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Converting a Grizzly G8689 Mini Mill to 3-axis CNC, Part 5:
Once I had the block fitted and bored, I scribed where clearances needed to be, and milled off the bulk of the extra...
And then belt-sanded the contours to follow the ballnut flange outline.
Now being more assured about clearances, I drilled and countersunk the second mounting hole for the block.
And as the counterbore for the first one had been partially milled away, I rebored it as well.
And using that as a locator, drilled and tapped the mating hole in the saddle slot.
If the previous owner hadn't drilled two grub-screw holes half a hole
width away from where i needed them, I could have
just put two screws in
to hold the nut in place and called it good. Two 8-32 screws might be a
little weak for this setup,
but let's face it, it's a minimill with a
Morse Taper spindle. We ain't gonna be doing any heavy hogging on it. :)
So, wanting to make it a little
stouter, I milled a recess in the end of the casting so the ballnut flange would sit mostly recessed.
That left a "wall" about .100" thick between the flange and the new
aluminum boss. I then located and drilled four 8/32 holes for the
And finally, I picked up some slightly longer screws to maximize how
much of the bolts were holding the boss in place,
and once snugged down,
I ran the saddle over to the mill and shaved off the excess. That's not a bearing surface,
it actually has some 40 thou of clearance
to the base casting, so I don't have to worry about it rubbing.
Now, with everything wiped down, blown out, cleaned and properly assembled.
Tolerances were still pretty close to the bed, so as a final tweak, I
had to mill just a hair off of one edge of the
inner passage of the
underside of the table.
That lets the table slide right past the mount and flange- it looks
tight, and it is, but there's no contact, and just a smidge of
And with the table gib installed, it's time to make the end caps and bearing mounts!
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