Hello,

Our Darwin makes repeatable errors when the Z-axis moves up and down. As it moves up and down, the Z-bed wobbles, tracing out small circles (1mm radius or so). The result of this is that each layer is slightly offset from the previous one in X and Y. It would probably be possible to correct the problem mechanically by adding bearings, realigning the rods, etc; however, this would be expensive in both time and money.

Without correcting this error, I'm concerned that print quality will be too low for self-replication; a vertical hole will become a corkscrew shape, and it will be impossible to fit a bolt through it.

Printing several copies of the same parts reveals that the errors are highly repeatable. Each part shows the exact same offsets at each layer.

In that case, the simplest correction is going to be in software: Measure the errors in a test part, and modify the G-code to correct for that error. Ideally, I would create a table in notepad of X and Y offsets at successive Z heights, and a program would use it to postprocess the G-code to correct for these errors.

Does software already exist to do this? Can I do it with Skeinforge or Host? If not, would anyone be willing to take up the challenge? I won't be able to work on it at the moment, due to my preoccupation with the SpoolHead. But if anyone else wants to, I would be very grateful!

jbayless Wrote:
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> Does software already exist to do this?
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Not to my knowledge.

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Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

I've had the same issue with my wood Darwin. The primary cause was that the drive rod and the motor shaft were not aligned well. Wanting to save on time, I bought an expensive shaft coupler that could handle the problem. I still have an issue with the bed constraint brackets which have too much play. I'm planning to print replacements to those which are more accurate.

I thought I was the only person with this issue. Is it common? What have people done to work around it?

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Darwin clone, Gen 2 electronics, Arduino Duemilanove w/ AtMega328, 5D Firmware, Pinchwheel extruder
[www.codeerrors.com]

I don't understand the problem. The bed is constrained by the 360 bearing in one corner so it has to follow the corner rod and is constrained by the 180 bearing in the opposite corner so it cannot rotate. It should not be able to wobble, even if your threaded rods are slightly bent.

In this video [www.vimeo.com] you can see my drive screws have lots of wobble, but the bed does not.

Is your 360 bearing not a close fit on your corner rod? I print these holes undersized and then open them up with a drill and reamer.

Edited 1 time(s). Last edit at 02/27/2010 08:58AM by nophead.

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[www.hydraraptor.blogspot.com]