"How brittle should my 3D models be?" Topic

Newbie with a printer here -- Creality Ender 3 using PLA from Hatchbox.

I've successfully printed quite a few items, but noted that some of them are rather brittle. For instance, when I print the "tribal ramparts" from Printable Scenery, (I print at 60% for my 15mm figures), some of the details seem very fragile. For instance, just putting the slightest pressure on the horns decorating the wall can snap them off (though it's more like they just fall off rather than snap -- there isn't much resistance)
Same thing with some of Bergman's 1/100 tanks. The barrels break with hardly any force, and in some cases, removing the supports also removes parts of the actual print of the turret.
Is this a function of PLA, or do I have some print settings wrong resulting in poor quality prints? I had been printing at 200 degrees, but after doing some research, upped that to 210 to see if it resulted in stronger prints. (Heated bed is 60 degrees in all cases) One initial test looked promising, but figured I would see if it's me or just normal for small items to be so fragile.
Thanks

Following …

First of all what size are the fragile bits? About 1mm diameter is the limit. I have done figures with 0.7mm bits but its very fragile if its exposed to impact.

Supports are always an issue. I paid lots of money for Simplify 3D as it makes easy removable supports.

The direction of print can be an issue. For instance a rod is stronger printed longways (really a series of rectangles) than if made up of circles.

A picture with dimensions may help.

You may be printing at too low of a temperature. So your analysis is correct. Different PLA types will print better at different temperatures.

I'd been printing with translucent green and white and found that they were reasonably strong with print temperatures of 195 degrees. The translucent white actually printed better at 185 degrees which is the accepted minimum temperature for PLA.

Recently I started printing with solid blue. Indeed it seemed kind of crumbly, especially with small models such as figurines. Raising the temperature to 205 degrees has improved matters greatly.

Of course, other manufacturers will have different formulas for their plastic and will likely have slightly different print temperatures from others.

I agree with the above. Temperature can make the difference. Sadly all temp readouts are just estimates and the same temp settings on one machine may not work on the next. Too low and the binding between layers is weak, too high can give lots of problems, but may weaken the plastic within a layer.

I have seen an ultrasonic knife used to cut supports, it looked very good in the sales video! But I thinks it is still several hundred dollars to buy one.

As above, temperature is No.1 to look at, and what one machine says is 200 may be anothers 190 or 220.

Another thing that can cause problems is how the spool is wound and how consistent the filament is, both can cause intermittent feed problems which can lead to layer separation or other messy failures.

Poor spool winding can cause the filament to jam, either entirely or just jerkily – you can sort of over come this if you look at how much filament is needed for a model and then just measure that amount out and let it hang loose. Sometimes it comes like that but it can also happen if the filament unwinds itself when changing spools.

Irregular filament is usually (but not always) found in cheap reels – some of it can look or feel rough or irregular but some is almost in spec. so you think you got good filament but it keeps having print failures.

DAMHIK.

So far, my experiments with higher temp prints have shown great promise. I first ramped up the temp to 210 using a 1/100 PzIV turret with the skirt as a test -- because the turret skirts have proven very brittle in earlier prints. The 210 print came out much stronger with no loss of detail. I then tried one at 215 and it was stronger yet. This is 5 degrees hotter than the recommended range for the Hatchbox PLA, but it seems to work with no issues so far.
Thanks for the help all.

PLA shouldn't be brittle. I've made various springs and springy clamps out of it.

You should certainly play with temperature. I would also suggest watching Maker's Muse on YouTube, pick out a handful of videos that focus on model orientation, temperature, strength, etc.

And just like virtually no metal miniatures have ankles or realistic proportions due to the need to connect the figure to the base, you need to adapt your model to your scale and medium. If you draw it perfectly to scale and print it you might find it unsound and funny looking. You have to fiddle with it.

Good luck!

The trick is to print a temperature tower with each filament to work out the printing temperature range.

Also small parts <0.8mm in diameter (assuming a standard 0.4mm nozzle) will be relatively weak and prone to breaking, changing the print angle will help, I've found printing at 15 degrees makes better barrels for 1:300 guns

What's a 'temperature tower' @Munster?

A temperature tower is a model that you print and slowly adjust the temperature by pausing, adjusting, restarting. The model, in theory will be printed at different temperatures. Useful if you are trying to figure out the optimal temperature for printing. Less useful for printers that can't handle "on the fly" adjustments.

You can also edit the gcode to change the temperature as it goes along, without having to do the manual pause, which could affect the results. Some slicers will even do this for you, I think.