Stijn here from 3D Hubs. As some of you already know we are working on a knowledge base: An extensive 3D printing resource for professionals.

One article we are working on, written by a hub, discusses the key 3D printing technology (FDM, SLA, SLS, Polyjet) selection- and design considerations for clearance, transitional & interference push-fits.

As a community experiment, I was wondering if you could provide your input on the technologies you are familiar with? I’m confident your input will help make this article very helpful and in-depth.

Please have a look at this gdoc and reply on my comments.

Cheers,

Stijn

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Any material that isn’t too rigid/brittle works. I have done push fit with regular PLA but it’s not ideal. Anything more rigid than PLA is not a good idea. I have had great success with Colorfabb XT and their PLA(which is a PHA blend). PET is another great choice as well as nylon. I also did a project in polycarbonate with some push fit parts once and it came out great.
For FDM, the more brittle the material, the more important the print orientation. If your layers are perpendicular to the pins(lengthwise) then they will most likely fail.

-Jesse

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Also layers/print orientation is very important for push-fit connections, an improperly oriented part can make a push-fit fail even if the design intent and tolerences are correct.

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Interesting. You say anything more rigid than PLA is not a good idea but on the other hand you did have good success with Colorfab-XT and polycarbonate which are both very rigid materials. Wondering when rigidness does become an obstacle for push-fit parts?

For what types of push-fits a more flexible (e.g. TPU) or soft (e.g. nylon) material would be better?

Thanks, something that will be covered

XT is “stronger” but definitely less rigid than regular PLA. Polycarbonate is somewhat in a class of its own but still applies. The rigidness is important in term of how brittle the material is. The idea is, when you apply force does the material bend before it snaps? XT is strong and PC is VERY strong. They may seem rigid but if you apply enough force they will bend before they break. Most PLA will snap under pressure instead of bending.

-Jesse

The Polyjet Rigur material is especially suited for this type of application. Good strength and elasticity combined in a material that gives high resolution details as well.

See technical data sheet : http://usglobalimages.stratasys.com/Main/Files/Material%20Cards/MC_PJ_Rigur_RGD450.pdf?v=636059923107028102

Regards

Pierre

ABS works quite well for me. I’ve printed around 600 pieces that all push fit together in ABS.

PLA I found to be too rigid, and PETG was a bit too floppy.

There’s a reason that Lego pieces are made from ABS.

PLA is hard and rigid but is also brittle. That means it has little elastic deformation before breaking (simple test is to bend the filament). So if you construct something where the tolerances are too high, forcing the PLA in might cause it to break or it won’t have the ability to “squeeze” in. Not really the best material for push fit.

ABS is not as hard as PLA but has a larger elastic zone before failing, i.e. it’s stress strain curve is steeper. To further illustrate this and trying my best not to use too many technical terms…

Referring to the image stolen from Wu et al. 2015 below, the horizontal axis is the elongation and vertical axis is the force required for that particular elongation. The end of the curves are for when it breaks. Comparing PEEK and ABS, ABS’s stress strain curve is steeper.

Here you see PEEK failing at about 60 MPa @0.09% elongation

ABS fails at about the same elongation but at 30 MPa.

In simple terms if you were to have two identical push fit parts with the above materials, assuming the same geometrical accuracies, both will fit but you need to push twice as hard for PEEK. So it depends how tight you want your parts to fit and whether you want to push it in by hand or with the help of tools? How high the force is also depends on your contact area and sizing.

The curve for PLA will be less steep (more vertical) meaning it will have less change in elongation and just snaps once you reach a certain stress.

TPU’s curve is verrry steep (leaning towards the horizontal axis), so you can push it in easily but it also falls out easily (ok this also depends on the compression… but this is the general idea). This doesn’t mean it’s bad, it just depends on your application.

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