Some questions about 3D printers

[aol000xw]

I've seen many of you design and print your own parts sometimes at home and sometimes using a third party service like Shapeways.

I'm more intrigued about making parts at home, not structural but mechanical ones, and more specifically suspension ones.

The basic Idea would turn around getting steel springs and o-rings from eBay and 3d printing the rest. Obviously the point is getting something closer to proper damping using some sort of fluid.

So what would be the recommended material given the specific use case? Nylon, PLA, ABS?

I am thinking on using some silicone oil so I guess it will be safe for any material.

Would steel rods be required or patience and lots of polishing would be enough to get a good seal?

Any recommended 3d printer for this kind of use?

[Mechbuilds]

Well lego is made out of ABS. It would be good to use the same plastic so the characteristics are the same. 
I'd also be interested in this 3d printing thing.. I think i made a thread like this once or asked about it once. Didn't get much answers.. 
If you can figure out a nice suspension with lots of travel and great steering lock then PM me with your ideas! 

[dr_spock]

Nylon would be the strongest but most difficult to print.  With ABS, you can try acetone vapour smoothing to rid the 3D layer lines to get a good seal.  It may be better and faster milling a block of plastic to make the custom shock absorbers. 

 

 

[allanp]

With a cheap mini lathe and cheap mini mill there isn't much you can't make from a solid piece of plastic or metal. Have you thought about going down that route? 

[Mechbuilds]

I think you should read this:

https://io3dprint.com/3d-printing-lego/

[aol000xw]

Nice, thank you for the link.

Regarding using power tools to create parts, I find it too laborious and too dependent on skills I surely lack. 3dPrinting looks relatively easy and opens the door to creating parts not possible with traditional methods, hence my interest.

 

[Cumulonimbus]

Speaking from considerable experience with FDM (Fused deposition modeling) 3D printers, both professionally as in my spare time , I’m afraid the news is not that good for your application. The FDM process which is used in almost all home 3D printers has its limits when considering functional models:

• Details can’t be smaller than the selected nozzle size, the smallest one being 0.1mm. Lego parts are made with injection moulding which allows for much tighter tolerances (think more like an accuracy of 0.01mm)
• Most complex shaped models need to be supported by a temporary structure to keep underlying layer in place while printing an overhang. Luckily, the slicing software figures this out for you, but you will need to remove this structure by hand after printing and it will leave a rougher surface behind.
• Sanding and smoothing 3D printed parts can be challenging. Sanding introduces heat which will quickly affect the materials (which are often optimized for a lower melting point). The result can lead to an even rougher surface than you started with. You can add fillers and primers to improve the surface quality, but this requires considerable effort. As mentioned, vapor smoothing is possible with some materials like ABS, but if you’re after a dimensionally stable part, this process will be purely guesswork and is likely to weaken your part.
• Although you can choose several thermoplastic materials, even with all kinds of additives to tweak certain properties, the limiting factor is the production process. The fact that any printed product is build up one layer at a time, means that the bond between those layers will always be the weak point. Clever orientation of your part in relation to the layer direction can improve results, but even then you can expect delamination under load. A workaround can be to increase material thickness, but since you are bound by the scale of the Lego system, there might not be enough room to do this.
• Since you talk about sealing a chamber:  In my experience, FDM printed parts always leak between layers, especially when the pressure is increased. You will need an extra layer like a coat of epoxy to really seal the surface of your chamber.
• In my professional functional models and prototypes, anywhere where mechanical loads occurred the printed parts just failed too fast under load. As a solution often extra hardware was added like threaded inserts, metal rods, standard bolts, standard O-rings, bearings etc.

Other 3D printing processes are possible in consumer 3D printers like SLA (Stereolithography) which can give you better level of detail (up to 0.025mm for a Form 2 for example) and it is possible to make watertight parts with this process. But I think the strength of the bond between layers will remain the weakest link in your part. Not to mention the laborious task of curing and cleaning your part.

Services like Shapeways use different processes,such as SLS (Selective Laser Sintering) or MJF (Multi Jet Fusion). Accuracy is as high or higher as SLA, and it's even possible to print in metal, but parts still have rough surfaces, unsuitable to seal. I have no experience with the mechanical strength of parts made with these processes, maybe @efferman can help you with this. I do know that parts ordered at these services are not cheap. If you are willing to splash out on services to get your parts made, why not looking for a service which can mill and turn your parts in more suitable materials.

If your goal is to get parts which can reliably handle mechanical loads, I agree with @dr_spock and @allanp: look at traditional manufacturing processes like milling and turning. The investment in parts and/or labor will probably be higher, but the functionality and reliability will be much higher, leading to a more enjoyable outcome.
However, if you enjoy solving the puzzle with lower costs and have no issues with iterating your design and learning from mistakes, then consider 3D printing and building a hybrid model with more durable purchased hardware at critical points.

Edited August 22, 2019 by Cumulonimbus
typos

[aol000xw]

Wow, very enlightening!

I'll need to consider if a small CNC and Acetal (POM) or even aluminium are better options. 3d printing just looked easier...

You gave me a lot to think about, thanks.

 

[Cumulonimbus]

1 hour ago, aol000xw said:

...  3d printing just looked easier...

Well, it is easier and quicker to get parts with 3D printing, but my point is that they will be of limited use unless you invest much more time en effort to make them really functional.

That said, I'm a big fan of using 3D parts during a developing phase. They can help you to find issues, iterate quickly, explore different concepts, figure out assembly sequences etc. Even though CAD software suites are getting better each year, nothing beats a physical model of your design. For a lot of those tests, your parts do not need to be fully functional. Only when you have full confidence in your design, you can invest in machined parts. And I must admit, seeing your parts getting formed in front of your eyes still is rather magical.

Edited August 22, 2019 by Cumulonimbus

[Jurss]

 

1 hour ago, Cumulonimbus said:

Speaking from considerable experience with FDM

Thank You for sharing Your experience!

[Cumulonimbus]

19 minutes ago, Jurss said:

Thank You for sharing Your experience!

Is this meant as a sarcastic comment?? I guess you think I was bragging, but I only wanted to illustrate that I had first hand experience that the OP might find useful. Thank you for taking your time to post such a valuable addition to this discussion.

[Jurss]

... why do You think I was sarcastic? Don't people thank other people in Netherlands for some good advice? Sorry for gratitude ... (now I sarcastic or something like that)

[Cumulonimbus]

My apologies, I read too much in your use of the capitals at the start of "you" and "your".