Litho problem...

[Arbo]

Have been cutting quite a few lithophanes. Has all been good, until recently. All the sudden I am getting some strange results.

In the attached pictures you can see the doubling of the rocks, in the flower picture you see it at the edge of the pedals. No idea what on earth could be going on... I can't figure how it could be the machine...

if it was a z problem, it seems it wouldn't be consistant as it is... kinda mind boggeling...

On the beach scene it was cut at a 45 angle, the flower was raster on the x at 0...

Thanks..

[Arbo]

Of note, I brought up the gcode in Mach, and tilted the toolpath and zoomed and looked nd found the toolpath does the edges correctly.

So that's not it.

Using a gecko 540... if they get too hot might such a thing occur? will go over the machine again, but I don't beleve anything is loose..

[Arbo]

Interesting, I was just out there, and cut out a little one, and it appears to be just fine. Now the machine was off, and cool. The other ones I was running the machine for hours, and it was really hot in the workshop... I am starting to wonder if it is the controller getting too hot...

I will get a little fan and have it blowing on it and run a 5"x 7" when I get the chance and see if that changes anything.

[Arbo]

I went over the machine... seems all is sturdy, can't twist or move anything. So I started another with the 1/8 bit... but I got down close to watch.

One pass (going -x) it is all fine, then it moves over slightly on the y and goes the other way (+x)... this is where the trouble happens. I took a video and it
is very obvious. The little bit of play in the Y is far smaller than how much you see the bit slip over... so I am not sure what is going on...

To test, I manually ran the bit -x to cut, then over a little on the y then back up +x real slow.. does the same thing... actually, it jumps over within the first 1/4 inch when only
moving about 20ipm. But I kept running it out that way, it obviously cut nothing, then without changing the y, ran back the other direction on X, and it moved back into place
and cut away the edge as it should have when moving the other direction...

Here is the video:

http://vimeo.com/14307039

[jhowelb]

Look for unwanted movement of your tool. Bearing slop in the router, gantry sway or something on that order.

Cutting one direction is conventional milling, the tool cuts on the way out of the material and tends to pull the bit into the cut.

Cutting in the other direction is climb milling and tends to pull the bit out of or away from the work.

[Arbo]

jhowelb,

It was the gantry. I found I could twist (is that 'rack'?) it some. So I made the needed adjustments, no more twist, and the problem is gone. Thanks.

[Stewey]

I had similar issues with heating & double edges- & found the problem was the delrin nut on the Z axis leadscrew getting hot & binding when asked to do a lot of movement in a tiny area of the screw. Changing to a ballnut leadscrew fixed that- but not before I burned out two servos.

What feed speeds, cutter diameter & stepover are you using?

[Arbo]

1/16 ball nose cutter, 10% stepover, feed at 40ipm, but the actual speed due to all the up and down of the z falls into the 20's or so (based on looking at what Mach says it's running at).