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.
Some general lapping information is available from lapping compound manufacturers such as:
But you probably need more specific information than they can provide.
Almost certainly your frequency spread is due to variations in the thichness of your quartz, due to out of flat or non-parallel surfaces.
The tolerances required for quartz crystal resonators is very similar to the tolerances required for gage blocks, and the lapping procedures are probably similar also. Some years ago I found a site that described the lapping procedures used in the manufacture of gage blocks, however I can't find it now in the few minutes I am willing to spend. I suggest you look for this, possibly someone on rec.crafts.metalworking can help.
The basic procedure is to lap a group of blocks (or crystals) in a holder between 2 lapping plates, with frequent swapping of positions of the blocks in the holder, such that the thickest blocks from one pass (Probably from one side or the other of the holder) wind up distributed around the holder on the next pass. Proper maintenance of flatness of the lapping plates is of course also critical, and requires being able to measure flatness fairly acurately.