Helmet Tips

As is stated in the description my helmet models are sized to my own average head by default. The way I size them is to be put on in one piece, which means the bottom opening needs to be large enough to fit the head through which can often make it seem a little large once it's on as the bottom is typically the smallest area. This does provide ample room for padding inside however. Alternatively while you are splitting the model into parts for printing if you do it in such as a way that there is a front half and a back half you can size it a lot tighter to your head, and put it on in two parts using magnets or velcro to hold together, that way the bottom opening isn't an issue. For sizing you can use the 'measure' tool in PrusaSlicer/BambuStudio/OrcaSlicer to measure the side to side and back to front dimensions of the bottom opening, and using the scale tool adjust those dimensions of the model to match those measured from your head IRL, do this before splitting into parts. If doing the two halves method you can measure the middle widest part of the inside of the helmet instead and matching area of your head. One way to get a perfect sizing from there is to cut off just a thin slice of the relevant part of the helmet, print it and see if that fits you, to avoid having to print the whole thing. 

My helmet kits have small dowel holes along the seams for alignment during assembly, this is for toothpicks cut to size, otherwise I would recommend the same process as for props, insert dowels, glue the seams (you can use masking tape to temporarily hold everything together while drying) and use a temp controlled soldering iron at 220C to 'weld' the seams permanently.