leadscrew slide specifications

Hello Reprap Enthusiasts! First off let me begin by stating "I am a newbie" and I have no clue on 3d printing calculations. With that said I am hoping to use a linear rail system to setup my first 3d printer. I have done a search and didn't yield the exact results I was looking for. If possible may I ask all the experts here at the forum something? I thank all of those who reply in advance!

I would like to know what kind of precision, accuracy and repeatibility we are aiming for when we build a printer? The leadscrew rail slide system I am looking into has the current specs:
12mm Diameter, 1.2nm turning force, Max speed 800mm/s, Repeatibility 0.03 - 0.05.

*Now before you guys say its wrong for a small sized application, we are hoping to build quite a large format printer. I understand that it will take ages to print, but we have a product we have been meaning to push out to the market which the mold must first be printed.

What kind of problems would we run into using those specs? We are going to drive it with nema 23's , and install antibacklash nuts. Is there a specific calculation that we can use to calculate based on the length we want to achieve? What are we trying to have resolution at for 3d printing? What should repeatibility be optimally?

I know you guys are thinking "wt..." I'm sorry I am asking so many questions, I have plenty of knowledge building cars, but 3d printing is such a new area for me. Any help is really apreciated!

Quote
takeshi
I have no clue on 3d printing [...] we have a product we have been meaning to push out to the market

Interesting combination!

That said, a resolution of 0.05 mm is sufficient for large format printers. But also: for making molds, milling is still the better process. Faster, more accurate, can mill aluminium/steel molds directly, smoother surfaces in ejection direction.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

thank you so much for your reply, i will go searching for how to calculate resolution, anyone can give me a clue on how to determine that? In response to the molding process, since we are making silicone molds we opt for abs as the molding material to keep cost down as we anticipate lots of changes in the design. thank you for the input though it is greatly appreciated!

Steps/mm describes your resolution: [reprap.org]

More precisely, it's the inverse: 80 steps/mm -> 1mm / 80 = 0.0125 mm resolution.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

50um positioning repeatability seems reasonable considering the generally oozy nature of extruded plastic coming out of a 250um+ nozzle. Your typical belt-drive has about 25-100um of repeatability and a nominal resolution of maybe 10um but that last number/"specifiction" is based on micro stepping and is entirely in the imagination as soon as there is non-zero load on the stepper motor. An acme thread will give great precision (if not linearity) so you're likely limited by bearing slop.

If you're using big steppers and driving them hard, use excellent stepper drivers with proper midband resonance compensation, eg gecko.

You can make the finish smoother though less precise by standing the print in solvent vapors to polish it.

If you're printing really big, you might want to carefully consider the resolution/time tradeoff and whether you can accept the month/year-long print times implied by a small nozzle that will give you 50um resolution on a metre-scale object. Printing at higher speed needs more powerful motors and a very rigid frame (to prevent flex while accelerating) and an extruder/hotend capable of melting filament rapidly without jamming.

Other technologies like SLS might be more appropriate for huge hi-res prints. Or at least don't shoot for the moon in your first build, just low earth orbit

Edited 1 time(s). Last edit at 09/30/2014 11:52PM by polyglot.