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Hi folks, I came up with a way to make a jig for cutting the complex shape of a keystone.
Step 1: Take 2 pieces of card stock or similar and trace/cut each piece to fit just inside the top as well as bottom of the keystone opening.
Step 2: Mark the center of each piece, then cut a slot in each to accept a small strip of wood (popsicle stick or similar. I used a strip of balsa wood). Orient the card stock pieces just inside of the holes and then super-glue or tape the stick into position. This can be tricky because you need both pieces to be oriented correctly to each other with respect to tilt and rotation. Super glue came in handy here since it instantly froze the pieces into position once i had them lined up.
Step 3: Sandwich the stick between two firebricks, and trace the outline of the card stock onto them. Remember you will need to cut just inside the lines to allow for a mortar gap.
Now you should have a nice custom cut keystone that fits like a glove! I took a few tries to get it in there since the small gap made the mortar want to "grab" more. I eventually used a lower viscosity mix and it worked fine.
Step 1: Take 2 pieces of card stock or similar and trace/cut each piece to fit just inside the top as well as bottom of the keystone opening.
Step 2: Mark the center of each piece, then cut a slot in each to accept a small strip of wood (popsicle stick or similar. I used a strip of balsa wood). Orient the card stock pieces just inside of the holes and then super-glue or tape the stick into position. This can be tricky because you need both pieces to be oriented correctly to each other with respect to tilt and rotation. Super glue came in handy here since it instantly froze the pieces into position once i had them lined up.
Step 3: Sandwich the stick between two firebricks, and trace the outline of the card stock onto them. Remember you will need to cut just inside the lines to allow for a mortar gap.
Now you should have a nice custom cut keystone that fits like a glove! I took a few tries to get it in there since the small gap made the mortar want to "grab" more. I eventually used a lower viscosity mix and it worked fine.
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