V-carve corners

[azlogger]

This one's got me stumped. If you look at the photos below, you'll see there are sort of some "bumps" between the sides of the "V" and the "X", and on the first photo, between the "I" and the "V". You can also see the same effect on the corners of the V-carved "blocks" in the first & second photo. It looks like the V-bit is getting just a little carried away with making the corner sharp, and going a bit too far. It has done this all along, but never quite this bad.

So…here are some facts: I am first hogging out the flat area with a end mill, then chamfering the letters with a *new* Whiteside #1550 60 degree V-bit. It's cutting 3/16" deep, 50 IPM, climb-cut. I'm using a profile toolpath for the chamfering. In the included pictures I had run the chamfering program twice because I thought that might help, if tool deflection was the issue (but I could tell no difference). Also should mention that the preview in Vcarve is perfect.

Thanks in advance!

[norseman]

If you are not pushing the machine into flex, it looks to me like something may be loose or you have some backlash. Maybe the router in the clamp is loose or possibly a coupler on one of the axes has moved or come loose…. You might also look at all the T-Nuts, making sure they are in place (not loose and/or not broken).

[azlogger]

I have checked and I cannot tell that there is any backlash. I have had this machine since September 2013 so I don't think wear is any issue?

[4DThinker]

On the original drawing zoom in as close as you can to see if where the bumps are there are ripples in the lines. I've seen where some fonts and shapes downloaded from the web will be poor scans with defects as if the original image was dirty leaving something other than smooth lines. VCarving generally follows the lines explicitly in my experience.

[milo30]

I was using my machine for several things today and on the first one I found mine doing what is showing in your pictures. It was the only one that did it for the day. I was able to trace mine to the font, which I had downloaded off the internet. I didn't notice it in the vcarve preview but I didn't look specifically for it. It was definitely noticeable on the final product. I think 4Dthinker's suggestion is a good place to start looking for the culprit.

[azlogger]

If I draw a straight line between the ends of the lines that make up the V, the lines look like they are perfectly aligned. Also I can snap to the ends and the middle of the line, if it was wiggly there would be more places to snap to, right?
I painted the part to improve contrast, here is another picture. You can see the bumps out in the corners of the rectangles here:

I'm still thinking it might be flex in the machine. But it seems like running the file twice would have done away with some of that...

[4DThinker]

I'm curious about the pass depth you have set for your v-bit. If the bit is asked to cut too much in a pass it'll eventually have to climb over chips. The Sharks have enough flex to allow that rather than force the bit to fail/snap. I had a bit snap today while helping a student. The problem was due to too deep of a cut on a pass. Before it broke you could see the path it was cutting get more and more ragged as the bit tried to power through chips.

[azlogger]

I'm cutting the full 3/16" in one pass. Pass depth is set at 1/4", but I've never cut that deep. Don't want to break a bit!
I'm kinda new to this so I don't know everything about feeds & speeds...

[4DThinker]

Try setting the pass depth to 1/8". See if that reduces the bumps. Feed speed shouldn't matter as much when v-carving as the bit has to change direction frequently.

[azlogger]

Alright. I'll give that a try as soon as I get a chance.