Cheap surface plate ?

We have a 12 year old Panasonic CRT TV and a 25 Year old Sony CRT TV, neither of them seem to have a protective sheet of glass/plastic in front of the screen. The front surface seems to be part of the CRT. (It my be thicker though)

Dave

Peter,

The later ones did

But back in the early 1970s we were still seeing trade-ins with the separate protective glass.

MichaelG.

P.S.   There is some useful info here

Oscilloscope tubes were always relatively safe because of their proportions.

... or maybe I'm wrong about 'scope tubes [see here]

Edited By Michael Gilligan on 26/12/2012 13:19:18

Edited By Michael Gilligan on 26/12/2012 13:46:56

When my dad had his own TV rental business he had a special technique for destroying failed tubes.

It was built on a steep hill, so there was a full storey basement where he stored old tellies and there was a shed right across the back, creating an open area sheltered from all directions.

He would place the tube on the ground face down with carpet or similar on top, then drop a brick on the neck of the tube from the steps about 12 feet above.

Neil

The glass from an old scanner/ photocopier could be placed on a bit of MDF, possibly with some cloth between would be good. I remember reading in an old ME of placing a peice of glass on a tray filled with some sort of tar to support the weight of things placed on the plate, and prevent it from flexing. One thing, if you get a granite one, when you "go", them that are left can get it engraved, and polished, reddy made headstone. Ian S C

Like it. Sort of taking it with you.

If you didn't have one already get yer headstone made up now and than get some use out of it first...starting to like this idea..maybe even do the M I your self ( strip in the date later...)...quite facied 50 mm toughened glass for mine ( head stone) laser etched inside ..( spooky floating images /text ) solar lamp in base to light it ... Doubt the powers that be would allow it.....

Jason,

Perhaps you could have this en"graved"

Here lies Jason Udall

Below this flat sheet

On which is this doodle

What are you guys using these "chopping boards" for?

I have a cast iron plate but ( I think on the recommendation of our esteemed Editor) some time ago bought a granite "chopping board" from J Sainsbury to keep handy on the bench. After the remarks here about inaccuracy I just went out and ran a dti over it. The max. variation I can find is less than 0.02mm. Now that's flat in my book! I know it cost me less than £5. Useful for bits of trial assembly and a much better place to rest your tea mug than the CI variety!

Headstones,epitaphs and immortality?

Remember the old adage - " Die and leave someone £1000 and they will remember you for a short while. Die owing them £1000 and they will remember you for ever!

Cheers

Norman

Edited By NJH on 27/12/2012 13:16:53

The last generation of flat CRT's have very thick front glass panels. The implosion protection is by having the very thick glass and by the steel "rimband" which holds the outer panel edge in compression. A lot of tubes have been scrapped due to shorted scan coils which have not been made for at least 7 years, the factory in Mexico has been flattened.

You need to be VERY careful in handling CRT's- think of it as around a ton of force acting on that glass bottle. I would suggest that anyone not trained in handling CRT's stays well clear.

Whatever you do don't chuck a brick at it or drop it in a skip, the glass will fly very fast and at random. Never pick up a large CRT by the neck- it will snap off very easily as it implodes.

All in all -unless you know what you are doing with CRT's -reclaiming the front panel is a lot more work and risk than using an offcut of marble or getting a second hand cast iron plate.

Billy

> around a ton of force acting on that glass bottle.

Good estimate!

Front area of a tube, say 18" x 20" = 360 square inches

1atm = ~14 psi so 14 * 360 = 5040lbs - about two tons.

> don't chuck a brick at it

I was definately NOT recommending that course of action

I have a large chunk of 'epoxy granite' worktop which is very flat but cost me an angle grinder to cut off a VERY heavy offcut!

Neil

Edited By Stub Mandrel on 27/12/2012 16:43:39

I am thinking of starting a thread on tangents. When i started this thread i never thought for one second that gravestones would come into it. Fantastic !!! best of it is I have a cast iron one.

Cheers Derek.

I obtained a real, small CI surface plate, £10. May I suggest that anyone using thick glass obtains a piece of felt to go under it? Probably cheaper than baize and just as good.

Hey Derek

A Cast iron gravestone - now that's unusual ( especially as,presumably, you are still with us!)

Norman

Nice one Norman. A senior moment on my part brought on by an invasion of six grandchildren all at the same time. That's my excuse anyway.

Cheers Derek.

Ah Derek

Excuse accepted - I recognise the situation - although not quite to the same degree!

 ( I mean quantity of grand brats - not senior moments - or should that be and senior moments - I really can't remember)

N

( P.S. Simultaneous delivery of sextuplets must be a rare occurance! )

Edited By NJH on 27/12/2012 20:33:15

Edited By NJH on 27/12/2012 20:44:41

Thanks to all for the very interesting info re CRT's

Peter G. Shaw

Sorry Peter,

Since my posting on using the glass from a TV screen I have been in bed with the mother and father of all colds. A disaster for Christmas. During the 90s my son ran a TV repair business and he had many different types of CRT sets in for repair. A few had a sheet of plate glass in front of the CTR which as many have remarked is made of very thick glass and unlikely to to be damaged in an accident with a broom handle.

I remember the one from which I salvaged my surface plate was from a set where the the colour had gone and a new tube cost more than a (then) modern TV. Most of the later CRT sets did not have protective glass screens. I guess the change to a more "square" tube made it neccessary to use thicker glass and therefore no need for the additional protective screen.

Ray

I had been using a marble chopping board as a surface plate, I think it may have come from Dunhelm Mills. Placing an engineers straight edge over both sides I was able to get a ten thou feeler under the middle on the concave side and on the opposite convex side it was similarly distorted. In truth it was bent. While being probably OK for marking out on non critical machining jobs, it was unreliable for measuring say with a vernier height gauge. and slip gauges with grinding in mind.

Next step, I have a glazier friend and he kindly cut and dressed a piece of laminated glass

30 x 35cm x 12mm thick. I expected much more accuracy with this but although it is a great improvement and will probably be ok for general machining it would still not be good enough for precision measurements.

Just a suggestion, a large thick piece of say, half inch thick good quality gauge plate would probably afford a better degree of flatness but the cost might be creeping toward a new, small commercial surface plate.

After all that, I have discoverd, a bit late in the day that the heavy duty length of kitchen worktop I use for a bench is flatter than the marble and the glass over a similar surface area - funny old world init?

Stuart

A great story, Stuart ... and there's a moral for us all.

Within reason; the choice of material is fairly arbitary

Flatness is what really matters.

and ... Shiny does not always equate to Flat.

MichaelG.

I was lucky, back in the 1980s the NZ Govt was selling off various departments, and when the Post Office Workshops in Christchurch went, i got a 14" x 12" cast iron surface plate for $NZ15, freshly back from being checked for flattness, the other one they had, had not been checked, and was known to be a bit out(but it had handles) went for$NZ50, go to auction- 2 items same, buy the second one, wait for the auctionereto drop his price, well it worked for me. Ian S C

A bit off topic but when I was working at the Mullard research labs in the 1970s we had some special CRTs sent over from Eindhoven for testing. The customs paperwork specified that they should be returned or destroyed after a certain date.

One day a customs officer came into the lab where I was working and asked to borrow a hammer. A couple of minutes later there was a loud explosion from across the corridor!

Russell.