Carved pocket bottom not flat

[AxGryndr]

I am working on a stove cover that I want to add an inlay to. I setup the inlay carve as a horizontal flip of the design, and a pocket carve using a steep V-bit and a 1/4" spiral end mill. To test my offsets and carve, I ran the carve on a piece of MDF. After the carve finished, I noticed that the cleared areas were not all flat.

In the picture I have attached, you can see the high spots I am talking about. My first thought was my bit was loose, so I tightened the collet, sent the file again, and no change. Based on the location and the pattern, the issue does not seem to be related to unevenness in the spoil board. I thought the issue might be the Z axis had slop allowing the carriage to move but I would think the second pass this would be less of an issue because there would be less material. I jogged the gantry to over one of the high spots, lowered the bit to the carve depth, and the bit would clear material to match the flat surrounding area.

So I figured the issue might be with the toolpath from VCarve, so I reduced the IPM of these cuts to make sure it was not skipping steps and I removed the ramping. These changes didn't really help, so I tried again and switched the path from offset climb to offset conventional, and sent it again. This time, the high spots got smaller but there was still some remaining. Right now I am trying a raster with a profile pass.

If these high spots are coming from VCarve, I am not seeing them in the preview. Has anyone else come across something like this or have an suggestions on what I should try next?

[Bob]

I can think of several things to check:
1. See if the material is shifting upwards during machining...see if the clamps are holding properly. It looks like you are using cam clamps. These can slip if the edges of the material are not gripping sufficiently.
2. Is the board warping as it is machined?
3. Try a down spiral endmill it will create a downward pressure, and help keep the material from moving up. (If it is moving up.)
4. Be sure that the collet is clean. There must be no lubricant where the collet jaws touch the bit.
5. Check your safe Z to verify that your gantry is not traveling too high and hitting the vertical limit.
6. If the preview shows a correct outcome, you have a problem with the machine. Either the bit is changing position, or the material is.
7. Be sure that you have the latest updates for controller software.
Bob

[AxGryndr]

Thanks for some ideas.

1. I am using double side tape, Intertape 591, under the material along with the cam clamps because I have limited material for the project so I need to carve as close to the edge as possible.
2. With my dust shoe it is hard to tell.
3. I can try this.
4. Will do.
5. The safe Z is set to 0.2 for the project, and the material is only 0.75, so I should not be hitting the vertical limit.
6. I agree, but it is odd that the high spots seem to be in the same location after changing material and swapping bits. It would seem to me if either the material or the bit was moving, the location of the spots would change but it doesn't seem like they are.
7. I have not updated the controller in a while so I can check this.

Another thought I had, I am not using virtual zero on this project, but I have on a previous. Is it possible the controller is applying those setting anyway?

[gjf1947]

Try making the cut without the dust boot.

[Bob]

Another thought: Does the bit return to the same Z zero position after the cut as when it started?

[Kowalsker]

You need to tram the spindle in. Your 'spindle' is at that angle to the table. It's a lot of loosening screws, addition of shim stock and some other bits.

https://www.cncsharktalk.com/viewtopic.php?t=6225

A place to start.

Word of warning. The gantry back plate/main plate plate is only rigid straight up and down. All the weight is hanging from one side. My HD520 with the spindle would "nod" about 0.032" in the center of travel. My fix was to counter-weight the other side. It's not pretty, but I brought the nod to +.003/-.000 in an dual s-curve each end of X is 0.0, the center is 0.0, in between each side and center the spindle nods .003" due to the main member twisting, which is has low moment to resist the load hanging from one side.

Some shim stock and a lot of forced patience I'm doing fairly well,

Good luck.

[markjonesranger]

Bit slipping in the Collet? I had that a few months back. After cleaning I tried it again and it slipped again so I threw it away.