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Thread ID: 65627	2006-01-25 00:07:00	HDD noises	SurferJoe46 (51)	Press F1

Post ID	Timestamp	Content	User
424146	2006-01-26 03:15:00	The tiny disks which IBM make, with 1GB in a Compact Flash package use a glass platter. It was the only way they could get a platter stiff enough, still having room for heads on both sides. As for the "natural migration of glass over time" ... over what time scale? People still use glass in telescopes. The lenses and mirrors must retain their shape to much tighter tolerances than needed in a hard disk. Many will still use aluminium alloy platters ... they know how to make them. Any change in technology is expensive.	Graham L (2)
424147	2006-01-26 03:39:00	It amazed me the first time I got my hands on the hard drive of a laptop, it was so tiny compared to a desktop hard drive. Rather cute really. :p	FoxyMX (5)
424148	2006-01-26 04:06:00	I think there are some drives with a case less than an inch wide, whereas your laptop drive is 2.5". I've got some 14" disks. They hold 2.5 MB. :D	Graham L (2)
424149	2006-01-26 04:19:00	You you're right, it does sound more rattly than clicky . Glass platters???? :waughh: wouldn't the natural migration of glass over time (accelerated by the centrifugal force) cause the outer edges to become thicker and cause head scraping etc?? heat wouldn't help either . . . I'm not 100% sure, but I really don't think glass is able to "migrate" . IIRC, that idea was derived many years ago from the checking of very old window glass, where the bottom of the pane was invariably thicker than the top . However, early glassmaking was not all that sophisticated and glass was spun out to produce sheets, the centre point making the "bullseye" panes you see in ye quainte olde english shoppe windows . The outer parts were cut into squares and for ease of installation the thickest part was placed at the bottom . If migration was an issue, you should be able to measure a thickness variation between the top and bottom of any very old mirror . We have a large 100+ year-old mirror here and there is no evidence of visual distortion, top or bottom . Of course I could be wrong, but Google should confirm or deny if anybody is that interested . Cheers Billy 8-{)	Billy T (70)
424150	2006-01-26 04:31:00	The bullseye glass was an early method . The size was very limited . I doubt very much if they made any more than about 4' in diameter . So the square pieces were very small . That's why very old windows use lots of panes . I saw the 3' diameter glass lampshades for the Christchurch Town Hall being blown and that was quite a performance . They cheated a bit by using a compressed air hose to finish the blowing . Most larger panes were made by blowing a cylinder . The ends were cut off (you have to have "ends" to be able to blow) then the cylinder was slit along its length and opened out into a (roughly) flat sheet . Glass windows were expensive .	Graham L (2)
424151	2006-01-26 17:04:00	I remember from my physical science classes in high school here in the US that glass is "plastic" . . . . . . (# Capable of deformation at constant stress once the yield point is exceeded . The ability of a material to undergo permanent deformation without returning to its original shape or failing . www . minesafe . org/training_education/terms . html) and as such, flows from the date of formation untill it is either destroyed or recycled . The fact that this happens is evident in the glass windows of very old homes here in Jamestown and the old original settlements like the Dutch colonies in New York . . etc . The glass over time has flowed to the effects of gravity and grown thicker at the bottom, thinner at the top . After the modulus has been exceeded, the glass keeps this new position rather well, as there is no true memory to it's original form from that time on . This does not consider the "eye" glasses that were so stylish in homes of grandeur and social status as these were basically part of a glass montage, as in pieces of glass bounded by a leaden form that held them in decorative and various positions, because, yes, glass was very expensive to produce in large forms . Much of the cost was attributed to the transport and shipping of the product, as much was lost that way due to rough portage and clumsy stevedores . The grand mansions of the old South and in Charleston especially, had artisans very nearby, and after import from England and Germany was discontinued because of local talent, the cost of glass dropped considerably . This allowed the more common houses to also have some beautiful glasswares and even stained glass became very prominent . Modern glass production has pretty well eliminated the flow problem with the inclusion of various additives to glassmaking, but the fact that glass is still "plastic" and that it by nature still flows, causes all sorts of compensations to engineering of the mounting and maintenance of things like telescope lenses and critical laboratory fresnels* to be very tightly designed and carried out . * The lens invented by Augustin Fresnel in 1821 which consists of concentric ridges radiating outward from the central lens (bullseye), with prisms positioned at the top and bottom of the ridges to refract the light from the light source placed behind the central lens . A term normally used only when referring to traditional cut glass style lenses, although the Fresnel principle is also found in more modern glass or plastic lenses .	SurferJoe46 (51)
424152	2006-01-26 20:24:00	I'm not sure that I agree with you there SJ . Here ( . org/science/glass . flow/glass_flow_the_thread . html" target="_blank">tafkac . org) is a forum discussion with a variety of views, that deals with the "plastic" issue in a fairly credible fashion . It would take a formal peer-reviewed scientific research paper with repeatable experimental results to convince me that gravity can affect the thickness of the bottom of a pane of glass . Bear in mind that the compression stress at the bottom of a large sheet of plate glass is many times the force of gravity on a small window pane, and you'd expect to see some measurable distortion in a shorter time period if glass was truly plastic and flow-deformable . Cheers Billy 8-{)	Billy T (70)
424153	2006-01-27 20:24:00	How ironic is this, after reading this thread and listening to those sounds, my HDD starts making those noises :groan: and not able to read half the data and taking 15 mins to load windows :eek: What can cause this? What should I do, it is still in warrenty?	The_End_Of_Reality (334)
424154	2006-01-27 21:35:00	I'm not sure that I agree with you there SJ . Here ( . org/science/glass . flow/glass_flow_the_thread . html" target="_blank">tafkac . org) is a forum discussion with a variety of views, that deals with the "plastic" issue in a fairly credible fashion . It would take a formal peer-reviewed scientific research paper with repeatable experimental results to convince me that gravity can affect the thickness of the bottom of a pane of glass . Bear in mind that the compression stress at the bottom of a large sheet of plate glass is many times the force of gravity on a small window pane, and you'd expect to see some measurable distortion in a shorter time period if glass was truly plastic and flow-deformable . Cheers Billy 8-{) Just a thought to toss in here Speed . . . . do you honestly think the distorted glass that we see in the Victorian era homes was made that way? Please remember that there are times when this distortion is wanted, as in obscurred glass in bathrooms and private dressing areas of the home, but I sincerly doubt that deformed glass was what was originally wanted or manufactured . I had the extreme pleasure to tour the Jamestown Virginia Exposition, in of course, Jamestown Virginia about the year . . . let me think . . uh . . . how about 1956? Anyway, I asked this very question at the glass-blower's display, and that was the first time I ever heard of glass being "plastic" . It has since become a general factoid that indeed glass does flow for the life of it's existance . I promise to research this situation and get a post up about it pretty quick . . OK?	SurferJoe46 (51)
424155	2006-01-27 21:52:00	Well . . . that was quick . . but I found the reason for the anecdotal reference to glass flowing here from "Antique windowpanes and the flow of supercooled liquids", by Robert C . Plumb, (Worcester Polytech . Inst . , Worcester, MA, 01609, USA), J . Chem . Educ . (1989), 66 (12), 994-6:ibid There have been many claims (especially by tour guides) that such glass is deformed because the glass has flowed slowly over the centuries . This has become a persistent myth, but close inspection shows that characteristic signs of flow, such as flowing around, and out of the frame, are not present . The deformations are more consistent with imperfections of the methods used to make panes of glass at the time . In some cases gaps appear between glass panes and their frames, but this is due to deformations in the lead framework rather than the glass . Other examples of rippling in windows of old homes can be accounted for because the glass was imperfectly flattened by rolling before the float glass process came into use . It is difficult to verify with absolute certainty that no examples of glass flow exist, because there are almost always no records of the original state . In rare cases stained glass windows are found to contain lead which would lower the viscosity and make them heavier . Could these examples deform under their own weight? Only careful study and analysis can answer this question . Robert Brill of the Corning glass museum has been studying antique glass for over 30 years . He has examined many examples of glass from old buildings, measuring their material properties and chemical composition . He has taken a special interest in the glass flow myth and has always looked for evidence for and against . In his opinion, the notion that glass in Mediaeval stained glass windows has flowed over the centuries is untrue and, he says, examples of sagging and ripples in old windows are also most likely physical characteristics resulting from the manufacturing process . Other experts who have made similar studies agree . Theoretical analysis based on measured glass viscosities shows that glass should not deform significantly even over many centuries, and a clear link is found between types of deformation in the glass and the way it was produced . Conclusion There is no clear answer to the question "Is glass solid or liquid?" . In terms of molecular dynamics and thermodynamics it is possible to justify various different views that it is a highly viscous liquid, an amorphous solid, or simply that glass is another state of matter which is neither liquid nor solid . The difference is semantic . In terms of its material properties we can do little better . There is no clear definition of the distinction between solids and highly viscous liquids . All such phases or states of matter are idealisations of real material properties . Nevertheless, from a more common sense point of view, glass should be considered a solid since it is rigid according to every day experience . The use of the term "supercooled liquid" to describe glass still persists, but is considered by many to be an unfortunate misnomer that should be avoided . In any case, claims that glass panes in old windows have deformed due to glass flow have never been substantiated . Examples of Roman glassware and calculations based on measurements of glass visco-properties indicate that these claims cannot be true . The observed features are more easily explained as a result of the imperfect methods used to make glass window panes before the float glass process was invented . . . . . . so, it looks like there is still some amount of dispute over this phenenoma and there is still room for dedicated studies . . . . . . but back to the original thought: NO, the glass platters in your HDD will not deform over time because unlike window glass, they are different in compound and manufacture . I did enjoy this little journey and the research it created . . . a good hijacking, wot?	SurferJoe46 (51)
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