Hi,

Any reason (other than the hard bits getting into the ways) I
shouldn't put a 1/4" diamond die grinder bit into a milling machine
collet to take a bit (a few thou) off some ferrite? RPM will be very
low (1750 RPM) but I guess I can just feed slow? A 0.394" diameter bit
will have a SFM of ~180. Mist coolant? Dry (doesn't seem to be
recommended for diamond)?

--sp

On Wed, 12 Dec 2012 11:43:44 -0500, Spehro Pefhany
wrote:

Hi,

Any reason (other than the hard bits getting into the ways) I
shouldn't put a 1/4" diamond die grinder bit into a milling machine
collet to take a bit (a few thou) off some ferrite? RPM will be very
low (1750 RPM) but I guess I can just feed slow? A 0.394" diameter bit
will have a SFM of ~180. Mist coolant? Dry (doesn't seem to be
recommended for diamond)?

--sp
The thing that seems to eat diamond bits is heat and lack of lube. I
know that running them dry will usually strip then diamond off in
short order. I don't know if it is heat or lack of lube or both that
strips the diamond. I use kerosene or WD40 or water or soapy water
depending on what I'm grinding. For ferrite probably WD40. I use WD40
not because it is so superior to kerosene but because it doesn't smell
so bad.
Eric

On Wed, 12 Dec 2012 09:26:20 -0800, wrote:

On Wed, 12 Dec 2012 11:43:44 -0500, Spehro Pefhany
wrote:

Hi,

Any reason (other than the hard bits getting into the ways) I
shouldn't put a 1/4" diamond die grinder bit into a milling machine
collet to take a bit (a few thou) off some ferrite? RPM will be very
low (1750 RPM) but I guess I can just feed slow? A 0.394" diameter bit
will have a SFM of ~180. Mist coolant? Dry (doesn't seem to be
recommended for diamond)?

--sp
The thing that seems to eat diamond bits is heat and lack of lube. I
know that running them dry will usually strip then diamond off in
short order. I don't know if it is heat or lack of lube or both that
strips the diamond. I use kerosene or WD40 or water or soapy water
depending on what I'm grinding. For ferrite probably WD40. I use WD40
not because it is so superior to kerosene but because it doesn't smell
so bad.
Eric

Thanks, Erice. At $26 a bit, I'm not too eager to strip the diamonds
off on the first try. I'll try the WD40.

On Wed, 12 Dec 2012 11:43:44 -0500, Spehro Pefhany wrote:

Hi,

Any reason (other than the hard bits getting into the ways) I shouldn't
put a 1/4" diamond die grinder bit into a milling machine collet to take
a bit (a few thou) off some ferrite? RPM will be very low (1750 RPM) but
I guess I can just feed slow? A 0.394" diameter bit will have a SFM of
~180. Mist coolant? Dry (doesn't seem to be recommended for diamond)?

--sp

If you use a die grinder bit as if it were a milling cutter, you'll leave
a whole bunch of parallel grooves in your ferrite. In my (admittedly
quite limited) experience, with abrasive media you need not only the
obvious fore- and aft- movement of workpiece against wheel (or wheel
against workpiece), but also side-to-side (or in a regular milling
machine, up and down I guess).

I'm not sure how you'll achieve that in your application. Multiple
swipes at slightly different quill height settings may do; if it were a
CNC machine I'd suggest programming it to pump the quill up and down at
the same time that it's moving the piece across the grinder.

Have fun gapping your cores, if that's what you're doing.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

On Wed, 12 Dec 2012 12:09:16 -0600, Tim Wescott
wrote:

On Wed, 12 Dec 2012 11:43:44 -0500, Spehro Pefhany wrote:

Hi,

Any reason (other than the hard bits getting into the ways) I shouldn't
put a 1/4" diamond die grinder bit into a milling machine collet to take
a bit (a few thou) off some ferrite? RPM will be very low (1750 RPM) but
I guess I can just feed slow? A 0.394" diameter bit will have a SFM of
~180. Mist coolant? Dry (doesn't seem to be recommended for diamond)?

--sp

If you use a die grinder bit as if it were a milling cutter, you'll leave
a whole bunch of parallel grooves in your ferrite. In my (admittedly
quite limited) experience, with abrasive media you need not only the
obvious fore- and aft- movement of workpiece against wheel (or wheel
against workpiece), but also side-to-side (or in a regular milling
machine, up and down I guess).

I'm not sure how you'll achieve that in your application. Multiple
swipes at slightly different quill height settings may do;

I may be able to leave the quill unlocked and just jiggle it up and
down as it's fed in x or y. I doubt I'll get a mirror finish that way,
but cranking the head up and down would not be pleasant.

if it were a
CNC machine I'd suggest programming it to pump the quill up and down at
the same time that it's moving the piece across the grinder.

A similar motion to a surface grinder, which is what I don't have.

Have fun gapping your cores, if that's what you're doing.

Usually I stick some plastic shim stock inbetween the E-core halves
(using a set I got from McMaster), which gives effectively double the
normal gap of the shim stock thickness, but I thought it might be nice
to try just gapping the center leg, which would be more representative
of the EMI situation, but mostly just because it would be fun to try.

On Wed, 12 Dec 2012 13:23:55 -0500, Spehro Pefhany wrote:

On Wed, 12 Dec 2012 12:09:16 -0600, Tim Wescott
wrote:

On Wed, 12 Dec 2012 11:43:44 -0500, Spehro Pefhany wrote:

Hi,

Any reason (other than the hard bits getting into the ways) I
shouldn't put a 1/4" diamond die grinder bit into a milling machine
collet to take a bit (a few thou) off some ferrite? RPM will be very
low (1750 RPM) but I guess I can just feed slow? A 0.394" diameter bit
will have a SFM of ~180. Mist coolant? Dry (doesn't seem to be
recommended for diamond)?

--sp

If you use a die grinder bit as if it were a milling cutter, you'll
leave a whole bunch of parallel grooves in your ferrite. In my
(admittedly quite limited) experience, with abrasive media you need not
only the obvious fore- and aft- movement of workpiece against wheel (or
wheel against workpiece), but also side-to-side (or in a regular milling
machine, up and down I guess).

I'm not sure how you'll achieve that in your application. Multiple
swipes at slightly different quill height settings may do;

I may be able to leave the quill unlocked and just jiggle it up and down
as it's fed in x or y. I doubt I'll get a mirror finish that way, but
cranking the head up and down would not be pleasant.

if it were a
CNC machine I'd suggest programming it to pump the quill up and down at
the same time that it's moving the piece across the grinder.

A similar motion to a surface grinder, which is what I don't have.

Have fun gapping your cores, if that's what you're doing.

Usually I stick some plastic shim stock inbetween the E-core halves
(using a set I got from McMaster), which gives effectively double the
normal gap of the shim stock thickness, but I thought it might be nice
to try just gapping the center leg, which would be more representative
of the EMI situation, but mostly just because it would be fun to try.

The world needs ferrite shim stock.

I'll bet Kapton tape would work well, but I haven't tried it, so I'm
nearly clueless there.

Report back on your results please? Probably on s.e.d, since the
interesting results are going to be if it makes any real difference in
shielding and other performance aspects (ultimately: is it worth the
effort).

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

On Wed, 12 Dec 2012 12:44:09 -0600, Tim Wescott
wrote:

On Wed, 12 Dec 2012 13:23:55 -0500, Spehro Pefhany wrote:

On Wed, 12 Dec 2012 12:09:16 -0600, Tim Wescott
wrote:

On Wed, 12 Dec 2012 11:43:44 -0500, Spehro Pefhany wrote:

Hi,

Any reason (other than the hard bits getting into the ways) I
shouldn't put a 1/4" diamond die grinder bit into a milling machine
collet to take a bit (a few thou) off some ferrite? RPM will be very
low (1750 RPM) but I guess I can just feed slow? A 0.394" diameter bit
will have a SFM of ~180. Mist coolant? Dry (doesn't seem to be
recommended for diamond)?

--sp

If you use a die grinder bit as if it were a milling cutter, you'll
leave a whole bunch of parallel grooves in your ferrite. In my
(admittedly quite limited) experience, with abrasive media you need not
only the obvious fore- and aft- movement of workpiece against wheel (or
wheel against workpiece), but also side-to-side (or in a regular milling
machine, up and down I guess).

I'm not sure how you'll achieve that in your application. Multiple
swipes at slightly different quill height settings may do;

I may be able to leave the quill unlocked and just jiggle it up and down
as it's fed in x or y. I doubt I'll get a mirror finish that way, but
cranking the head up and down would not be pleasant.

if it were a
CNC machine I'd suggest programming it to pump the quill up and down at
the same time that it's moving the piece across the grinder.

A similar motion to a surface grinder, which is what I don't have.

Have fun gapping your cores, if that's what you're doing.

Usually I stick some plastic shim stock inbetween the E-core halves
(using a set I got from McMaster), which gives effectively double the
normal gap of the shim stock thickness, but I thought it might be nice
to try just gapping the center leg, which would be more representative
of the EMI situation, but mostly just because it would be fun to try.

The world needs ferrite shim stock.

I'll bet Kapton tape would work well, but I haven't tried it, so I'm
nearly clueless there.

Kapton and Mylar tape work fine, but they don't come in such a range
of thicknesses, and you have to take into account the adhesive
thickness. Shim stock and wrap tape around the core (or use spring
clips) gives you a pretty controlled gap.

For a mere $35 you get 15 sheets 5" x 20", color coded:0.0005"
0.00075" 0.001" 0.0015" 0.002" 0.003" 0.004" 0.005" 0.0075" 0.01"
0.0125" 0.015" 0.02" 0.025" 0.03", with tolerance +/-0.2 thou.

Report back on your results please? Probably on s.e.d, since the
interesting results are going to be if it makes any real difference in
shielding and other performance aspects (ultimately: is it worth the
effort).

Ha. Okay, when I get to it. No promises on when the EMI testing will
be done, I'm just playing with the new spectrum analyzer atm.

"Spehro Pefhany" wrote in message
...
On Wed, 12 Dec 2012 09:26:20 -0800, wrote:

On Wed, 12 Dec 2012 11:43:44 -0500, Spehro Pefhany
wrote:

Hi,

Any reason (other than the hard bits getting into the ways) I
shouldn't put a 1/4" diamond die grinder bit into a milling machine
collet to take a bit (a few thou) off some ferrite? RPM will be very
low (1750 RPM) but I guess I can just feed slow? A 0.394" diameter bit
will have a SFM of ~180. Mist coolant? Dry (doesn't seem to be
recommended for diamond)?

--sp
The thing that seems to eat diamond bits is heat and lack of lube. I
know that running them dry will usually strip then diamond off in
short order. I don't know if it is heat or lack of lube or both that
strips the diamond. I use kerosene or WD40 or water or soapy water
depending on what I'm grinding. For ferrite probably WD40. I use WD40
not because it is so superior to kerosene but because it doesn't smell
so bad.
Eric

Thanks, Erice. At $26 a bit, I'm not too eager to strip the diamonds
off on the first try. I'll try the WD40.

If you're concerned about damage to the bit, forget the idea. Unless you
run such that the bit never sees red heat at the point of contact, you'll
destroy the diamond, even if it isn't ripped from the matrix.

Reason?

Iron has an affinity for carbon. If you heat the diamond to the point of
redness, the iron will absorb the carbon (diamond) dulling it quickly. It
may still be there, but will have lost the sharp edge one relies upon for
cutting.

If you can run it slow enough to not raise heat, sure, give it a go.

Harold