Wednesday, October 27, 2010

Building a Prusa i3 printer - Wood box frame

I am using the modified box frame.  The blueprint for this may be found here.  It's cut out of 1/2" (12mm) plywood.  Get 5 ply if it's available, it'll be more stable than 3 ply.

I really think that it's necessary to use "cleats" - that is, glue in square wood backers on all the right angle joints.  This will vastly increase the strength of the box.  I made my cleats by ripping down a 1x6, so they're 3/4" deep.

You'll also need about 20 #6 x 1" wood screws, wood glue, the correct drill for a clearance hole (bigger than the screw size to drill the top layer of wood) and to do a neat job, also a countersink.  As I just used softwood (pine/poplar) I didn't use a pilot hole, I just shot the wood screws into the cleats after gluing.

Gather all the parts:

Lay the cleats onto the bottom plate.  Make your marks and decide where you're going to put the screws in.  Drill clearance holes and countersinks in the bottom (you don't want the screw heads sticking out the bottom), then glue and screw the cleats down.
Do the same to the front panel, adding the two long cleats along the sides.  Be sure to leave room at the bottom for the cleats that you just attached to the bottom.

Drill clearance holes and countersink the triangular side pieces.  When you use the side pieces to attach the bottom and front, you need to use a square to make sure that the front is plumb (perpendicular to the base). 

What I did was to attach one side to the front first, because that's the most visible so having it nice and flush looks nice.  Then I test fit it and determined that in my case it leaned back just a bit (about 1/16") so I glued the bottom cleat, shot the FRONT screw in first, then leaned the front piece out until it was square then shot in the back screw.  This leaves a tiny gap under the bottom at the back where it's not visible.  You don't want to have the side piece sticking out the bottom as it will make the unit unstable.

Then do the other side the same way and you're done with this part.


Dorotea Td. said...

Hi! I'm building a prusa i3 with wood box frame but when I try to attach the build plate assembly to the floor of the frame, the parts that are supposed to hold it on don't reach the frame when I put them over the big threaded rods. The wood is 12mm and the parts (rectangular parts with 4 screw holes that go over the threaded rods) float a few cm over the actual base when placed over the rods. Is there something I'm doing wrong? Any help would be appreciated. Thanks!

John Ridley said...

A few CENTIMETERS over the base? like, a couple of finger widths extra space? I don't know how that could be.

I guess I'd feel free to add spacers if need be. Put some rubber feet under the frame to bring it up? I'm guessing you meant millimeters and only need a little more fill.

On my printer kits that I print, I use a larger threaded rod there to increase rigidity, and adjusted the print of the Y axis feet so it fits with standard 1/2" plywood available in the US.

Dorotea Td. said...

I'm using 12mm plywood- I misspoke, it's a few mm difference not a few cm. Using washers or spacers won't throw off the calibration of the axis? I can't find any close up images of the axis fixed to the base so I'm worried I'm doing it wrong.

John Ridley said...

Spacers there won't bother it any. The only real critical bit is that the top of the print bed is parallel to the smooth rod (you'll achieve that during bed levelling) and that all the axes are orthogonal to one another (right angles) otherwise you'll be printing parallelograms instead of rectangles.