K2 CNC position error - please help !

[Geetar-ist]

Guys, I have a K2 3925 that I use for making guitars.

I have used it for some months without any problems apart from gcode...

my problem now is that I have jigs and regular positions for all of my various body shapes etc but..
its got pretty cold in my workshop now and the CNC at first wouldnt even move without stalling but I fired up the workshop heater and it started to work OK !
then I ran a program that is a common one and the X axis was out by around 6mm. I didnt notice until I removed the workpiece and the centreline of the timber was not in the centre of the body..

I restarted the PC and ran it again dry and this time the X axis was out by 3mm ???????
is it losing counts or something in the cold ?? ive checked the temperature range for teh gecko drives and cant find any details - ive asked K2 about the motors that they use but they didnt reply.
is it simply that I need to clean the ballscrew and regrease it?

help ! - BTW, there are no work offsets set in Mach 3 other than Z axis !

Oh, of course I would ask K2 - but their customer service is the worst ive ever experienced, they have NEVER EVER got back to me when ive contacted them.

[gmfoster]

Sounds to me like its getting cold and the lube or something is sticky enough to cause loss of steps..

You will have to do some troubleshooting..

Garry

[Geetar-ist]

Garry, I wish it were that easy - Ive cleaned and gresaed the rails and bearings...
ive added electrical mat heaters to the motors but that didnt work... eventually I opened up the K2 control box and wrapped the heater mats round the gecko drives - that worked immediately

my only problem now is registration - the CNC is now about 5-6mm out in x-axis registration than was before all this started.
thats the only part I cant get my head around... I know that the ballscrews aint biding because I opened up the drive belt housing and turned it very easily with the motors disabled.

its like having a permanant work offset - but there are no offsets that I can find - even my really old drawings have all moved

ive also tried to see if the home (zero) switch has moved - but its as solid as a rock...

any reason why this would happen anyone ?

Jaden

[njitnjau]

We had this problem too but we got a tip from a very experienced Cnc owner
"Never trust the home switches!".

We came up with this solution:

The jigs are aligned to the table top with indexing pins. And all the jigs have a 1/2" "zero hole".

I put a dial indicator clock in the spindle chuck. (specially made for this purpose, sold in machinists shops)
I jogg out to approximate location of the hole.
Then I jogg the tip of the clock slowly down in the hole, then I move the x and y axis in very small steps until I get the same readings as I turn the spindle manually 360 degrees around.

When I´m satisfied with the readings I type in x0 and y0 in the DRO´s and your ready to go... after you zeroed the Z!

This must be done every time I start up the machine or if it looses it´s coordinates for some reason.
We tried to upgrade the switches to very expensive waterproof ones But they´re still not accurate enough. We had a feeling that the wood dust got into the housing of those cheap switches...

The expensive ones are better but the dial indicator clock trick is much more accurate. Works really well!!!

We also have had issues with rigidity. The frame is too weak!! We put in stiffening bars inside of the X rails. made of 1/2" x 2-3/4" solid alu sheet metal. It got better but not as rigid as one could wish..

Btw,We run a KG3925

Hope it helps!

/J

[dahui]

Actually Mach III does have work offsets. They moved it to a different menu from MachII...It's now under Config/Fixtures.

1) Return all axis to home
2) Zero XYZ
3) Jog to XYZ of desired work offset
4) Zero XYZ
5) Go to Config/Fixures and select Save

That offset should now be saved to G54. If you loose steps or the machine faults out you can just "return all home," zero out XYZ and the machine should go right back to the G54 offset that you saved. You should be able to save several different offsets by using G55, G56, etc. You just have to reference the correct work offset in the program startup code.

If your machine is loosing steps check the encoders. They can pack with dust. Just take the caps off and blow them off with dry compressed air. I would also suggest wraping the encoders with self adhesive ACE bandage from the drug store. It' also called vet-wrap (at your vet) and it comes in pretty colors (if you aren't into skin-beige). We used to use it on RC car motors to keep the grit out of the brushes.

By the way, what kind of cold are we talking about?

Oh, and I've run 2 K2 machines and haven't had any accuracy issues with the home switches. Just be sure the little blocks that trip the switches are lined up correctly. And don't forget to sync the A/Y axes, this can lead to positioning errors too. Sorry if I've stated anything too obvious.

[Geetar-ist]

man, since i originally posted this ive had some very poor experiences with the K2 machine, i think im going to write about them here to inform people of what they get when they part with money to K2.

I finally got most of the issues ironed out but not all.