3d printing rookie trials and tribulations - Prusa MK3S+

[Honza]

5 hours ago, BuggyDad said:

Well, I dried out the black PETG filament and went to Prusa default temperatures at the same time, so not scientific and I don't know what improved it but something did. 

It could be both. High temperature can cause excessive stringing, which then causes filament to adhere to nozzle and deposit randomly. Same with wet filament, that causes bubbles. Good telltale of wet filament is purge after filament load.

The IKEA cabinet looks great. I still haven't got into making mine 😃

[BuggyDad]

1 hour ago, Honza said:

It could be both. High temperature can cause excessive stringing, which then causes filament to adhere to nozzle and deposit randomly. Same with wet filament, that causes bubbles. Good telltale of wet filament is purge after filament load.

The IKEA cabinet looks great. I still haven't got into making mine 😃

Thanks. 

I think the cabinet should be good. It'll enable me to at least try some different materials and it's an efficient use of space. If I was doing it again I'd set thicker perimeters than the designer has done, to give the parts just a bit more solidity. I got a childish kick out of watching the printer just crack on and make a print of many parts over like 14 hours, even though it's someone else's design. 

[BuggyDad]

I'm a bit further into my 3d printing journey now and I feel like it's time for a bit more experimenting. PETG has been easy to print and I've printed loads with it with no failures during printing or visual quality issues once I'd got through some teething setup issues. But, I had thought I could make some quite tough parts with it after (not very scientifically) concluding that the orange parts I made had a useful bit of give and seemed fairly strong. In the hand they feel much less brittle than PLA, and I think they are. I think the reality though is that impact resistance still isn't great, and so suitability for RC parts is, er, impacted. It's the sudden shock where they fail. It's good for some stuff, but also limited. And that orange stuff was the by far the most flexible of the PETG filaments I've tried - I haven't been able to repeat it.

An example is here, where supporting GRP strips (not pictured) will I think have prevented the part from bending too far, and the whole arm was still perfectly fine for running (the broken part is really a dimensional filler rather than a support member) but the part has broken anyway in an impact.

So, I'm thinking about ordering some PCTG. Apparently this is very similar to PETG in most regards including printability but much better in impact resistance:

https://www.3djake.uk/3djake/pctg-black-1

Now it's also the case that when I look at filament reviews online they tend to consider quality vs USA cost, and often rate stuff like Prusament as being worth the extra over eg ESun (cheap but still reviews OK). But the extra cost in the USA is fairly modest. The UK cost differential is much greater - the better rated filaments are either unavailable or very expensive in the UK because they tend to be shipped from abroad, while ESun is cheap as chips. Makes it more difficut to put online information into perspective.

[Wystan Withers]

My current workhorse filament Polymaker "Polylite PLA Pro". It's reasonably priced (in the States anyway, dunno how it looks on your side of the pond) prints beautifully and has just a tad of give to it so it's not brittle. I don't do anything fancy for adhesion, I'm a painter's tape and hairspray kinda guy. As I sure you've discovered by now, printed parts often need extra reinforcing here and there that injection molded parts don't so it's often a balance between functionally and creating an exact visual reproduction of that obsolete vintage part, and accepting that certain things just aren't good candidates filament printing.

Also printing parts solid isn't stronger than printing with some 'air gaps' inside the part. Saw a video years ago where a guy tested lots of different infill patters and percentages and the verdict was that gyroid with 98% fill was noticeably stronger than 100% infill. I rarely print this dense, for parts that need to be 'strong enough' I don't go much above 50% gyroid, the idea being that the whole point of having the printer is that if something brakes I just print another for a couple pennies.

[BuggyDad]

4 hours ago, Wystan Withers said:

Also printing parts solid isn't stronger than printing with some 'air gaps' inside the part. Saw a video years ago where a guy tested lots of different infill patters and percentages and the verdict was that gyroid with 98% fill was noticeably stronger than 100% infill. 

Interesting. I'll try that. How many perimeter layers do you go for? I'm never quite sure whether "more is better" or there's a sort of optimum.

For me I have tended to print at 100% for running parts, but this is in part because my parts are generally small enough in the relevant dimension that the impact on time and materials of reducing the percentage is fairly minimal. Although on my suspension arms I simply created the internal cavity I wanted in the CAD model because I couldn't accurately adjust the infill in just that area in Prusa Slicer, and that part (or that part of the part) I suspect is plenty strong. My points of failure are unlikely to be in the areas where there's volume enough for infill at all, rather they'll tend to be where I'm space constrained. 

[Wystan Withers]

Perimeter layers rally varies with the part. Something like a flat damper stay I'll bump it up to 4 or 5 to make sure there's plenty of meat in plates where a screw might need to thread or pass through other item which have more volume I'll keep the wall count low but add holes in the design of .1mm or so that pass all the way through which the slicer will threat as a perimeter and thus add extra internal strength to the interior.

For example, these are some bicycle handlebar extensions I came up with. If you notice those little slits passing through the transition from the larger diameter cylinder to the smaller diameter cylinder, since the slicer treats those as perimeters there will now be a nice strong X in the middle of the step rather than the smaller cylinder 'sitting' on top of just a couple layers of infill. The gap itself is so thing it is essentially solid. Also works if you have a column or screw stand-off standing proud of a flat face to put a tiny hole all the way through the part that way there will be a small columnar 'anchor' going all the way through the part.

[BuggyDad]

5 hours ago, Wystan Withers said:

Perimeter layers rally varies with the part. Something like a flat damper stay I'll bump it up to 4 or 5 to make sure there's plenty of meat in plates where a screw might need to thread or pass through other item which have more volume I'll keep the wall count low but add holes in the design of .1mm or so that pass all the way through which the slicer will threat as a perimeter and thus add extra internal strength to the interior.

I like that idea. Will do that next time I print something chunky and solid. 

3d printed bike handlebar extensions is ballsy. That tube of alu/CF is a pretty important thing in my life and I rely on its strength in an emergency. I probably wouldn't even trust commercially available ones! 

[Wystan Withers]

Yeah, I do tell guys to only use them on their carpet queens, like 70's BMX frames that are too tiny for grown men to ride (allegedly), and to be honest they just exist to upsell guys on the aluminum ones I machine from solid barstock (and sell for a bit more) but are bombproof. I really only sell into the vintage BMX market, I don't cross over much into the MTB world, and since most of us have crossed over into our 50's not a lot of wild riding going on anymore.