Hi guys,
last night I've spent some hours trying to improve the cross table gibs of
my mini mill. Dismounting the x-axis I've notice that gib was bent, so using
the drill press I have straightened it. Then, using the belt sander, I've
smoothed the dovetail-side surface of the gib taking care to keep it
parallel to the other one as was at the beginning. I've spent about half an
hour, using as small pressure as I can on the gib and changing often the
orientation in respect of the belt movement. At last I've used a special
rubber abrasive disk on my dremel to mirror-lap the contact surface of the
gib.
Then
I've mounted it on, registered the screws and tried the table movement. It
is smoother than before. I've then measured the movement of the table in
tightening the locking screw. My quality digital comparator reports 0.035 mm
(about 0.0015"). In the past it was much more, I don't know how much. No
matter, it could be acceptable since I'm going to install a digital scale on
the x axis.
So
I've done a careful look at the gib in place and. surprise. the gib surface
do not adheres completely to the dovetail surface. I've done a look to all
other gibs, in the mill and in the lathe. No other one was perfectly plane
aligned. To be more precise either gib surface and dovetail one are good
flat plane, the problem is the alignment between the top side and bottom
one. When I tight the set screws the gib adheres only in the bottom part of
its plane with the bottom part of the dovetail plane (in some gibs the
planes are the upper ones). Practically I've discovered that the pressure
between gibs and dovetail is not over the entire planes but only on a thin
line, all gib / dovetail long, of contact between them.
Now my questions are:
Is it normal? I've expected a complete planes contact.
There is someone has noticed the same thing on his machine?
If it is an abnormal situation, which could be the cause and which the
solution?
Gianni
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