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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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Flat Lapping
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. |
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Pankaj, remember that the frequency is set by thickness AND the other
two dimensions as well. Are you only trying to control thickness? Doug |
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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 --- |
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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. |
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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? |
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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 |
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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 ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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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. |
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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 |
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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." |
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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 ================================================== |
#17
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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 |
#18
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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 |
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