PDA

View Full Version : Start&end elipse on Shenhui



Zlatko Kursar
02-28-2014, 12:10 PM
Start and end point are not always on same place. How can I resolve this problem.

283572

Dee Gallo
02-28-2014, 12:31 PM
If you zoom in really close, can you see if there are extra nodes there? If so, eliminate the extras.

Michael Hunter
02-28-2014, 12:42 PM
My Epilog has been doing that for the last 9 years - Tech Support could not suggest a solution, even after my local dealer sent them samples.

It can be minimised (but not completely eliminated) by adjusting the belt tensions and ensuring that the X cross beam is exactly square to the Y axis.

Scott Shepherd
02-28-2014, 1:17 PM
My Epilog has been doing that for the last 9 years - Tech Support could not suggest a solution, even after my local dealer sent them samples.

It can be minimised (but not completely eliminated) by adjusting the belt tensions and ensuring that the X cross beam is exactly square to the Y axis.

On the Universal it's a sign that the bearings and pulleys are worn. On it, you buy a kit that comes with all the bearings, belts and pulleys that move the X and Y Axis. Once you replace all of them, the problem will go away. My guess is most people just replace the belts and it doesn't fix it. It makes it a little better, but doesn't fix it.

Some times you can fix it, and some times it's the plastic being melted and it shifts right before it finishes the cut. Cut a thin strip of plastic and watch the thin part pull towards the cut. That movement can cause mismatches too. I've seen that many times. You can usually change where it starts and finishes on an object to minimize it, but it's often a sign of too much heat in the part.

Dave Sheldrake
02-28-2014, 2:28 PM
Step count on the Y axis is out.

Cut a square, flip it over and see if it fits in backwards. Do the same with a circle then measure both to see if the sizes are the same in both axis.

cheers

Dave

Rich Harman
02-28-2014, 11:48 PM
The step count being off would make for a wrong size part but I don't see how it would affect the endpoints not lining up.

I would first verify that the mechanics were in good order then you should be able to adjust out the rest using backlash compensation.

Kev Williams
03-01-2014, 12:43 AM
I've had the same problem forever as well. Even the new Triumph does it.

Hard to understand why the things can perfectly line up a .010" wide vertical line while rastering at 50 inches per second in two directions, but misses lining up the last dot with the first dot by a mile while making a circle at 1.5" per second... ???

Rodne Gold
03-01-2014, 3:33 AM
In RDCAM/laserworks use the lead in and lead out functions - will give you a perfect elipse
Look in the edit menu - edit cut in property...

Balsanu Gabi
03-01-2014, 5:22 AM
If you use RDCAM look at lead in and lead out. I choose arc with 5mm.

HTH
GB

Dave Sheldrake
03-01-2014, 7:41 AM
If one axis is moving more than the other the total travel of one will be greater so making the ends miss.

cheers

Dave

Kev Williams
03-01-2014, 7:41 PM
Well, I'm no genius about this stuff, other than I've been running CNC equipment since 1981, and it seems that vector cutting by laser is a typical matter of the machine moving to specific X-Y coordinates like any other CNC machine. And since the starting and ending point of any closed object is the same coordinate, a very loose belt(s) nowithstanding, there should be no variance of the start and end position. While this is mostly just a guess, I'm of the opinion that mismatched start and end points are caused by the head moving towards the next point while while the laser is still firing. The "Lead in-lead out" function mentioned above may be the way it's compensated for..?

Zlatko Kursar
03-03-2014, 3:26 AM
Thanks guys, I will try with lead in and out. I was try to uncheck "path optimisation" and then is better.

Martin James
03-07-2014, 6:11 PM
On the picture it looks like your start stop position is at 6 o clock, that is the thinnest area. It is not unreasonable to assume that thin plastic bends when heated. If that is causing the problem then:

You could set it up to always finnish on the uncut side of the run, or move the start stop point 1/4 of the way around.

You could set up a vacuum table. mdf + silicon caulk + silicon O rings + tubing Make holes, counter sink a bit where the o rings go, then make channels on the underside that connect to the holes, connect the tubing. Each piece needs its own o ring to vacuum clamp it in place.

cheers Marty

Zlatko Kursar
03-08-2014, 3:23 AM
This happens on all materials. On picture is some kind of textile. Yes, when it start/stop on left or right side is much better. But how Rodne says, lead in/out is solution.

Frederic Gagnon
03-10-2014, 6:33 PM
I have experienced the same problem on my Shenhui (1200x900). Look at the gears that hold the Y-belts on the left and right sides. The gears are mounted on the ends of the shaft in the back. This shaft has no flats so when the gears' set screws loosen, they slip a little bit, creating this problem. The one on the right side keeps loosening in my machine.. I am still considering using thread cement on them. There are 3 set screws for each gear (1 was gone during shipping, I had to find a new one). You will have to tighten each to the max. Move down the gantry a little bit until you see the next set screw inside the belt , and do all three. Check both sides.

Dan Hintz
03-10-2014, 8:07 PM
This shaft has no flats so when the gears' set screws loosen, they slip a little bit, creating this problem. The one on the right side keeps loosening in my machine.. I am still considering using thread cement on them.

You would do well to file a flat spot on the shaft instead of using thread-lok (though using the thread-lok won't hurt).