Flat Lapping of Quartz Crystal.

You need a way to monitor the frequency of the crystals as you lap them. I used to work at Petersen Radio, one of the largest manufacturers of crystals in the U.S., and the clever trick they used was this. You take a communications receiver and tune it to just below (a few KHz) the frequency you want for your crystals. Place the receiver just next to your lapping machine and connect a short wire to the antenna terminal of the receiver. Drape the wire over to the lapping machine and near the lapping table. When the crystals are being lapped, the repeated mechanical shock of the lapping process causes the crystals to generate radio frequency noise at their resonance frequency. You can hear it on the receiver and as the crystals come up in frequency, you can stop just before you get to the desired frequency. Then you can lap them one at a time and get very close to the final result. The crystals will change frequency a little as a result of cleaning, and with a little experience you can tell where to stop lapping so that after cleaning, they will be spot on.

used to work

and the

it to just

just next

receiver.

the crystals

the crystals

it on the

get to the

the final

and with a

they will be

That is so elegant, it reminds me of the early story of extracting DNA from cells, complex schemes were thought of, then an assistant said, why not use a food blender... it worked

martin

In message , martin griffith writes

Definitely monitor the noise spectrum as you lap but also; batch in groups dependent on frequency regularly remove the blanks from the carrier, turn over, transpose positions on carrier and individually lap/polish to final frequency which should be 4? kHz high allow for electrode mass, i.e. evaporate down to exact frequency.. .

You don't need no steenkin' machine, you can do it by hand:

Mark L. Fergerson

In my younger days as a novice, I used toothpaste as the abrasive. If I ground it too far, a little pencil lead would bring it back down.

Jim

What type of lapping machine would you use to lap / polish individual (single) crystals ?

Thanks

In message , Alt Beer writes

I recall transposition helps parallelness of blank. Blanks grouped into sets with similar frequency then lapped close to frequency individual blanks lapped by finger directly on blank on flat glass plate .

I have a small double sided Pin lapper. The carrier can take up to six blanks but the top plate is light enough that you can lap a single crystal for final adjustment before plating. I wouldn't like to move it too far using the Pin lap before loosing parallelism. Got the Pin lap from QCC before they closed down. I think they had it made as I've not seen another like it.

Thank You very much for your suggestion Mr Phanton

I am already using an Automatic Logic Controller which keeps track of the frequency while lapping and stops the machine when the target frequency is reached. But my problem is that after lapping the blanks upto 20 MHz, the machine stops and when all the blanks were measured there was a difference in frequency of 200KHz between the maximum and the minimum frequency crystals from one load. Can you please suggest some means of reducing this frequency spread.

Cheers Pankaj.

I thought it would be interesting to have a 1F capacitor, a 1H inductor, and a 1 Hz crystal.

Does anyone know how big a 1Hz crystal would be?

If you measure the frequency of each blank taken from consecutive carrier positions, you may notice the extreme high and low of the spread can occur at opposite carrier positions. (or opposite side of the lapping plate if you are using a multi carrier machine) Therefore, when you have detected that the spread has widened you transpose the blanks into different carrier positions. Also turn them over. The spread quickly narrows. When it widens again, you transpose again. Are you conditioning your lapping plates every so often? Just as the blanks go out, your lapping plates will go out over time. They also need lapping. Usually on a large single sided machine. Test your lapping plates for flatness using an optical flat and a monochromatic light.

"Aubrey McIntosh, Ph.D." wrote: ...

-jiw

A tuning-fork style would be almost practical.

Here's a steel tuning fork that rings at 70Hz:

Best regards, Spehro Pefhany

Just OTTOMH, about the size of a city block - what was the resonant freq. of Galloping Gertie?

Cheers! Rich

Let's not forget the Foucault Pendulum! And then, of course, there's the

Anybody remember the "caterpillar" in "Hunting Red October"? ;-)

What's the resonant frequency of an ordinary diving board?

The resonant frequency of your _heart_ is (typically) higher than one Hz - who was that guy all those hundred years ago?

Cheers! Rich

Thanks Mr Alt Beer

Your suggestion sounds very interesting to me, and I tried it and its quite a time consuming process and in the process I lost quite a few crystals because of manual handling (causes chipping and beakages), you sound to me as some experienced dude, Can you please suggest me how can I optimise this lapping process to achieve very low spread, low processing time, less loss because of chipping and breakages. But the most important issue thats bugging me at the moment is the high spread and long processing time. I highly appreciate your help.

Thanks Again Pankaj Trivedi.

Some things to consider that WILL make a difference to your processing:

What type of lapping machine do you have (planetary / pin / poker arm. Single / double sided. Weight of the top plate - how often do you condition the lapping plates, carrier thickness / carrier material / single carrier / multi carrier) Is the carrier reinforced at the circumference. Weight of top plate divided by number of blanks in the load What is your lapping medium and grit size Are you using oil or water slurry Are you applying slurry by hand when you think its needed or continuous flow Are you using square or round blanks Are you contouring single side / double contour How far are you moving the blanks (What is your starting / stopping frequency) What is your transpose pattern

Commercial manufacturers have breakages too so they have 'overmakes' What if the crystal maker gets an order for just one crystal? (you cant easily lap just one crystal)

Quartz crystal processing has been likened to a black art. Processing is a closely guarded secret for many manufacturers. Having said that, if there was a book on all steps involved and you had all the equipment at hand, it would still take a long time before you could make a decent crystal unit. That's without even thinking about yield or processing time. Try it for fun or interest but commercially forget it.

Thanks for your suggestion mate

I am using a planetary machine, double sided lapping, maximum top plate weight on the workpieces = 150 gms/sq.cm conditioning the plates after every 4 runs, using multicarrier, water slurry, grit size - 3 um, continuos flow of slurry, rectangular blanks, starting point 20 MHz and stopping point 24 MHz, transposed after every

Cheers Pankaj.

Rectangular blanks at 24 MHz - Why are you using rectangular blanks at that frequency ? If your holder styles are HC18/U or similar you will have less breakages, better spreads, faster lapping, lower costs using round blanks. To reduce spread during lapping, use smallest diameter blanks you can get away with... not too small a diameter or you'll get edge damping with spring and paste mounting.

How can you pick up a signal using water slurry?

Where are you located? I'm in the UK