It's kind of ironic that only last week Belinda posted this to clayart. Ironic because two days ago after lots of sanding of the ceiling to try and flatten it, I moved it on the kiln. Um, it didn't fit so good.
None other than Arnold Howard confirmed that the method to use to flatten it is a big round piece of MDF with sandpaper glued to it. Presumably something like 50 grit. Unfortunately, I didn't believe that was an option for me, since the cement that I put into the grooves is so hard that it just tears the sandpaper.
I considered putting the lid on my Shimpo, and trimming it just like a pots foot, but I don't think I could tap-centre a one hundred pound slab.
Of course, I haven't used my router yet on this project. This seemed like a good opportunity to rectify that shortcoming. So I made this jig. The plan was to raise the aluminium skin on the lid so that the jig ran on it like on a pair of rails. The router would stick down and grind out a seat for the kiln walls. Perfectly flat. Unfortunately, the pop rivets prevent the skin from being raised up. Damn.
It's ok, using a big long piece of MDF like this pretty much averages the unevenness of the floor, damping out the hills and dips. The plan was to mount the router to the jig so the bit sticks through the big hole, and a nail in the lid would stick up through one of the small holes. Then just routing a circle out through a bunch of the little holes would grind out my seat.
My lid isn't very round. So, I had to find the centre of the lid. If you remember some grade 9 geometery that's pretty easy. Just get a string the length of the radius, and then scribe a circle arc from two places on the circles perimeter. Where they intersect is the centre. Unfortunately, the lid is not quite a circle, so after scribing about twenty arcs I had the centre surrounded.
It worked like a charm. Here's the result after a couple of passes. I didn't grind out too much so the dust wasn't too bad, but you should definitely still wear a mask. If you have a speed control for your router, I'd recommend it to cut down on the dust. Of course, you might want to use an old crappy bit, I don't think IFB is too good for the knives.
I haven't moved it to the kiln yet but I'm hopefull that it will fit like a glove.
