I have just printed my second helmet and am having issues getting them the right size . i know i have a large head but ! is there a way of getting these to fit , without printing half a dozen ? many thanks
slice and print a ring out of the middle of the helmet, or where it is smallest. Only needs to be 1/4" tall. See how that fits over your head.
I do the same thing with arm and leg armor. Model it... print a sizing ring for confirmation... adjust if needed. THEN the full thing.
Oh this helps. Circle calculator. Measure the circumference of your head. Plug that number in. Get the diameter. Now check the diameter of the helmet interior using something like 3d Builder.https://www.omnicalculator.com/math/circumference
You should print it with proper size and dimensions.
If your head is large then you should try something Extra-large: above 24.75 (63cm)
if you have a wrong (for your needs) size print from an stl its just down to scaling, measure what the stl gives, measure the size you want, and scale it by that much percent. e.g. you have a model its sized to be 100mm tall, you wanted it 120mm tall scale it up to 120% sort of thing, would be my suggestion
If you have access to a cellphone with face ID type cameras (newer iphones and samsungs) there are 3d scanning apps that you can use to do a rough scan of your head, with a little help from a second person to man the phone.
I did the front half of my head alone and was able to import it to my slicer and use that as a 1:1 digital representation so I could size helmets that extra 1-10%. Don't forget to account for foam if you plan on adding any to the inside. I guess this only works if you're using a full helmet model.
Not sure if this helps, but i would use a slicer to cut a thin layer out from it to print to see if it fits around your head. You can even slice out a layer vertically too to be sure height is right. Assuming you have a full model not cut up already