And now, the moment probably nobody but me had been waiting for... The test fit!
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Looking down into the top of the casting, you can see the boss on the X3 Z slide poking through the boss receptor plate. You can also see the overhang of the casting flanges. I will probably make some filler strips to pad out the Z slide so it doesn't look so goofy. Otherwise, I'm tempted to say the fit is perfect - exactly what I intended! I love it when a plan comes together.
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The left-right tramming action seems just about right - I think I should be able to dial it in without a lot of hassle, then pin it in place. I did oversize the bolt holes a little bit to give me more wiggle room in tilting it left-right. I'm really glad I decided to make the plate to accept that boss, I think I would have been in for a world of misery trying to tram it otherwise. As it is, it rotates on a point perfectly centered in the middle of the four bolts, which is exactly what you want.
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So that's where we stand for now. After a long Friday evening and two solid 8+ hour days down in the shop, I needed a break so I called it a day before I made a stupid mistake and regretted it. I removed the Tormach head, and left the X3 head jacked up on 246 blocks, though I centered the table so it wouldn't be overhanging. If you ever have to remove your X3 head and you've got an operational table, this is actually a really nice way to do it - no lifting required, and no drama.