Catch-up time. I decided to extend the Y-axis as part of the conversion instead of a later upgrade. Since I didn't have any steel in a suitable size (I wanted a piece 2 1/2 x 2 1/2 x 6), I picked up that piece of mystery-cast I had used to make the base for the surface gauge (
http://www.hobby-machinist.com/showthread.php/5435-Surface-Gauge). It had eaten a 10' bandsaw blade when I cut off the first piece, so I have been hesitant to use it for anything.
I figured one of the previous problems could have been grit and such in the surface from the mold. I used my radial arm angle grinder to cut about 1/4" into the piece all the way around.
Then, out to the big bandsaw, running at its slowest speed. And yes, I did use a bit of coolant. No problems.
Some careful facing with an indexable end mill ...
And on to cutting the dovetails. The portable bandsaw would hardly touch this metal, but drills and shaper work fine. It even dulls centre punches. I drilled rows of holes and broke out the waste outside of the dovetails, then smoothed it off with the indexable. I took out all the waste I could below the slopes with a 1/8" woodruff cutter.
I spent most of the day today using a brand new 3/4" dovetail cutter to very carefully cut the dovetails, 0.010" at a time.
I carefully measured the original dovetail with a pair of 1/4" carbide shafts and I was quite proud of myself when I finally finished the extension to the same measurement. I took it out of the vise and held it up to the base of the mill. For all my life, I never expected that the mill would have a different angle than 60[SUP]o[/SUP]! And it's not 45[SUP]o[/SUP] either. It's only a few degrees off, but it totally screws up all the work I did today.
I think what I'll have to do is mount the block on the base, then mill them both to 60[SUP]o[/SUP]. But first, I'll make an indexable dovetail cutter. With the change in angles, I'll need a new gib anyway, so I'll make it thick enough to counter the loss of metal from the correction.