bit pecking at wood

[cwestwood]

I'm having a problem with some of my carvings. The edge of the carve areas are getting "pecked" by the bit on the pass or two before it actually plunges into the wood (see pics). Almost looks like it is trying to feather the edge of the carved areas although the feather setting is set to zero. The confusing part of it is that when I carve the exact same image in reverse (with the letters sticking out) it looks great. Both carvings were done using the exact same image, highest carve quality, bit optimization at best, and zero feather. I also notice that when the reverse of the image is carved, it still takes some wood out of the high areas so that the tops of the letters are actually a bit lower than the original wood surface. I am wondering if these two things are a result of the Y-axis being slightly out of calibration. Or is it something completely different? Any ideas? Thanks, Craig

[HandTurnedMaple]

Did you import these images into Designer? Or did they come as patterns?

It may be that they are some extra pixels from the pic you imported (if you went that rout). When you import it, turn the image in the second screen and see if there are any "fibers" (as I call them) sticking out of the image.

[Cliff]

What does the graphic it was created from look like? With 256 steps in carving just the slighest bit of difference can cause unexpected results. I've seen this in some of my pratice carvings and when I enlarged the graphic used to create the pattern noticed the shade differences. Either not totaly white or totaly black depending if I was running an inverted image. The machine is accurate to say the least when it comed to detail.

Cliff

[cwestwood]

Images were created in Corel Draw as black and white images and exported as a jpg. Then imported into designer. I tried looking at the second screen during import and didn't see any thing that looked out of the ordinary, but then again, I couldn't zoom in to really see any irregularities. Why would one image be so clean and sharp, and the invert of it all chipped up on the edges? Craig

[Cliff]

Not sure one is cleaner than the other. While one show the pecks at the top level around the edges the other is inverted so the reverse is at the base of the letters and not as noticeable but I believe they are still there. The image looks as if it was carved in mdf.

Cliff

[cwestwood]

I see your point that the irregularities may be at the bottom of the carving and therefore less noticable. From looking at the carvings themselves however, I can't see any signs of these "irregularities" in the inverse carving - it's very clean. Yes it was in MDF. Same problem noticed when carving pine and oak, although less noticable (I think the grain of the wood tends to mask some of it). The artwork is "clean" as a jpg so if the problem is from the artwork, it would have to be as a result of the import process. When I zoom in on the image in Designer it looks good there too as best I can tell. Any other ideas?

[BoardSilly]

Looks like pixalation occuring between the color used in the lines, letters and the background. This is a small but distinct bleeding from one color to another. Almost a 'shadowing' if you will. Decrease your color depth in the jpeg and see if it cleans up.

[CallNeg151]

I see your point that the irregularities may be at the bottom of the carving and therefore less noticable. From looking at the carvings themselves however, I can't see any signs of these "irregularities" in the inverse carving - it's very clean. Yes it was in MDF. Same problem noticed when carving pine and oak, although less noticable (I think the grain of the wood tends to mask some of it). The artwork is "clean" as a jpg so if the problem is from the artwork, it would have to be as a result of the import process. When I zoom in on the image in Designer it looks good there too as best I can tell. Any other ideas?

A couple of ways to tell if it is the jpg. Try carving the image twice. Does it have the same problem in the same places? If so, you almost certainly have a jpg problem. Otherwise, try carving a small piece created completely in designer, using no imported images. A simple carved square with a raster letter would work. Look around the edges. If the carving is clean, you likely have a jpg issue.

It looks like you are having some issues around the edges of the letters and lines. That mostly resembles jpg artifacting. Keep in mind that a 1/256th difference in darkness between pixels can create an nick from the carving blade, but is likely invisible to the naked eye on the computer screen.

Unless your bit is wobbling, or the markings are inconsistent between carves and appear on items not incorporating jpgs, then you likely have a jpg compression artifact problem.

Good luck!

[Rickrljones]

On my last carving, My CW machine started pecking on the flat surface of the carving... I was carving the Great Seal of the USA... It's a dished VA3D pattern... The only thing I did different was the carving height... I used .500 for depth and 350 for height... That was the only time my machine pecked at the carving...

[BobHill]

Could you have set the carving quality to other than BEST?

Bob