Help with designing a printed mold

I am working on a printed mold with a silicone liner. I plan on scaling it up to 300mm from 100mm after the initial test printing. Can someone help with how much smaller the alignment keys need to be than the hola they go into for a slip fit?

Your best bet is to print a key/hole set only and determine the tolerances from there by adjusting the model and print settings. Be cognizant of the fact that scaling your item will loosen the tolerances. For example, if a 0.1mm gap on all sides for tolerance worked at 100mm, scaling 3x to 300mm will then make the gap 0.3mm which, in this example may be too loose. So… you may need to adjust the keys/holes after scaling in your modeling software of choice.


I’ve made loads of silicone molds, some with 3d printed jackets. I can probably help but im struggling with understanding what you’re trying to do. Can you clarify?


I think when I 3d print I use .1mm for a tight/snap fit, .2 if I don’t feel like struggling today.


Is that in metric or standard?

0.1mm is a good starting point for tolerance… again, consider doing a small representative test print. This will flush out variations in slicer settings, printer, and filament.


Hey Pip! This post inspired me to do a test run to see what it takes to make parts that fit together on a 3d printer. I posted my results to tiktok:

It’s currently going viral - 300 comments of people telling me I don’t understand machine tolerances. Ah, social media. So much love. I used the makeict hashtag so you all can be the judge of whether I’m representing us well or not!

BUT ANYWAY my results were…

I 3d printed a design that called for an 8mm square, 8mm hole. The 8mm square can be held in place by an 8.2mm hole, falls through an 8.3mm hole.

On the laser cutter, the square can be held in place by a 7.7mm hole, falls through a 7.8mm hole.

Of course tolerances will depend on your materials, calibration, whether the laser bed is level, the day, humidity, who knows. I just wanted to use two tools to make the same design to demonstrated tolerances to consider.


Empirical tests are always better than theoretical ones. Down with the naysayers…


I did a test print the night I posted this. I went with.2mm and it seems satisfactory for what I want to do. Waiting on the pieces to print. Sadly one of my printers is giving me problems so this is going to be a long wait.


I don’t think it is still sitting there, but I actually printed a test piece a while back that had little circles in it to demonstrate the tolerance. It had been sitting on the table next to the computer for the longest time. Not sure if it got thrown away, or stashed with the 3D Printer stuff. But it was an interesting example.


haha I’m so sorry for adding commentary regarding vector graphics during your laser class. There are too many nerds on the internet.

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Spaghetti Pants FTW…


This is great content.

Barely related, I skimmed through your TikTok to see your other great content and laughed aloud when I saw the one about the Sewing Room seam rippers because it made me, too, very happy for the same reasons. They are absolutely the 10mm socket equivalent. Also, when I was in there this past week, there were six :laughing: unheard of phenomenon, a lost socket being found.