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-