Stepdown is not as expected

[sylayo]

Hi, I've put my first model on the CNC and everything seems to works fine except on a few spots where it looks like the machine was taking too much at the same time.  So much wood at the same time the spindle got stuck and stop spinning (missed a few heartbeats there...).  So I went back in simulation and try to figure out what had happen.
As far as I know, my settings are to only take 1mm of wood on each pass (Maximum roughing stepdown) but if you look at the picture, you can see the bits is taking more then expected:

Any idea what could be the reason and how to prevent it to save my machine and my nerves...

[mattdlr89]

I think it's taking steps of 1mm and 0.5mm. 

It will go down in steps of 1mm then back up in 0.5mm steps. This is set in the "Finestep down" box

[sylayo]

First thanks for your quick answer!
So I guess this is not my problem otherwise I'd have that problem all the time. Like I mention, it works most of the time but here and there it literally bite into the wood and jam everything.  Any other idea?

[HughesTooling]

---

@sylayo wrote:

Any idea what could be the reason and how to prevent it to save my machine and my nerves...

---

What you show above is the fine stepdowns of 0.5mm and the pocket is 1mm.

Here's what I'm seeing and you can see the finer 0.5mm steps in the middle of the part and what looks like your image with the 1mm maximum step

[HughesTooling]

---

@sylayo wrote:

First thanks for your quick answer!
So I guess this is not my problem otherwise I'd have that problem all the time. Like I mention, it works most of the time but here and there it literally bite into the wood and jam everything.  Any other idea?

---

Looking at this area again I noticed you have the ramp angle set to 15°, might be worth decreasing this to see if it helps.

[sylayo]

Looks like my problem always happen on the edge of the stock.  I've retried after increasing the 'Stock side offset' to make sure it's bigger then my bit but again it seems that everything is ok, the bit is removing material layer after layer and then suddenly it try to bite outside the edge of the stock where nothing has been removed so far.  We can't really see it in the simulation because the bit goes over the edge of the stock in the simulation but we don't see what's beyond that edge... 

Any suggestion?  Is there a way to leave some material on the edge of the stock?

[HughesTooling]

Are you saying the stock on your machine is bigger than what you've setup in Fusion? You need to set the stock the same as real life or Fusion doesn't know it is pocketing and needs to helix down. You also need enough room for the helix outside of the part, seems to work if I set the additional offset to 10mm and the minimum helix diameter to 2mm. You can probably reduce the offset.

Setup with bigger stock I now get a pocket and no plunges at the edges. See attached file. I turned off smoothing and feed optimisation to speed up calculation while experimenting.

[sylayo]

Ok but if I setup the stock to the exact size of my piece of wood, how am I supposed to clamp it down?

is there a way to cut exactly to the defined size of the stock and not touching what is around of it?