Tool paths off after bit change.

[sudo]

Ive recently done a few jobs and after I change bits and resume cutting, the tool path is off.

For example. I used my laser engraver to engrave a few smiley faces. Then used a .25 bit to cut them out. Every single one is off sides in the same way. It should be a perfect circle within a perfect circle. Im getting a lopsided smiley face cutout. Both the laser and cut out are perfectly round, but they are not seated within one another perfectly.

Ive done a few recent jobs and have noticed this trend. Ive only noticed when switching between the laser and a cutting bit.

When doing these jobs, I only reset the z axis to accommodate the new bit length. The first time I setup the xyz axis to the laser. Made the engraving. Sent the shark back to xyz zero and raised the z axis to swap bits. Swapped bits and lowered to work piece and reset xyz. The second time I used the vcarve bit to set the xyz zero and then swapped out to the laser bit. Did the engraving and swapped out back to the vcarve bit. It was off in the same way.

When I run multiple paths with the laser alone or a bit alone, its perfect. It only seems to be happening when I change out bits.

Has anyone else seen this with the laser? Any tips on getting these to align?

[SteveM]

I am not the expert here, but I don't think you should reset the X & Y axis. Only the Z with your touch plate.
I hope someone else chimes in so I know if I am rite or wrong.
The X & Y are where you already want them to be, You just need to reset your Z because of the bit change.

[Kayvon]

The laser doesn't have the same X,Y as the bits, so it makes sense that he'd need to change more than just the Z axis.

Can you describe the lopsided cut? Is it stretched out in a single axis? If you could post a couple pictures, that'd be great. We love pictures.

[sudo]

Here is a pic. All the cuts are a little up and right of the laser engraving.

[Kayvon]

If I edit your picture, I can draw almost perfect circles on the cutouts. I attribute the slight inaccuracy I'm seeing to the angle of the camera, so the cuts don't appear to be lopsided. Same thing with the laser etching.

Both the laser and cut out are perfectly round, but they are not seated within one another perfectly.

Oh, right. I guess I should have read more closely the first time.

The laser and mill are misaligned. I don't know your laser configuration well enough to tell you how to permanently align them, but aligning them during a job isn't all that difficult. Try this:

1. As part of your laser engraving, have the laser etch a single dot at a known point. Pick somewhere simple, like 0,0 or 1,1, that won't interfere with your project.
2. When you switch to the milling portion, start by installing a bit with a small point--either a thin end mill or a V bit. Use the control panel to manually align the tip of your bit to the dot you engraved in step 1.
3. Once the bit is aligned with the dot, tell the control panel what the new X,Y coordinates are. They'll probably be off by the amount you've been seeing in previous cuts. If you repeatedly notice that the coordinates are off by a constant amount each time, you'll be able to skip steps 1 and 2 in the future and just apply the offset in the control panel each time. You might also use this information to help permanently align the laser in the future.
4. Now you can install the cutting bit you actually want to use and align the Z axis for the new bit. Move to the new 0,0,0 and perform your cut as you normally would.

[Rando]

One other thing to consider is that the human brain is VERY good at detecting visually off-center things. So much so that it's very difficult to get anything reliably centered without achieving accuracy typically under 0.010". One way to overcome that, if you're already close (after you solve the significant registration errors you're seeing here), is to use non-circular profile outline or design. E.g., intentionally make it slightly oval or football shaped, or apple shaped, or some thing that doesn't immediately make people thing things are misaligned.

For not, it looks like circular is how you want to go; so tuck the above away for future projects .

But yeah, I'm going with mis-registration, given they're all off by what appears the same amount and direction.

Regards,

Thom

[sudo]

Thanks all for sharing your wisdom. It really helps