Well, I have a few hours in the shop and was able to make some progress on a trial fitting using the procedure I outline earlier. Here's a few pics:
After completing the test block used to determine the measurements for the placement of the mouth, I laminated some cherry and machined it into a billet. Bed was cut into that while still square and then it was placed on the sole template for flush trimming. I took readings on smallest wall thickness at seven places along the rear infill's area and determined the best thickness to shoot for with the rabbet that would not be cut along the bottom. This is cut at the same height as the rear rabbet because that it the lowest part of the casting. Fortunately it provides plenty of bearing surface for continuing the rabbet to the shoulder lines with a chisel and judicious paring. Anyway, here's the blank fresh off the router table's rabbeting procedure (fence set with two test cuts and calipers):
It bears mentioning that by this point I'd already laid in the shoulder lines for the overstuff. This required the creation of side templates. I ended up using a $3 "fire extinguisher here -->" sign from Lowes because it was the perfect mix of flexible but rigid. And because it was thin steel I could file it to close dimension if my cutting with the sheers was not up to snuff. I used layout fluid and a carbide scribe to lay out the pattern, which was wedged up to the side of the casting from the inside for maximum accuracy:
[imagehttp://farm6.staticflickr.com/5457/9715055076_51432a229d_b.jpg[/image]
I transferred the pattern to the blank by clamping a flat reference to the bottom of the blank so I could concentrate on getting the back lined up.
Then set in the line with light touch and marking knife followed by heavier strokes to set it in Then a little chisel work to extend the rabbet to the lines:
At this point we have a very tight friction fit at the front and the back, but material must be removed to accommodate variances in wall thickness and the rough inside corners of the casting. I did this with a combination of shoulder plane, chisel, and file. As you can see, it doesn't take much to get it down in there and eventually nearly seated.
However, I was getting interference that was causing the blank not to seat all the way into the back where it should have. You can see the small difference in this picture of the mating of the back
(note, you can see here what happens to a corner when you screw up at the demon router table!)
After trying removing wood from a number of possible places, I finally figured out that it was the lateral rear corners that were preventing full seating. This is because the wall thickness changes considerably in this corner and I did not notice it when taking my readings. Two chisel cuts and we were home, but the next difficulty was revealed:
As you can see, the meeting of the infill with the shoulders leaves much to be desired. After some examination, I believe I have pinpointed the root cause. Because the inside corners are rough, the patterns sit more on the roughness (think: cove) than all the way down at the lowest point as would be allowed were the casting to have clean and square inside corners. By messing with the location of the pattern, the template, when scribed to the blank, yields a gap equivalent to the offset created by the roughness of the inside corner. The larger offset closer to the ramp may be worsened by something else so I will have to continue to investigate.
I believe there are two ways to counter this. One would be to make up for the offset by shimming out the blank (but not the pattern) from the reference during transfer. A 16th would probably do it, allowing the shoulders to be scribed "too low" which is in fact right where we want them since the pattern couldn't seat in the casting perfectly to begin with. The other option (which I would have if I was fitting an actual infill and not this trial piece) would be to plane 1/16" off the bottom of the infill to effectively bring the shoulders down. This would actually be reasonably easy, as one could use a marking gauge to indicate the amount needing removal and simply plane to the line as one would when bringing a board to final thickness.
Unfortunately, we're getting close to a deal on the house, so I may soon have to pack up my shop for storage until perhaps February. To be continued!
Reed
You don't need a parachute to go skydiving unless you want to do it more than once. . .
