to the Y or Z stepper driver and the X driver motor over to the Y or Z stepper motor

to check the X axis stepper driver is working correctly as it could be gaining steps

either due to electrical noise counting as extra steps or not changing direction as quickly as it should


what does the inside of the box look like ?

it may be possible to swap the motor connections inside

possibly swap the Z & A axis drivers

John

Thank you for your reply.
I have created a small test process which a simple 25mm square with a smaller square inside of it and the code has 3 passes, 1mm depth increase with each pass. I will test with that to see what the problem is.

I have checked the Screws and they all seem fine. They are as tight as I can make them by hand tools
I would post a screenshot of the feed and speed setting and the mill bit I use but I can't in a reply message.

I thought about swapping the x axis stepper motor with the y to see if it happens. that would rule out the motor itself.

Here's an easy test.
Remove the stepper motors and wind the ballscrew, by hand ,full travel, in both directions.
If you feel any binding at particlar points in any direction, they need to be fixed.

UPDATE

I have taken off the X axis stepper motor. It moved freely as far as I can tell.
What I have noticed is that when the machine is moving on the Y axis, the X axis stepper motor shakes very slightly resulting in the Y axis cut not parallel to the Y axis, but slightly angled. When the X axis is being cut the Y stepper does not move at all. I suspect something is wrong there.
Why would my X axis turn tiny bits when its a straight cut along the Y axis? it should not.
Also when i touch the opposite end of the X axis lead screw(where it has the nut holding it to the machine body), i can feel a bit of rattling. It's almost like something is grinding on the X axis. When I touch the Y axis it is a smooth rotation.
Also when the X axis is turning is sounds like something is rattling somewhere.

I don't know what is going on.

Sounds like you are on to something or somethings.....It does seem strange.
Be aware that you may come across more than one anomaliy that by itself, should not be a problem, but then you add them all up, it is a problem.....
Its happened to me.....

I have an update on my issue.
After removing the X axis stepper motor, rotating it 90 degrees so the screws are not in the same place anymore and reconnecting the wires to it, the CNC seems to have fixed the problem.
I have also disconnected the main controller cable from the CNC and reconnected it
I honestly can't tell what it was.
- It could either have been the wire not connected perfectly to the stepper motor,
- the screws holding the stepper motor to the body of the machine were too tight causing tension on the the stepper motor body
- the stepper motor head might have been a bit loose on the lead screw


I honestly don't know, but at the moment it seems to work fine with excellent accuracy.
It is a slight worry thought that it did what it did and I still don't know the exact cause of it so it can come back any time.

Thanks for the help

Maybe you had misalignment between your Stepper and Coupling?
Anyway...good result.

Quote:

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Originally Posted by Plapath

I have an update on my issue.
After removing the X axis stepper motor, rotating it 90 degrees so the screws are not in the same place anymore and reconnecting the wires to it, the CNC seems to have fixed the problem.
I have also disconnected the main controller cable from the CNC and reconnected it
I honestly can't tell what it was.
- It could either have been the wire not connected perfectly to the stepper motor,
- the screws holding the stepper motor to the body of the machine were too tight causing tension on the the stepper motor body
- the stepper motor head might have been a bit loose on the lead screw


I honestly don't know, but at the moment it seems to work fine with excellent accuracy.
It is a slight worry thought that it did what it did and I still don't know the exact cause of it so it can come back any time.

Thanks for the help

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Next time could use AC servo instead of stepper, could be more reliable.

@cncmakers001: Would you put AC servos on a flimsy 3020 made in PRC?

Quote:

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Originally Posted by ZASto

@cncmakers001: Would you put AC servos on a flimsy 3020 made in PRC?

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Since hes posting from China,I suspect he might put anything you can think of on about any machine you can imagine.

Welll.. yes, 3 750W AC servos on 3020 :D :D

Quote:

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Originally Posted by ZASto

Welll.. yes, 3 750W AC servos on 3020 :D :D

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400W and call it a dream machine :cheers: