The test you described would tell you if the spindle axis is not
parallel to the Z axis (the column). It would not tell you if the
column is tilted relative to the table. I don't know which type of
error you suspect - I'd think the latter would be more likely.
Update: I went and looked at some pictures of a G704. It looks
like the head can be tilted sideways? So you are worried about
that adjustment? If that is the only thing you care about, then
you could test it with a straight rod in the spindle and an indicator
on the table. But again, that test will NOT tell you if the column
is tilted.
There are three things you might want to check (and each one
needs to be checked in two planes, XZ and YZ.
A1) Is the spindle axis parallel to the quill travel
A2) Is the quill travel parallel to the Z-axis (column)
A3) Is the column perpendicular to the table
If the quill is locked, you can reduce it to two items:
B1) Is the spindle axis parallel to the Z-axis (column)
B2) Is the column perpendicular to the table
Note that traditional tramming tells you if the spindle axis
is perpendicular to the table, but that is NOT the same as
knowing A1-A2-A3, or B1-B2. Imagine that the column is
tilted 10 degrees to the left. You could tram the spindle to
be perpendicular to the table by tilting the head 10 degrees
the other way. But the Z-axis would still be totally screwed
up.
You either have to measure all three (or two) items, or trust
the chinese that the castings and machining are correct and
the only problem is mis-adjustment of the head tilt. I wouldn't
trust them and would try to measure everything.
I don't see any need to remove the fixture and workpiece and
indicate to the table. You should be able to indicate to the top
surface of the work itself.
You really want to mount an indicator to the spindle, with as much
reach as you can get (2-4"). Then zero it in one location, turn the
spindle 90 degrees, take a reading, turn another 90, take a reading,
turn another 90 take a reading, and turn once more to get back to
the original position. That will tell you if the spindle is perpendicular
to the surface you are indicating to, whether it is table, fixture, or
workpiece.
What is your biggest collet? Can you stick a chunk of 3/4 rod in a
collet and then stick a mag-base to it? Or C-clamp a V-block to it
and then mag base to the flat surface of the V-block? Seems like
you should be able to improvise something.
There is absolutely no need to use a 0.0001 indicator. If you get
it trammed to 0.001 over a 4" span (indicator tip 2" from spindle
axis) you are going to be more than good enough for even the
finest woodworking project.
On Tue, Aug 18, 2015, at 08:32 AM, Gene Heskett wrote:
> Greetings all;
>
> I am getting an artifact in my carving such that when the mating pieces
> are turned around and the joints meshed, indicates the head may be
> tilted a fraction of a degree. The indicator pointers location prevents
> it from being viewed headon because you can't see thru the quill, so
> some parallax error is possible. It is also possible the tool is
> flexing as its currently moving at 50 IPM cutting about .225" deep per
> pass, so the chips from an all climb cut are decent sized. And its a
> used mill, having cut some alu in its history. It was a handy bit in
> reach at the time.
>
> I do not have a dial holder that would hold a .0001" dial indicator in
> the spindle for a rotational check to see if its dead perpendicular to
> the table AND the table currently has the work holding jig/pallet
> mounted and in the way of accessing the tabletop. Its just clamped, but
> I think I'd glue a T-groove fitting stick to each end of it so it
> becomes keyed to the table before I'd remove it.
>
> As a method to show grosser errors, I am thinking of chucking up an 8"
> section of A2 rod, verifying any runout, and dialing the side of that as
> I run it up & down the post.
>
> Would this be a suitable method of checking the alignment ("tramming")
> between the post and the axis of a mounted tool?
>
> Thanks all.
>
> Cheers, Gene Heskett
> --
> "There are four boxes to be used in defense of liberty:
> soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> Genes Web page <http://geneslinuxbox.net:6309/gene>
>
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