Knee mill cuts differently going up from going down.
 

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

Knee mill cuts differently going up from going down.
 

On Dec 16, 11:53*pm, "
wrote:
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?

Maybe. How heavy is it?

are the knee gibbs loose?

Probably, but that ought to be easy to check

What is going on?

See above.


TIA

Knee mill cuts differently going up from going down.
 

On 12/16/2011 11:53 PM, wrote:
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

Is your mill aligned properly with magnetic North? Did you account for
deviation?

Knee mill cuts differently going up from going down.
 

On Dec 17, 4:01*am, Tom Gardner mars@tacks wrote:
On 12/16/2011 11:53 PM, wrote:

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

Is your mill aligned properly with magnetic North? *Did you account for
deviation?

Could you possibly give a more useless answer to a genuine
metalworking question?

Knee mill cuts differently going up from going down.
 

On Dec 16, 11:53*pm, "
wrote:
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

You may well do better to do your Z-axis motion with the quill rather
than the knee. Use the kne to position the work, then lock it in
place, then use the quill to make your cut.

Knee mill cuts differently going up from going down.
 

wrote in message
news:14522200.383.1324097638634.JavaMail.geo-discussion-forums@yqio4...

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.

--
Ed Huntress

Knee mill cuts differently going up from going down.
 

"Ed Huntress" wrote in message
...


wrote in message
news:14522200.383.1324097638634.JavaMail.geo-discussion-forums@yqio4...

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.

Knee mill cuts differently going up from going down.
 

"PrecisionmachinisT" wrote in message
news:G6ydncTps7y8RHHTnZ2dnUVZ_rKdnZ2d@scnresearch. com...

"Ed Huntress" wrote in message
...


wrote in message
news:14522200.383.1324097638634.JavaMail.geo-discussion-forums@yqio4...

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.

Knee mill cuts differently going up from going down.
 

"PrecisionmachinisT" wrote in message
...
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.

I've found several similar gotchas when I try to bore a cylinder on my small
Clausing mill. They can be measured and hopefully corrected or dodged with a
dial indicator and a good precision angle plate.

jsw

Knee mill cuts differently going up from going down.
 

Tom Gardner wrote:

Did you account for deviation?


That's funny, coming from the group's resident lesbian! ;-)


--
You can't have a sense of humor, if you have no sense.

Knee mill cuts differently going up from going down.
 

On 12/17/2011 3:06 AM, rangerssuck wrote:
On Dec 17, 4:01 am, Tom Gardnermars@tacks wrote:
On 12/16/2011 11:53 PM, wrote:

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

Is your mill aligned properly with magnetic North? Did you account for
deviation?

Could you possibly give a more useless answer to a genuine
metalworking question?

Actually, it can be relevant since there is a large ferrous mass(mill
spindle) spinning in a magnetic field (Earth). This could deflect the
alignment of the spindle to the knee, especially since these little
mills aren't all that rigid.

OTOH, not REALLY likely.

David

Knee mill cuts differently going up from going down.
 

On 12/17/2011 3:31 PM, Michael A. Terrell wrote:

Tom Gardner wrote:

Did you account for deviation?


That's funny, coming from the group's resident lesbian! ;-)



But, but it's TRUE!

Knee mill cuts differently going up from going down.
 

On 12/16/2011 11:53 PM, wrote:
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

Oops, I offended a liberal! (good for me!) But, think about the force
vectors involved and visualize what's happening. It's a moving
mechanism and the force, friction and tolerance (slop) aren't the same
as you raise or lower the knee. Think: "Kentucky Windage". In a
perfect mechanism all is equal. (no such thing)

Knee mill cuts differently going up from going down.
 

On 12/17/2011 4:06 AM, rangerssuck wrote:
On Dec 17, 4:01 am, Tom Gardnermars@tacks wrote:
On 12/16/2011 11:53 PM, wrote:

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

Is your mill aligned properly with magnetic North? Did you account for
deviation?

Could you possibly give a more useless answer to a genuine
metalworking question?


Yep, I could have given him YOUR answer!

Knee mill cuts differently going up from going down.
 

On Sun, 18 Dec 2011 00:28:52 -0600, Jon Elson
wrote:

wrote:

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?
Use a dial indicator to check Y-axis movement when moving the knee.
Yes, it is quite common for the knee slide to cock when the elevating
screw pushes it up or down. Generally, the knee will snug up against
the base when raised, and flop outward towards the operator when
lowered. I never machine anything using the knee. I set the knee to
the right height and use the quill to make up-down movements.
If I need to move the knee to accommodate a different-length tool,
I move it while not cutting, and then always finish with a lifting
movement to keep the knee snug against the base.

Jon

Thats what I do as well. While the knee may be dropped down..I go at
least an inch or 3 below the desired spot..then crank it upwards to
position, then lock it. My Gorton Mastermill has a heavier and beefier
table than a Bridgeport/Clone and even it requires this treatment.

Gunner

One could not be a successful Leftwinger without realizing that,
in contrast to the popular conception supported by newspapers
and mothers of Leftwingers, a goodly number of Leftwingers are
not only narrow-minded and dull, but also just stupid.
Gunner Asch