Heat resisting plate with hole made in middle

I'm making something, and I need to produce a heat resisting sheet or plate that will take up to about 200 degrees centigrade. Plate needs to be very broadly about 100mm x 150mm x ((say) 2 or 3mm).
I was thinking about using a regular wall tile, but the thing is the plate needs to have a hole made in it in the middle of about 50mm diameter.
A glass plate would also probably do.
I just don't know how to make this item, I don't have the tools to make that hole. I could get some glass cut to 100mm x 150mm but there is no way I could form the hole in the middle.
It's not a commercial activity, I'm just wanting to make a one-off for a gadget I'm making.
I think I, or someone, would have to make this hole.
Can anyone be of assistance to me? I live near Wakefied. Thanks.

On 09/11/2010 20:10, Richard wrote:
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Aaah, I see that you would drill the hole with a 50mm diamond core drill bit. They are about £20.00
But, if there is someone local near me that who has a drill of that size and who will be willing to drill the hole for me, please let me know. :c
BTW, I live near Wakefield, W. Yorks. Rich

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Got a drill press? For glass, a copper tube drillbit is easy and works surprisingly well. Use a piece of copper pipe (or even copper sheet on a wooden former) and notch the business end with a hacksaw. Try to get the end nice and square, so that it cuts evenly.
Place your glass on a piece of scrap ply on the drill press table and build a moat of vaseline around the hole. Drop some white spirit in there, then blobs of valve grinding paste on the cut line. Bob the rotating copper tube up and down gently and saw through the glass by abrasive action. Top up with grinding paste as needed.
For tiles, chain drill with a small tile bit (again, lubricate this) and grind the hole smooth.

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1. Get some clay and mould it. Plaster might even work.
2. The traditional drill for glass is a brass tube. Make a dam around the hole from putty and pour in some abrasive slurry or even fine sand, which will embed itself in the soft metal and grind away the hard glass.
Cast iron is said to work well for laps, so maybe you could turn a narrow-edged cylinder out of a pipe fitting.
jsw

On Tue, 09 Nov 2010 20:10:08 +0000, Richard wrote:
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Put a piece of masking tape in the area of the hole you want to make, use a carbide drill to drill the hole. Mark/remark the hole you want to make then thread an abrasive saw blade through the hole and mount in saw frame and cut out.
The saw blades (most fit junior saws) can be bought at diy sheds and some good tool stores have jigsaw fitting blades.

wrote:
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    Does it have to be ceramic tile or glass? Could you not use a 'simmering plate' available from any good kitchen shop for use with gas cookers and, I think, easily cut with hand tools. You might also drop into a DIY shed or plumbers' supplies and look at the protective mats used when soldering pipework, also easily cut. --
Chris Edwards (in deepest Dorset) "There *must* be an easier way!"

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I was going to suggest the sort of heat resistant board which is used above woodburners. Cement reinforced with glass fibre, I think. Typically 6 mm thick, if this is acceptable. Can't remember the names for the moment but any decent builders' merchant stocks it. Relatively easy to cut. If using glass, I would be worrying about the effect of temperature differences (unless going for pyrex). Does it have to be a good insulator? The themal conductivity of stainless steel is relatively poor, for a metal.

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Get a piece of tufnol and cut the hole by chain drilling and file round Peter

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The standard phenolic resin stuff will start to smell at ~ 200 C, although I think there are (expensive) heat resistant products. You might consider PTFE if you are sure it will never get much above 300 C.

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What's wrong with mild steel? Cheap, widely available, easy to cut, resistant to temperatures far higher than 200º.
Cliff Coggin.

On 11/11/2010 07:47, Cliff Coggin wrote:
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Well, I'm trying to heat up something that can be "fixed" if it gets hot for several hours. The thing itself (electronic valve) has heaters, but the heat needs to build up, so it will be shrouded in rock wool. So, this plate must really not conduct heat too well.

On 11/11/2010 19:04, Richard wrote:
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As an insulator I'm using something that was used as insulation in the attic. It's about 4 or 5 inches thick. I think it's called rock wool, in any event the insulation put in the loft. I believe it can stand 200 degeees C.

"Richard" wrote...
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I assume it has a bit of gas in it? It should have a "getter" in it, usually a single turn of magnesium, fairly thick, which in the manufacturing stages is used as a shorted-turn with a highish frequency, highish power magnetic field to get it nice and hot - the magnesium picks up the traces of gas and helps get a proper vacuum in the envelope quite quickly. You *could* try to emulate this arrangement with a high-power audio amplifier and a hefty coil, although the frequency would be a fair bit lower than the manufacturers used! I suppose an AC arc-welder might be suitable with a little ingenuity, too? That would probably need an iron core though, so a higher frequency would probably be better - have a Google for induction heating?
Dave H.

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In that case maybe you could drill a hole in a firebrick.
This afternoon I went shopping around town for insulation to repair a heat-treating oven and came home with a free box of remnants of >2000C graphite fiber blanket.
jsw

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A similar, less messy source of it is the black pads sold to protect woodwork from a plumbing torch flame. The graphite (carbon) fiber doesn't burn in a propane flame. You can see the tiny surface fibers glow bright red but they aren't consumed. I blew a piece hot all over in a charcoal forge. When I pulled it out a few small areas continued to glow for a few seconds without leaving holes.
The furnace insulation is electrically conductive, the soldering pad isn't.
jsw