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Archive for April 19th, 2017

3D Printer Design Conversation: Part 3

More musings in response to questions about building a large-format 3D printer.

(Continued from yesterday)

make a direct clone of the M2. No thinking required.

The present-day M2 has survived four years of rather fierce Darwininan winnowing, so it’s a much better thought-out product than, ahem, you may think just by looking at it.

To build a one-off duplicate, you’ll spend as much money collecting the parts as you would to just buy another M2 and start printing.

Should you buy cheap parts to save money, without considering the requirements, you’ll get, say, the same Z-axis motor Makergear used on the original M2, the complete faceplant of Thing-O-Matic electronics, or crap from eBay described as being kinda-sorta what you want.

Sometimes crap from eBay can be educational, of course:

https://softsolder.com/2013/01/24/hall-effect-sensors-from-ebay-variations-on-a-specification/

I encourage thinking, particularly with numbers, because it leads to understanding, rather than being surprised by the results.

increase the rigidity of the X and Y axis

In round numbers, deflection varies as the fourth power of length: enlarge a frame member by 50% and it becomes five times bendier. If your design simply scales up the frame, it won’t hold the tolerances required to produce a good object.

https://en.wikipedia.org/wiki/Euler%E2%80%93Bernoulli_beam_theory

If you add more mass (“stiffening”) to the Y axis, then the Z axis motor (probably) can’t accelerate the new load upward with the original firmware settings and the Y axis motor may have trouble, too. Perhaps you should measure the as-built torque to support your design:

https://softsolder.com/2013/07/02/makergear-m2-better-z-axis-motor-calculations/

Reduce the acceleration and lower the print speed? Use bigger motors (if you can find a Z motor with the correct leadscrew) and lose vertical space? Make the frame taller and lose stiffness? Use two Z motors (like the RepRap Mendels) and get overconstrained vertical guides? Try building a kinematic slide and lose positioning accuracy? Your choice!

If your intent is to print more parts at once, buy more M2 printers, which will not only be cheaper, but also give you more throughput, lower the cost of inevitable failures, good redundancy, and generally produce better results. Some of the folks on the forum run a dozen M2s building production parts; they’re not looking for bigger print volumes to wreck more parts at once.

Conversely, if your intent is to learn how to build a printer, then, by all means, think about the design, run the numbers, collect the parts, then proceed. It sounds like a great project with plenty of opportunity for learning; don’t let me discourage you from proceeding!

However, I’ll be singularly unhelpful with specific advice, because I’m not the guy building the printer. You must think carefully about what you want to achieve, figure out how to get there, and make it happen.

To a large extent, searching my blog with appropriate keywords will tell you exactly what I think about 3D printing, generally with numbers to back up the conclusions. Get out your calculator, fire up your pencil, and get started!

(Continues tomorrow)

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