Thursday, December 27, 2012

One way to fail (3D printing)


I’m printing some fairly small ducks (20mm high) and the heads were printing all blobby.  Turns out I had entered the filament size a bit too small, 2.83mm instead of 2.95.
On larger items, I have not found filament size to be all that critical, but as you can see from this print (corrected value on right) on small items (or probably detail) it can be quite important to get it right.  As you can see the bottom bits are pretty much OK (there is some trouble) but it really falls apart higher up.  What you can’t see is that those are the areas where Slic3r decided to start using 100% fill due to the very small size.  At 100% fill if you overfill, it blobs out the side.
Also, I think the smaller the nozzle diameter, the more important it is. I do not know why this is, but when I printed with the same filament and the same (wrong) diameter entered on my printer with a 0.5mm nozzle rather than 0.35, the print is actually pretty decent anyway. I will have to try the right values with the 0.5mm nozzle later.  I imagine that the 0.35mm nozzle will produce better detail, but the 0.5 is more forgiving and the detail level is close even with the wrong values, so I’m not sure the difference is that big.

Wednesday, December 5, 2012

Recovering from a failed drive


If you have a drive that is starting to fail, there may be a chance to get a lot of the data off it.  Here’s a method that’s worked for me twice so far. It requires a second hard drive as large or larger than the failing drive.  It clones the drive completely, resulting in a copy of the drive that can be inserted and used just as the original, with data and partitions intact.  It does rely on the failing drive to be mostly readable. If your drive is totally failed, this won’t work for you.
First, download the ISO from http://www.sysresccd.org and burn it to a CD (I use ImgBurn to make CDs).
Unplug all the drives from your system except the failing drive and the new, blank, good drive.  Boot to the rescue CD.  Type “startx” (optional since we’re going to just use the terminal anyway, but it’s nice to be able to have multiple terminals visible at once sometimes)
Insert a USB thumb drive.  It will be used for logging the progress of the rescue program.
run “fdisk -l” – scroll around and make note of the devices – in my case, /dev/sdf is the new drive, /dev/sdg is the old, failed drive, and /dev/sdh is my thumb drive.  Run these commands, but be SURE THAT YOU GET THE SOURCE AND DESTINATION RIGHT or you’ll wipe your data without warning.
> mkdir /mnt/usb0
> mount /dev/sdh1 /mnt/usb0
> ddrescue -r3 -v --force (dev id of failing drive) (dev id of new drive) /mnt/usb0/recovery.log
The first two commands create a mount point and mount the thumb drive. The last one starts the copy.  -r3 means try reading each block up to 3 times before moving on.  -v means be verbose, –force is necessary to make it overwrite the destination device.
ddrescue will try its best to copy the data, skipping stuff it can’t read in 3 tries.  Once it finishes, you can run exactly the same command again. It will use the copy of the log that it wrote to the thumb drive to know (and skip) what has already been copied successfully, and proceed to try to just read the problem areas.  If you like you can now increase the retry parameter.
In my case I had a 1.5T hard drive which had developed a LOT (hundreds) of errors, but they were all soft – the data would eventually read.  I was able to recover 100% of the data on the drive and just slide the new disk in where the old one was and boot right up as if nothing happened.

Saturday, December 1, 2012

New thing: flat wall switch cover


We needed a cover to keep people from flipping this switch at the church, and I couldn’t find one to buy, so 45 minutes on OpenSCAD, load white filament, print and voila. The switch is still accessible through one side.