How to Fix the White Outline on xTool O1 Omni Rotary Prints

You've got your O1 Omni and the rotary, you print your first tumbler, and there's a white line down one edge of your design. That's exactly what happened to me. The image looked great, but the white line down the left side was really off-putting, and there was nothing on the right.

The fix is a calibration that lines up the white layer with the color layer, plus one setting you can fine-tune afterwards. I didn't discover this myself. Credit goes to Sarah Nenni-Daher, who shared the solution in a Facebook post. I'm just passing it on.

Jump to: Why it happens · What you need · Prepare the cylinder · Load the rotary · Run the calibration · Read the pattern · White ink choke · Test print

Why you get a white outline

On a tumbler, the O1 Omni puts down white ink first and then prints the color on top. If the two layers don't line up exactly, the white peeks out along one edge. On my first tumbler it showed all the way down the left side of every figure. The calibration below tells the machine how far to shift one layer so they sit on top of each other.

I'd recommend doing this before your very first rotary print. You can go straight to a tumbler like I did, but there's a good chance you'll run into this.

What you need

• The O1 Omni rotary, installed and connected.
• A plain cylinder of the right size. xTool asks for a straight body, a round cross section, the same diameter all the way along and no handle. The recommended size is 60 to 100 mm across and 150 to 200 mm long.
• White paper and tape. Cut the paper to 130 x 130 mm. I used some old packing instructions.

I couldn't find anything lying around that fit those sizes, so I designed a cylinder in CAD and 3D printed it. It's free to download from my Free Files page with an L3D account. It's also handy for practicing wraps and other rotary prints.

Open the calibration in xTool Studio

1. Connect your O1 Omni in xTool Studio. If the rotary is fitted, it should say the rotary attachment is detected. Click Switch to change to the rotary workspace.
2. Click the Device settings button on the right.
3. Choose Calibration on the left.
4. Find Rotary Attachment Dual-Head Calibration and click Start. If you hover over the little info icon, it says it improves print quality issues and white over color coverage accuracy. That's the one we want.

The first screens explain what the calibration does and list the materials above, so you can check your cylinder against them.

Prepare the cylinder

1. Tape the 130 mm square of paper onto the cylinder, roughly in the middle like the picture in Studio, and don't let it go past the end of the cylinder. It doesn't have to be perfect.
2. Make sure the tape is completely flat. Smooth out any ripples and fold over any raised bits. When the printer measures the cylinder it takes the highest point, so a lump of tape will throw it off.
3. Wrap it all the way round and tape the end down flat too.

Load it onto the rotary

1. Turn the knob on the left anticlockwise (counterclockwise) to close the grips.
2. Push the end of the cylinder flat against the three rollers at the back.
3. Hold it there and turn the knob clockwise. The jaws will grip it and the cylinder may lift a little as they pull it into place. Keep tightening and keep it butted up against the back.
4. Check all three contact points. The cylinder must sit flush on all of them, or you'll get an error when it tries to measure the diameter and rotate it.
5. Turn the cylinder so the paper is facing straight up, with equal coverage either side. That's where it will print.
6. Press the button on the machine to take it back in.
7. Open the rear hatch. The machine checks this before it will rotate the cylinder and run the calibration.

Run the calibration

1. Back in Studio, tick the Done box to confirm you've set up the cylinder as shown.
2. Click Start calibration in the bottom right.
3. The rotary turns while the machine measures the diameter and length, then it prints two sets of lines on the top of the paper.
4. When it's finished, press the button on the machine to bring it out.

Read the pattern and enter your value

You'll see a row of line pairs numbered from 0 down to -10, each with the lines in a slightly different position. Look closely and find the number where the two sets of lines overlap best. It's easiest to read while it's still on the rotary.

Mine was somewhere between -2 and -3, and looking really close, -2 was the best. Yours will probably be different, because every machine is calibrated slightly differently.

1. Scroll down to the Calibration value box.
2. Type in your best number (I typed -2).
3. Click Apply.

That's it, you're calibrated. With the default settings you should now have no white showing around the outside. It isn't guaranteed on every item though, because surfaces at different angles can give different results. That's where the white ink choke comes in.

Fine-tune with the white ink choke

When you print an image, Studio puts a very fine edge of white around it by default. The White ink choke (mm) setting on the right controls that. It shrinks the white ink area inwards so there's less white showing at the edges.

• The default is 0.05, which can leave a very light white line around your design.
• Too much white showing? Increase the number.
• Not enough white? Decrease the number.
• Go too high, say 1, and the white starts shrinking into your image and can cut off its outer edges.

I printed my logo at different choke values to compare them side by side. It's a quick way to see what each number does on your own machine.

Test it with a print

1. Click the Modeling button. Choose Cylinder (mine has no handle, so I left the other options off) and click Start modeling. The rotary turns the cylinder and builds a 3D model of it.
2. Bring in your design. I used an Iron Man image with the background cut out.
3. Click Preview to check where it will land on the cylinder.
4. Click Process. You'll see the time and cost in the top right. Mine was 12 minutes and about 2 cents.
5. Click Print.

I was really happy with it. There's a very slight white line around the edge, but that's from the image itself, where I cut the background out. Compared with my first tumbler, where the misalignment was really obvious, it's now lined up and looking good.

Did it fix yours?

Let me know in the comments on the video what calibration number you ended up with. If you're printing batches of flat items on your O1 Omni too, have a look at my O1 Omni jigs.