Bespoke Wheel Centre Caps Using Z-Hop Method

thingiverse

This is not so much a "thing", more an essay on using the Z-hop technique I saw on Chuck Hellebuyck's YouTube channel a couple of weeks ago. It's not something a complete novice should attempt, as it isn't just upload 'n' print!! Chuck used a 0.4mm (2 layer) print height for his logo, but I used a 0.6 (3 layer) for mine, with an appropriate increase on the Z-hop height. My pal Alan recently bought a small, newly converted camper based on the Mazda Bongo minivan. In an amusing example of half-hearted badge engineering, some of these vans - Alan's included - were badged with "Ford" logos, front and rear, even though the wheel trims and steering wheel centre boss still carried the standard "Mazda" logo! Alan's original wheel trims had seen better days. So he obtained a cheap set of universal wheel trims to replace them. These new trims complimented the vehicle extremely well but, being universal, had plain centres where importers and end users might wish to add a suitable logo. This tiny missing detail left the trims looking unfinished in a way that was a little jarring on the eye. As we stood looking at it, Al remembered that I had a 3D printer, and asked if it was possible to create something with a personal touch to fill the void. After some discussion about whether a "Mazda" logo or a "Ford" logo would be better, obviously, we decided on a custom design. That's when I hit the first problem: When the ABL kicked in for the second colour print, the first print obstructed the probe again. The solution is simple enough: Both parts of the model need to be placed away from the centre point (still properly lined up with one another, obviously), so that the probe can do its thing without the first print getting in the way. So began attempt #2. That's when I hit the second problem: When the ABL kicked in for the second colour print, the first print obstructed the probe again. Again, it's an easy one to fix: This time it's dealt with in the slicing software. I had to temporarily edit the G-code in the slicer's machine settings to disable the G29 command in the start code for the second print. With the ABL inactive, the printer could get on with the second colour - provided, of course, that the bed was good and level when the first print pass was made! At this point I had a third hiccup. I suspect this might be one that doesn't trouble everyone: My slicer (Cura) likes to print a hot end priming line at the left of the print bed before getting on with the actual print. I've never been fond of this line, but I live with it because I get consistently better first layers with it. But, when my print head came in for the second colour, it tried to print another priming line in EXACTLY the same place, not realising that the first print's priming line was in the way. In my case this just gave me a "snotty" nozzle and a few unsightly blobs on the print. But I could easily see it disturbing the printer's movement enough to cause the belt to jump, destroying any alignment between the two separate print runs. To be honest, I could have easily edited this out of the start up code, like I did with the G29 code. But for the sake of simplicity it's easier to just pick off the first print's priming line when you change colours for the second print run! My final niggle came about through my filament runout sensor, and might well be exclusive to my machine: You see, I use a home made sensor assembly - basically a microswitch in a custom mount. But, for some reason, the rapidly oscillating Z-hop motion caused false triggering on this, launching my machine into "filament change" mode with an annoying frequency. Whether this was down to a dry joint in my wiring, a fracture in the switch wire, or just plain ol' contact bounce in the switch is unknown, and I wasn't going to investigate as it works fine the rest of the time. So I simply disabled the runout sensor whilst I was producing the two stage prints and, Bob's yer Uncle, problem solved! I'm indebted to the wonderful Mr Hellebuyck for introducing me to this technique. I find him to be a very relatable guy (although I probably don't watch nearly as many of his videos as I should) and I recommend checking out his channel and giving him a like or three. I also hope that between his video and my over-wordy description, it will encourage those who haven't tried this before to give it a shot. Happy printing folks, and remember that you're never alone with a 3D printer!