printing previous print atop a new one

[johannessssss 0]

Dear Community,

I have been using my Ultimaker 2+ with succes for a year now. However, recently my printer is starting to print my previous print atop my new print. More concrete, it starts printing the new print for about 20 layers and suddenly it starts printing the previous file. you can imagine that this does not go well and i end up with a pile of plastics. I switch sd cards everytime i start a new print. Does anybody have a suggestion about how to fix this?

Thanks in advance

[gr5 2,167]

This is bizarre.  It sounds like a corrupt SD card.  Make sure you do a "eject" before removing the SD card to be sure the file system isn't corrupt.  You might want to "repair" the SD card.  For example windows will usually prompt you to repair the SD card when you stick it in a windows computer.

 

If that's not the problem you should definitely open the gcode file in a gcode viewer before you print the object.  One simple one is at the website: http://gcode.ws

 

Just drag and drop your gcode file FROM THE SD CARD!  Not from the hard drive.  Onto the box in gcode.ws.

 

[johannessssss 0]

@gr5 Thank you for your quick reply. Of course, your first mentioned steps with regards to repair and ejecting the SD card, I paid extra attention to the first time the problem occurred.  

I am going to take two fresh SD cards, view every uploaded .gcode with a gcode viewer. I will keep posting positive or negative results.

[geert_2 557]

That looks like a writing-action to the SD-card was interrupted half-way, for whatever reason. For example: the user pulled the card out of the computer while it was still writing data to it; or a software crash stopped the writing prematurely; or there was an unrealiable connection, e.g. dirt or oxydation on the connector pins.

 

When you "delete" a file on a disk, its file-contents are *not* deleted. Only the reference to it in the index is deleted. But the old file itself is still intact. That is why you can recover deleted files with special software.

 

So the disk space occupied by the old file is listed as free, although it is still full of the old data. A new file will then overwrite these old data. At the end of each file, there is a code indicating "end of file", so any software that opens the file knows where to stop reading.

 

If the writing of the new file is interrupted half-way, then that damaged part of the file has no "end-of-file" code yet, of course.

 

So the next software that is reading that file (here the printer) does not know that it should stop reading at the end of the damaged new file, and it continues reading the old data from the previous file which were still there.

 

Maybe this is what happened? That would give exactly those phenomena you describe. It is a guess, but an educated one.  :-)

 

Writing to SD-cards may go slow, especially if there is an antivirus active, or if the SD-card controller has to move large blocks of data from unreliable memory cells to reliable cells. Or if the data are very fragmented (=spread all over the card in small pieces, instead of in big continuous chunks). This can cause unexpected delays. So that is why you always need to use the operating system's software to eject a card or portable hard disk, and wait for the message "This disk can now safely be removed", or something equivalent.

 

Personally, I would completely reformat the old SD-card (after backing up any important data). And then do a thorough disk check, which also checks the hardware (=memory cells / hard disk surface). And then try the card with a couple of big video files or so.

 

[johannessssss 0]

@geert_2 thank you for your extensive reply. I am no flash memory expert, but i guess something like this could happen. Although i formatted both sd cards every time before uploading a new .gcode after the first time this happened. I am going to do some experimentation with ejecting the old sd card faster, viewing in a .gcode viewer and print to try to evoke this problem in a controlled manner. 

 

With the new SD cards i have printed 2 projects successfully now.

[geert_2 557]

I don't know how flash memory works internally either (apart from that charge is stored in insulated cells).

 

But maybe the same effect as I describe could happen if a defective controller writes to the wrong memory blocks? Or if it writes to the right blocks, but the write-function is defective, so the old data can't be overwritten?

 

If it still happens after formatting, I would discard the old SD-cards.

 

[johannessssss 0]

I have now tried to reproduce this issue on purpose and i was unsuccessful. after that i thought it was business as usual (printing successful prints with new SD cards). This morning i found that the issue reoccurred, resulting in the intended print being printed about 30 layers with an older (week old) print on top ("sort of" since it was damaged).