Kossel – The Ratio


I came across this problem, when looking into building and sourcing the parts for a Kossel printer in Bangkok.

The correct length of the push arms of a Kossel 3D printer is a bit of an enigma. The length is related to the length of the Horizontal frame lengths, that form the triangle. The ratio between the length of the push arms, from eye to eye, and the length of the horizontal lengths, is apparently 80%, or 0.8.

However, not all designers stick to this ratio, and often go higher, up to 92%.

I wondered why this is. Surely it is simple enough to cut a length of aluminium extrusion to the correct length? Certainly it is easier to cut aluminium than a carbon fibre rod to the correct length, although the latter is still certainly possible.

There are constraints, the most likely of which is the sizes of borosilicate glass discs (commonly 170/180/220/260 mm), and custom heated beds, but there may be others, such as a minimum horizontal length (in order to accommodate the steppers), the carbon rods come in pre-cut lengths (seems unlikely?).

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Thermal fuses and 3D Printers


I had the idea of employing thermal fuses in my 3D printer designs, after reading Build a 3D printer workhorse, not an amazing disappointment machine. Coincidently, I had been replacing thermal fuses, when repairing fans and rice cookers in Bangkok, and so I was familiar with them.

The question that came to mind, however, was “Where would you place a thermal fuse, and would you use more than one?”. Would you use them at the power supply, on the heat bed, on the hot end, for each of the stepper motors?

From Build a 3D printer workhorse, not an amazing disappointment machine:

It’s rare, but 3D printers can catch fire. Use the safety features provided by the firmware, but don’t solely rely on them. Both plain MOSFETs and solid state relays typically fail in their conducting state, which can result in runaway heating with disastrous outcomes. Thermal cutoff fuses are $1 components, but they are well able to prevent a runway heated bed from turning your workshop into a crater.

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MKS Base V1.5


Following on from 3D Printer control boards, the description below is taken from eBay – US MKS Base V1.5 3D Printer Controller Remix Board (Mega2560+Ramps 1.4+5*A4988)

Note that MKS have a bad reputation. From Google Forums – MKS Base 1.5:

And here’s the problem with MKS.  They produce other people’s open source projects.  Generally not adhering to the MKS.  Generally not contributing back to the community. Generally sending their customers to the author of the project they produced for any assistance.  There is a absolute hatred of MKS in the smoothie ecosphere, and I, personally, put them in the same build quality as Geeetech.

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