How to fix non round shapes?

All my prints seem to have a shift. See it on the cube near the bottom. Then it goes straight.




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Peter, As Tesseract asked, which axis is the shift on? I can't tell from the photos.

• Did you do the Y axis manual control move and resist with your hand experiment that I suggested?
• Please print that simple large flat circle again. Only a few layers is necessary. Does it exactly repeat the original photo?
• You can post the circle gcode and I also can look at it.

 

It's longer on the x, shorter on the y
The picture shows the top where the circle is, is where the extruder hits home position. The left side of the screen is where the front of the printer is.



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Hemostats and an allen wrench were what I used to tighten the y-axis toothed gear set screws so that I didn't have to remove the build plate. If you purchased your Robo3d pre-assembled as I did, you may want to double-check all of these. I'm sorry I didn't mention this sooner but somewhere in this post someone was ready to remove their bed.

 

Wow, I am visual so this helps a lot. Thanks


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I've been having the exact same issues with my prints. @SteveC, I took my bed off the printer and discovered a very loose set screw in the Y-axis motor. There are actually two set screws in that piece and you need a very short hex wrench to tighten those down. There is only ~4mm of clearance between the edge of the inset hole in the base and where the set screw needs to be tight. I trimmed a piece off the long end of a 1mm hex screw and used some pliers to position it in there to tork it down a bit. Only done one print since getting the bed back in place, but taking that slop out of the Y-axis gave me a near perfect circle.

Before and After: http://t.co/AKwkokvm9V

@Peter, if you're still having problems, take off your print bed and try turning your Y-axis attachment. I bet there's some play there. Tighten that down and I bet you'll see better prints.

 

Not perfect but looking better.



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So Peter what changes or fixes have you made? Posting nice photos without commenting on what you did does not mean much.

 

I levelled the bed and tightened my y belt. I took tesseracts advise on setting up my level and adjusting the z height screw.

I also increased my PLA temp to 220 from 190

I also added Hairspray with the two chemicals on my 55 degree heated bed.

Here is a chart I saw showing why to increase PLA to the temp of 220




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Ok so it looks like you have a reasonable confirmation that the funny non-round circle was due to the Y belt slipping somehow. Were the Y pulley set screws loose? Otherwise how did you tighten the Y belt?

I'm not sure what that Natureworks slide is showing other than the L and D optical isomer mix changes as they go up in temperature. This is an interesting presentation is about the history and future of the bioplastics industry but does not discuss PLA properties in respect to FDM printing. http://www.biocom.iastate.edu/workshop/2012workshop/presentations/bopp.pdf. Did you see this elsewhere with more details on what the slide is trying to convey?

 

I had tightened the y belt a little more. Set screws ok. I kept measuring how far the belt was currently and moving it up a notch till it felt tight.

The video is called
Improving the heat resistance of polylactide (PLA)

don't have the link but search youtube



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Thanks Peter, That video is talking about a stereocomplex PLA which is a mixture of L and D isomers which increases the melting temperature of the PLA. Natureworks is suggesting using this for thermoformed plastic packaging. I don't think this applies to any FDM PLA filament that you are using. Some mixtures such as the PLA/PHA like in the Colorfab filament does have a higher melting point though.

. The full lecture costs money to view.

"Polylactide (PLA) biopolymers are currently enjoying strong commercial interest as sustainable alternatives to commodity petroleum-based plastics in a wide variety of thermoformed packaging applications. ​

Typically, the properties of unmodified PLA resins are sufficient to meet the performance requirements of these applications, providing the temperature-performance requirement remains less than about 50°C.

For higher-temperature applications, the heat resistance of neat PLA resin is largely constrained by two fundamental physical limitations: a moderately low temperature glass transition (in the vicinity of 60°C) and a fairly slow crystallization rate.
​

This video discusses the results of a development effort within NatureWorks LLC to improve the practical temperature resistance of IngeoTM PLA sheet in thermoformed packaging applications through modification of polymer composition, crystal nucleation, and the thermoforming process."​

 

I noticed that my red PLA at 220 is a lot more stable. At 190, it seemed brittle and sometimes the layers were weak and could be pulled apart. 220 is working nicely.


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Lately I am getting shifting. I think it's time to take the bed off and find out if anything is loose underneath there. It's getting worse.



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If you haven't made z supports yet, that could be a big part of the problem. I printed that one too but then I printed two of these... http://www.thingiverse.com/thing:273962 A better option because they print lying down and they have a bigger footprint for more double-sided tape. Another thing you might check is whether or not your hot end can move at all. Hold your x-carriage still and try and wiggle the hot end. I was seeing this same sort of thing. If there was any plastic sticking up from the previous layer, the hot end would catch on it and change it's position slightly. This is something to eliminate before removing your bed.

 

I agree with donhuevo, that Z rod support will work much better with its larger surface area to stick and it will be stiffer. Enclosed is a similar design that includes a wire harness clamp in the right support. It should be spaced just right if you back it with a couple strips of the regular 3M double-sided tape. You might want to measure on your machine to make sure if you use it. May need a bit of very light filing to get the rod to fit just right.

I doubt a lack of Z supports is causing Peter's problem though. Yes, he should look closely at the hot end mount looseness and at the Y carriage. Also look at filament temperature and cooling. Those prints are quite a mess.

 

Both bolts were loose. I tightened them. I also noticed that the y stops switch is not actually seated onto the board. It's got screws but they are just sitting there in their holes. Freely moving screws. As if the hole is oversized for those screws. So I glued it into place.

After putting everything back together, my extruder does not extrude. The wheel is not moving.

What could be the problem? Is there a something I can check quickly to find out if a wire is loose? Is it underneath the printer is at the extruder itself?

Ugh!


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