Minimum accuracy needed?

I was wondering,

When printing a RepRap yourself. How accurate do the parts have to be? Just take you make I end with two holes for rods, the distance between the holes is 60mm, you make the other end to put the rods in, the distance between those holes is 59,5. When you insert the rods, they are not parallel and thus the bearing on the carriage are not parallel as well, wil lthe carriage bind on the end where the holes where only 59,5, when you designed it like 60?

I want to print my own reprap, and want to know what to expect from my current printer

Depends on how rigid the design is. If you are using aluminium brackets and linear rail then 0.5mm (or even 0.1mm) will bind for sure. If you are running 8mm rod held together with zip ties and printed ABS you have more room.

In a lot of cases you have the option of leaving parts loose or designing in some flex, but obviously its not ideal.

Precision can be a problem, especially if you're trying to print parts to make another printer. Getting beyond the basic precision and accuracy of the positioning mechanisms, how many people bother to actually align the axes of their machines and calibrate their extruders?

Using printers to print parts to make other printers is a nice philosophy, but if you think about it, you come to the conclusion that it's a really bad idea. It's like making a copy of a cassette tape, then using that copy to make another copy, and so on. Pretty soon all you have is noise. If you're going to print parts for other machines, the machine they are printed on will always be better than the machine made from the parts it prints. If you start with a good machine, you might get a couple generations of copies that sort of work OK. If you start with a crappy machine, your next generation will be extra crappy.

Quote
the_digital_dentist
Precision can be a problem, especially if you're trying to print parts to make another printer. Getting beyond the basic precision and accuracy of the positioning mechanisms, how many people bother to actually align the axes of their machines and calibrate their extruders?

Using printers to print parts to make other printers is a nice philosophy, but if you think about it, you come to the conclusion that it's a really bad idea. It's like making a copy of a cassette tape, then using that copy to make another copy, and so on. Pretty soon all you have is noise. If you're going to print parts for other machines, the machine they are printed on will always be better than the machine made from the parts it prints. If you start with a good machine, you might get a couple generations of copies that sort of work OK. If you start with a crappy machine, your next generation will be extra crappy.

I don't get your point, all repraps are made with printed parts, what do you want to say, we should all stop with it? lol

If all you care about is squirting out some plastic and calling it a printer, continue. The errors in the printed parts add with each generation of copy. Each generation of copy degrades the performance of the original design. When the design/construction/calibration is questionable in the first place, how many generations of poor copies will it take to render the thing useless? Maybe that's why there are so many crappy printers out there and so many people struggling to get them working properly.

I think people are under the impression that 3D prints are "digital". That they can be copied perfectly. It doesn't work that way. Each machine has tolerances. If you print a part and the guide rails holes aren't spaced exactly the same in the printed parts, and you build a machine with those flawed parts and then use it to print the same parts for yet another machine, what do you think will happen?

If you care about quality, yes, stop. Printers printing printers was a nice philosophy and inspired a lot of people to make printers, but like laser cut plywood frames, we learn from our mistakes and abandon the things that don't work. Poorly designed/constructed/calibrated machines printing parts to make more of the same machines just ends up turning people off to 3D printing because of the effort required to get such machines to produce acceptable output.

If you use printed parts, they should be used where their limited strength, stiffness, and poor dimensional tolerances won't cause problems. They are great for enclosing electronics, mounting fans and idler pulleys and even motors, but leave them out of the places where precision, accuracy, strength, or rigidity are required.

Yeah, but you think dentist are digital...

If you print a printer and then put in the time to get accurate prints, and then print another... You get another accurate printer. Last I checked .1mm is still .1mm...

Copying a cassette tape, copying an electronic file, and copying a printer are all inherently distinct processes.

Copying a cassette tape is analog and lossy. The magnetic media are not going to wind up in exactly the same places as on the original medium, and the net effect will be deteriorative.

An electronic file is digital. Barring DRM or file system corruption, you can make as many copies of the ones and zeros as you want, with no loss or gain.

A printer is a complex system, with ultimate system accuracy being related to the quality of the parts, the quality of the assembly, and the quality of the calibration. The better the parts you can start with, the easier it will be, but it is absolutely possible to creatively prep, assemble, and calibrate substandard parts and get a machine that, at least temporarily, produces better tolerances than the tolerances that went into it.

In a similar example, the legacy RepRapPro Mendel came with PLA Y axis belt clamps that sat right under the heated bed (they've since moved to MDF). They advised in the instructions that, if you wanted to print ABS, the higher bed temperatures would soften the PLA Y belt clamps and allow the Y belt to lose tension and skip teeth, but the PLA should hold up long enough for your first ABS print to be new Y belt clamps.

It´s all about a clever design...
If you can´t make parts with high precisicion, like equal rod distance, just design it in a way to make it fit.
Use clamping screws and wider holes for the rods and you can mount them in any distance from 60.x to 59.x
-Olaf