cross posted to rcm. Thanks for letting us use the dropbox

Inspired by Anthony, here's another "How would you do it?"

A couple of years ago we got an email from a customer who wanted a =
special
part grounded. After taking one look at the pics I thought "No way!" =
The
part was impossible to grind, at least on our equipment. =20
I called the customer back and told him: "Sorry, but this is out of our
league" and quickly forgot the whole thing - or so I thought, because =
later
that day the light bulb inside my head actually began emitting light. A
flickering and shimmering glow, but still a light.

I had an idea!

http://www.metalworking.com/DropBox/ Search for "pigtail" (four files)=20


About the part:

The "pigtail" is a core for a mold, forming a helix hollow inside the
finished molded part.
The size is approx. 3" dia. at the base, the length is about 7" and
the tail is 3/4" thick. The last two inches of the tail has a taper.
The pigtail is bolted on the flange of a guide spindle, and runs inside=
a
large multi-thread bronze nut. When the core is pulled from the mold, =
the
threads provide the necessary rotating motion to unscrew the core.

So here's the deal:

The part was to be grounded on the cylindrical (white) part of the tail
roundness +- 0.0005" as it had to seal against the stripping plate.
The fillet at the base, and the tapered part should also have a "grind
quality" surface finish. Actual size was not too important.

There was a catch, though. The roundness of the tail was measured
perpendicular to the centerline of the helix, not the centerline of the =
part.

The part came from the customer hardned and pre-milled to about 0.05
oversize. Since they only had 3axis VMC, the part was milled from four =
sides
rotating the part 90 degrees each time. (I did suggest the part could be
milled to finished size, but they didn't think it was possible to achieve=
the
necessary finish/roundness.)

The grinder I used was a Jungner US-450 CNC with four axis - think of =
an
ordinary lathe, and swap X with Z & Y with X. Tool up&down =3D third =
axis [X]
Spindle =3D fourth axis [b] ) =20
=20
The Siemens 810 control only allow for three axis to move simultaneously.

To make an already too long story short; I somehow managed to solve the
task, but it did make my head hurt at times. =20

How would you have done it?

For those interested in the challenge, I'll post the solution on Monday.
(not like that spoil sport & teaser, Anthony) G =20
--=20

-JN-

"J. Nielsen" wrote:

cross posted to rcm. Thanks for letting us use the dropbox

Inspired by Anthony, here's another "How would you do it?"

A couple of years ago we got an email from a customer who wanted a special
part ground.


http://www.metalworking.com/DropBox/ Search for "pigtail" (four files)

About the part:

So here's the deal:

The part was to be ground on the cylindrical (white) part of the tail
roundness +- 0.0005" as it had to seal against the stripping plate.
The fillet at the base, and the tapered part should also have a "grind
quality" surface finish. Actual size was not too important.

How would you have done it?


Jan:

Send it out? LOL We don't have a 4th axis grinder.

But if I HAD to give it a try, I might *try* to do it in a vertical
mill. Mount the base in some bored soft jaws, mount a surface grinding
wheel in an extended holder, radius dress a full radius on the edge of
the wheel making sure the radius on the bottom of the wheel matches the
fillet radius. And *mill* it going round and round the part like a
sideways ball end mill. Gibbs allows geometric tool definitions that
might cover this. Chatter would probably be a problem until the exact
speed (normally 3600 RPM for grinding wheels), and feed were worked
out. I have no idea if this would actually work, be fun to try though,
and I hope they would furnish a solid model. g

--
BottleBob
http://home.earthlink.net/~bottlbob

J. Nielsen wrote in
:


cross posted to rcm. Thanks for letting us use the dropbox

Inspired by Anthony, here's another "How would you do it?"


Hehe...


How would you have done it?


Hrm...
This will take some thunking....

For those interested in the challenge, I'll post the solution on
Monday. (not like that spoil sport & teaser, Anthony) G


Haha...If I _could_ I would...but I _can't_, so I won't :P


--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

http://www.machines-cnc.net:81/

On Fri, 20 May 2005 18:53:26 GMT, BottleBob
wrote:

Gibbs allows geometric tool definitions that
might cover this.

I gathered that they might be used for *verification purposes*
only, not for actual machining tool/work calculations.
Which is actually the case?
--
Cliff

Cliff wrote:

On Fri, 20 May 2005 18:53:26 GMT, BottleBob
wrote:

Gibbs allows geometric tool definitions that
might cover this.

I gathered that they might be used for *verification purposes*
only, not for actual machining tool/work calculations.
Which is actually the case?


Cliff:

Special tools can be drawn and used in toolpath verification as well as
the actual cutting of material. My most frequent use of this feature is
in drawing and using corner rounding tools, but I've used it for weird
tool shapes as well.


--
BottleBob
http://home.earthlink.net/~bottlbob

On Sat, 21 May 2005 00:30:59 GMT, BottleBob
wrote:

Cliff wrote:

On Fri, 20 May 2005 18:53:26 GMT, BottleBob
wrote:

Gibbs allows geometric tool definitions that
might cover this.

I gathered that they might be used for *verification purposes*
only, not for actual machining tool/work calculations.
Which is actually the case?


Cliff:

Special tools can be drawn and used in toolpath verification as well as
the actual cutting of material. My most frequent use of this feature is
in drawing and using corner rounding tools, but I've used it for weird
tool shapes as well.

BB,
I think you may have missed my question.
Are the surfaces of those tools, ALL OF THEM, actually
used in computing the toolpath?
IIRC This was not the case ... did they upgrade things?
--
Cliff

Cliff wrote:

On Sat, 21 May 2005 00:30:59 GMT, BottleBob
wrote:

Cliff wrote:

On Fri, 20 May 2005 18:53:26 GMT, BottleBob
wrote:

Gibbs allows geometric tool definitions that
might cover this.

I gathered that they might be used for *verification purposes*
only, not for actual machining tool/work calculations.
Which is actually the case?


Cliff:

Special tools can be drawn and used in toolpath verification as well as
the actual cutting of material. My most frequent use of this feature is
in drawing and using corner rounding tools, but I've used it for weird
tool shapes as well.

BB,
I think you may have missed my question.
Are the surfaces of those tools, ALL OF THEM, actually
used in computing the toolpath?

Cliff:

Do you mean, on a special tool with 4 separate diameters, does Gibbs
simultaneously calculate ALL of those diameters when a simple perimeter
tool path is chosen? No, not that I know of. Are there any programs
that do?


--
BottleBob
http://home.earthlink.net/~bottlbob

J. Nielsen wrote in
:

How would you have done it?

For those interested in the challenge, I'll post the solution on
Monday. (not like that spoil sport & teaser, Anthony) G

Nice one Jan.

I am sittin here thinkin how I would do it manually for Pete's sake seein
as I dont have any fancy grinders.

CNC some trodes for each half of the helix and EDM it one half at a time,
then polish it.

Then my mind wandered to using a thin wheel and the shaft to grind it, but
no go there.

I'm up to something simular now but using a cam based off the helical data.
Geesh. I'm wide awake now! Thanks!

I think I'm gonna wait till Monday.

ciao
Bing

"J. Nielsen" wrote in message
...

The part was to be grounded on the cylindrical (white) part of the tail
roundness +- 0.0005" as it had to seal against the stripping plate.
The fillet at the base, and the tapered part should also have a "grind
quality" surface finish. Actual size was not too important.

There was a catch, though. The roundness of the tail was measured
perpendicular to the centerline of the helix, not the centerline of the
part.

Hmm - this might actually make the job /easier/.

The part came from the customer hardned and pre-milled to about 0.05
oversize. Since they only had 3axis VMC, the part was milled from four
sides
rotating the part 90 degrees each time. (I did suggest the part could be
milled to finished size, but they didn't think it was possible to achieve
the
necessary finish/roundness.)

The grinder I used was a Jungner US-450 CNC with four axis - think of an
ordinary lathe, and swap X with Z & Y with X. Tool up&down = third axis
[X]
Spindle = fourth axis [b] )

The Siemens 810 control only allow for three axis to move simultaneously.

I'm completely ignorant of the Jungner machine /and/ the Siemens control. My
only experience is with my own 3-axis router (for which I have a fourth axis
accessory that allows mounting a geared stepper-driven "headstock" and
"tailstock" wherever I choose on the 96"x48" table. With this lash-up I can
move the spindle around in (x,y,z) and rotate the part on the accessory axis
(r). I'm making the assumption that the tooling you've described can be
configured similarly.

How would you have done it?

[1] Mount the headstock and tailstock so that the accessory axis is aligned
with the machine's y-axis and perpendicular to the x- and z-axes.

[2] Mount the part on the accessory headstock so that the axis of the helix
coincided with the accessory axix.

[3] support the "tail" of the helix at the accessory tailstock to minimize
error due to flexing of the helix.

[4] Chuck up a cylindrical grinder. In my woodworking world, this would be a
mandrel with a sandpaper sleeve. I'm making the assumption that there are
similar tools in the world of metalworking - something like a HSS or
micrograin carbide rod with a bonded fine diamond abrasive. (Is there
actually such a tool?)

[5] I grind longitudinally. IOW, rotate the workpiece to the next angle,
position the tool in x- and z-axes and grind the full length of the helix
moving the spindle only in y and the part in r. Then move the tool back to
the starting point, rotate the workpiece slightly, and repeat.

Rationale: It's easy to calculate points on the helical curve and my tool
need only be moved parallel to the central axis of the helix. If my grinding
surface is a vertical cylinder, I can get away with needing to control only
two axes and can use constant feed rates for each of them.

It's an interesting problem -- and I'm looking foreward to learning how you
solved it!

--
Morris
(CNC woodworker)

Friday Challenge status, so far

BottleBob:


Send it out? LOL We don't have a 4th axis grinder. =20
=09
But if I HAD to give it a try, I might *try* to do it in a vertical
mill. Mount the base in some bored soft jaws, mount a surface grinding
wheel in an extended holder, radius dress a full radius on the edge of
the wheel making sure the radius on the bottom of the wheel matches the
fillet radius. And *mill* it going round and round the part like a
sideways ball end mill. Gibbs allows geometric tool definitions that
might cover this. Chatter would probably be a problem until the exact
speed (normally 3600 RPM for grinding wheels), and feed were worked
out. I have no idea if this would actually work, be fun to try though,
and I hope they would furnish a solid model. g

I was thinking along the same lines initially, but like you say; =
chatter
would probably be a problem, and if you move the tool around the part,
supporting the "tail" is kinda difficult! We do have a 4th & 5th axis
on our Cinci, but if the part should be machined horizontally it would =
limit
the size of the grinding point (see my reply to Morris)=20


Bing:

I am sittin here thinkin how I would do it manually for Pete's sake =
seein=20
as I dont have any fancy grinders.

CNC some trodes for each half of the helix and EDM it one half at a =
time,=20
then polish it.

I suggested to the customer they 3D milled a "female" electrode, and =
then
EDM'ed the core using the centerline of the helix as toolpath, but they =
didn't
sound too enthusiastic. g=20

Then my mind wandered to using a thin wheel and the shaft to grind it, =
but=20
no go there.

I'm up to something simular now but using a cam based off the helical =
data.
Geesh. I'm wide awake now! Thanks!

I think I'm gonna wait till Monday.


Morris:

[3] support the "tail" of the helix at the accessory tailstock to =
minimize
error due to flexing of the helix.

The raw part was shaped much like a dumbbell, with a center hole in =
the
"tail" end. It was cut off after the grinding. =20

[4] Chuck up a cylindrical grinder. In my woodworking world, this would =
be a
mandrel with a sandpaper sleeve. I'm making the assumption that there =
are
similar tools in the world of metalworking - something like a HSS or
micrograin carbide rod with a bonded fine diamond abrasive. (Is there
actually such a tool?)

Yes there are. A multitude of them actually, but since the radii at the=
base
of the helix should be 4mm or less, the diameter of the grinding point =
would
only be max. 8mm (5/16) =20

[5] I grind longitudinally. IOW, rotate the workpiece to the next angle,
position the tool in x- and z-axes and grind the full length of the =
helix
moving the spindle only in y and the part in r. Then move the tool back =
to
the starting point, rotate the workpiece slightly, and repeat.

You're onto something here, Morris,

Rationale: It's easy to calculate points on the helical curve and my =
tool
need only be moved parallel to the central axis of the helix. If my =
grinding
surface is a vertical cylinder, I can get away with needing to control =
only
two axes and can use constant feed rates for each of them.

It's an interesting problem -- and I'm looking foreward to learning how =
you
solved it!

I have a few pictures of the setup laying around somewhere.
In the meantime; can anyone spot the error on the spindle?
The customer couldn't g
Remember the spindle act as a guide for the "pigtail." =20
--=20

-JN-

"J. Nielsen" wrote in message
...


In the meantime; can anyone spot the error on the spindle?
The customer couldn't g

Not sure I understand the problem well enough to question anything other
than placement of the bolt holes. They don't look like they'll line up very
well if you plan to use more than two bolts to join the spindle and helix
parts...
--
Morris

"Morris Dovey" wrote in message
...
"J. Nielsen" wrote in message
...


In the meantime; can anyone spot the error on the spindle?
The customer couldn't g

Not sure I understand the problem well enough to question anything other
than placement of the bolt holes. They don't look like they'll line up
very
well if you plan to use more than two bolts to join the spindle and helix
parts...

Heh heh! And of course, there's the "handedness" of the spirals...

J. Nielsen wrote in
:

The grinder I used was a Jungner US-450 CNC with four axis - think of
an
ordinary lathe, and swap X with Z & Y with X. Tool up&down = third
axis [X] Spindle = fourth axis [b] )

The Siemens 810 control only allow for three axis to move
simultaneously.

To make an already too long story short; I somehow managed to solve
the
task, but it did make my head hurt at times.

How would you have done it?

For those interested in the challenge, I'll post the solution on
Monday. (not like that spoil sport & teaser, Anthony) G

If I had my choice of methods, I would try whirling it on a thread
whirling machine. I've seen similar parts in Leistritz' display case at
machine tool shows. I can't find any pics of them on their web site.
These parts are different but may give you an idea.

http://tinyurl.com/bvevh

Not being a grinding guy makes it difficult to know what I could get away
with on a CNC grinder. If it would work I would dress a full radius on a
narrow wheel and and interpolate the work spindle with what would be the
x-axis and z-axis on a lathe. In other words the wheel axis would move to
stay in contact with the work as it rotated, while traversing the length.

Looking at the two pictures and not having all the info it would seem
that the wheel could remain perpendicular to the work spindle.

The main problem with this method would be wheel wear and loading of the
wheel. Maybe a CBN wheel and very high pressure coolant would solve those
problems?


--

Dan

J. Nielsen wrote in
:

I have a few pictures of the setup laying around somewhere.
In the meantime; can anyone spot the error on the spindle?
The customer couldn't g
Remember the spindle act as a guide for the "pigtail."

Again hard to say from the picture but it looks to me that the pitch of the
helix on the shaft doesn't match the pitch of the helix on the pigtail. So
the linear and rotational motion of the shaft won't coincide with that of
the pigtail. Something will bind, bend or break if that's the case.


--

Dan

On Sat, 21 May 2005 18:28:50 -0500, "Morris Dovey" =
wrote:

Heh heh! And of course, there's the "handedness" of the spirals...

Bingo!!

We got the a blank spindle & a huge bronze guide bushing with the helix
already EDM'ed through it. This was a couple of weeks before the =
"pigtail"
arrived, so I just ground the helix to match the bushing, and we shipped =
them
both back.

A week later another spindle & and bushing arrived...=20

You know, Morris, I think we can get a good "metal man" out of you. All =
you
have to do, to switch from wood to metal, is mentally adding another zero=
to
the right of the decimal point on the drawings. g =20
--=20

-JN-

"J. Nielsen" wrote in message
...
On Sat, 21 May 2005 18:28:50 -0500, "Morris Dovey" wrote:

Heh heh! And of course, there's the "handedness" of the spirals...

Bingo!!

We got the a blank spindle & a huge bronze guide bushing with the helix
already EDM'ed through it. This was a couple of weeks before the "pigtail"
arrived, so I just ground the helix to match the bushing, and we shipped
them
both back.

A week later another spindle & and bushing arrived...

You know, Morris, I think we can get a good "metal man" out of you. All you
have to do, to switch from wood to metal, is mentally adding another zero to
the right of the decimal point on the drawings. g

Thanks for the good thoughts - but but I don't think my 3-axis router was
really designed to handle metal. Replacing it with a CNC mill to handle
metal projects would probably add at least another zero to the /left/ of the
decimal point - and I already can't afford the 5-axis router I really
wanted!

I'm working on three new CNC machines - built mostly of wood (with some
aluminum and plastic parts). Two of them are for metalworking and one is for
woodworking. Building useful machinery with wood poses some interesting
challenges but does allow me to go fast and cheap - and will provide me with
tooling that I couldn't buy even if I won the lottery.

I'm starting to enjoy building the tools more than I enjoy using 'em - and
I'm not sure that's a completely Good Thing.

Anyway, I enjoy the kind of challenge you presented. I enjoy seeing what
people here have done with metal. And I feel privileged to be able to learn
from people who've spent entire careers doing what I'm trying to learn about

--
Morris