Ridges when carving using Offset Fill Method

So I’ve recently started using PVC after @SteveMoloney showed off some excellent projects and gave me some wonderful tips. With PVC, I’ve noticed that I’ve gotten some unusual ridges where the bit stops and meets another bit stop. This spot that I’m talking about is in the image below, with RED arrows.

You can see this clearly in the finished carve images below:

You’ll see that the ORANGE arrows I put in my first picture actually carve through a section (as the bit does not lift), to carve out a tiny section at the top right of the 7.

Anyone have any tips? @SteveMoloney - Have you run into this?

It’s PVC board, so I’m doubting that the material is uneven (as it carves completely into the material…if this was the case, I’d expect a difference in height from one side to the other).

I’m using a 10% stepover, and used a 40% stepover in the image below (different carve).

You can even see above the stars above the RED…they were a different workpiece, so the machine was re-homed prior to that carve.

Can you share the project file? Possibly this?

I get these occasionally as well, Looking forward to see what else shows up. I have found clamping sometimes will raise the center up just so slightly so I put it off to just that, I would suspect the blue tape method would eliminate that. Looking forward to see what else shows up on this as well.

Sorry cant help but thanks for the shout out!

Neil, here’s a link to the file.

Thanks. Thinking about this, carving this 7 out should only make the Z axis go down once, and then up. It should remain the same level, the entire carve. Can the Z-Axis slowly slip? and if so, what would the fix be for that? Is there something wrong with my Z-Axis Screw?

For clarification, I’m using 30423-03, which is the 1/32" fishtail upcut bit. I’ve tried running this at Dewalt Speed 1 and 3, with no difference. Is it the fact that this is a fishtail?

As for the 3rd image (one painted red), the white section there was roughed using a 1/8" Solid Carbide 2 Flute Straight End Mill. The Detail pass did not go over this section.

@ChrisTech Unfortunately, I think it’s a combination of a bad toolpath (you normally wouldn’t cut across a pocket at cut depth like that) and something with your Z. Are you running dust collection? If so, make sure you’re not pulling the Z down / tilting it with your hose. I’ve seen that on an X-carve.
This would be in addition to what @SteveMoloney about evenly clamping.