[Emc-users] Nurbs question

[Gene Heskett]

Greetings all;

I've not noted any great amount of mention of nurbs on the list, and I am
wondering how usable it is in doing something like a barrel taper
at "different" contours.

I am thinking in terms of a 6.5 Creedmoor, in 30" SS, which I can't get
any slimmer than whats called a medium Palma contour, which will likely
put old meat in the pot north of 15 lbs since its 13 and change with a
26" sporter weight barrel in it now.

What I'd like to do is put the last 20" of it on a diet to see if I can
get the weight, and balance back to what I've been used to since the
middle '60's.

What I have in mind is a 5 or 6 point curve that I can compose to look
like what I want, but about 6" long, then scale it in the Z axis to fit
the length by extending each anchor point by a scale factor multiplied
by that points position on the short modeling plot. I am assuming that
stretching the z with a fixed scale, will not distort the x shape to a
noticeable degree?

Secondarily, since facing it off against the side of a diamond wheel will
destroy the factory satin finish, how is the best way to restore that
when I've reached the size & weight goals?

Thanks for any hints, particularly about shapes that will reduce the
muzzle whipping on discharge since thats the vertical stringing on the
target, given that its vertical, since bedding errors can throw it in
any direction.

Many thanks for answers from the experts here.

Cheers, Gene Heskett

[Gene Heskett]

Post by Gene Heskett
Greetings all;
I've not noted any great amount of mention of nurbs on the list, and I
am wondering how usable it is in doing something like a barrel taper
at "different" contours.
I am thinking in terms of a 6.5 Creedmoor, in 30" SS, which I can't
get any slimmer than whats called a medium Palma contour, which will
likely put old meat in the pot north of 15 lbs since its 13 and change
with a 26" sporter weight barrel in it now.
What I'd like to do is put the last 20" of it on a diet to see if I
can get the weight, and balance back to what I've been used to since
the middle '60's.
What I have in mind is a 5 or 6 point curve that I can compose to look
like what I want, but about 6" long, then scale it in the Z axis to
fit the length by extending each anchor point by a scale factor
multiplied by that points position on the short modeling plot. I am
assuming that stretching the z with a fixed scale, will not distort
the x shape to a noticeable degree?
Secondarily, since facing it off against the side of a diamond wheel
will destroy the factory satin finish, how is the best way to restore
that when I've reached the size & weight goals?
Thanks for any hints, particularly about shapes that will reduce the
muzzle whipping on discharge since thats the vertical stringing on the
target, given that its vertical, since bedding errors can throw it in
any direction.
Many thanks for answers from the experts here.
Cheers, Gene Heskett

And I just had my first point rejected because it did not include a y
point, so now I'm asking what if any command will make it work in xz
mode?

Cheers, Gene Heskett

[dave]

Post by Gene Heskett
Greetings all;
I've not noted any great amount of mention of nurbs on the list, and I am
wondering how usable it is in doing something like a barrel taper
at "different" contours.
I am thinking in terms of a 6.5 Creedmoor, in 30" SS, which I can't get
any slimmer than whats called a medium Palma contour, which will likely
put old meat in the pot north of 15 lbs since its 13 and change with a
26" sporter weight barrel in it now.
What I'd like to do is put the last 20" of it on a diet to see if I can
get the weight, and balance back to what I've been used to since the
middle '60's.
What I have in mind is a 5 or 6 point curve that I can compose to look
like what I want, but about 6" long, then scale it in the Z axis to fit
the length by extending each anchor point by a scale factor multiplied
by that points position on the short modeling plot. I am assuming that
stretching the z with a fixed scale, will not distort the x shape to a
noticeable degree?
Secondarily, since facing it off against the side of a diamond wheel will
destroy the factory satin finish, how is the best way to restore that
when I've reached the size & weight goals?
Thanks for any hints, particularly about shapes that will reduce the
muzzle whipping on discharge since thats the vertical stringing on the
target, given that its vertical, since bedding errors can throw it in
any direction.
Many thanks for answers from the experts here.
Cheers, Gene Heskett

Gene,
Try fitting the curved part to a 2nd order polynomial. Stick some points
out there, modify until the
the curve looks right, then fit. A small program can then output gcode
as z vs x with whatever point
spacing you want.
Polish: cover the bed of your lathe with a oiled cloth to catch the grit
and polish between centers until
you get the surface finish you want. Cleanup the last bit with the next
finer grit by hand and parallel
to the bore. I usually finish up with well worn 320 grit but you can
polish to your hearts content.
You could even swamp it if you wanted to. ;-)

Hint: excel ...however I'm certain there is something already compiled
that will do the job.

Dave

[andy pugh]

Post by Gene Heskett
I've not noted any great amount of mention of nurbs on the list, and I am
wondering how usable it is in doing something like a barrel taper
at "different" contours.

I think it sounds like you are using a lathe. Sadly it seems that G5, G5.1
and G5.2 only work in the G17 (XY) plane.

http://linuxcnc.org/docs/2.7/html/gcode/g-code.html#gcode:g5

[Gene Heskett]

Post by andy pugh

Post by Gene Heskett
I've not noted any great amount of mention of nurbs on the list, and
I am wondering how usable it is in doing something like a barrel
taper at "different" contours.

I think it sounds like you are using a lathe. Sadly it seems that G5,
G5.1 and G5.2 only work in the G17 (XY) plane.
http://linuxcnc.org/docs/2.7/html/gcode/g-code.html#gcode:g5

I see it (g17 only) mentioned for g5.1. Since the g5.# stuff probably
has a common code core, and it would be at least as handy on a lathe as
on a mill, the adjective is indeed sad. Since the huge majority of LCNC
is orthogonal, would it do to file a bug?

In which case, in the armhf branch, there is another buglet that needs
attention from the usability viewpoint. When in the MDI window, an up
arrow will recall an older entry, but it can only be edited by carefully
placing the cursor with the mouse, the arrow left-right keys are
impotent.

It may be related to the fact that both the MDI line, and the line
recalled in the history window are both highlighted, but the flashing
cursor in the MDI's leftmost character position doesn't apparently
indicate focus is actually in the MDI line.

Thanks Andy.

Cheers, Gene Heskett