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Author Topic: inconsistant dial gauge readings on axes  (Read 2822 times)

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inconsistant dial gauge readings on axes
« on: April 25, 2010, 12:47:25 AM »
hi,
I have installed a kit from Promica for the Super X3 Mill. On Testing the accuracy after install ,the readings (gauge indicator) indicated a bad backlash problem. I was advised the check the alignment of the ball nuts, leadscrews etc. and find any inconsistencies and remedy them. At the same time to install a dedicated PC running Mach 3 only and checking it with the Drive Test software. I did all this. The slides run smoothly and no virtually no backlash exists The readings now indicate practically zero on the Y axis but almost no change on the X axis.
I've tried to use various settings in the config/backlash settings in the correct procedure and motor velocities etc. I'm thinking that the problem lies in the software! I don't think the controller is faulty.
Can anyone please help?

Offline Tweakie.CNC

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Re: inconsistant dial gauge readings on axes
« Reply #1 on: April 25, 2010, 02:15:11 AM »
Silly question perhaps but how did you correct the backlash you found on the Y Axis ?.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: inconsistant dial gauge readings on axes
« Reply #2 on: April 25, 2010, 05:38:15 AM »
Thanks for responding Tweakie,
I completely stripped down the X and Y tables, removed the double ball nut blocks and remove the balls; washed them in kero etc. I elongated the holes in the Y table that the y nut housing is fixed to -  due to side-pull on the Y lead-screw. Then put sufficient loading on the backlash adjustment screws etc.
The same procedure with the Y axis. The Y axis ball nut housing was a little loose! The lead-screw alignment was acceptable though. I made sure the loading on the backlash adjustment was acceptable and reassembled it. Also I made sure the gib strips were assembled as Promica suggested and oiled the system.
When I checked the backlash by turning the pully - without the motor belt - all seem well enough to reassemble.
I don't know why the X axis is still a problem. I did notice today that when jogging by very small increments the gauge needle behaved quite strange at times. As I incremented back and forth while the gauge needle was connected to the fixed block (mag. base V block) the needle would persist to continue (very slightly) in the same direction even though the direction was changed. I'm therefor thinking a pulsing problem (maybe pulse skipping) is occurring. But I'm new to the game and at a loss to know what's up.
I very much would like to find out and and try to correct it.
Thanks again 
 

Offline Tweakie.CNC

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Re: inconsistant dial gauge readings on axes
« Reply #3 on: April 25, 2010, 09:11:43 AM »
Could possibly be missing steps or the driver not translating the direction signal voltage well.
Assuming you are using stepper motors, any missed steps can often be heard by jogging an axis from one end to the other and listening carefully to the motor - a short 'tick' or momentary change of note is an indication.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline RICH

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Re: inconsistant dial gauge readings on axes
« Reply #4 on: April 25, 2010, 10:28:07 AM »
How much non-movemnet are you talking about?
How small of a step move are you talking?
What is the resolution for that axis?

Do you have an idler on the belt to keep the tension rather consistant?
I say this because we did some testing some time back ( actualy when were doing thread testing ). We were checking the mechnical part of the system and trying to compare physical movement to steps actualy sent from the pp as compared to what the stepper recieved. He could follow the
electrical signal path anywhere along the pulse path. BTW, the pulse counter was custom made for the company. So each electrical component  was isolated and related to each mechanical part or combinations. It was interesting to find that we could actualy find the number of steps " seemingly lost " due to varying belt tensions. Now we were cutting hairs, but never the less, interesting.

In fact we found that not all steppers are created equal such that when microstepping some steppers did better than others.

So large non-movements as they relate to the system can be measured conventionaly, but as you try find what part of the system contributes what fraction of the non-movement it can become very time consuming and difficult. You need to be meticulous as hell when measuring. Dial indicators
are calibrated ( we measured small distances opticaly/ eliminates the non movement of the indicator or non liner movement).

It is very easy to have backlash just do to bearing mounting and bearing preload can add to backlash. The screw can be non linear, the preload on the
nut can add backlash, inaccuracies in the belt ( inclucing timing belts ), lets not forget the gearing, etc, etc. So there are a lot of things that come into play and cumulatively they add up.

So i will not guess at your problem.
FWIW,
RICH

Offline Hood

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Re: inconsistant dial gauge readings on axes
« Reply #5 on: April 25, 2010, 01:31:31 PM »
I don't know why the X axis is still a problem. I did notice today that when jogging by very small increments the gauge needle behaved quite strange at times. As I incremented back and forth while the gauge needle was connected to the fixed block (mag. base V block) the needle would persist to continue (very slightly) in the same direction even though the direction was changed.

Did you have the block fixed at an edge of the table or was it in the middle?

Hood
Re: inconsistant dial gauge readings on axes
« Reply #6 on: April 28, 2010, 04:38:25 AM »
Thank you everyone. I didn't expect so much help. It's great to know there's lots of people around to help you!
In order to answere the above questions I'm going to go over everything, and when I can I will get back to the forum let you know how I went - and be better equipped cope with answering your questions relating to my problems.
Thank again