Z results change during program

[sentrum]

Hi All, I have raised this topic maybe more than a year ago and received some advice from a few. I have since tried everything they mentioned, and due to the nature of the proposed remedies such as upgrading and improving the "insides" (I think it is the memory? anyway it is two pieces of micro circuitry the guy replaced) of my computer, it took some time to get around trying my luck with a Photo V Carve project again. As I think a lot of improvement happened when doing normal V Carving and Engraving, I was very hopefull that all problems have been sorted out.

However, my machine is still losing the actual -Z values as reflected on my display and read-out of the depths to be cut.........in other words, although, according to the tool path, the machine should be cutting at say eg. 1 mm, it does not even touch the surface! That being the case even although I have started cutting at the start of the program at the correct depth - that is 1 mm on the display=1 mm actually being cut. However, as the program progresses, say for example as from about command (coordinate) around 10 000 onwards, it increasingly looses depth until it does not even touch the surface where it is supposed to be cutting about 1.200 mm deep. The material is also 100% flat MDF product.

To prove that there is no structural or any other defect with the machine, I have actually proceeded to cut (in "jog" mode) a frame or square on 0.02 mm depth all the way around the picture and it is perfect. Yet, when the cutting of the Photocarve program has to be done, this gradual and ever increasing loss of depth occurs. I have even, as suggested, tried to run it as slow as 25% speed to prevent the loss of steps etc, etc.

I cannot say how frustrated and disappointed I am, as I am sure that I'm not the only grandfather who wants to do photos of the grandchildren.

If anybody out there have experienced a similar problem and can kindly share the secret to the solution, I shall be extremely grateful. Sorry for the lengthy post.

Mike

[Adrian]

It's definitely going to be an issue with your machine/controller rather than the program itself.

Lost steps are usually caused by binding or slipping on the axis in question. They can also be caused by the machine trying to retract higher than the physical movement on a safe Z move. Check that the the bit is not slipping in the collet as well.

I've also read of issues where the weight of the Z carriage, router etc was too much for the Z stepper motor and steps were lost that way.

The action of cutting a photo is a great deal different from cutting a square at a constant depth. With the photo there is constant movement of the Z axis so any failings there will show up.

[martin54]

Like Adrian has said your test doesn't prove that it's not a machine issue at all. Photo carving where you have a lot of rapid z moves will show up problems that other forms of machining may not.
Go back to the very start & look at everything again, check for backlash, any tightness, loose couplings etc etc.
What control software are you running? Have you tried reducing the z axis acceleration & velocity? If you are using micro stepping what have you got it set at?

[garylmast]

I’ve been fighting the problem of losing ‘Z’ height ever since I bought my machine. Although I agree, when milling, if I hit a spot that causes a bind or hit something like the hold down, it will lose steps and cause it to go out of calibration, however that is rare. I tried everything including changing the UBS board and the stepper motor, but still had the problem. I then changed the stepper motor to an oversize, two-phase, high torque thinking my 6 HP spindle (that weights the size of my car engine) was just too heavy for the stepper motor to hold it up. I had to retrofit because it would not fit where the original went, but that solved the problem, for a while. Once the motor got some wear, the heavy spindle would lower more than the stepper motor would hold. The most recent fix was adding a heavy spring. I have since tried a job that required a lot of ‘Z’ movement, which failed the first few times, but worked perfect after adding the spring.

[RickCNC]

Like Adrian has said your test doesn't prove that it's not a machine issue at all. Photo carving where you have a lot of rapid z moves will show up problems that other forms of machining may not.
Go back to the very start & look at everything again, check for backlash, any tightness, loose couplings etc etc.
What control software are you running? Have you tried reducing the z axis acceleration & velocity? If you are using micro stepping what have you got it set at?

+1
I think you problem is here somewhere.. What CNC are you running and controller software.. I'm amusing Data cut CNC based on your profile.. I had the very same issue you are seeing with my Joe's 4X4 and the problem was loose couplings. They felt tight however when I cut an intense Vcarve project (lady in the woods) I would loose steps. If your Z axis looks anything like the one below (found it searching for Data Cut) I would check the set screws to ensure they are tight and do they have a flat spot on the shafts to prevent slippage.

[Leo]

I’ve been fighting the problem of losing ‘Z’ height ever since I bought my machine. Although I agree, when milling, if I hit a spot that causes a bind or hit something like the hold down, it will lose steps and cause it to go out of calibration, however that is rare. I tried everything including changing the UBS board and the stepper motor, but still had the problem. I then changed the stepper motor to an oversize, two-phase, high torque thinking my 6 HP spindle (that weights the size of my car engine) was just too heavy for the stepper motor to hold it up. I had to retrofit because it would not fit where the original went, but that solved the problem, for a while. Once the motor got some wear, the heavy spindle would lower more than the stepper motor would hold. The most recent fix was adding a heavy spring. I have since tried a job that required a lot of ‘Z’ movement, which failed the first few times, but worked perfect after adding the spring.

+1 here.

My spindle is 15 pounds and the stepper would fail to overcome the inertia of the "Z" changing direction.

I had to add a counterweight to my machine. That solved the problem. I do plan on a much larger stepper motor.

Martin is right about your testing not proving that the machine is OK.

I had another similar problem where my "Z" axis was irregular. I did the same sort of testing on my machine. I eventually replaced the BOB and upgraded to Mach3 - that solved the irregularity problem.

Don't give up - the grand kiddies can have their stuff - but they must wait for it.

[sentrum]

Hi again everyone,
WOW, where else will you find such overwhelming response and kind assisstance!? Thanks to all - BUT - I suppose with English not being my first language, it is harder to find the correct words to effectively describe what I want to say, especially in very Technical Terms for an old and "Technically Retarded" guy.
I have studied all the remarks and advice and comprehend about 95% of it all, except for a couple of places where you refer to detail with which you are obviously perfectly au fait and I have not yet achieved or mastered. My actual problem, which I desperately tried to explain, is actually the EXACT OPPOSITE of what you have experienced, namely that MY MACHINE CUTS LESSER AND LESSER DEPTH - in other words, the cut fades away until nothing is cut. The weight of my cutter (Makita Router) is not a problem at all. Also, I can not find a screw or bolt or grub screw of any kind, which I have not yet checked and re-tightened. And THAT is why my limited experience, ability and know-how is frustrating me immensely!
For the record: My machine is a Data Cut, my post processor a Flash Cut and the stepper motors have no markings on but seems to be very sturdy and well designed. The screws(three threaded shafts which moves the cutter) work on ball nuts so I do not know how to improve or better on this - especially for a hobbyist.
Please advise if more information could better the chance for information on a possible solution.
Thanks,
Mike

[IslaWW]

Mike...
Yours is not an uncommon issue. There is a 90% chance the solution has been given by the guys above. There are three things that cause this:
1) Mechanical connection that is slipping, things to check:
a) stepper motor to screw connection is loose (coupler)
b) spiral type coupler that "unwinds" in the down direction
c) bit is not held securely in the collet
d) other mechanical connection on the Z axis (router bracket etc) that is not secure
e) reduce feed and rapids by half to see if there is change

2) Weak electronics:
a) Swap driver and motor (1 at a time) with another channel to see if problem repeats
b) check for loose wiring
3) Movement caused by static discharge:
a) remove dust boot and hoses for a test cut

Make 'sharpie" marks on bits, shafts, screws and couplers
Make changes to above one at a time, write them down, with results
Do an aircut test:
Zero the bit to a secure known location (block of wood off to the side)
Run problematic file in air (no cut load)
Recheck z height when complete
Repeat as needed until problem is found
Verify that Z plunge and rapid rates are appropriate
Post a pic of your Z assembly
Post your file for audit
DO NOT ASSUME ANYTHING IS CORRECT (opposite of your post above) Until you find what is incorrect.

[Jozua]

I fully understand your frustration.

I had a similar dilemma.

My machine would cut perfectly and then for no reason at all the Z-axis will randomly starts to cut “air” then the next time it will refuse to rise and simply “plough” through the material to the next point immediately destroying the work piece.

Like in your case I had all the very helpful and experienced members on the Forum tried their utmost to assist me with possible solutions to the problem.

Whatever I tried, Nothing solved the problem.

I had a CNC manufacturer from South Africa looking at all possible solutions; he could not find a problem with the hardware.

I had John Johnson from Ez-Router in Texas connected online to my CNC computer; he made all possible adjustments to Mach 3, again in vain.

I replaced all 3 stepper motors, all 3 limit switches and all 3 Gecko Drives and still the problem persisted.

Then I called an electrician with an IT background to see if he might be able to assist. He solved the mystery.

The problem was on the PC board, in my case the power to the stepper motors runs through LED's. The Z-Axis LED was defective and after replacing that all my Z-Axis trouble was at an end.

I reported this to Ez-Router and that was a First for them as well.

I am not sure how your machine is set-up and built, but this may be a possible solution.

Joz

[sentrum]

A big thank you to all who assisted by posting replies. I shall now try to find someone who knows enough to come and assist by taking each point which was raised by you guys and check them one by one and hopefully the efforts will meet with positive results. I was amazed and pleasantly surprised to hear from Joz in my old fatherland and especially from Naboomspruit which conjures up many fond memories of my younger days at the three hot water resorts! Wonder if they still exist?