Help me grok slicing

This may not be specific to the Mendel90 but I thought this would be a good place to start just in case it was. In any case, I have virtually no 3D printing experience as you'll see below.

Myself and my sons finished a Mendel90 build a couple of days ago. This was from one of Chris' recent kits and I have nothing but good things to say about the design, the materials in the kit, and the build instructions. The first prints went great. However, we quickly grew bored of printing the Android model whose G-code was included with the kit.

Picked out another model (Yoda-Lite) on Thingiverse, used Meshlab to tweak the STL (scale it down by half), fired up Skeinforge using what I believe are the settings included with the kit, looked over the slices (which looked centered to me) and exported the G-code. Uploaded the G-code export to the SD card using Pronterface, and selected SD print.

After the normal warm up, it began to print on the front left of the build platform, knocking the paper-clip nearly off, and began tracing out the first layer, but very tiny, and extruding plenty of plastic. It took me about 10 seconds to figure out something was wrong and pause the print. I was left what looked like a glob of chewed gum.

I just need a nudge in the right direction here.

Edited 1 time(s). Last edit at 11/29/2012 10:02PM by Rural.

Figured it.

I wasn't using the Skeinforge settings that were included with the kit. I thought I was, but that thinking was wrong. My guess is that I had a Skeinforge window up when I copied the .skeinforge directory to my ~ directory. I probably used the running Skeinforge and overwrote the copied settings.

Yoda is printing as I type. My sons are checking on him between short boutes of Minecraft.

Yoda's waddle was too much of a challenge for this noob. Tried pausing the print and turning on the fan. Yoda popped off the table at that point.

This is going to be fun to figure out.

Edited 1 time(s). Last edit at 11/30/2012 07:23PM by Rural.

I have never succeeded in printing a yoda because the steep overhangs cause the plastic to curl up and catch the nozzle. However, I haven't tried it with PLA and a fan yet.

Try increasing the bed temperature to 70C and turning the fan on after the first layer by inserting M106 into the gcode where the Z value changes.

The reason for your first problem is most of the Reprap world have the origin in the corner whereas I have it in the centre.

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[www.hydraraptor.blogspot.com]

The origin issue makes perfect sense.

I'll try the tip on raising the bed temperature and turning on the fan. I actually tried raising the bed temperature to 55C and turning on the fan after the forth layer. Yoda popped off the bed pretty quickly. Looked like it was the fifth layer.

The reason Yoda popped off the bed on my first attempt was that while I paused the print to enable the fan, enough of a blob of plastic oozed out to cause an issue on the next lap around the outside.

But I think I have to revisit my initial settings (like extrusion rate) before I attempt anything remotely challenging. Everything about my first print of the X Carriage Dial Gauge Mount is pretty darned embarassing.

I'd raise the bed temperature to 60 and turn the fan on for the entire print (even the first layer).
If you're using PLA either blue painters tape or a thin layer of PVA glue on the build plate will help it adhere.
There are parts of the Yoda print that are just plain bad geometry, but it will print and can look quite good, just don't be surprised when on some layers you are just extruding plastic into mid air.

Thanks for the tip. I heard about the PVA and will try it as soon as I can make a trip into town. Since I didn't have any PVA glue, I tried ordinary printer paper. Paper has a big downside, but definitely works. The downside is that you will have paper stuck to the bottom of your prints. Maybe the right type of paper wouldn't have that issue.

I've got a ways to go before I make another attempt at Yoda, but I'm looking forward to giving it another go.

Edit: I should add that paper won't keep objects from warping up off the bed during a print.

Edited 1 time(s). Last edit at 12/01/2012 08:09PM by Rural.

The green PLA supplied in the kit should have no problem sticking to the glass in the kit. Are you printing in a cold, drafty or damp environment?

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[www.hydraraptor.blogspot.com]

My work room is on the cool side. (Par for the course in Canada during winter.) Come to think of it, the weather was a lot nicer when I did my first prints. They definitely turned out better then than they have the last couple of days.

The bed temperature is measured under the bed but the surface temperature is what is important. If the room is very cold you may need to increase the bed temperature to compensate. If it is too cold the first layer tends not to stick. If it is too hot it will stick but peels off as the build progresses.

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[www.hydraraptor.blogspot.com]

One VERY useful tool is Repetier Host. I (still) use Pronterface to control my printer but if I want to see how my GCode will build up before committing to plastic, Repetier is the way to go and will enable you to see a 3D graphical representation of your model as it will finish up on your printer and also to build it up layer by layer on your computer so that you can watch for potential overhang problems.
You need to set it up to match your printer 'shape' - for the Mendel90, go into "Printer Shape" and set Print Area width, depth and height to 200, X Min and Y Min to -100, X Max and Y Max to 100 and Bed Left, Bed Front to -100. (You will also need Home Z to be set at Max, Home X and Home Y to Min).

Alan

Thanks Alan. I'll give Repetier-Host a try. It could save a lot of time and plastic. Might help with my ledge problem too.

Gotcha nophead. Understanding that behaviour is really handy. I don't really have much control of the temperature in my work-room, but that may change. In the meantime, I'll try to find a workable bed temperature given the ambient work-room temperature.