We have a few different depictions of a grozing iron:
From a modern reconstruction (Images sourced from Corpus Vitrearum Medii Aevi) we have the following images, which are similar to a display set up by the Dean and Chapter of Canterbury:
From the 15th century or so, we have this coat of arms:
This seems to be the image we draw our charge from in the SCA. A handful of us, myself included, have grozing irons in arms and badges.
The point is to provide a fulcrum for breaking glass, like modern running pliers and techniques.
I purchased a 3' length of flat stock at my local hardware store. I consulted with a blacksmith friend on my metal choices for this project and decided that, as the iron itself will never be an A&S entry, it was ok to use steel. Of course, I'm also using a drill and dremel so...
Some interesting facts for those of us who do not often work with metal. I was afraid of the shower of sparks I knew must happen. You see it whenever something is grinding on metal. I was assured they wouldn't hurt. They didn't! Granted these are smaller sparks than people working on "real" metal might get, but I barely noticed them, and I'm a wuss.
I've had my dremel kit for a while now. I've used it for many things, but never cutting metal. I wondered why they gave me so many cut-off wheels. Now I know, they are consumed in the cutting:
I used the dremel to cut about 10-11" off the stock. I then took the corners off and will use a bench grinder or file to give it a more rounded appearance. More on this below in "lessons learned"...
I used a normal drill with a metal bit to put the hole in. I will do this again on the other end, with a deeper hole, for somewhat deeper cuts.
The iron worked just fine. I scored a piece of glass and used the iron on the underside. I thought it would break off small chunks, the nibbling effect I expected, but it popped off the entire score. The end result looks like my modern running pliers, to my surprise.
Well, certainly not much about medieval blacksmithing!
I took as my model the more heraldic style of grozing iron, or what I thought of as that. I pictured flat stock with a hole chiseled or punched out. I now realized this is probably a stylized design (shock! Imagine that!) and that the end of the tool should not be as thick as the charge is usually drawn. In terms of physics, however, it should be just fine. In fact, it WORKS just fine. In the future I will try to get a more proper one. Late period irons have been seen and depicted that are much like this,a notch out of an bar, however.... really, I am not overly worried about it right now.