heated glass

Here's a thought...

Yesterday I just purchaced a small desktop ceramic heater for my office.
They have two settings, 1500 watt and 750 watt. Plus they hay have
thermostate to control the temp. It cost me $30.00. Putting my hand by the
face of the heater I can tell it is much hotter than 150 degrees.

A constant flow of hot air on the glass would do it without any danger of
direct contact of the heater on the glass. I'm sure you could dial in the
right temp range with a little trial and error.

Using Mike's suggestion to coral and contain the heat would make a big
difference.

After your expanded explanation, I agree you need a thicker plate. Just keep
in mind that glass is a poor conductor of heat. It will take a while for the
heat to saturate a thicker mass of glass. But in time it will do it.

Just thought that might work for you.

Randy Hansen
SC Glass Tech.
Scam Diego, Comi-fornia

"Mike Firth" wrote in message
...
Yes, but will the thin glass hold enough heat to allow the wax to lay
flat, etc.


I would think so as long as he has a constant heat source. If the heat
source is removed, the glass will cool quickly.

Randy Hansen
SC Glass Tech.
Scam Diego, Comi-fornia

"600 Watt halogen shop light a foot below"
will produce several hundred degrees at this distance from a black surface.
we are only talking about needing 150F folks.

--
Mike Firth
Hot Glass Bits Furnace Working Website
http://users.ticnet.com/mikefirth/hotbit46.htm Latest notes

"Mark Jones" wrote in message
...
Mike Firth wrote:
I would have suggested a hot plate or warming tray if I thought you
could
get one as big as you want. And with what you are pushing on, I think
you
need 1/2" or 3/8" glass, not window glass
I still think you will be much better off with a box to buffer the local
effects of whatever heating source you use, which could be a small
warming
tray or a hot plate. I think that putting Pyrex directly on a hot plate
will create a wobbly work surface and depending on how you control the
temp,
may still get too hot locally, even for Pyrex. If you moderate the
voltage,
say with a dimmer or variac, it might work temp wise but still be wobley.
To be honest, you might be able, with a wooden box lined with thin
fiberglass insulation like used in ceiling panels, to get up to 150 with
a
hundred watt light bulb or two and use a cheap light dimmer to control.
Since you are well below the boiling point of water, you could put a
baking
pan in the box and pour boiling water in from a teapot but getting it out
and keeping the temp near 150 might be a drag (he said having softened
pitch
for repousse)



Perhaps you could try making a covered stand and "bowl" for the glass
plate. Make it open underneath and paint the backside of the glass
black with enamel paint, then suspend a 600W halogen shop-light about
a foot under it, pointing up at the black surface. This will get very
hot (and heat evenly over the full surface.) The lamp will need
ventilation though. If yer into electronics, there are several methods
for controlling the temperature accurately.


-- At it's heart, all a fractal is is a simple unbalanced dynamic,
like cos(1/z)*z. A fractal is unbalanced in such a way that it can
never be solved, and the longer it is "computed", the more complex it
becomes. It is literally a twist or gotcha, on infinity.

Mike Firth wrote:
"600 Watt halogen shop light a foot below"
will produce several hundred degrees at this distance from a black surface.
we are only talking about needing 150F folks.


600W is only applied initially to decrease the warmup time.
Electronic PID algorithm modulates the light intensity to any preset
value.



-- "Perhaps it isn't that people are intentionally redefining
standards, just that our logic is changing faster than our
technology." Mark Jones / Helios Studios 20050109

"Mark Jones" wrote in message
...
Mike Firth wrote:
"600 Watt halogen shop light a foot below"
will produce several hundred degrees at this distance from a black
surface.
we are only talking about needing 150F folks.


600W is only applied initially to decrease the warmup time.
Electronic PID algorithm modulates the light intensity to any preset
value.

halogen lights don't like to be switched on/off a lot, and they don't like
dimmers on them either. both lead to premature aging of the bulb and quick
burnout.



-- "Perhaps it isn't that people are intentionally redefining
standards, just that our logic is changing faster than our
technology." Mark Jones / Helios Studios 20050109

Actually, high voltage halogen, like shop lights, don't have the problems
with dimmers that low voltage decorating lights do and almost any dimmer
with sufficient rating (since many shop lights are 1000w and most dimmers
are 600w and shouldn't be used at full rating without cooling) will work.
However, 600 watts is still too much and a couple of hundred watts at most
will do the temp needed with a cheap household dimmer, not a $100-200 PID
controller.

--
Mike Firth
Hot Glass Bits Furnace Working Website
http://users.ticnet.com/mikefirth/hotbit46.htm Latest notes

"Charles Spitzer" wrote in message
...

"Mark Jones" wrote in message
...
Mike Firth wrote:
"600 Watt halogen shop light a foot below"
will produce several hundred degrees at this distance from a black
surface.
we are only talking about needing 150F folks.


600W is only applied initially to decrease the warmup time.
Electronic PID algorithm modulates the light intensity to any preset
value.

halogen lights don't like to be switched on/off a lot, and they don't like
dimmers on them either. both lead to premature aging of the bulb and quick
burnout.



-- "Perhaps it isn't that people are intentionally redefining
standards, just that our logic is changing faster than our
technology." Mark Jones / Helios Studios 20050109

Mike Firth wrote:
Actually, high voltage halogen, like shop lights, don't have the problems
with dimmers that low voltage decorating lights do and almost any dimmer
with sufficient rating (since many shop lights are 1000w and most dimmers
are 600w and shouldn't be used at full rating without cooling) will work.


I'm not fully sure about this. I thought the halogen concept worked
on the basis of needing that high temperature for sustained operation.
In any case, a design where the light remained "mostly on" rather than
"nearly off" would probably be better for it. That design might best
using two lamps - one large one for the fast initial heating, and a
smaller one to maintain a set temperature.


However, 600 watts is still too much and a couple of hundred watts at most
will do the temp needed with a cheap household dimmer, not a $100-200 PID
controller.



600W was only a guesstimate. I assume, with a chunk of glass a half
inch thick and a foot square with a few pounds of wax on top of it, it
would still take at least 15 minutes to warm at full power. That's a
lot of thermal mass to heat. Of course this too is speculation; I've
not tried it. Nor do I fully understand exactly what the OP is trying
to accomplish.

I've used a 500w halogen light before as a heat source and must say,
it does make a good deal of thermal and radiant heat. However, even
though the glass plate would be painted black, the coefficent of
conduction would not be all that high. The goal would be to modulate a
halogen in the last 10-20% of "fully on" for the desired temperature.
Increasing the surface area of the bottom of the glass and/or using a
higher-conductivity coating will obviously help thermal transfer
efficiency and allow an even smaller lamp to be used. I recall some
black paints or powders used in telescope design which boasted like
98% absorption or so. That would work nicely. They do make 250W
halogen lamps for indoor lighting fixtures, and of course the lamp
could be moved further from the glass and opened to more airflow as to
reduce the end temperature. But then the warmup time is increased.
Perhaps the best method may be one lamp on a movable track underneath
the glass. Put it close to get it the glass hot fast, then move it a
set distance away to keep that temperature. Again, "fast" is a
relative term (especially with uneven heating of glass!)

As for PID, the average weekend warrior might hop on over to
sci.electronics.design and ask about PID alternatives. It's not too
difficult anymore for someone adept in electronics to implement PID
using today's jellybean microcontrollers. The cheapest PID solution
for a non-electronics guru might be to have someone there build a
controller for them. The parts wouldn't be too expensive, but
programming/labor might put things back in the same ballpark (unless
someone has already made a PID controller for a similar use.) But
there are other solutions also. A simple (precision) linear
temperature regulator might work just as well. A one-off design could
probably be engineered, built, and shipped for under a hundred bucks,
but I assume someone will have already made something similar. And
like you said, a household dimmer (like a wall-mounted dimmer switch
or a router speed control) could also work, provided the lamp is okay
at reduced temperatures. If the wax needs to remain a precise
temperature though, a dimmer might give you fits. I suppose the
temperature would stabilize at some point, but it would be difficult
to "fine tune" it without a lot of fiddling. Perhaps with experience
this would become predictable and usable. Maybe try the "distance"
method first, then if that doesn't work try the dimmer method, and if
that doesn't work, upgrade to a linear or PID controller?

Regards,
Mark

high voltage halogen? shop floods and torchere lights both use 120v, and use
virtually identical bulbs. you can dim them a bit, but too much burns them
out pretty quickly.

somewhere i saw a link to someone who used one of them in a small refractory
lined box to make a kiln which was capable of melting glass.

regards
charlie
cave creek, az

"Mike Firth" wrote in message
...
Actually, high voltage halogen, like shop lights, don't have the problems
with dimmers that low voltage decorating lights do and almost any dimmer
with sufficient rating (since many shop lights are 1000w and most dimmers
are 600w and shouldn't be used at full rating without cooling) will work.
However, 600 watts is still too much and a couple of hundred watts at
most will do the temp needed with a cheap household dimmer, not a $100-200
PID controller.

--
Mike Firth
Hot Glass Bits Furnace Working Website
http://users.ticnet.com/mikefirth/hotbit46.htm Latest notes

"Charles Spitzer" wrote in message
...

"Mark Jones" wrote in message
...
Mike Firth wrote:
"600 Watt halogen shop light a foot below"
will produce several hundred degrees at this distance from a black
surface.
we are only talking about needing 150F folks.


600W is only applied initially to decrease the warmup time.
Electronic PID algorithm modulates the light intensity to any preset
value.

halogen lights don't like to be switched on/off a lot, and they don't
like dimmers on them either. both lead to premature aging of the bulb and
quick burnout.



-- "Perhaps it isn't that people are intentionally redefining
standards, just that our logic is changing faster than our
technology." Mark Jones / Helios Studios 20050109

MR11 and MR16 lamps are small halogen floods that run of 12 volts and are
widely used for decorative and specialty lighting. Under counter
lightstrips that have two, three or four hockey puck shaped lights come in
two version, one of which takes 120 volt bulbs the other takes 12 volt
bulbs. All the the 12 volt require a special dimmer to deal with the power
supply, commonly a small switching power supply these days.
Quartz-Halogen and metal-halide bulbs remain bright by a complex chemical
reaction that takes the metal boiled off the filament that would normally
condense on the "glass" tube and reunites it with the filament at the
hottest spots, which are the thinnest and most likely to break. The glass
tube is quartz to stand the heat.
Dimming them is possible-most theater lighting is now halogen-although I
would not be surprised to hear that life is shortened.

--
Mike Firth
Hot Glass Bits Furnace Working Website
http://users.ticnet.com/mikefirth/hotbit46.htm Latest notes

"Charles Spitzer" wrote in message
...
high voltage halogen? shop floods and torchere lights both use 120v, and
use virtually identical bulbs. you can dim them a bit, but too much burns
them out pretty quickly.

somewhere i saw a link to someone who used one of them in a small
refractory lined box to make a kiln which was capable of melting glass.

regards
charlie
cave creek, az

"Mike Firth" wrote in message
...
Actually, high voltage halogen, like shop lights, don't have the problems
with dimmers that low voltage decorating lights do and almost any dimmer
with sufficient rating (since many shop lights are 1000w and most dimmers
are 600w and shouldn't be used at full rating without cooling) will work.
However, 600 watts is still too much and a couple of hundred watts at
most will do the temp needed with a cheap household dimmer, not a
$100-200 PID controller.

--
Mike Firth
Hot Glass Bits Furnace Working Website
http://users.ticnet.com/mikefirth/hotbit46.htm Latest notes

"Charles Spitzer" wrote in message
...

"Mark Jones" wrote in message
...
Mike Firth wrote:
"600 Watt halogen shop light a foot below"
will produce several hundred degrees at this distance from a black
surface.
we are only talking about needing 150F folks.


600W is only applied initially to decrease the warmup time.
Electronic PID algorithm modulates the light intensity to any preset
value.

halogen lights don't like to be switched on/off a lot, and they don't
like dimmers on them either. both lead to premature aging of the bulb
and quick burnout.



-- "Perhaps it isn't that people are intentionally redefining
standards, just that our logic is changing faster than our
technology." Mark Jones / Helios Studios 20050109

I agree with this, and for that matter, I think he would get by just
fine with an ordinary 100-watt incandescent bulb. They get plenty hot,
and it only takes them a few minutes to heat up. If I were in charge of
this project, g, using the combined input of others here I would take
a wooden fruit crate and line it with tin foil. Then I would take a $6
clip-on utility light, remove the aluminum reflector, equip it with a
100-watt long-life bulb, and place it in the center of the box. I'd
simply lay the black-backed Pyrex sheet on top of this assembly, clamped
in place if need be. If needed, an inexpensive rheostat could be easily
added.

Mike Firth wrote:
Actually, high voltage halogen, like shop lights, don't have the problems
with dimmers that low voltage decorating lights do and almost any dimmer
with sufficient rating (since many shop lights are 1000w and most dimmers
are 600w and shouldn't be used at full rating without cooling) will work.
However, 600 watts is still too much and a couple of hundred watts at most
will do the temp needed with a cheap household dimmer, not a $100-200 PID
controller.


--
-Kalera
http://www.beadwife.com