Strategies for Structural PLA parts

[spooner777 0]

I was wondering what your strategies for structural PLA parts is.

For an example, lets say you want to print a heavy duty mount for a book shelf:

1. Print with 100% infill.

2. Print with 10/20/30% infill.

3. Print hollow and fill with construction foam. (Or some infill?)

4. Print hollow and fill with epoxy resin.

5. Wrap with epoxy drenched carbon fibers or Kevlar.

So far I tried 100% infill parts which are amazingly strong but also take forever. Epoxy Resin was also quite strong but created a mess.

Have you tried any of these? Has anybody else? How would you do it?

If there are no good answers I might consider it for my final year project at University.

 

[IRobertI 520]

I'll be the boring guy because I'm feeling that way lately. Personally what I'd do is go buy some cheap metal brackets that are made for the job. To me it's not worth the risk to rely on prints for heavy duty stuff. I'm sure it'd hold up but in the back of my mind there would always be some lingering doubt that would drive me crazy.

 

[spooner777 0]

I just chose that example because everyone knows what is meant. Some things you can't buy.

 

[owen 19]

I usually only go for about 20% fill just to give something for the top skin to print on to. Make thicker walls and top and bottom for more strength. It all depends where you need the strength (top to bottom, sideways or twisting). Shape is important and you can usually look at how similar things are made/engineered and copy that. One thing which is a bit different than other constructed things is the weakness between layers, so this has to be taken into account when choosing the orientation when you print.

 

[nick-foley 5]

I don't think there's much magic to printing extremely strong PLA parts... and contrary to frequently posted opinions, I believe PLA parts are generally much stronger than ABS parts (at normal temps) due to the much weaker interlayer adhesion of printed ABS.

My "strong" parts usually have 3mm walls and 20+ infill, but don't expect infill to do much... with most parts you'll probably get the most efficient strength just by increasing your walls. Just make sure you're printing hot enough that your parts don't break along your build lines.

Using a larger nozzle, or simply telling your machine you're using a larger nozzle in Cura, can do a lot to make big, strong prints happen quickly. It also makes infil more meaningful, since 0.6mm beads, for example, bond much better to themselves and others when making infil.

These parts I printed are quite strong: http://www.thingiverse.com/thing:278290

So are these: http://www.thingiverse.com/make:71656

Both describe their settings.

 

[spooner777 0]

I don't think there's much magic to printing extremely strong PLA parts... and contrary to frequently posted opinions, I believe PLA parts are generally much stronger than ABS parts (at normal temps) due to the much weaker interlayer adhesion of printed ABS.

My "strong" parts usually have 3mm walls and 20+ infill, but don't expect infill to do much... with most parts you'll probably get the most efficient strength just by increasing your walls. Just make sure you're printing hot enough that your parts don't break along your build lines.

Using a larger nozzle, or simply telling your machine you're using a larger nozzle in Cura, can do a lot to make big, strong prints happen quickly. It also makes infil more meaningful, since 0.6mm beads, for example, bond much better to themselves and others when making infil.

These parts I printed are quite strong: http://www.thingiverse.com/thing:278290

So are these: http://www.thingiverse.com/make:71656

Both describe their settings.

 

 

Wow I can't believe they didn't break.

 

[jameshs 42]

I print quite a few 'structural' parts in PLA - the toughest support my body weight as I have a chinup bar that is supported between two bookcases - the top bar is scaffold pole that sits in a triangular PLA foot in either end (to give it a flat bottom. These are in compression - so no big deal.

From the scaffold pole I hang a timber broom handle - so 48mm diameter to 24mm diameter pole using a kind of tear drop shape. The offset from the pole diameter is about 10-15mm to make the object as fast to print as possible and they are 20mm deep - I printed with 20% infill as when I did 10% I got some tortion. I did 1.2mm top, bottom and walls.

Then, from the pole I have D handles - like triangles, so I can exercise different muscles and these are again in 25mm flat profile and 20ish mm deep with rounded edges (radiussed).

Have been using these continuously for almost 8 months and never had a failure or felt unstable.

I did try to print the triangles with a 25mm opening in it (i.e. so I could just pop it onto the pole) and they did not survive - the tortion was just too much and they failed - the second I closed the loop their strength was phenomenal.

A set I printed prior to a nozzle block has severe under-extrusion and were squidgy, but they still managed to hold me until I twisted them to failure (deliberately)

So with the right 'design' playing to the strengths of the material PLA printed can be incredibly strong.

This was before I drilled out a nozzle to 0.65mm which would really drop the print time, and started using Colorfabb XT which would allow me to reduce the cross sections.

I also print wedges that go under my feet on a rowing machine and in a rowing boat. I use 0.8mm walls and 10% infill to keep the weight down (weight is important) - I have done 300000 metres on the rowing machine and 200000 metres in the single sculling boat - in the outside rain etc (and the boat is stored outside) with no failures.

So you just design test to failure, change and print again - steel it is not, but I can't print steel:)

Am about to try nylon bridge which may allow some thinner profiles, but I find every filament type takes about a month to get the best out of!

Will post photos if it is useful?

James

 

[gr5 2,167]

Please post photos of some of the parts you described, yes!

 

[jameshs 42]

Please post photos of some of the parts you described, yes!

 

Will do when I get into work tomorrow - I also have some part finished showing the internals.

James

 

[spooner777 0]

Thanks!

 

[spooner777 0]

What is stronger? Infill or actual internal honey comb structure maybe 1mm thick?

 

[jameshs 42]

 

Here are the images of the prints that I hang from - one set either end of the pole and I do chin-ups and pull ups with no sign that they are going to break yet so not just strong in static loads - but dynamic too.

 

The white one is an example of a partial print with the infill showing - from memory this was 20% infill.

 

Colorfabb PLA/PHA mix

 

I do use quite a thick perimeter - these were early prints in my printing career - I would probably go thinner now

 

James

 

[colorfabb 3]

Another tip is to slow your print speed down to a speed that you won't need the external cooling fan anymore. Once you've reached this print speed, you can turn down, or turn of the cooling fan completely. This makes the layer adhesion between layers much better, just takes a little longer to print.

 

[yellowshark 153]

A thought floating around in my mind recently. Which is stronger, thicker walls and less 100% infill or thinner walls and more 100% infill?

 

[Dim3nsioneer 557]

Another thought, maybe a quite heretical one: does 100% infill really give the strongest parts? I think it depends on the kind of load you're applying to the part...