I drilled and reamed the dowel pin holes today.
Here is the process for locating them
First locate the center
Then figure out where the holes are. I think I could have just located on one shoulder screw and been fine, but taking an average of two of them seemed like a better choice. The 12 inch scale is about the straightest thing in my shop, so I used that to indicate off of. It does have about 0.0015 bow in it over the length, but that's close enough.
Now indicate the center
Then the left side
and the right side, and close enough. I'm not doing work for NASA.
Then rotate 15 degrees to put the dowel pins halfway between the bolts, now it's in position for the first dowel pin hole
Then mount up the spoil board, I made this for another project so it bolted right on. I drilled and reamed through both the spoil board and mounting plate. I drilled through with a 1/4 drill, but only went 0.75 deep in the mounting plate with a 0.360 drill and a 0.376 reamer. With the 1/4 through hole, I can punch the pins out from the back side if needed, but they should be a tight slip fit in a 0.376 hole, so should come out easy with a pair of pliers.
We had a 48x48x1 chunk of MIC6 plate on the shelf, but it looked like Swiss cheese, so had to find a location on it that I could get a 20'' circle out of without the holes impacting my finished piece. The first thing we did was locate all the holes and make a drawing of the locations.
Then overlay the part and move it around until we could find a suitable location.
Then slice & dice to dig the raw stock out. And we come out with a 21 inch x 1 inch thick stop sign. We have an Evolution circular saw, 9 inch. I don't think they make these any longer.
https://www.trick-tools.com/Evolution-Steel-Saw-5-TCT-Circular-Saw-with-Laser-Guide-SteelSaw5-6806 This saw does some serious cutting, cuts through aluminum plate like butter. We have cut 3 inch thick material with it.
Then up into the mill with it, and center it up. Rotate so that hole on the right is in the proper location to not interfere with the machining.
And that 6.5 inch aluminum cube is going to be a clamp for the work so I don't damage the rotary table when I start seriously machining on that chunk of aluminum. The rotary table gears just aren't designed for those kind of loads on a 20 inch circle.
That's my project for tomorrow