Plate glass as a surface plate?

It may be that no-one cares enough to research and publish : there are credible reports of glass flowing though, see about half way down :

I'll give the quote here to save a search :

"Sorry to pop yer bubble, Ray, but guess what - we do! There was even a bit in New Scientist a while back about a ghost image formed by a 200-yearold mirror that had flowed downwards. The mirror was thicker at the bottom than at the top. Due to a fairly complex optical phenomenon this caused a ghost image to hover a few mm off the surface.

The sad fact is that glass *is* a liquid, but of a type known as a nonNewtonian fluid. It has astonishingly high viscosity, but it's a liquid nonetheless.

I would suspect that the impurities introduced into glass to colour it raise the 'melting' point (i.e. raise the viscosity). Also, remeber that most pieces of glassware in museums have been buried until fairly recently. You do get voids in glass panes that are sufficiently old. Take a look at some of the glass in Canterbury Cathedral if you're in the UK. "

Not according to most scientists. It is an amorphous solid. There are lots of web sites about this, this one sums it up quite well

non-newtonian liquids are something else entirely -and great fun for kids of all ages!

Regards Kevin

And very useful for reverse imprints of tooling and moulding features too, although mine is now extremely grubby after too many ears of service!

Pe

When glass visibly flows it becomes a conductor - just about red heat.

Steve

Good tips Jim, thanks

Steve

Ah yes, the experiment with the bunsen burner and the car battery. Not quite as much fun as thermite but still ...

I take it you've all seen the Ribbands Explosives Power and Precision dvd?

Chris

Interesting site, note the quote "As kinetically frozen forms of liquid, glasses are characterized by a complete lack of long-range crystalline order and are the most structurally disordered types of solid known.

[Jeanloz & Williams, 1991, p. 659]"

I presume a kinetically frozen liquid is one that flows but at a zero rate ?

:-)

Chris Eilbeck wrote: >> When glass visibly flows it becomes a conductor - just about red heat.

Wassat ?

Nope. Where it is, shirts ?

You get a glass rod clamped horizontally and put jump leads from a car battery at opposite ends. You heat the middle of the bar with a couple of bunsen burners which make the glass conductive before it melts. The current then flows and heats the glass until it melts. Very spectacular when I saw it.

They have a bit of a thing for Billy Bass. They also show a pot of thermite on a table above a butane tank. Naturally there are lots of sparks, molten iron and kaboom.

It's worth looking out for.

Chris

Bugger, you mean you don't need a mains lamp for the demo?

Not seen the DVD though -

Steve

This comes up A LOT in woodworking circles.

Float glass is flat, but not terribly rigid. And (as I'm sure you know, accuracy is meangingless without rigidity)

If you end up needed to support it (in large sizes) the resulting (composite) object is as flat as the support, not the glass.

Granite plates are now cheap enough that I would recommend them (depending on your requirments)

BugBear

if anyone cares, this is why I care about surface plates

Bugbear - very interesting. And, if you want a really fine scraper to continue your efforts, see

David

Thanks - but it turns (turned) out that square files and 80 grit AlZi were more appropriate and/or convenient to what I was doing.

"true" scraping is overkill, I'm just using (and advocating) the "print" part of the process in conjunction with rather more rapid metal removal techniques.

(one guy used a 4" angle grinder in the early stages!!)

BugBear

Ahem. At the risk of being monumentally off topic, can I ask a question about the Sugden Au51-P ?

BugBear

I bought one of these from Argos earlier today. It's Item No.

842/0486 - " Granite Worktop Saver" - price was £ 9.99p and is mounted on four small rubber feet. Most importantly, mine has a dip of at least two thou in the middle...the only feeler gauge I had to hand!

In spite of that, it has the prospect of being a useful, cheap-and-cheerful workshop accessory for those jobs which don't require a great deal of accuracy and you need a reasonably flat, clean surface. --

Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"

I can recommend them. But for that work, the 20mm wide type is better. But then again, the carbide plates with 20mm have the same radius as the 25mm plates. And that requires regrinding to a smaller radius ... Then it is a perfect tool.

Nick

No problem if the group will indulge......ask away

In article , Chris Edwards writes

Chris,

I wonder if the "four rubber feet" are contributing to the problem; try supporting the slab all over and see if that helps. Even granite bends.

As an alternative, buy another two plates, then you can generate 3 plates as flat as you want by grinding them together A -> B, B -> C, C

-> A, A -> B and so on until satisfied.

David

I have one, from a different source (right time, right place) and enough inserts to keep me going (different ditto). They are vastly better than carbon steel for flat work. The carbide edges only need honing every three or four hours rather than every five or ten minutes for the steel. A file is still much faster for most work though.

Mark Rand RTFM