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Inconsistent alignment between mills despite no change to XY Home

Hi all,

I’ve taken the plunge into CNC routing, and I’ve been refining my approach and workflow, but I’m having trouble with a reliable, consistent workpiece home/origin position. This last experiment I thought was going to be nigh on perfect but not so much. Here’s my approach and a pic of the results, any suggestions or advice? Many thanks!

  • I design and generate toolpaths from Fusion 360.
    • Toolpath plans:
      1. Adaptive Clearing with a 2F Straight 1/8" (Black collar from Inventables) - rough clear to .2" around the model’s top surfaces
      2. A second Adaptive Clearing with 2F Fishtail Upcut 1/16" (Blue) to exactly the model’s top surfaces
      3. A 2D Contour with 2F Fishtail Downcut 1/8" (Neon Yellow) to cut out the model from stock
  • Export toolpath with Easel post processor, import g-code into Easel.
  • Workpiece is secured over a second MDF wasteboard to protect my precious new workspace :slight_smile:
    • Piece was previously planed down to the appropriate height
  • I set up the machine for it’s first carve, following the Z-Probe process to set height, then X & Y home
  • I run the first carve to the ooo’s and ahh’s of friends
  • After the carve, I have to jog the machine to get the dust shoe off and change the bit
  • I click “Carve” and run through the Z-probe process, this time using the previously set X & Y home
  • Change bits again for the third carve, same Z-probe process

The first two cuts seemed well aligned on top of each other.

The final cut was off (see picture). I expected the third Countour path to cut out relatively close to where the Adaptive Clearing paths stopped (radially), but it was off by a good half centimeter to the left and bottom. Pretty sure nothing was bumped between cuts, and the material was down quite tight and didn’t move, but even if it was shouldn’t have using the previous X & Y realigned?

I want to do more complicated pieces that will require carving from both sides of a piece, so I’m really trying to get this consistent-origin workflow down right. Thanks!


Something is slipping - either mechanically, loosing steps along the way or design reference point is different.

What Xcarve or other machine do you have?

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@HaldorLonningdal I have the X-Carve 1000mm

As far as the design reference point, it’s all built off the same stock setup in Fusion 360 (though I think has been my issue with previous multi-mill cuts).

Are you homing between toolpaths?
If not, you may be manually moving the gantry when changing bits.
What’s your $1 grbl setting?
Do you have idle current reduction switched off (dip switch #4 near axes drivers in X controller)

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What are your feeds, feeds, and depth per pass settings? If you’re too aggressive it can cause slipping of the belts and whatnot. Another this to check is of the current adjust needs to be bumped up for you x axis motor.

@NeilFerreri1 - I was not homing between toolpaths, so I spent time on the weekend getting up close and personal with better understanding how grbl manages positions and such. Now I’m using a combination of homing more regularly and G28 to programmatically set the start position. That worked! I got a clear, three-bit carve completed just I wanted.

Thanks, all!

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  • Note that G28 is only a stored offset to machine zero (homing position)
  • G28 and G30 are freely assignable parking points and have no impact or related to work zero in any way
  • G28 is not a requirement to your work flow and not using was not the cause for your issues

Ideally:

  • You home the machine once at start-up or whenever you think steps are lost / reference lost
  • As work zero is also stored as an offset from machine zero it will be stored and reusable between power cycles etc, just as G28/30

Your machine have (pics in first post) lost steps, rehoming between stages will help - but will not remove the reason for the lost steps in the first place. I suggest you also spend a little time going over the machine mechanically and finding its sweet spot for that wood - so you can carve with confidence :slight_smile: