How accurate RepRap is in front of other open source 3D printers ?

Hi,

I am writing instance of robotic student group at university of oslo(www.robotica.no). We have applied to get fund for buying a RepRap from our university, but got in reply that there are several Open Source printers available and why have we chosen RepRap ? They were wondering if the others are more precise than RepRap so the actual parts being printed by the printer would be usable in robotic projects that we have in our community here. So my question is :

1. Is the outcome from Mendel good enough(tolerance, accuracy, etc) to be used in a robotic project? E.g. parts of a chassis ?
2. Are other Open Source 3D printers, like Fab@Home, Makerbot or any other more accurate than RepRap in printing out particles ?

Do you have any good reason that we can write in our new application about choosing RepRap ?

Thanks alot in advance for helping us in that paper work :-)

Shahab.

Hi Shahab

I think you will find that Fab@home and Makerbot and some others are in fact commercial implementations of the Reprap itself.

I am sure others will correct me if I am wrong, but it looks like the Makerbot printer is in fact a commercial implementation of Darwin, which if you follow the Reprap project is somewhat out of date.

Commercial products neccesarily need to follow a reduced schedule as you want a stable and proven product rather than a cutting edge product which will include cutting edge problems... not to mention anything about stock levels etc.

Personally I am pleased I am following the reprap path rather than one of the commercial paths as the reprap path is evolviong all the time. You only need look at the electronics where many potential solutions are coming out all the time.

good luck

Hi Shahab,

As with all DIY projects, the precision depends partly on how well you assemble and calibrate the machine, and on the quality of the parts used (flatness of print bed, etc). It will depend on how well your parts are lined up, how your stepper motors are driven, on the software you're using, the quality of your extruder, etc. But assuming that you take an equal amount of care with all projects, I believe that RepRap will give the most best results.

As for mechanical design, I believe that Mendel is more precise than Makerbot cupcake. Makerbot's Z-axis rides on the threaded rods directly, without vertical smooth rods for lateral constraint. This gives the Makerbot some amount of wobble from on layer to the other. I don't know about the new Makerbot, as I haven't seen it in action.

Fab@Home should have good mechanical precision in the axes, but as far as I know they haven't adapted a thermoplastic extruder for it. As a result, I believe they can only print with thermosets and gels, which tend to be less useful than thermoplastics for most applications. I haven't followed their recent progress, so maybe the Fab@Home 2.0 has a thermoplastic extruder.

As I'm sure you've observed, the quality of RepRap parts varies widely, and tends to be a function of the experience of the operator (compare parts made by Adrian and Nophead with the prints many people make in their first months). Also, I advise you not to take shortcuts if you can - since you're working at a university and are getting funding, you probably will be able to afford quality parts, and will be able to use proper machine shop tooling.

Something to consider as well is that RepRap is an evolving project. We now have electronics that can do 1/16th stepping, which is bringing slightly more accuracy. People are experimenting with smaller 1.75mm filament, which is reducing back-pressure in the extruder. The design is slowly getting more and more refined, and in some cases it's just a matter of tweaking some parts.

In an open source design like RepRap, you can always print your own new parts, make or buy the remaining pieces and build a new variant that gives you exactly what you want. It's possible to do with the commercial variants, but in some cases not as easy. Here the community will usually give you advice or follow with interest. In the other commercial communities you'll either be unsupported or ignored. This also means that non-printable part reuse plays highly in the designs people come up with.

An example here is the people who build a repstrap by getting the electronics and motors going on a standard Cartesian bot. Many of these people are planning to reuse all the electronics and motors on the printer they finally print, which saves money in the long run.

Hi & thanks all of you guys for your answers :-)

I have more question from jbayless.
jbayless Wrote:
-------------------------------------------------------
>...
>
> As I'm sure you've observed, the quality of RepRap
> parts varies widely, and tends to be a function of
> the experience of the operator (compare parts made
> by Adrian and Nophead with the prints many people
> make in their first months). Also, I advise you
> not to take shortcuts if you can - since you're
> working at a university and are getting funding,
> you probably will be able to afford quality parts,
> and will be able to use proper machine shop
> tooling.


Can you guide me to a quality vendor who is trustable with quality products ? Because we are dependent on the output of this 3D printer for our other robotic projects at our student group and we can not afford failing and buying again ...

Hi shahabfm

I am not sure I understand your requirement here, but Nophead is selling the plastic parts for Mendel on ebay. He has well over 50 sets to his name and is IMO a trusted supplier.

Of course, the accuracy of your printer depends on so much more than simply the plastic parts, but you cannot go wrong with his.

Hi Shahab,

I'm not sure I can recommend for or against any specific suppliers - I haven't purchased from very many, so I'm not sure how the quality varies from one to the next. I think that most of the stores selling parts are quite reputable. Also I'm in Canada, so I'm not sure what good parts suppliers are in Norway.

My point was more generally that, if you are aiming for maximum precision, always ask yourself "will an error in this part affect precision?". A minor error in a structural framework part might not be a problem at all, but a minor error in the belt pulleys could appear in all of the parts you print. For example, if the hole in the pulley is not perfectly concentric with the pulley itself, then it would result in skewed prints. That's not to say that many people have had problems with pulleys, but just to be aware of any possible sources of error or imprecision. Chances are that the defects from a very small error in the pulleys (or the gears in a geared extruder) would be small enough as to be very hard to detect. But if you were obsessive about precision, you could (for example) purchase commercial timing pulleys and still use the same Mendel design.

Likewise, I'd recommend using a print bed that you can guarantee is as flat as possible, and handle it with care so that it stays flat. The flattest available material I know of is float glass, and I think many people have done well with heated glass print beds (including Adrian). The only tricky part might be cutting it to size - if you can have a glass cutting shop make it, or if your university has a waterjet cutter, that would be ideal. Also, make sure you mount the print bed in a way that doesn't stress or warp it. =)

Make sure your smooth rods are high quality and very straight... etc. Make sure the endstops are mounted in a very stable way, and use locknuts whenever possible so the screws don't loosen. And of course, above all, make sure that your axes are straight and square when you do assemble the machine! If you have good measurement tools available, that will help.

With care and effort, I see no reason why Mendel can't be made into a very high-precision machine.

That said, there are some design improvements to Mendel that have been suggested recently, which would improve quality even more. As Nophead pointed out, the current 10-bearing axis design is overconstrained, and using 8 bearings should result in smoother operation. I'm not sure if anyone has made 3D models of an 8-bearing Mendel yet, let alone if they are being sold. Also the current design of Mendel uses a circuit board for added stiffness; this is not very effective. A far better solution was found, where the threaded rods are inclined inwards slightly to turn the triangular prism into more of a pyramid shape. Again I think that one was done just by bending the existing parts; I don't know if anyone has uploaded an updated Mendel design that includes this upgrade in it.

I'd better check if those updates have made their way into the latest Mendel version. If not, someone really ought to update the files. But either way, I think that even the un-upgraded Mendel is probably one of the best designs around.

If you contact a supplier like Mendel-Parts or Botmill and ask about these modifications, they'd probably be happy to print custom versions of Mendel for you.

Hi Shahab,

For what it's worth, I am in a similar situation to yourself. I have recently sourced a 3D printer for my universities electronics research group. We have relatively basic requirements (mounting brackets for PCBs, winding bobbins for transformers etc.) but decided to go with a commercial product.

The printer we purchased was from www.pp3dp.com and has proven to be a very nice little unit. It came with absolutely everything required (even tools for removing the models from the bed, trimming support material etc.) and was printing successful models from thingiverse within 10-15 minutes of removing it from the box.

I am not trying to knock the RepRap project at all, in fact I am in the process of printing myself a set of Mendel parts on our new printer but I have seen many projects where people have tried to build tools (PCB router, CNC mill, Laser cutters) and all have failed. If you are going to build a RepRap, do it for the joy of doing it as a project, not for the final result.

If it is a tool that is really going to be useful for your research group, the extra cost of a commercial unit will be easily justified.

In many ways I agree with Jono. If you can afford a PP3D, and if your end goal is to print parts to use for robotics, and if the PP3D meets your requirements in terms of build volume, then it's probably the best choice. The time you save might be well worth it.

On the other hand, if the PP3D falls short in any way of your requirements, then you won't be able to improve it very easily.