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I try to print a stamp with flexible filaments. The problem I encounter is that the filament is flexible, but not soft. This leads to small differences in height to parts of the stamp not working.

One solution would be to add a small 'cushion' to add some squishyness to the stamp. I designed the stamp and the 'cushion' but now the question arises: "Which infill will provide the best uniform squishyness (in one axis)?"

I did a test with cubic infill of Cura, and although it becomes quite squishy, some parts are squishier than other parts of the block.

TLDR; Trying to print a squishy cube, where in one axis all areas of the cube have the same squishyness.

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As the rubber stamp needs to be soft in one axis for the whole area, you could use an infill that causes the same softness in all directions, but is sliced as such that the stamp experiences the same softness. Alternatively you can use the specific infill types for flexibility, but beware of the orientation:

  • Concentric
  • Cross
  • Cross 3D

First, to get the same softness in each direction you need to use an infill pattern that has similar/uniform properties (isotropic) in all dimensions.

It is suggested to look into the infill type called "gyroid" (see question What are the advantages of gyroid infill?).

This type of infill is described as:

Gyroid infill is one of the strongest infill types for a given weight, has isotropic properties, and prints relatively fast with reduced material use and a fully connected part interior.

Second, since the stamp has relief, slicing the part may cause different infill height. You could look into Different infill in the same part to e.g. get a solid infill for under the relief to get a uniform infill for the "cushion".

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  • $\begingroup$ The main problem with Gyroid is that it has been designed for high 'strength' applications. It mainly excels in compression tests (which is highlighted by the links you provide), which is exactly what we do not want. I think for this we need something like a rotated wiggle pattern. $\endgroup$ – E Doe May 7 '19 at 7:56
  • $\begingroup$ @EDoe No, not if printed in flexible filament! Note to not use a very high infill percentage! Look up the examples on internet for examples how flexible parts you get. I've seen fantastic flexible results. $\endgroup$ – 0scar May 7 '19 at 8:00
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Sinusoidal infill provides great squishiness in the infill direction, but you'll still have the problem that where the infill meets the perimeter wall, it'll be less squishy than where the perimeter wall isn't touching any infill. You can reduce this effect by using a stiffer filament for that wall (if you can print with multiple filaments), by adding more perimeters, and by reducing the gap between infills (i.e. increasing the infill density). You can even explicitly design an extra-thick wall on the face that takes the pressure (the engraved face of the stamp), and then a section behind that with the squishy infill.

TBH, I'm not sure that flexible filament is really what you need for a stamp. Soft materials are commonly used for traditional stamp-making more because they're easy to etch than because the stamping works better that way. Print-making uses wooden or metal plates (the equivalent to the stamp) and produces better, more repeatable images than rubber stamps. When you're printing a stamp, you don't need to etch it, so the softness of rubber isn't an advantage for you. My outsider recommendation would be to try using a normal, rigid filament, and sand the surface to the smoothness you need. If you print with the stamp face on the bed, and your first-layer quality is really good on a smooth build plate, you can probably get better results without sanding.

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