On what does 'the build quality' depends and how to increase?

In response of jbayless I agree that this might have it's own thread because I am quite curious on how to increase. This might also become a good reference point for anyone starting with a reprap.. (like me!!) and want's to know from the experienced guys what makes it tick!

I am still in the impression that anything can become a reprap as long you can position the x,y & z. But what makes it accurate and how to increase this.. Is this due to the extruder, the software, the steps?


The original question was:
What makes the precision of the reprap...
is it the x,Y and Z movement or is it more the extruder part that makes all the difference.

I see so many differences in quality that I would like to know of what it is depending!

Is it also the slower the better or not? or is this again the extruder that makes all the difference!



the 2 reponses to that are:

BeagleFury:
If by precision, you mean how accurately can the positioning system can select target points in the model space (I.E is the point at 1.003 selectable separately from the point at 1.002? If so, you have precision to at least 0.001), then only a one factor contributes for stepper base motion -- how far does a 'step' on the motor take the axis in an ideal perfect machine (by 'step', it considers a half-step to be a 'step' if your electronics have been enabled for halfstepping your motor.) Precision is adjusted by stepper resolution, gearing, and strategies such as half-stepping.

If by precision (Usually termed 'accuracy' rather than precision), you mean how accurately can the positioning system select one particular specific point, then many factors and variables will affect it: Precision, stiffness of the frame, motor speed (steppers skip have a tendency to skip more steps at higher RPM), backlash, quality and tolerances on linear bearings and guide structures, wear on parts, etc.

I believe the RepRap Darwin and Mendal design goals (and achieved, I believe) are around 0.1mm for both precision and accuracy or so, which means, it can select any 0.1mm cubic 'pixil' in model space, and put a blob of plastic about .5mm in diameter there. Some machines may have greater precision than accuracy, others may have greater accuracy than precision.

> Is it also the slower the better or not? or is
> this again the extruder that makes all the
> difference!

Generally, if you slow down your motions mechanically, using gearing, then you'll increase precision. You may or may not increase accuracy, depending on all the other factors, and the error the gearing introduces.

Jabyless:

"is it the x,Y and Z movement or is it more the extruder part that makes all the difference. I see so many differences in quality that I would like to know of what it is depending!"

All of these can make a difference, and probably the limiting factor varies from one machine to the next. I think that usually the extruder is the limiting factor. Also for any one machine there's usually a tradeoff between print quality/precision and print speed.

It might be interesting to do a full theoretical/experimental analysis of Mendel's printing errors to find ways to minimize them.

BeagleFury didn't mention his Theta, Phi, Z machine:
[reprap.org]

and Energetic and Reinoud have a nice lasercut Delta coming online soon:
[reprap.org]

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-Sebastien, RepRap.org library gnome.

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Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

... with the naming conventions: - a RepRap is mainly built with printed parts (self-Replicating Rapid prototyper) ... all other systems should better be named RepStrap

And for the accuracy: - my CNC-mill has an accuracy of 0.0125mm in halfstep-mode and corresponding better with microstepping - the repeatability of the XYZ-position is depending of the mechanical setup and even with high microstepping (i have 1/256-microstepping-drivers with 51200 steps per turn for a common 1.8°/200steps-motor) i can reproduce between 3 to 5 microns best.

For higher accuracy/repeatability i'm building another machine with finer/stronger motors, 0.1 micron accurate reference-switches (inductive highres-sensors), much more accurate and rigid mechanics and bearings - here i hope to reach 1 micron repeatable accuracy ...

The other side is the accuracy of the extruder or toolhead - this is depending of the layer-thickness and extruding diameter accuracy. With a really good FDM-head (high pressure, perfect temp. and extruding velocity controlling) you can achieve around 130 microns thread-diameter with maybe 5 microns diameter accuracy. But when layering the thread on the surface you have other issues with ambient temperature, feeding speed and maybe humidity too

For this reasons i'm busy with paste-dispensing (motordriven volume-dispenser, whats much better controllable) and laser-cutting/sintering with a laserspot below 10 microns and moving resolution/accuracy below 10 microns too ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Another point to consider when trying to increase precision and accuracy -- you have to consider first and foremost how much you must have -- more is not always better... "good enough" is the engineer's "perfect", and anything more than that is just wasting time and money.

So, part of the discussion would be: Why? How much is "good enough"? I suspect that the .1mm is probably "good enough" given the limitations on the extruder (it is 5x the actual print resolution afterall -- .5mm thread is going to be bumpy no matter how accurate or precise you make the machine.)

If we can improve the extruder to smaller, precise, and accurarate filament, we'll need to figure out how to increase print rate -- .05mm filament for example, would take 100x as long to print at the same linear print speed compared to .5mm filament for similar volume. Complicating the issue is that as you get higher precision, you will tend to *slow* your print speed: 1000 steps per second at .01mm is about half the speed of the typical RepRap (60cm per min, vs. about 120cm per minute I've seen reported by some people). So now you'd need to buy more accurate, more powerful, more expensive motors and electronics. Is it worth it? Maybe. What's the application that needs it?

Indeed what is good enough!! I know this part oh so well!! As a Software Engineer you always are working to get the last 5% finished but that always takes the complete time you've spent for the first 95%. :-)


And sometime you have to say that things are ok knowning that otherwise the costs would get out of control.

But WOW .. I am impressed about the Delta Bot.. I have follewed the discussion but never have seen that picture.. Hope to see some video's of it soon!!! I want to make one :-)

First let me build my mendel.. a repstrap to build a reprap :-) Got it VXD! :-)
But I hope to see some tips on the aspects of getting the repstrap as precise needed to print the parts for a reprap mendel!