Z-probe V3: Now With Wings

In previous posts I described a z-probe modification I made to Squirty the RepRap. The major issue with this z-probe was that the point probed was about 30mm away from the nozzle, which meant that the probe could not reach the entire bed. I’ve designed a new version that resolves that issue. By mounting the microswitch on the same side as the hotend the microswitch for the z-probe is almost directly underneath the nozzle. Mounting the z-probe in this way required creating “wings” that stop the servo arm from colliding with the z-axis at low/high x values. In this post I’ll describe how to assemble and set up this z-probe on a RepRap Huxley. I hope this is useful for anyone out there who is still, like me, printing on a 5+ year old design. If you do try it then please let me know how it works out!

The video below shows the probe in action.

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Multi Setting Calibration Prints

3D printing is, of course, the most frustrating hobby in all existence. Browse through any 3D printing forum and alongside the beautiful prints you’ll come across posts that compress incandescent rage into a few choice words like “I’m throwing my ******* printer out the window”. In my case most of this rage comes down to keeping the printer properly calibrated, in particular keeping a correct height for the first layer. 90% of my failed prints fail because of some issue with the first layer, and often it is because the height is wrong. In theory you should be able to set the height correctly using the time-honoured piece of paper technique, but it always requires a little bit of dialing in for the best quality. This post describes a way of simplifying that dial in process by printing multiple test pieces in a single print with a range of starting heights.
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Unmelting a printer

After my printer almost killed me I needed to get my hands on a new hotend. RepRapPro, which made my printer kit, has unfortunately closed down so I got a new nozzle, heater block, heatsink block, heater cartridge and thermistor from emaker.io. The nozzle is the new “quickset” design, which is clamped in place rather than screwed into the heatsink block. It’s also designed for a dual nozzle setup, so rather than having one central slot for a hotend it has one on either side. This dual setup requires a different design of x-carriage, which could be easily printed if one’s printer is not melted. Since mine was VERY melted I could have gone and used someone else’s printer, but that would have required leaving the house and possibly even social interaction, so I tried to think up a way of setting it up with the parts I had.
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Meltdown

After a period of relevant dormancy, Squirty has had a lot of work done recently. I have replaced most of the original plastic parts, which were starting to crack, and put in new bearings. I also designed a new x-carriage ducted fan adaptor that put better air flow on the printed part and put in aluminium pulleys to replace the badly worn plastic ones. I’d even made some progress rebuilding the case after its destruction in 2014. Little did I know the printing gods had a plan ready to knock poor Squirty back and severely terrify me into the bargain.
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Measuring a 3D Printer Bed’s Flatness

Once I got my printer’s z-probe and autoleveling set up I was struck with a sudden paranoia that my printer bed was saddled. The standard autoleveling in Marlin can deal with a printer bed that is not level, but it cannot fully correct for a bed that is not entirely planar*, e.g. one that is bowed or saddled. To try and set my paranoia to rest I decided to test whether my bed was truly flat.
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Stripey kapton tape for glass beds

Some time ago I put a borosilicate glass bed on Squirty. I really like it because PLA will stick firmly to it when it is hot, but will pop off easily once it cools down. It is also really easy to clean. The only issue I had was how to attach it to the aluminium print bed surface. I know a lot of people use binder clips, but they have the disadvantage of slightly reducing the print area and also jut out above the print surface, risking collisions with the nozzle. Up until now my approach was to use kapton tape along the sides of the bed. It wasn’t a great solution because the glass still could slide back and forth slightly relative to the aluminium bed and it also tended to peel off over time. Today it occured to me that what I needed was double sided kapton tape. Such a thing does exist, but rather than ordering it I decided to cheat by alternating stripes of kapton tape with one “sticky side up” piece of tape stuck down by two “sticky side down” pieces. This arrangement holds the glass in place really firmly and yet I think I could still remove the bed without causing any damage.

This is a really simple idea that probably should have occurred to me years ago, but I am unreasonably pleased with it!

The bad old days. Tape around the side of the bed ineffectively holding the glass in place
The bad old days. Tape around the side of the bed ineffectively holding the glass in place

Alternating stripes of tape - one "sticky side up" piece of tape is held by two adjacent "sticky side down" pieces
Alternating stripes of tape – one “sticky side up” piece of tape is held by two adjacent “sticky side down” pieces

Melzi holder and new wiring

In the last couple of posts I described how I put a z-probe onto Squirty the RepRap. Adding the z-probe meant new wires. These wires ended up jumbled all over the place and occasionally got caught on the z-axis threaded rods, causing all manner of chaos to break out. The z-probe also requires a lot of clearance, which means that the printer carriage spends more time up at the top of the build area than it used to. Once up there, it has a nasty habit of bumping into the Melzi control board. To try and tidy things up, I collected all the wiring for the z-probe and ducted fan components together and designed a new set of Melzi holding clips.

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