3D Printer Bumper Repair
d. bodnar  revised 11-30-13

Every Christmas I run a Bachmann Christmas trolley on the stone railings that surround our front porch.  The point-to-point trolley runs from December 1 till January 1, averaging 5 hours on week days and up to 16 hours on weekends.  Some video and notes are here:  Christmas Trains - information on how I get the trolley to be so reliable are here:  http://www.trainelectronics.com/AC_Trolley/ and here:  http://www.trainelectronics.com/PicaxeSpeedController/AC_Trolley_Modification/

This year, while preparing the main trolley and my backup trolley, I noted that the bumpers were cracked and one section was missing.  I decided to use this as an opportunity to test my design skills and to do a head-to-head test comparing the Afinia 3D printer that I have had for over 6 months and the FlashForge printer that I have only had for only a few days.  

Design
I used Sketchup to design the replacement bumper.  I had used it for a number of projects but never with one that involved a large curved section.

To get the curve just right I held the bumper section that had broken off of the trolley against the screen as I stretched an arc to match.

Printing
The first few prints that I did had the bumper laying on its side.  The prints were OK but it was difficult to cleanly remove the material that the printers use to support sections of a print so that it does not sag while it is being printed.

I then reprinted on both printers with the curved part of the bumper up in the air.  The prints went well so long as I instructed the printer to use a tight support structure.  This photo shows the new printer and its way of supporting the curve of the bumper as it is printed.

Here the support material has been removed.

Here the Afinia's support material is shown - it is quite a bit more dense.

Note that there is no support material between the bumper sections.

Here the bumper has been temporarily mounted on the trolley.  It is just a hair too narrow but that is easy to fix in Sketchup!

Here it the revised bumper (mounted) and the original.  The revised one is slightly wider and a bit less curved.

You should notice a series of flat areas in the curved bumper as in the photo above.  This is due to the way that STL files, the standard for 3D printers, store files.  The image below shows the STL file for the bumper in Sketchup - its curve is shown as a group of connected rectangles & triangles.  This can be improved either with sandpaper or from making some adjustments in the software.

All-in-all the project went well.  The new printer is a bit faster than the Afinia.  The print quality is about the same.  The main difference is in the software that is used with the two printers and the way that the automatically generate the support material.