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I know I am late to the party with building a Repstrap in 2021 with all the cheap chinese printer kits around, but the idea of bootstrapping a self replicating machine has a beauty to it which I find very intriguing. So here it goes:
My Repstrap is mostly derived from the popular Prusa i3 Mk1/ MkII and heavily inspired by the iTopie and the "Easy wooden Repstrap" by user skeat and a bunch of others. The Batten i3 roughly resembles the Prusa i3 Bear Upgrade which uses aluminium extrusions instead of wooden battens for the frame. The emphasis of the Bear upgrade is performance, print quality and print speed, the design goal of the Batten i3 was acessibillity, ease of construction for hobbyist wood workers and price.
The focus of this repstrap was ease of construction. To not have to deal too much with the (kind of hard to assemble) threaded rods as structural parts, it mostly uses wood for the frame.
The printed parts of the original Prusa i3 are replaced by simple wooden parts and a lot of hot glue (aka analog 3d printing;-)).
The problem with the grand old wooden repstrap, the old WolfStrap was, that after it printed the parts for your reprap, it was pretty much done for and most of the vitamins could not be reused in your new reprap. For upgradeability of the batten i3, the wooden parts are very compatible with the original i3s printed parts. So these can then be replaced bit by bit with the original parts further down the line.
Unlike other repstraps there is no need to build a completely new machine after you are done printing the parts for your reprap. The frame of the repstrap and the vitamins can be reused. Finally you should end up with a bootstrapped i3- like printer.
Only basic tools like a drill and a jigsaw are needed. A drillpress is very helpful though.
Since I do not have access to a laser cutter I wanted to construct my frame from ordinary lumber. To keep warping to a minimum you should get quarter sawn lumber, engineered lumber or use strips of plywood/ osb- board.
If you already have a 3d printer and want to make yourself a new Prusa i3 like printer, the frame from the Batten i3 can still be of use to you. It is a very cheap, very fast and very easy to make frame for an i3 like printer.
The following is a list of the wooden parts and the printed parts that can eventually replace them.
|Quantity||Name||Repstrap part||Drawing||Comments||Printed part||3D-file|
|2||z- axis bottom||made from thin plywood||Prusa i3 Mk2 part|
|2||z- axis top||made from thin plywood||Prusa i3 Mk2 part|
|1||x- axis motor||made from wood and plywood||Prusa i3 Mk2 part|
|1||x- axis idler||made from wood and plywood||Prusa i3 Mk2 part|
|1||x- carriage||made from thin plywood||Prusa i3 Mk2 part|
|1||hotend mount||made from thin plywood||Prusa i3 Mk2 part Prusa i3 Mk2 part|
|1||extruder body||made from thin plywood||Prusa i3 Mk2 part Prusa i3 Mk2 part|
|1||extruder idler||made from thin plywood||Prusa i3 Mk2 part|
|1||y- axis belt clamp||made from wood||Prusa Bear Upgrade part|
|1||y- axis motor mount||made from duck tape||derived from Prusa bear Upgrade|
|1||y- axis idler mount||made from tin, nuts and bolts||derived from Prusa bear Upgrade|
|4||y- axis rod holder||made from tin, nuts and bolts||derived from Prusa bear Upgrade|
|1||y- carriage||made from a 22 cm x 22 cm piece of plywoodf||if you really want to print one ... or this one (15 cm rod spacing though!)|
The extruder used, although working, is probably the first thing that gets replaced by a 3D printed part.
If you only have weak motors or you are using 3 mm filament, it might be beneficial to use a geared extruder. The original Prusa i3 has STLs for this on their github page. If your motor is strong enough, and you are using thin filament, then go with a MK2 Extruder. This one uses a normal, cheaply available hobbed gear and some ball bearings. The MK3 has the fancy dual drive gears which are probably a bit better, but also much more expensive.
The next item to replace are probably the x- ends. These should be a drop in replacement any of the different versions if the Prusa i3 will do. If you are using M5 threaded rods as z- axis lead screws, then the MK1s are suitable. If you are using proper T8 lead screws, then go with the MK2 since they still have the lead bolt holes for the x- endstops. The MK3 uses the "stallguard" function of their stepper drivers to home their printer, so they do not need endstop switches.
While you are at it, you could also swap out the z- axis top and bottom pieces. Any version will do, the Mk2 ones work fine.
The y- axis of the Batten i3 is wildly different from the original Prusa, so there are no printed parts for that from Prusa itself, I went with slightly modified parts from the Prusa Bear Upgrade project which I posted here.
8 mm stainless steel rods are surprisingly cheap when you buy them new. If you are lucky you might even find them used in the scrap yard.
|2||x- smooth rods||370 mm|
|2||y- smooth rods||330 mm|
|2||z- smooth rods||300/ 310 mm|
The original z-smooth rods have a length of 310 mm. You can of course use this, but if you cut your smooth rods from 1m stock you would need 3 pieces. If you use 300 mm long z- rods, you loose 1 cm of z- height but just need two 1m pieces.
The frame for this i3 clone consists of seven pieces of 1x2 (24x48 mm). I used a batten of about 2.4 m. As a proof of concept I bought the cheapest lumber I could find. The price was under 1,5 € for 2 meters. I selected the straightest pieces from the lot. Buy a bit more, so you can leave out the worst parts of the battens with major defects.
|2||31 cm||y-axis frame lengthwise|
|2||27 cm||y-axis frame crossmember|
There are no fancy woodworking skills involved. Just cheap drywall screws and lots of wood glue. Try to get the angles as close to right angles as possible. This will save a lot of time with the installation of the smooth rods later on. Cutting the pieces by hand and gluing up the parts was done in about 1,5 hours. Then you have to wait over night for the glue to dry.
Use three feet with shims so no rocking occurs on the surface the printer is sitting on. Use shims to get the X/Z- gantry as perpendicular to the surface as possible.
The two smooth rods for the y- axis will be attached to the frame with hot glue. They have to be parallel to each other, in one plane and perpendicular to the z- axis, so take your time. If necessary, use shims to get the rods level. Use the surface of the table as a reference. Depending on the bearings you are going to use, you may need to slide the bearings on before gluing the rods to the frame.
1. I used three small rubber feet under printer to get a stable, non rocking frame. Make sure that the gantry posts are perpendicular to the table (see above).
2. Glue one of the smooth rods to the frame. To get the rods level and in the same plane, I used two small blocks of wood with exactly the same height. These are tiny bit higher than the frame. The smooth rod is then placed on these blocks and glued to the frame with hot glue.
3. Do the same with the second smooth rod. Make sure that it is parallel to the first one. BTW- the original Prusa used a rod spacing of 17 cm on center, so if you use an original y- carriage you want to make sure you use that.
The smooth rods for the z- axis have dedicated wooden parts. The parts for top and bottom are pretty much the same apart from the mounting holes for the stepper motors in the bottom parts. The location of the holes for the smooth rods are critical. They have to be in the same spot on all four pieces. Otherwise it will be very hard to align the z- axis properly. Drill the holes of the first piece and use this as a template for the other ones. Mount the bottom pieces first, slip the smooth rods in and align the top ones.
X- Axis Ends
The x- axis ends are the most complicated parts. Two pairs of smooth rods have to be perpendicular to each other and we need a place for a toothed belt and a motor. This is what I came up with.
The x-carriage is nothing to write home about. Basically just a piece of plywood with three linear bearings ziptied and glued to the back and a small ledge to mount the hotend to.
For a hotend I'd love to make something from home depot parts, but these days you can get an E3D V6 clone for about 6 € from a local vendor in Europe. So even I cannot justify making a hotend from scratch since you would need at least some basic metal machining tools for it. I used a bowden setup, so the x- carriage only has to hold the hotend and everything