In this paper, we build on a previously developed notion of 'learning as Making' to examine mathematics thinking and learning in a highly transformative and technological Making environment: one that involves a handheld 3D printing technology which enables 3D models to be created instantly via one's moving hand. In particular, we present two examples of Maker-centred lessons for teaching and learning of primary mathematics. In these lessons, the students actively constructed artefacts with 3D Printing Pens while engaging in inquiry-based learning activities, where the target concepts were properties of prisms and cross-sections at the primary 5 (age 10-11) and primary 6 (age 11-12) levels respectively. We use diffractive analysis to capture the fine details in students' body-material interactions while engaging in the tasks with or without the 3D Printing Pens during the lessons. Through the lens of Making as a material act of creation and seeking to update Papert's constructionist view of learning, we propose to rethink Making in school mathematics according to a four-fold characterisation: "Making is co-constructing meanings," "Making is mathematising," "Making is assembling with technology" and "Making is inventing." We discuss our contribution towards advancing a materialist perspective of learning mathematics and implications for a 'learning as Making' pedagogy and curriculum.