[marq_torque]

Hello.

Herewith i have completed mini milling machine for light/micro machining work.

Specs :
Working area: 450x250x150mm
Spindle: 2.2KW@24000RPM motorized 400HZ HF spindle.
Sliding: Profile rail Guide-way Hiwin make.
Ball-screw: Rolled Type preloaded with zero backless.
Axis Drive: Ac Servo Fuji make 0.4KW 3000RPM 17bit encoders for each of axis.
VFD: Delta make M series 3.0Kw


Rapids: set to 8000MM/min(was able to go faster but stayed to this fig.)
Resolution : 2.5uM.

[marq_torque]

Tested machine for repeatability and backless almost 0.5uM for all tests Great!!!

But still not getting round circle accuracy withing 10uM with Mach3 G2 G3 modes!!!

Every time X-axis reading gets 80~100uM higher then Y-axis.

assumed there should be some mechanical error but nothing is there checked all bearing pre-load and backless.


Lot of frustrated wat to do!!

tried all servo tuning wizard with different gain setting but not getting at least X-Y Result perfect in circle @90 degrees!!

if it gets X-Y 90 degree result right then only I'll be able to check random angle for diameter!!!



trying hard for constant circle diameter value within 10uM!!


((((

[HuFlungDung]

I cannot really help you directly. I used to test some of my old cncs with a 45° linear interpolated movement. I would fasten down a straightedge to the table, at an exact 45° angle, and then write a single line interpolated movement to make the table move along this line. With a dial indicator in the spindle, and resting against the straightedge, any delay in one axis would result in a displacement of the indicator needle. If both axis were identically tuned, then the needle would not move at the start, during motion, or end of the test movement.

I wish I could remember what it was that I adjusted to fix this, but they were old analog drives without any sort of digital PID settings, so it may have been a combination of tweaking the gain or maybe the balance pot. Balance pot adjustment was actually an initial setup adjustment, where no command signal was sent to the motor, I simply adjusted this so the motor did not drift either direction when it was supposed to be at zero speed.

Perhaps this will create some new methods of testing your own setup.

When I see the terms "rolled ballscrew, no backlash" in one description, I see a contradiction I do not think that rolled ballscrews have enough precision to operate without some sort of floating backlash adjustment, because otherwise they would bind up here and there in the travel, or be loose in other places. So even though the illusion of no backlash may exist, this does not mean that high accuracy is ensured. You need high accuracy ballscrews to have a hope of doing high accuracy circular interpolation.

[marq_torque]

Ohhhhhh Great!!!

First of thanks for reply HU


Agreed, i also not intended to say i have high precision ball-screws.

just was saying screws are rolled and preloaded against backless!

Anyways, so should i map ball-screw lead deviation? but i dont think Hiwin makes such ball-screws which having lead error of about 0.100mm within 50mmof length!!

Any other possibilities?? what should i fight for first????

am going to release some amount of pre-load of X-Axis which is created with card spacer between 7203 AC bearings outer rings!!

Either it help or not m not sure! but tried almost all gain setting of servo from 1-20 and tried auto tuning of axis drive with function in drive.

[Khalid]

check the flex in the Y-axis also runout in the tool...something may be loose..

[marq_torque]

And yess you are right in other words that is called ball-bar test. i know about!!! thanks again.

[marq_torque]

@ Khalid, m not getting how run-out in tool will play roll in this case?!!

even tried lowest feed rates possible to higher feed rates for cutting circle. i have used some acrylic blank pieces for testing! spindle speed is 24000rpm with ceramic bearings. TIR is under 3uM which is not measurable with traditional instruments.

[marq_torque]

Wooooooooooooohhoooooooooooooooooooooooooo

Cheers!!! i got my machine within +/-10um in roundness @ any angle of circle!!! time for celebration.

Found some sticks in both axis at certain lengths!! Done some realignment of motor mount of x and y axis. left machine to run whole night for dry run at rapid rates. next day again auto tuned servo for new alignment and seat. got full smooth arc with +/-10uM difference at any point. really HU it requires lots of patient to do some type of tuning of machine. trying circle and diamond test next day!!!

Thanks for replies friends!!