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.

Building a Prusa i3 printer - X and Z axis

The X and Z axis get assembled together and then screwed to the box frame.

Step 1 - make sure that all the holes in the printed parts will accept the bits that go into them.  The 8mm holes that the smooth rod goes into on the motor and rod holders is often too tight.  Clear the holes with the appropriate drill bit size.  The smooth rod should be snug, NOT LOOSE.  If you overdo it and it's loose, you'll have to make it snug again with tape or something until you can print replacement parts.

Get the X end without the motor mount and clip out the support piece that is in the way of the idler.  Insert two linear bearings and put in a pair of 6-32 x 1" screws and nuts to secure the linear bearings.You may have to use a tiny nut to clear the M5 nut trap on one of the linear bearing holders (the one on the left below)

Build the belt tensioner in the same way that you built the one for the Y axis, using a 6-32 x 1" screw and nut plus a #8 nut and screw for the bearing axle, and a pair of 624 bearings:
Insert this into the X end that you prepared in the previous step, then secure it in place with a 6-32 x 1" screw and nut through the X end and the tensioner (I have the smooth rod in place here - it's probably a little early to do that).

Use the M5 threaded rod to press fit an M5 nut into the nut traps on both X ends:

SORRY I don't have good photos of the rest of this sequence.

During the next few steps, keep in mind that the motor mount end goes on the left and the linear bearings all face the same way, when assembled the linear bearings will all face the back of the printer.

Insert the two linear bearings into the motor-side X end and secure with 6-32 screws and nuts. 

Insert the two longest smooth rods (470mm) into the X end that has the motor mount on it.  Push until they hit a stop inside.

Put three linear bearings into the X carriage and secure them with three 6-32 x 1" screws and nuts.  Slide the X carriage on with the two bearings on the bottom, one on top, bearings facing the same way as on the X end.  Finally, slide the idler side X end onto the smooth rods.

Slide the short smooth rods (Z axis rods) into the linear bearings on the X ends.

Use three M3 x 10mm screws on each side to attach a motor to the Z axis motor/rod holders.  I like to arrange the motor so that the wires face the center of the printer when assembled, just for neatness.  NOTE that if your motor has a raised center section around the axle, you may have to trim the smooth rod holder a bit to get the motor to be flush.

Screw the M5 threaded rod into the nut in the X end.  Spin it in about half way.  Do this on both sides.  Attach the M5 threaded rod to the Z drive motors using a bit of vinyl tubing on each side.  Just let it be a friction fit for now.

Slide the top smooth rod bracket onto the top of the Z smooth rod a little bit, and insert the bottom of the smooth rods into the smooth rod socket on the motor end.

Lean the whole assembly up against the box frame with the motors sitting on the work surface.  Start by attaching the LEFT side motor then the top support to the box frame with #6 x 3/4" wood screws.  Adjust the position of the right side X end until the Z mounts on the right align properly with the wood frame, then secure that side with wood screws as well.

Use three M3 x 10mm screws to attach a stepper motor to the left X end.  I like to have the wires facing up here for neatness.  Put a pulley on the motor shaft so that it lines up with the opening in the X end - you will probably have to put the pulley on backwards - with the setscrew collar facing out.

If you can't get to the back of the X carriage through the opening in the box frame (IE if it's too high up), adjust the Z drive screws manually until you can get to it.

Attach the belt to the X carriage, around the motor pulleys, through the gap in the X carriage, through the idler pulleys and back to the X carriage, using the same zip tie technique as with the Y belt system.

Building a Prusa i3 printer - Pictorial parts list

Y axis corners
download stl
Y axis to box frame connectors
download stl

Linear bearing holders
download stl

Z axis motor and smooth rod mounts
download stl

Wire guides
download STL

X carriage
download STL

X end (motor), X end (idler) and idler holder
download STL

Extruder gears
Small gear STL
Large gear STL

Y axis belt holder
download STL

Power supply brackets
PS bracket STL
short PS bracket STL

Power switch bracket
download STL

Y drive - idler and motor mount
download stl

Extruder idler, body and spacer
extruder STL
spacer STL

LCD control panel case and knob
NOTE: obsolete, see this newer design
panel STL

3/16" ID vinyl hose

Endstop holders - hall (Z), compact (X) and classic (Y)
Classic STL
Compact STL
Hall STL

John's tactile switch Z stop for i3
Download STL

Zip tie anchors

AC power input, fuse and switch module

RAMPS electronics mount plate
(no longer used, just screw the board directly to the wood)

Endstops - Hall (Z axis, with magnet) X and Y axes

Extruder spring (6-32 screw for scale)

Hobbed bolt and nylock nut

608 bearings (bolt for scale)

40mm fan for hotend cooling

40mm fan bracket
fan mount STL

Building a Prusa i3 printer - Y axis assembly

Before we get started, a note on working with printed parts.  You'll want to use a drill bit to make sure that the holes are clear enough to accept whatever's supposed to go into them, usually just a screw.

Refer to the "Y axis" page on the parts list to gather your parts for this part.

Refer to the photo below for these steps.  Take one of the 7/16 (or M12 if you're using metric bits) rods.  Spin a nut into about the center of the rod, then put a nut on either end and spin them in a bit.  Put one of the rectangular feet onto each end, making sure that the slot on top has the stops to the outside (so that the smooth rod can be inserted and the stops will keep them from sliding out the end).  Secure each end with another nut.  Do this again for the other rod and two ends.  Get your ruler and make sure the corners on each rod are the same distance apart as close as you can make it - this will make your axis as square as possible to start with.

Get your belt tensioner and secure a pair of 624 bearings into the end using a #8 x 1" screw and nut as shown:

Put a nut into the nut trap in the belt tensioner and thread a #6-32 x 3/4" screw into it until the screw just barely protrudes into the larger opening as shown:

Now assemble the 5/16 (or M8) threaded rods, nuts, washers, motor mount and the belt tensioner as shown in this photo:

Take one of the large threaded rod/corners assemblies and put these small threaded rods in, putting a washer on the small rods first, then securing the other side with a washer and another nut for each rod.  The motor mount side mounts with the motor mount bit pointing towards the inside, with the longer bit up (towards the top of the corners).  The idler side has the belt tensioner/idler on top, the plain rod on the bottom. Refer to the following two photos:

Also as seen in the above photo, press three linear bearings into the three holders, put them onto the two Y axis smooth rods (the medium length ones) and snap them into the top as shown.

NOTE: be careful to put the two on top and one on the bottom with the idler on the left and the motor on the right.  We are putting the motor in the FRONT of the printer, unlike many assembly guides, because it works better that way with the plywood frame.

Now you will want to start tightening things up.  On ONE end of the two large rods, screw the end nut to flush with the end of the rod, then clamp the other nut down tight (pretty tight but don't crush the plastic) onto that corner for both on that end.  Then do the same at the other end but you can bring that side in a little to give a little room for adjustment later.

Now tighten one side of the short, small threaded rods in the same way.  Then when you move to the other side, use a ruler to make the assembly be 165mm exactly between the two rails (center to center, easier to measure left to left or right to right) as shown below.
When you've done that, check that the assembly is the same length on the other two edges as well, to make things as square as possible.

Now use four large zip ties to secure the smooth rod to the axis assembly as shown (do this in each corner):

Once you've tightened that all up, get the square plywood print surface.  Mark a line along one side 20mm in from the side.  Though most assembly guides have you assembling the print surface centered, with the box frame I've found that you need to offset about 25mm towards the front, otherwise you will not be able to achieve the full 200mm of travel.  So with the line you just marked at the top, make a mark along the line at 33mm from the right, another 83mm from the left.  Then make a mark at the BOTTOM of the plate 25mm right of center (140mm from the left).

These photos combine a view of the marks with the next step, attaching the plywood to the axis.

Also make a mark along the center line of the board to mark where the belt holder will go.

Lay the platform on your work surface and place the Y axis assembly over the top, with the side with two bearings towards the side with the line 20mm from the edge.  The two marks that you made mark the location of the OUTSIDE edge of each bushing holder.  Secure each with a single #6 x 3/4" wood screw (if your 3/4" screws are long and stick out the top, you may have to use 1/2" screws).  The mark in the center on the other side marks the location of the third bushing holder.  Secure that with another screw, then put in the second screw into each bearing holder.

Once you have put in all the wood screws, you can put the 6-32 x 1" screws and nuts in on top of the linear bearings and snug them down, securing the linear bearings in place.

Get your belt holder and clip out the support section as shown - ONLY the part shown.  The middle supports are needed for strength.  This one just gets in the way.

When you are done it looks like this:

Get one of your stepper motors and a pulley, install the pulley on the motor (with the collar facing out to keep the belt as close to the motor as possible - this gives the belt less leverage to twist the motor out of square).  If your motor shaft has a flat side, put a set screw on it.  Then use two M3x10 screws to attach the motor to the holder.  Adjust the nuts holding the motor holder to the frame so that the pulley is centered in the frame and the motor is level.  Center the idler on the other side too so that it is in line with the pulley.  Now screw the belt holder to the plywood, centered along the line between the bearings.

Get a length of timing belt. You need to fish the end of it through the belt holder attached to the plywood - I find the easiest way to do that is to use the end of a zip tie as a tool as shown.  Be sure the teeth are facing up.

Secure that end of the belt to the holder using a small zip tie as shown
Route the belt through the idler pulley and around the motor pulley and back to the belt holder, fish it through and secure it as you did the other side.  You should take most of the slack out of the belt but you don't need to get it very tight at this time because you can do that with the idler/belt tensioner.

Finally, clip the excess belt and zip tie end - don't cut the belt SUPER close to the zip tie, in case you have to remove it and redo this procedure again later.

Get your long endstop switch holder and secure a switch to it using two #4 screws and nuts.  If the leaf on the switch is long, bend it over so that when it is mounted on the smooth rod, it comes close to the rod but does not touch it.  The linear bearing will be pushing on this.  Then mount the switch to the smooth rod on the side with just one linear bearing, between the bearing and the side of the base away from the motor.  Secure it with a #6 screw and nut.  Don't tighten it up quite yet, we need to adjust it later.

Be sure to mount it exactly as shown, with the screws facing down like that.  The holder will not clear the print platform in other positions.

You can attach the Y axis to the main plywood frame now as shown above. Center the assembly from left to right (make sure the print platform clears the frame on either side) then put the rear block in FIRST leaving the screws a little loose.  Then slide the Y axis up snug against those blocks and install the front blocks.

Y axis done!  Good job.