UPDATED belt holder (see below)
This is an ridged and precise y carriage for mendel and prusa printers.
This owl shape y carriage features some advantages over the original frog design:
- It utilizes all 5 mounting holes of the heatbed to achieve maximum stiffens for the heatbed.
- It utilizes 4 linear bearings to improve accuracy.
- It uses 3 point bed leveling (4 point leveling is over constraint. 4 Point leveling only seams to work if the construction is flimsy enough)
- 2 guiding rods are used to eliminate rocking in the leveling screws.
- No need to sacrifice flexibility of the print bed to gain accuracy
- The distance between the two bearings on one smooth rod can be extended by 36mm to achieve more precise guiding of the y carriage. See Printbed Diagnosis Pattern
- SC8UU bearings can be used
- Even LM8UU bearings can be locked in the bearing holders to prevent them from slipping out.
- The bearing blocks are a bit shorter and the mounting screws are a bit narrower then in the original design. This reduces the force on the bearings in the case of (slight) misalignment.
- The carriage can be removed with out disassembling the y frame just by pushing the bearings out of the holders.
- The belt is held a bit lower to eliminate the triangular deformation of the belt path. This reduces wobble in the belt tension, witch on one hand improves the belt tension if the carriage is near the center (where most parts are printed). On the other hand it will prevents the belt from going baggy by the wobble of the tension.
Explanation on Youtube (sorry german)
UPDATE: i3 y Belt Holder with Tensioner
UPDATE: I added two versions of cable support brackets to guide the wires of the print bed.
=> See also my other Prusa i3 reworks in my Collection
=> This Part is also used in my Prusa i3 master reworks
I recommend using ABS or PETG. PLA might get problems with the heat of the heated print bed.
Print the belt clamp with the slot downwards. If you do so, the shape is not pron to warping.
The bearing holders should be printed as it is shown in the screen shot from the slicer (see above).
You need 4 bearing holders and 8 spacers.
The owl on an scroll saw
Cutting the Owl
The owl should be made from an 5 or 6mm thick piece of acrylic glass (Plexiglas, PMMA).
If you have access to, use an laser cutter. If not, a scroll saw will do the job too. If you are less lucky use an fretsaw. It will be worth the afford.
I do not recommend using aluminum. This will make the carriage a lot heavier. The stability in this design is obtained by construction, not by the materials.
Print the template and glue it on to the protection foil. Check the dimensions before cutting or drilling. Drill the holes on an drill press with an 3.2 mm Drill bit.
Bearing locked with gardening wire
Mounting the bearings
The holes are layed out for SC8LL Bearings. If you wish to use normal LM8UU bearings (witch is ok), you have the choice of using the holes closer to each other or the ones more apart. The closer ones are featuring the same distance as the ones on the original frog design. I recommend using the ones more apart to get better guiding.
The screws are driven directly into the plastic. If you wish to use Nuts there should be enough space.
The bearings will be locked by the burr of the holders. But if you wont more reliability you can use gardening wire to secure them (see picture)
The guide rods (witch are actually fins) are made from 0.5mm gfk (FR4). I cutted them with a tin snips.
4 Spacers are use to rise the fins over the surface of the carriage. They should end up roughly in the middle between the carriage and the print bed.
The guide rods (fins) mounted with spacers to the owl
Mounting the belt clamp
The belt clamp is just screwed under the owl using 4 M3x20 screws driven directly into the plastic.
The holes in the carriage can also take a standard belt clamp with 45mm hole distance.
The Belt is just pushed into the slot. There is no further afford needed.
Mounting the carriage into the y frame
The reason of using only 3 linear bearing was to cope with low accuracy of the orientation of the guide rods. So make sure that your rods are exactly parallel. Check the distance on both ends and in the middle with a caliper. Also check the vertical distance to the desktop. Al these distances should be equal.
If you don't have access to precision measurement instruments you can find a good approximation by following this procedure:
- Install the y assembly as usual, but don't tighten the Nuts yet. Also the screws witch are holding the block of the linear bearings should be loose.
- Push the y carriage back and forth to feel the resistance of the friction and hear the noise of the bearings. Some rattling will help to align the rods properly to.
- Place rolling object (a marble, a ball bearing or so) on top of the carriage. Put shims under the legs of the printer to level the rods. (Self adhesive labels are working great as shims.) The rolling object should not roll to the left or to the right. Neither if the carriage is pulled to the front nor if it is pushed to the back. Rollng back and forth is less critical.
- Tighten the screws and nuts while continuing checking sound and friction of the movement.
This procedure is necessary to work around some design flaws of the mendel and prusher design.
Removing the carriage is quite easy. This can be done by just pushing the bearings out of the holders. The carriage than can be lifted from the frame.
Mounting the print bed
Find the side of the heated bed where are the solder pads for the wiring and the 3 holes. Insert M3x20 screws in the two holes on the edges and lock them with two nuts. The second nut is only to provide some distance. You can use washers instead.
Lay down the print bed on to the carriage and align the two just installed screws with the holes in the guide rods (gfk/FR4 fins). Use two washers and a nut on each edge to connect the print bed to the guide rods.
Then install the 3 leveling screws and springs in to the remaining holes as usual.
I generally recommend to use medium size washers on any surface where a screw is mounted to an plastic part to distribute the force and reduce wear.
Guide rod mounted