A weak section is recurring

I have a new problem (to me), when I print I get good solid structure for ~1/8" in the "Z" direction, then for the next approx 1/8" the structure is really weak. Then it returns to solid structure for the balance of the print. This is happening on tall and short item in the same relative position ie. starts at 1/8", continues for 1/8" then is OK.

Any sugggestions as to cause and cure?

Bob

Do you have a fan or something that comes on around that height?

Do you change temperature of the hotend after the first layer?

Edited 1 time(s). Last edit at 12/13/2013 02:49PM by ShadowRam.

I have a fan directed at the extruder, above the heater. It is directed away from the printed part. It is controlled by Slic3r/Repentier.

My temperature is set to 185c (PLA) for entire print.

I have tried several prints with these results and while occuring at the same "Z" height the print would be reaching this point at different times of printing precluding something caused after a specific time of operating.

I have also seen this problem. I found sometimes turning your filament fan off works, and other times just letting it extrude filament (not printing) for a while. If you can, clean your drive gear mechanism.

Yeah, check the fan. I experienced bad quality prints when I turned off the fan to control warping, due to creeping of the heat upwards I guess.

*this is not a bot

I have tried fan on, fan off, fan auto, all without success, still have weak section and still at same "Z" height of the print. I have tried temeratures from 180C to 195C, also no success.

With this a continuing problem my printer is useless for making usefull items!

Am I the only one to have this problem?

Bob

This may not exactly be related, but I have found the layer bond strength to be a little bit too low when I print PLA at under 200°C. The best temperature was 210°C, at which the parts become rock solid. However, this doesn't explain why the part becomes strong again after a weak section.
In which way is the structure weak? Bad layer bonding or irregular extrusion or...?

Quote
BobHewson
Am I the only one to have this problem?

Maybe. But on the plus side, at least your problem is really interesting. Any chance you can get a photo up on here?

To troubleshoot, I'd start with a couple of sample prints.
* A 25mm cube (hollow)
* A 75mm x 25mm x 25mm (35% infill or so)

I ask for these because I'd like to see if...
* ...the problem is directly related to z-height or the time the printer has been running. (The long cube with infill will take longer than the cube without.)
* ...any repeating z artifacts are present. (With 25mm height, we get to see 8 1/8in strata.)
* ...the problem is somehow confined to a specific x or y location (hence the 75mm length.)

Also, it's not clear if your printer used to work, and then starting having this problem, or if you've just built/got it and it has always behaved this way.

My printer was printing without this problem before, it is a recent but contiuously recurring problem.

I have had the problem in differing sized prints, and the problem occurs at the same height of the print i.e. about 1/8" above the bed and persists for about 1/16".

I have retuned my X,Y belts and relevelled everything, but while my prints have improved in genert the problem still exist.

The weak section is lighter color, almost looks like a foamy interior where the break occurs. I have not seen any fluctuation in temperature when it gets to this point while printing (print appears normal as it is laid down. The weak section occurs across the full layers of multiple items being printed at the same time, all at the same height above the bed. Same for subsequent prints done at the same session or another day.

I wonder if the stepper drivers could be malfunctioning or need tweaking but don't think they would cause this. If overheating, stopping and starting cold happen, but wouldn't this cause voids, shorter dimensions in x or y.

I have been printing at 185C - 190C which is also the temp reccomended by my PLA filament supplier. Areas other than that under discussion are well bonded and can't be separated.

I'll try to get some up-close photos and add to this message later.

Bob

I have been unable to get any decent photos to show the problem.

I have however resolved my problem.

My printer was built about 2 years ago and while it was not used for long periods it is still 2 years old. A number of problems had crept into the unit from sitting; loose nuts, and movement of the plastic parts under pressure, slack in drive belts.

I invested some time in re-leveling, re-squaring, rewiring, belt tightening, and general tightening and re-alignment of nuts and fittings. While I did these maintenance things during a single session I'm not sure which one cleared my problems, but my printer is now printing like it should.

So, problem resolved. Thanks to contributors for suggestions that helped guide me along.

Bob

Edited 1 time(s). Last edit at 01/26/2014 03:50PM by BobHewson.