Odd final 1/3 of print

Hi thanks for taking the time to look at my problem, and hopefully for helping!

I have finished by prolonged build of a Prusa i3, which has been testing but finally I have been able to print, Yeah!!

However a new issue cropped up. I started with a simple 5 mm cube to test but on both tests the top appeared to deform with many gaps, but as this was small it was hard to see what had really gone on. So I went complicated and tried the little maker bot and it suffered the same issue, see attached images. To be honest the lower 2/3 printed really well, was quite chuffed until this but it does not show this on the images.

Can any one help with what might be causing this problem, looking at it there does not appear to be enough plastic, but as the first 2/3 printed so well this seems unlikely the feed rate was the cause.Looking at the forum I have seen similar image and this was caused but to much heat or to fast a print, but the print is cooled??

Any thoughts??

When printing tiny things like a 5mm cube, its best to print 2 at once to give the objects a chance to cool.

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Waitaki 3D Printer

I was thinking it looked a bit like a cooling issue too. Do you have a fan to cool the printed object? It helps tremendously with PLA.

I do have a fan pointed at the price as I printed, I will give printing to cubes a try, and see the results. What I don't understand is if it is a heat build up what happens to the rest of the material as there was deffinatly some loss but there were no disposits on the print or printer

Perhaps the extruder motor or the stepper driver is getting hot and starting to skip steps later in in the print?

Also, the lower part seems to be bigger which takes more time to make the layers and do the infill. Towards the top, if it doesn't have as much time to cool, you may see the heat issues...

Try the fan on the other side of the print and see if the problem remains on the same face of the print job. If it changes, it'll be a cooling issue. If it stays the same...likely it's elsewhere...

Thanks for the replys, looks like you righ itklein, just been testing and it appears to be the extruder. I was doing a cude again which so far has never worked so tried the makerbot again and watched it like a hawk. Noticed that the it was not extruding currently after a while and was starting to get quite warm, I had knocked the pot earlier as this was a bit low so this must have speed things up.

Looks like the culprit is the small gear on the extruder, the hole is off center causing it to rotate slight off center, and adding extra load to the motor, Heck knows how I missed that before, looks like I need a new one befor I try again !