Erasmus
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Release status: concept
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| Description | an easy to build repstrap
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| CAD Models | none, true repstrap
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Introduction
Erasmus was the granddad of Charles Darwin. In his book Zoonomia he wrote "...shall we conjecture that one and the same kind of living filament is and has been the cause of all organic life?" So if his name is not a fitting name for a repstrap, then I don't know which is.
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 .
Key features
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 MkI are replaced by simple wooden parts and a lot of hot glue (aka analog 3d printing;-)).
The problem with 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 Erasmus, 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. 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.
The following is a list of the wooden parts. Most of them are made from 5 x 2 cm boards, just like the frame:
| Quantity | Name | Comments | Picture |
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| 2 | z- axis bottom | 
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| 2 | z- axis top | 
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| 1 | x- axis motor | 
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| 1 | x- axis idler | 
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| 1 | x- carriage | made from thin plywood | 
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| 1 | hotend mount | 
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| 1 | y- axis belt clamp | 
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| 1 | extruder body | made from thin plywood | 
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| 1 | extruder idler | made from thin plywood |
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| 1 | y- carriage | made from thin plywood |
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Upgrade Path
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 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 Bondtech 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 endstops.
While you are at it, you could also swap out the z- axis top and bottom pieces. Any version will do, from the looks of it, the MK3 parts look the sturdiest.
The y- axis of Erasmus is wildly different from the Original Prusa, so there are no printed parts for that from Prusa itself.
Hotend
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.
