RepRap: Blog

I've been finding a few moments to cut & fit M8 bracing to the Wedge wooden prototype (The Wedgewoods were a good friend of Darwin BTW). Four lengths of 325mm (could probably go to 330mm) seem to make it stiff enough. I discovered that 5 holes in bits of MDF turns them into handy clamps that work at a variety of planar junctions. The top of the horizontal threaded bar is 305mm above the upper surface of the base, in case you want some scale.

I've roughly laid out where the vertical Z axis drive rods will go (like the reprap'd bearing holders?), and a possible place for mounting the Z motor - maybe a little closer to the horizontal crossbars though. For the moment I'll drive the 2 vertical shafts with printable Z gears as used in the Darwin Child, but might switch to a driveshaft or at least give one as an option to avoid buying chain. Using a driveshaft would require 2 more bearings, reprap'd gears and more threaded rod but I can see some people might want to do it.

Now which to do? I want to work on the paste extruder, the Wedge Y axis and the Wedge Z axis (which will have to evolve in parallel with the X axis and carriage). Place your votes while I go to First Responder training...

Vik :v)

Labels: bracing, wedge

Ed has been discussing a proposal for a wedge-shaped version of the RepRap, using fewer components and being more easily manufactured than the existing box frame. One of the things we wanted to know was how badly it needed cross-bracing. So, I sliced & diced some MDF to give us an idea of how things might be spaced out, and to experiment with the bracing so I can have the rigidity and still maintain the same build volume as a Darwin.

Well, just 4 struts definitely isn't a stable design. Things wave about quite a bit under moderate load - which bodes badly for movement at just the wrong vibration frequency. Further mucking around revealed that this could be much reduced by bracing and I'm still fiddling with that to see how little I can get away with.


Here's a shot showing the underside. Two of the X sliders are RepRapped by the way, and two are made from galvanised corner brackets and Polymorph. I thought it might be a good idea to make as many parts as possible in a way that could be replicated by hand if necessary.

I'd like to have the option of moving the axes with either motors & belts or threaded rod in the next design. In some parts of the world, high-quality steppers are unobtainable and so it makes sense to leave the path open to using current stepper/belt systems, develop DC-servo systems, and if all else fails drive it with a slow, old-fashioned threaded rod.

I'm not expecting this particular model to actually move properly, but if it does it'll be a really cheap way of putting RepRaps together.

Vik :v)

Labels: mdf, wedge

I've been playing with ideas on part count reduction for Darwin. Having an elevated XY table requires a fair bit of support structure. After brainstorming with Adrian we came up with this as a concept - I will try to do a feasibility on it at some point. Interestingly the rolling table concept could lend itself well to a large-batch production machine: if the table was pimped with a conveyor we'd have an infintely long work area.

Labels: cartesian, wedge