Retraction solution with Marlin, Pronterface and Slic3r

I’ve just fixed some key settings in Slic3r. Retraction Speed is now 7mm per second (down from 100!), and the Retraction Distance is 1mm. There is still slight room for improvement, but this is the best I’ve had it running for, well, ever. No stringing. Very little blobbing.

[Update: 2012/01/06 – I’ve now cautiously increased the retraction speed to 20mm/sec. It seems to be working, but I’m not fully convinced I’m not missing a few steps now and then during retraction.]

It turns out that one of my many theories was right as to the cause of my overextrusion. Thanks to a comment from Triffid Hunter with the phrase “as fast as you dare”, I thought of a way to test my MakerGear Mendel Prusa’s maximum safe retraction speed.

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Retraction, Huh! What is it good for?

Retraction is the technique of sucking molten plastic back up into the heated extrusion nozzle of a 3D printer. Like squeezing the edges of a toothpaste tube to suck back in some of the toothpaste you accidentally squeezed out. The printer does it by turning the extruder motor in reverse.

I’ve been fighting a losing battle with retraction since Boxing day (December 26). Not a single print worth displaying on my blog has emerged from my printer since then. So I thought I should blog about that!

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Getting your motors moving on a MakerGear Mendel Prusa

Here’s a quick and dirty guide to getting your motors working on a MakerGear Mendel Prusa 3D printer kit.

I assume you:

  • installed your arduino software
  • installed the Pronterface printer control software
  • installed your copy of MakerGear|Rick’s version of Sprinter, and
  • have flashed your Sprinter firmware to the RAMPS board.

If not, you may need to follow the steps in the “Getting Started Guide” (and followup comments) on the MakerGear Google Group.

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Updated build instructions – for z-motor mounts

I’ve just learned a better way of assembling the z-motor mounts on the MakerGear Mendel Prusa kit. The two main references are either outdated or confusing (ie, I was wrong and/or confused), so I’ve added some paragraphs to my mechanical build instructions explaining how to do it right.

If you just want the updated info, search that page for

[Updated 2011/12/26:- Spacing of the z-motor mounts]

Doing it right gets you 10mm more x-axis movement than I’ve got on my printer, and maybe slightly easier mounting of the RAMPS electronics board.

I’m not excited enough by 10mm that I’ll be rebuilding my printer, but if I was building from scratch, the new instructions are how I’d do it.

Thanks to Mark Boszko for asking the question (on the MakerGear google group) that brought this to light, and to MakerGear|Rick (of course) who answered Mark’s question.

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ATX power supply 5V load resistor for better 12V regulation

4R7 Ohm 10 watt wire wound resistor attached to 5 volt pins on ATX power supply molex connector

4R7 Ohm wire wound load resistor on 5V line of ATX power supply

Various people (Triffid_hunter in particular) and web sites (e.g. the reprap wiki) have explained that ATX power supplies are a bit cheap in their voltage regulation circuitry.

If you want to get the most power out of your 12V cables (for your extruder nozzle, motors and especially your heatbed), you have to draw some current from the 5V wires as well. Stupid, but that’s how the ATX is designed. Continue reading

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Essential tools for building a MakerGear Mendel Prusa kit

This is a list of tools I found invaluable (hey, I’ve no idea what your workshop situation is like – I hope this is not your first experience with nut and volts…) Continue reading

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Thermistor connections – screw terminals vs Molex crimping

Screw terminal strip used to parallel the two Z-motors on a Mendel Prusa

Screw terminal strip used to parallel the two Z-motors on a MakerGear Mendel Prusa

A couple of days ago I decided to smarten up my Prusa, by covering the exposed threaded rods with plastic “loom tube” (available locally from Jaycar). The 7mm variety fits nicely over the 8mm threaded rod, and also over the Z stepper motor wiring, as you can see in the photo on the left.

The red twisted plastic stuff came with the kit, and Jaycar calls it “spiral binding” and only sells it in black. I’m using it to tidy and brace the extruder motor’s wiring.

While doing this prettification, I broke one of the leads from the nozzle thermistor to its tiny Molex plug. Oops. By special request of Gary, here’s a photo showing how I fixed it. Continue reading

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