Having temporarily run out more productive things to do, and having a
half rainy, partly sunny, muggy day, I decided to tram the head on the
HF mini mill and find out how bad it was. Well, really bad. Side to
side, no problem, front to back, .016" across 3 1/2 ". That's bad.
First thought was the column, and a little checking proved that it was
not square. The problem wasn't the column, it was the bracket that
holds it to the base, but it didn't seem all that bad. It wasn't,
squaring it up brought the front to back all the way down to .014".

The spindle was not parallel to the column. A quick look at the book,
and the block on top that looks like it's carrying the upper bearing,
isn't carrying anything but the motor. The head is two castings, so
one of them had to be out of square. Well, almost. Checking the
casting with the gibs on it, only .001" out of parallel, gibs to front
face. The problem was chips between the castings, and the tapped
holes looked like maybe Noah had started using the tap, and it hasn't
been sharpened since. The finish on this face looks like it was done
with a fly cutter and about .030" per rev feed, it's rough, but when
the burrs around the bolt holes were removed, the chips removed and a
stone run over the surface, it's flat and parallel, although not
pretty. Putting it back together, and getting the spindle parallel to
the column again, it is now zero from front to back and only .0005"
side to side, and I'm not going to try to bump that out. A screw
adjustment would be nice, but as it doesn't have one, bumping with my
hand, having it as close as it is, is close enough for almost
everything I'll be doing.

On Mon, 06 Sep 2004 16:49:49 -0500, wrote:

Having temporarily run out more productive things to do, and having a
half rainy, partly sunny, muggy day, I decided to tram the head on the
HF mini mill and find out how bad it was. Well, really bad. Side to
side, no problem, front to back, .016" across 3 1/2 ". That's bad.
First thought was the column, and a little checking proved that it was
not square. The problem wasn't the column, it was the bracket that
holds it to the base, but it didn't seem all that bad. It wasn't,
squaring it up brought the front to back all the way down to .014".

The spindle was not parallel to the column. A quick look at the book,
and the block on top that looks like it's carrying the upper bearing,
isn't carrying anything but the motor. The head is two castings, so
one of them had to be out of square. Well, almost. Checking the
casting with the gibs on it, only .001" out of parallel, gibs to front
face. The problem was chips between the castings, and the tapped
holes looked like maybe Noah had started using the tap, and it hasn't
been sharpened since. The finish on this face looks like it was done
with a fly cutter and about .030" per rev feed, it's rough, but when
the burrs around the bolt holes were removed, the chips removed and a
stone run over the surface, it's flat and parallel, although not
pretty. Putting it back together, and getting the spindle parallel to
the column again, it is now zero from front to back and only .0005"
side to side, and I'm not going to try to bump that out. A screw
adjustment would be nice, but as it doesn't have one, bumping with my
hand, having it as close as it is, is close enough for almost
everything I'll be doing.


Sometimes the light at the end of the tunnel isn't an oncoming train :-)


Mark Rand
RTFM

Well done!

On Mon, 06 Sep 2004 16:49:49 -0500, wrote:

Having temporarily run out more productive things to do, and having a
half rainy, partly sunny, muggy day, I decided to tram the head on the
HF mini mill and find out how bad it was. Well, really bad. Side to
side, no problem, front to back, .016" across 3 1/2 ". That's bad.
First thought was the column, and a little checking proved that it was
not square. The problem wasn't the column, it was the bracket that
holds it to the base, but it didn't seem all that bad. It wasn't,
squaring it up brought the front to back all the way down to .014".

The spindle was not parallel to the column. A quick look at the book,
and the block on top that looks like it's carrying the upper bearing,
isn't carrying anything but the motor. The head is two castings, so
one of them had to be out of square. Well, almost. Checking the
casting with the gibs on it, only .001" out of parallel, gibs to front
face. The problem was chips between the castings, and the tapped
holes looked like maybe Noah had started using the tap, and it hasn't
been sharpened since. The finish on this face looks like it was done
with a fly cutter and about .030" per rev feed, it's rough, but when
the burrs around the bolt holes were removed, the chips removed and a
stone run over the surface, it's flat and parallel, although not
pretty. Putting it back together, and getting the spindle parallel to
the column again, it is now zero from front to back and only .0005"
side to side, and I'm not going to try to bump that out. A screw
adjustment would be nice, but as it doesn't have one, bumping with my
hand, having it as close as it is, is close enough for almost
everything I'll be doing.

On Tue, 07 Sep 2004 00:20:46 -0500, Don Foreman
wrote:

Well done!

Thanks.

But a few follow up notes,

THis hammered home the one thing I don't have, and that's a good,
small, cylindrical master square. Something 2 1/2" to 3" diameter,
maybe five or six inches tall. I had one in the gage lab, and while I
seldom needed it, having a good supply of precision angle plates, when
It was needed, it was worth it's weight in gold. I'm thinking right
now, a piece of 1045, turned, centered, hardened and ground, solid not
hollow, I want the weight.

Secondly, it's a small machine, and even though it has the power to
pull a 3/8" endmill, full cut and 1/4" depth of cut, it doesn't have
the rigidity for that. 1/4" endmill, no problem. Finishing with a
1/8" endmill, as fast as it will go, .010" left for clean up and climb
cutting worked beautifully. (2024 aluminum, pocket milling 1/4" deep
with no object other than to remove metal.) Across the bottom of the
pocket, you can see the individual passes, but I can't feel anything
other than a nice smooth cut.

The gibs on the column have to be a little tighter than I'm used to,
but if they're not, when you tighten the lock, the head will move
slightly. Not really a problem, just more than I'm used to.

I reground the gib strip, mainly because I didn't like the way it
looked, and didn't like what my micrometer showed me. Maybe didn't
have to, but I did it anyhow. (Tapered and wavy, about .002")

The "fine downfeed", with the handwheel driving a worm, which drives
the pinion, and neither the pinion or rack being what I'd call
precision, using a dial indicator to show the actual feed seems to
make more sense than trusting the dial. There is also a rather sloppy
universal joint in this shaft, which makes using the indicator make
even more sense.

(Next victim, the HF $40 drill press.)