"PrecisionmachinisT" wrote in message
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"Ed Huntress" wrote in message
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wrote in message
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Last night on my little Rockwell 21-100 mill, I was changing the radius
on the underside of rifle scope base with a boring head.

As I raised the knee, there was cutting close to me, and then as I
lowered the knee there was a new .001" of cutting on the mill side.

Is my vise too heavy? are the knee gibbs loose?
What is going on?

TIA

It could be several things, but the most obvious is that your cutting
tool has different geometry relative to the part when it's cutting in one
direction versus the other. It's either digging in more in one direction,
or it's pushing away from the work more in the other direction.



This is typical with knee mills--the table wants to "slope" towards the
column by a small amount when there is pressure on the screw and away from
it when the pressure is removed.

And though it might seem counterintuitive, gibs that are too tight usually
tend to exacerbate the behaviour.

That makes sense actually. If they are adjusted properly the downward force
is always more on the screw. If they are a little snug then the screw can
pull or push against the friction of the gibbs. I might never have thought
of that on my own though. LOL.