In article .com,
rashid111 wrote:
Here's what I am trying to accomplish:

when making accordion reeds, the highest notes (piccolos) are

O.K. With reed making, you have my attention. (Though my focus
is on concertina reeds, not accordion reeds. They are different in the
mounting (concertina reeds mount on individual dovetailed carriers,
sometimes called "shoes" from the shape.

extremely critical to profile dimension. Typical piccolo reed will be
made out of .012 thick blue steel (48-50 RC), .4" in length, .050 in
width (they are typically narrower toward the tip, may be .050 @
root,.040 @ tip).

O.K. More width taper than a similar concertina reed.
The reed gets to be about 0.0015 thin @ the tip and has a profile where
the thickness will linearly decrease from .012 @ root to .002 halfway
and then it will be 0.0015 the rest of the way toward the tip. Filing
by hand is extremely time consuming (for piccolos only, other, lower
reeds, can be easily filed by hand)

Lower concertina reeds may be similarly thickness tapered along
the length, or may be thinner at about the 1/3 point from the root to
the tip, depending on which specific reed, as about four consecutive
reeds use the same physical dimensions of reed and reed shoe.

So I am thinking about 2 possibilities: a) pantograph-type surface
grinder b) CNC driven SG.

CNC sounds like fun ...

Agreed.

Most important thing is vertical accuracy - need to have downfeed
accuracy of .0005 or thereabouts. To that end I have bought a complete
liner assembly: 1.5mm pitch precision ground ballscrew, linear rails
complete with NEMA motor Sanyo Denki 103-540-0351
(from what I could read from the image of the assembly on the Web).

O.K. First suggestion -- design in ways to keep the grinding
swarf out of the ball screws. It will *kill* them fairly quickly.
Grinding is dirty and nasty. You'll want bellows around the ball-screw
-- both sides of the nut, or some other protective shape. There are
some which look like a clock spring which has been stretched out from
the center. You want to mount those so the cracks are on the bottom, so
there is less likelihood that grit will work its way to the inside.

Even Acme screws have special protective housings around them of
some form or other.

Today being my second day into CNC exploration I understand this is
unipolar motor(more than 4 wires). What I am not sure about is the
torque. I am hoping it will be sufficient, as travel weight of grinder
head assembly will be around 6-7 pounds and I don't see much in a way
of forces acting on it - unlike typical mill Z-drive. I hope to grind
around one thou per pass - not to overheat the steel.

Ball screws take an amazingly low amount of torque under normal
circumstances.

Assuming I can get CNC to drive half-step mode, I am looking at
downfeed resolution of 1.5mm/400 = 0.00015" which is great . 1/4 or
1/8 get me into sub-angstrom area Of course I will never get close
to these tolerances as other components will not allow for it.

That sounds good.

In terms of linear travel I need about 3" tops ( in case I want later
to grind longer, lower reeds). I am thinking about acquring
and building a liner slide assembly: small ball screw, linear slide.

Again -- look for ways to enclose it to protect it from the
swarf. My Sanford grinder (manual) has the table running on one
inverted V way and one flat way, held in place by gravity only (not much
lifting force in a grinder), but has a lot of overhang in all
directions, so the ways are never exposed to the swarf.

I
am not sure what I want to drive: the grinder head assembly or the base
with mag chuck ( 5x7" are available new on Ebay for $100 or so).

Note that you can get mag chucks with either a fine pitch pole
spacing or a coarse one. The coarse one is fine for holding big chunks
of metal, but for something as thin as your spring stock, you will want
a fine pitch one. And you will want a permanent magnet one, not an
electromagnet, to allow you to use coolant while grinding without
opening a shock hazard (Of course, a well isolated power supply will do
that too, but a permanent magnet just does not *have* any high voltage
to worry about.)

And in terms of the travel -- understand that when you mount the
chuck, you will have to grind the entirity of its top surface to assure
that it is truly parallel to the travel of the table. This is important
to me because the nice fine-pole Permanent Magnet chuck which I got from
eBay is about 1/2" longer than the X-axis travel, so I will have to take
it to the milling machine to remove some of the ends to allow a proper
complete dressing. So -- for now, I still have the electro-magnetic
chuck in service -- and *no* coolant.

Not a
whole lot in terms of accuracy reqs for linear travel - definitely not
anywhere close to vertical axis.

Agreed.

I only need X-travel, no Y (with 2" OD of the wheel and .040 wide
contact area the grinding plane will be flat enough).

I disagree here. You will want to take multiple passes at right
angles to the reed stock, with the rim of the wheel dressed to a gentle
curve to avoid steps in the thickness of the reeds, which could act as
stress concentrators, leading to fatigue cracks after hard playing. The
X-axis could carry the wheel over a whole row of reed stock, and the
Y-axis is changed with the Z-axis in small steps to make the contour you
wish.

And -- you will want both axes to be capable of moving a greater
distance than the dimensions of the mag chuck, so you *can* grind it
flat at the start. (Just after you mount the chuck on the table, and
just after any time you remove and re-mount the chuck.

One way around this, at least for production of a single reed
profile, would be to dress the wheel (a wider wheel) to produce the
profile in a single path over the reed stock. But that has two
disadvantages that I can see:

1) It will take more horsepower (and at least a 1/2" thick wheel).

2) Cutting the full width in a single cut (even if you sneak up
on the depth) will put a lot more longitudinal force on the
reed stock, and is likely to overcome the grip of the mag chuck,
thus destroying that reed, and perhaps wedging and shattering
the wheel.

Thinking about DIY Xylotex $87 3-axis unipolar kit. I might get into
building a CNC-mill down the road, so I should be able to re-use the
Xylotex for it. I will need to get a stepper for X-axis. Will probably
shoot for something like 140+Oz so, again, I will be able to re-use it
for future CNC machinery (I ordered some Oldham couplers so swapping
these in and out should be easy).

I am planning on using a speed-controlled router/rotary head with 1/4"
- 1/2" shank and may be 1/8 - 1/4" thick 2" OD grinding wheel @
4000-10000 rpms. For my accuracy reqs I will definitely need to true it
up nicely. Spindle will need to be accurate as well. Really hoping that
typical $50 rotary tool variety will work for me. Does anybody know a
nice router type motor that can, ideally, be face mounted ?

A router motor has the disadvantage of lots of bulk too close to
the mag chuck, so it might limit your travel.

And I'm not sure that the bearings in any router will be
sufficiently precise for surface grinding.

My Sanford, and other surface grinders that I have seen, have a
long spindle with precision bearings at both ends (well sealed, to
protect them from the swarf, again), and a belt drive to a motor set
behind the column and much lower, so the weight distribution is better.

Otherwise I
will need to bore out a mounting collar. I don't see much in a way of
power reqs here - 1/4 HP should work fine?

I think that the motor on my Sanford is a 1HP -- but it is
driving a wheel of 4" diameter.

I don't care if it will
take few secs to bring the spindle up to required RPMs. From what I see
in HD, Sears and Lowes almost all of the routers/rotary tools nowdays
use plastic outer shell ... not good

The time to spin up is not a serious problem. The ability to
drive a full width wheel dressed to the profile would be, however --
even if you downfeed by only 0.0001" per pass. You can use lower power
if you dress the wheel to a '(' profile, and cut only a narrow path per
pass -- but that needs Y-axis automation in addition to the X and Z
which you were planning.

So what do you think ? Any advice is most welcome

You have the things which have occurred to me above -- some of
them based on my experience running the Sanford as a manual surface
grinder, which helps to get a feel for what is happening.

Harold Vrodos (or should that be Howard?) will be able to offer
lots of information on grinding, but he has managed to avoid the CNC
side of things, so perhaps some of my thoughts will be of help.

Good Luck,
DoN.


P.S. FWIW, I think that my Sanford might be a good candidate for
CNC conversion on the X and Z axis (with ball screws), but the
Y-axis is a rack-and-pinion drive, which would take a bit more
motor to drive it.
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