Once you have a well modeled crab the slicing into the tangram parts will be straightforward.
The ‘parts’ - like legs etc - look to lend themselves to modeling as separate parts - as groups or components.
That way you separate geometry and they are easier to fix.
Make sure all outward looking faces are the ‘front’ [off-white] - you should NOT see any blue-gray ‘backs’.
Once the ‘part’ reports as a solid in Entity Info you know that bit is OK.
Continue around the crab and a make all of the ‘parts’.
Once all of the parts are reporting as ‘solid’ you can merge them into one combined part using the ‘shell’ tool.
Now you should have a single group that is a solid.
Intersect it with he tangram edges to get cuts on the faces of the crab.
Now copy the crab group into the number of parts needed [7 in all ?]…
If might help if you named the parts 1 to 7 ?
Edit each group in turn and delete the unwanted bits.
Each edited group will now report without ‘solid’ in Entity Info.
This is because there will currently be ‘holes’ in the external surface where the ‘cuts’ were made and the adjacent unwanted faces erased.
You should be able to edit a group and draw over an edge of a hole to re-face it.
Once all such holes are ‘healed’ it should report as ‘solid’ in Entity Info.
Now you should have seven ‘solid’ groups forming the tangram.
You can 3d print them and a base plate separately: or. depending on your 3d-printer. you might be able to print them all at once, BUT you will need to arrange them with suitable gaps between the individual sections so the a made a unconnected pieces…