In article , Gary H says...

Hi. I have one of those Chinese mini-mills. I know it has its shortcomings
but I just tinker around in my garage so it is OK for me. However, the gibs
seem hard to adjust... but since I don't have a real machine to compare it
to, I don't know how bad it is. I would potentially like to improve the
gibs and adjustment screws if possible. Could some one send a picture or
describe how the gibs adjusters work on a nice quality machine?

The Chinese mini-mill has gib strips with small dimples in them. The gib
adjustment set screws are pilot dog set screws that ride in those dimples.
Pretty simple. Unfortunately, for some reason, the gibs tend to tilt and
only a thin strip comes in contact with the opposing dovetail instead of
staying parallel to the opposing dovetail and having the entire gib strip
act as a wear area. I hope that makes sense and I look forward to hearing
how the good machines do this.

A lot of times you'll see that there are pins in the slide that serve
two purposes, one is to keep the gib from slipping out the end of the
slide, the other is to help keep the gib bearing correctly on the
dovetail.

If your gib is cocking then you need to look to be sure that it really
is the correct trapezoid shape in cross section. It basically needs
to 'fill up' the space between the slide and the dovetail way. If
it's shaped properly, there is pretty much no way it can shift and
bear on a line rather than on a plane.

The cup point setscrews typically like to bear on spot faces on the
gib, and because the screws are horizontal and the gib face is
at an angle, the spot faces need to be at an angle to the gib face.
Many times you will see inexpensive slides where they try to 'finess'
this by simply using sharp pointed setscrews and have them bear directly
on the gib. Those tend to induce cocking.

But the general idea is you the pressure from the screws is being
applied in a horizontal direction, that has to be so because the
threaded holes in the slide are horizontal. But the gib resolves that
force into some part that keeps the gib's long surface bearing on the
dovetail, and another part that tends to keep the gib socked upwards
into the slides female dovetail.

The problem happens when the upper edge of the dovetail is at the
wrong angle so it does not seat in that upwards direction.

Jim


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