Tuesday, September 1, 2009

Linear motion or, “How I got the shaft”

If you haven’t already, now is a good time to decide how big your build envelope will be. Obviously the width is limited by the printer you chose, but the length and depth are up to you. I chose 8.5” wide by 11” long (the size of a standard letter sheet) by 10” deep. I could have made it longer but then my slides would have to be longer. I could have made it deeper but that’s a lot of powder to fill and a lot of weight when full. Also, the larger the build chamber, the larger the supply side needs to be (unless you want to refill it mid job). In order to save space my supply bin is ½ the length of the build bin. I’ll just have it raise twice as much each time so it delivers the same volume as a full size bin. Unfortunately since it only holds ½ as much I will have to refill it for large jobs.

Now that you know how far the printer has to move (don’t forget the powder roller has to go all the way to the back of the supply bin), you can find a slide mechanism to make it so. I started with a set of drawer slides I had that were good and tight. You want the motion to be nice and smooth without any excessive “wiggle”. No sooner had I bolted the printer to the slides that I hit my first snag. The sheet metal of the printer was never intended move and would bend if only one side was moved. I added a system of cables and pulleys (like I had seen in an old analog copier) to make sure both sides moved together, but now the system was too stiff and didn’t move easily. Perhaps it would work with a lighter, more flexible cable.
Anyway, about this time I found a pair of 13mm precision shafts with 1 bearing block. Even though they were a few inches shorter than I wanted, the price was right (free) so I scrapped the drawer slides and upgraded to the shafts. I figure the added precision can only be a bonus and the bearings were soooo smooth. I did have to buy some more linear bearings, but I made my own bearing block from hardwood (Poplar I think). I bolted the printer to the blocks and attached the rails to a sheet of MDF which will become the top of my printer. (I forgot to take a picture at this point but you can get the idea from this one)

No comments:

Post a Comment