Hello Group


I have a Flat lapping machine with me and have been trying to lap some
quartz blanks but after lapping when i measure the frequency I found
that the frequency spread is too high all the time, Can someone give
me some expert comments on how can I decrease the frequency spread.
Also I will highly appreciate if someone can please provide me links
to some helpful documents about flat lapping and some Do's and Don't
to improve the quality of my workpieces.


Thanks in Advances
Pankaj Trivedi.

Pankaj, remember that the frequency is set by thickness AND the other
two dimensions as well. Are you only trying to control thickness?

Doug

In article .com,
wrote:
Hello Group


I have a Flat lapping machine with me and have been trying to lap some
quartz blanks but after lapping when i measure the frequency I found
that the frequency spread is too high all the time,


I'm not sure that this is the correct newsgroup for this
question -- though I'm not sure that one exists.

From your question, I'm presuming that you are attempting to
make frequency controlling crystals, not optical flats or some of the
other possible products which might be made by lapping quartz.

I've never done it, but I would expect that flatness (on both
side) is not the only important criterion. I suspect that the two
surfaces must be very parallel as well. Have you tried measuring the
thickness at all four corners -- and in the center? And you may need a
something with more resolution than a micrometer capable of reading down
to 0.0001" (or even 0.001mm)

Also, it may depend on how the crystals are mounted. I know
that really old ones in my collection are mounted between two plates of
metal so designed that they contact the crystal only at the corners. I
have seen others were the crystal was apparently vacuum plated with
metal on both sides (and perhaps the edges were ground free, as these
were round), with wires bonded to the center on each side.

I also believe that I remember that the orientation of the blank
relative to the original quartz crystal changes the behavior -- one
orientation may give a lower frequency, another may give a narrower
response curve, and a third orientation may give a lower temperature
coefficient relative to the frequency.

But -- this is really faded memory of something read over forty
years ago.

Can someone give
me some expert comments on how can I decrease the frequency spread.
Also I will highly appreciate if someone can please provide me links
to some helpful documents about flat lapping and some Do's and Don't
to improve the quality of my workpieces.

Just some thoughts, and a lack of hard information.


Thanks in Advances
Pankaj Trivedi.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

wrote:
Hello Group


I have a Flat lapping machine with me and have been trying to lap some
quartz blanks but after lapping when i measure the frequency I found
that the frequency spread is too high all the time, Can someone give
me some expert comments on how can I decrease the frequency spread.
Also I will highly appreciate if someone can please provide me links
to some helpful documents about flat lapping and some Do's and Don't
to improve the quality of my workpieces.


Thanks in Advances
Pankaj Trivedi.


Please define what you mean by "frequency spread". I'm interpreting it
as you're saying that the Q isn't as high as you'd like it to be, but
perhaps that's not what you mean to tell us.

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."

Hi Pankaj,

The last time I did crystal grinding (which is what you are
*really* doing, I used a very flat piece of 1/2" plate glass
for the surface. The agent (grinding compound) was jeweler's
rouge and a bit of distilled water as a vehicle.

We held the crystal with our fingers (in Platex gloves) and
took a few very measured circular passes. We counted the revs.
A wonderful ham we knew (Mr. Irvine), designed and built a very
neat tester/oscillator to judge the results before sticking the
futtering FT-243 crystal holder all back together.

It consisted of wide respsonse oscillator using a computer
switching transistor (2N706 or thereabouts), a *very* thin
copper wire soldered to a small brass flathead woodscrew. The top
of the screw was polished down and could be lifted and placed
anywhere on the surface of the rock ... errh ... crystal.

The crystal sat on a polished brass flat (an old brass gear).
The gear and the wood screw served as the two contacts for
the rock.

I suspect that your "Flat lapping machine" may be taking too much
off the blank. Go easy with it. We also fooled around with HcFl
- hydroflouric acid - VERY bad stuff to play with - grinding your
rock is much safer.

Good luck.

Carl - in another life WB2YHE

wrote in message
oups.com...
Hello Group


I have a Flat lapping machine with me and have been trying to lap some
quartz blanks but after lapping when i measure the frequency I found
that the frequency spread is too high all the time, Can someone give
me some expert comments on how can I decrease the frequency spread.
Also I will highly appreciate if someone can please provide me links
to some helpful documents about flat lapping and some Do's and Don't
to improve the quality of my workpieces.


Thanks in Advances
Pankaj Trivedi.

On 30 May 2005 01:08:32 -0700, wrote:

Hello Group


I have a Flat lapping machine with me and have been trying to lap some
quartz blanks but after lapping when i measure the frequency I found
that the frequency spread is too high all the time, Can someone give
me some expert comments on how can I decrease the frequency spread.
Also I will highly appreciate if someone can please provide me links
to some helpful documents about flat lapping and some Do's and Don't
to improve the quality of my workpieces.


Thanks in Advances
Pankaj Trivedi.

http://www.sentrymfg.com/crystalclear.htm

Thank you very much for your replies.

By frequency spread I mean that the when heaps of crystals are lapped
at one time in the lapping machine, the difference in frequency from
one crystal to the another is quite big which is the frequency spread.
How Can I minimise this spread.

Cheers
Pankaj.

wrote:

How Can I minimise this spread.

Isn't the orientation of the crystal important?


Ni-NotHavingLappedAnyCrystalAndNotSoMuchInElectronics-ck
--
"Wissenschafts"-Sendung auf einem der Privat-Kanäle:
"Der Behälter fasst 200.000 Kubik-Liter."
Wie viele Quadrat-Stunden braucht es dann wohl, um ihn voll zu bekommen?

In article .com,
says...

Thank you very much for your replies.

By frequency spread I mean that the when heaps of crystals are lapped
at one time in the lapping machine, the difference in frequency from
one crystal to the another is quite big which is the frequency spread.
How Can I minimise this spread.

1) define "quite big" in numerical terms. What is the frequency
and what is the rms deviation?

2) have you done the obvious things such as

a) measuring the actual thickness of the finished blanks
and correlating that with the frequency variation?

b) controlled the other dimensions of the blank, as another
poster has suggested?

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

Carl Hoffmeyer wrote:

Hi Pankaj,

The last time I did crystal grinding (which is what you are
*really* doing, I used a very flat piece of 1/2" plate glass
for the surface. The agent (grinding compound) was jeweler's
rouge and a bit of distilled water as a vehicle.

We held the crystal with our fingers (in Platex gloves) and
took a few very measured circular passes. We counted the revs.
A wonderful ham we knew (Mr. Irvine), designed and built a very
neat tester/oscillator to judge the results before sticking the
futtering FT-243 crystal holder all back together.

It consisted of wide respsonse oscillator using a computer
switching transistor (2N706 or thereabouts), a *very* thin
copper wire soldered to a small brass flathead woodscrew. The top
of the screw was polished down and could be lifted and placed
anywhere on the surface of the rock ... errh ... crystal.

The crystal sat on a polished brass flat (an old brass gear).
The gear and the wood screw served as the two contacts for
the rock.

I suspect that your "Flat lapping machine" may be taking too much
off the blank. Go easy with it. We also fooled around with HcFl
- hydroflouric acid - VERY bad stuff to play with - grinding your
rock is much safer.

Good luck.

Carl - in another life WB2YHE

wrote in message
oups.com...

Hello Group


I have a Flat lapping machine with me and have been trying to lap some
quartz blanks but after lapping when i measure the frequency I found
that the frequency spread is too high all the time, Can someone give
me some expert comments on how can I decrease the frequency spread.
Also I will highly appreciate if someone can please provide me links
to some helpful documents about flat lapping and some Do's and Don't
to improve the quality of my workpieces.


Thanks in Advances
Pankaj Trivedi.




Are you doing this for a few amatuer crystals, or is it for production?
What kind of reliability do you want?

My understanding of short-run crystal manufacture is you calibrate the
machine for how much it'll change the frequency per pass (or whatever),
you measure the frequency of a part-way-done blank, then you take off a
controlled amount from the blank.

AFAIK crystals need to be etched a bit if you want them to be resistant
to frequency changes as they age. Time-controlled etching is also a
good way to take off a controlled amount of material. But HF acid is
nasty stuff, so I wouldn't play with it unless you're in it for money.

--
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

wrote:

Hello Group


I have a Flat lapping machine with me and have been trying to lap some
quartz blanks but after lapping when i measure the frequency I found
that the frequency spread is too high all the time, Can someone give
me some expert comments on how can I decrease the frequency spread.
Also I will highly appreciate if someone can please provide me links
to some helpful documents about flat lapping and some Do's and Don't
to improve the quality of my workpieces.


Thanks in Advances
Pankaj Trivedi.

try these links
http://www.sentrymfg.com/crystalclear.htm
http://www.icmfg.com/planttour.html

Carl Hoffmeyer wrote:

Hi Pankaj,

The last time I did crystal grinding (which is what you are
*really* doing, I used a very flat piece of 1/2" plate glass
for the surface. The agent (grinding compound) was jeweler's
rouge and a bit of distilled water as a vehicle.

We held the crystal with our fingers (in Platex gloves) and
took a few very measured circular passes.

When I did it I was told to make those passes in a "Figure eight" movement.

We counted the revs.
A wonderful ham we knew (Mr. Irvine), designed and built a very
neat tester/oscillator to judge the results before sticking the
futtering FT-243 crystal holder all back together.

It consisted of wide respsonse oscillator using a computer
switching transistor (2N706 or thereabouts), a *very* thin
copper wire soldered to a small brass flathead woodscrew. The top
of the screw was polished down and could be lifted and placed
anywhere on the surface of the rock ... errh ... crystal.

The crystal sat on a polished brass flat (an old brass gear).
The gear and the wood screw served as the two contacts for
the rock.

I had pretty good luck raising the fundamental frequencies of some WWII
"war surplus" FT-243 crystals up into the 40 meter ham band circa 1950.

If I overshot a and raised the frequency a bit too much, I used to lower
it a little by rubbing soft solder (cold) onto the center of the crystal
blank, adding a little mass back onto it. Those crystals were the types
held between two metal plates formed to grab them at their four corners.

I've still got about twenty of those FT-243 crystals in a box somewhere.
I guess they'll stay where they are until my survivors toss them out,
along with a couple of stacks of QSL cards from those halcion days.



snipped

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."

wrote:

Thank you very much for your replies.

By frequency spread I mean that the when heaps of crystals are lapped
at one time in the lapping machine, the difference in frequency from
one crystal to the another is quite big which is the frequency spread.
How Can I minimise this spread.

Cheers
Pankaj.


Well, at least we know what you meant now Vicky......G

I'm out of my element on this subject now.

Did you try posting to one of the "sci.electronics" newsgroups, like
sci.electronics.design or sci.electronics.components?

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."

In article , Jeff Wisnia says...

I've still got about twenty of those FT-243 crystals in a box somewhere.
I guess they'll stay where they are until my survivors toss them out,
along with a couple of stacks of QSL cards from those halcion days.

I had one for 40, one for 80, and one for 15 m. I think the
15 was an overtone xtal.

Then I got my general ticket and a VFO. No more xtals.

I still have a irrational desire to build a xtal controlled
transmitter using two 45s in P-P, to work with my national
SW-3.

I'd have to get a new license though.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

wrote:

Thank you very much for your replies.

By frequency spread I mean that the when heaps of crystals are lapped
at one time in the lapping machine, the difference in frequency from
one crystal to the another is quite big which is the frequency spread.
How Can I minimise this spread.

Cheers
Pankaj.

Lap to the exact same thickness and naturally the same 'cut' direction.
A slight deviation off this cut angle and all bets are off.

Crystal material is just that - crystal lattice that must be in a specific plane.

Martin

--
Martin Eastburn
@ home at Lion's Lair with our computer lionslair at consolidated dot net
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder

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The frequency that I am lapping the crystals upto is 20 MHz and the
average spread observed is around 200 KHz,
This frequency spread is the difference in the frequency between the
highest frequency crystal and the lowest frequency crystal obtained out
of one batch of crystals i.e. when few hundred crystals were lapped
together the highest frequency crystal observed was of 20,150,000 Hz =
20.15 MHz while the lowest frequency crystal was around 19,950,000 Hz =
19.95 MHz thereby giving a spread of 200 KHz.
I hope its very clear now.
My target is to bring this spread below 50 KHz.......I want some help
Please....

Thank you very much for your time
Pankaj Trivedi

In article . com,
says...

My target is to bring this spread below 50 KHz.......I want some help

OK, what thickness variation does this correspond to?

Ie, if you measure two samples at the extremes of the distribution,
200 khz apart, what's the size difference?

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

jim rozen wrote:
... says...
My target is to bring this spread below 50 KHz.......I want some help

OK, what thickness variation does this correspond to?

Ie, if you measure two samples at the extremes of the distribution,
200 khz apart, what's the size difference?

The http://www.sentrymfg.com/crystalclear.htm ref given earlier has a
formula, about 40% into the page: Thickness = 66.2 / Frequency
(Thickness in inches, frequency in KHZ) for AT cut crystals. That
would give: 66.2 /20000 - 66.2 /20050 ~ .0000083 inches difference,
ie about 8 millionths for 50 KHz, and about 33 millionths for 200 KHz.
Near the end the page says, "a film of water one molecule thick will
lower the frequency of a 10 MHz crystal about 10 parts per million."

Note, 50 KHz at 20 MHz is 2500 parts per million. About the
cheapest crystals you can buy are 100 ppm; for a few cents more,
20 ppm is common in cheap crystals. So y2kvickyindia (Pankaj Trivedi)
must have some serious material, measuring, or process control problems,
being out of the commercial ballpark by a factor of a hundred.

As someone else recommended, Trivedi started a thread in
sci.electronics.design, " Flat Lapping of Quartz Crystal."
vs. "Flat Lapping" here, and has more details all in one post,
http://groups-beta.google.com/group/...8e258afee008bf
-jiw

In article , James Waldby says...

jim rozen wrote:
... says...
My target is to bring this spread below 50 KHz.......I want some help

OK, what thickness variation does this correspond to?

Ie, if you measure two samples at the extremes of the distribution,
200 khz apart, what's the size difference?

The http://www.sentrymfg.com/crystalclear.htm ref given earlier has a
formula, about 40% into the page: Thickness = 66.2 / Frequency
(Thickness in inches, frequency in KHZ) for AT cut crystals. That
would give: 66.2 /20000 - 66.2 /20050 ~ .0000083 inches difference,
ie about 8 millionths for 50 KHz, and about 33 millionths for 200 KHz.
Near the end the page says, "a film of water one molecule thick will
lower the frequency of a 10 MHz crystal about 10 parts per million."

Note, 50 KHz at 20 MHz is 2500 parts per million. About the
cheapest crystals you can buy are 100 ppm; for a few cents more,
20 ppm is common in cheap crystals. So y2kvickyindia (Pankaj Trivedi)
must have some serious material, measuring, or process control problems,
being out of the commercial ballpark by a factor of a hundred.

That's the question. If he's measuring thicknesses that are inconsistent
with the spread in his frequencies, there's some other uncontrolled
parameter in his process.

If he would list up the extremes of thickness that correspond to the
extremes in frequency, then it would be obvious if this was a
routine exercise in process control (goal to get thickness controlled)
or if it is a snipe hunt, where the goal is to find the mystery
parameter that's pulling the frequencies, in *spite* of good statistical
process control.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

wrote:
The frequency that I am lapping the crystals upto is 20 MHz and the
average spread observed is around 200 KHz,
This frequency spread is the difference in the frequency between the
highest frequency crystal and the lowest frequency crystal obtained out
of one batch of crystals i.e. when few hundred crystals were lapped
together the highest frequency crystal observed was of 20,150,000 Hz =
20.15 MHz while the lowest frequency crystal was around 19,950,000 Hz =
19.95 MHz thereby giving a spread of 200 KHz.
I hope its very clear now.
My target is to bring this spread below 50 KHz.......I want some help
Please....

Thank you very much for your time
Pankaj Trivedi

Lets start with what you are lapping. Is it a sawn disk ? I suspect so.
From a large xtal. This then would be one of the issues.

From Semiconductor background, the wafers (a xtal themselves) are lapped
but across the surface - up to 300mm now - the flat isn't flat. There are
hills and valleys all across the wafer. There are machines that measure this
and qualify a wafer to use. Sometimes it is lapped again. Often the wafers
are very think and after testing the die are back lapped for packaging.

SO I suspect the source and the lap is not to the spec level it needs to be.
After lapping - measure the flatness of the material. Light helps, but there
are machines. Research mirror lapping and measuring. Good stuff there!

I suspect you are fighting some of this - microscopic hills and valleys.

Martin

--
Martin Eastburn
@ home at Lion's Lair with our computer lionslair at consolidated dot net
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder

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