Wednesday, 20 March 2013

chinese power supplies ... the bad ones,

This is a Chinese Powersupply

believe it or not, under the nice aluminum cover lurks a few big problems consumers just don't know about,

1 - overload protection doesn't work
2 - short circuit protection doesn't work
3 - fan is mounted upside down so gravity wants to pull it apart
4 - if the fan fails casing can get hot enough to burn skin
5 - will burst into flames before failing

this particular one failed because of the fan, and i sported a small burn to my finger when i touched the casing of it, here's an autopsy

how the fan looks when the cover is off, this faces down and blow air out of the case - this is actually a brand new one i now turn the fans around to stop them from destroying themselves, it make no difference to the running temperatures though

 not much to see here,
this is what happens when the fan finally fails with this one i got lucky,  that it was just the fan, the previous one self destructed because somthing metalic came away from the fan and shorted somthing it shouldn't, and delivered and nice high voltage to all my stepper drivers and heaterbed, thankfully the drivers were unharmed however the printer had to be completely rewired

Tuesday, 19 March 2013

Thin Wall Engineering and the problem with classic infill

The structural issue with infill is that this kind of support structure doesn't really do much and to it's full potential, here's why:

this is what infill currently looks like,

in the image below you can see the contact points between the two layers of infill,  as can be seen there isn't much linking the two layers, this essentially leaves you with towers of dotted links from the bottom of the print to the top,

 the result is a parallelogram type of effect, while the object will feel solid and behave in a fairly rigid fashion under compression when under a shear type of load its no where near as string as it could be, this however depends on the part too

 the solution to this problem is simple, like in a lot of inject molded  parts ribs are usually added to make the part stronger and to a very successful effect in our case where we have the luxury of being able to print the whole object including internal cavities , with the up comming version of slic3r we can do this:

because the internal ribs are solid walls as opposed to a 3d mesh you can get a stronger object, the main advantage however is that you can customize and reinforce specific parts of the object like holes with extra ribs to make specific parts of the object strong

the cylinder in the above photo is the most successful, it's just as rigid if not more rigid than if it was fully infilled,  currently however slic3r has no infill settings for this just the classics so it's up to the designer to draw everything, internally,