Stuff Michael Meeks is doing

This is my (in)activity log. You might like to visit Collabora Productivity a subsidiary of Collabora focusing on LibreOffice support and services for whom I work. Also if you have the time to read this sort of stuff you could enlighten yourself by going to Unraveling Wittgenstein's net or if you are feeling objectionable perhaps here. Failing that, there are all manner of interesting things to read on the LibreOffice Planet news feed.

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Repstrap gear construction

Reprap ?

The reprap project provides the designs and drawings necessary to make a self replicating, plastic extrusion 3D printer. There is only one hitch: self replication; you need a plastic printer in order to make one. Failing that you need to bootstrap your printing world by building a 'repstrap' - something that can (just about) print the pieces.

An ad-hoc repstrap

I have knocked together such a thing from spare bits of floating timber (mostly MDF and ply-wood), which has some unpleasant calibration problems: related to thermal issues, and a lack of an adjustable, (or even better heated) bed. Nevertheless it can be persuaded to print useful things. Indeed - arguably it is easier to cut a nice, rigid sheet of MDF, than to create isometric triangles made of studding with complicated plastic verticees. Anyhow - the beastie re-uses almost all the parts: steppers, controllers, belts etc. from an existing reprap - so you can re-use them in the final product (in theory). It also requires only simple hand-tools (except for the extrusion nozzle, and knurled driver which is a pain generally). It looks a little bit like this:

my repstrap

Notice the horrific warping problems that come from poor print head - bed spacing calibration, and the lack of a heated bed. Still, this is one of the largest, and most problematic prints necessary to bootstrap. I have the vague intention to create useful drawings, and instructions to replicate/iterate it for others with low-precision tooling - but the joys of LibreOffice are ship-wrecking this aspiration currently. Please also note that the all-important safety goggles are just out of frame somewhere.

Making large z axis gears

One of the most fun problems of repstrap construction are the gears. After several attempts - to whittle gears from acrylic rod, to make them from MDF, and so on I hit on a near perfect solution, reproduced here for your gear-constructing pleasure.

It turns out that simple 30mm panel-pins fit rather snugly into the required timing belt, creating a nice firm fixing. So - this makes the construction of the large gears a matter of rough cutting vague disk shapes, (or better using a nice large circular cutter) four disks from thin ply-wood, then using the stencil linked below - marking out the pin locations, drilling them through (as vertically as possible) with a 0.5mm drill, and then simply pressing the pins through. This and a pair of nuts in the centre yields a beautiful, functional z drive, as modelled by my youngest, as she concentrates on reprap assembly thus:

large gear - with model

Stencils for gears

It turns out to be remarkably hard to draw gears, or lay them out manually by measurement. Luckily most people have a phenomenally accurate ink-jet printer. Thus simply print out this file: gears.odg - clearly using LibreOffice if you don't have it. Then use a bradawl to make holes to enlarge with a drill in the right positions.

Making stepper gears

These smaller gears present a real problem for ply-wood - which would just crack and split, and not provide enough purchase on the shaft of the stepper. After some initial semi-functional attempts with some aluminium, I discovered that the perfect material for small pin gears is near to hand, and luckily is stocked in your kitchen, it looks like this:

small gear - raw material

Naturally, it is only a matter of explaining to a suitably patient wife, her desparate need of a new chopping board, and the invaluable nylon is procured. To satisfy yourself that it is indeed a wonder material, try driving a panel pin into it 5mm from the edge, and then breaking it out. Attack the chopping block with a junior hack-saw or some such device, to make an octagonal piece of suitable diameter. Again use the bradawl, stencil, and 0.5mm drill as above. Drill a larger central hole, which should be of a slightly smaller diameter to the drill shaft (which should have flats filed onto it). Simply 'drift' (ie. wallop with a hammer) the nylon onto the shaft for a fool-proof fix. Eventually you end up with something beautiful like this:

small gear - finished

Why bother ?

Hopefully, after much more wood hackery, adjustment, suffering, remedial medical treatment and so-on you can finally produce a working 3D printer, and hence something actually worthwhile. While this is only a prototype - and died on the first attempt of a lawyer to bend it, the full (more solid) version has resisted the attempts of a long line of hackers in their eagerness to break the end off; enjoy:

prototype bottle opener

Of course, you really need to use RepSnapper on openSUSE for controlling that sort of thing.


My content in this blog and associated images / data under images/ and data/ directories are (usually) created by me and (unless obviously labelled otherwise) are licensed under the public domain, and/or if that doesn't float your boat a CC0 license. I encourage linking back (of course) to help people decide for themselves, in context, in the battle for ideas, and I love fixes / improvements / corrections by private mail.

In case it's not painfully obvious: the reflections reflected here are my own; mine, all mine ! and don't reflect the views of Collabora, SUSE, Novell, The Document Foundation, Spaghetti Hurlers (International), or anyone else. It's also important to realise that I'm not in on the Swedish Conspiracy. Occasionally people ask for formal photos for conferences or fun.

Michael Meeks (michael.meeks@collabora.com)

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