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Converting a Grizzly G8689 Mini Mill to 3-axis CNC, Part 7:
While I was waiting for some parts to arrive, there was another major
part of this build I thought I'd get to.
Whatever idiot designed these
small mills added a "pivot" at the base of the column, so that it could
be tilted left
or right in order to mill angles and chamfers. The problem with it was, that the pivot is very
and comprises a serious weak point in the structure of the
machine. So much so that after a few years, the
manufacturers of these
small mills ditched the pivot entirely, making a much stronger fixed
between the base and column.
Well, I don't have one of those later models, so I had to figure out a
way to reinforce what I already had.
I am not, as some may have noticed,
an engineer, and I have no software for performing finite
analysis of stresses and strains, but on the other hand, neither am I
trying to design an
ultralight aircraft or space vehicle. Therefore, I
can overbuild the piss out of it and
throw a pile of heavy steel at the
First thing I needed to do was dismantle the head assembly and get just the column itself.
The column is actually a fairly thin-walled cast-iron box section- if
the rest of the machine weren't so wimpy,
a quick fix for this might be
to buy a section of solid Dura-bar and mill an entire new column.
But, any benefit to the solid column would be lost to the wimp pivot
anyway, so that's the part we need to focus on.
I went and chatted with
the guys at my local metal supplier and came home with a couple pieces
if 1/2" hot-roll steel plate.
The larger of the two I took a flap wheel
to to break the corners and smooth up the sharp edges...
That piece will form essentially a new base plate.
That's the pivot in question. The whole thing. The column simply slips
over that shaft and is secured with a wide washer
and a big nut. But
that thin little bracket then has to support all the weight and cutting
forces of the headstock and column.
To remedy this, the other piece of plate was marked...
And test-fitted in place.
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