Home Made Electric Glass Fusing Kiln

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About: I am an electronics engineer working in telecommunications in the UK. Generally I work on chip design for digital radio receivers. I like all things arty and consider chip design a bit arty :) Basically I...

Good evening anyone interested,

My name is Dave and I am from Bristol in the UK. Before Christmas I was out shopping in a market with my daughter Ava (8 yrs old) when she spotted some fused glass jewellery on a stand. Ava thought it was fantastic and immediately wanted to know if it was possible for her to make some. Obviously, I said yes without thinking as we make lots of interesting and arty stuff together. Once home I looked into the subject and realised we were going to need some type of Kiln to fuse the glass. I looked into the cost of a kiln and to be honest found the prices quite offensive so we (Ava & me) decided the way forward was to build a glass fusing kiln from scratch.

The first issue was an enclosure - luckily this was solved by my work. They were dumping a large aluminium radio test enclosure which seemed perfect. The enclosure already had an aluminium control box on the side and was generally very robust. The enclosure didn't have a lid but was otherwise good. I did some reading around and decided early on to heat the kiln from the top as this gives the glass a better gloss finish. So I knew from day one I was going to have to fabricate a top lid with integrated heating system. To fuse glass you need a sustained temperature of about 800C and aluminium melts at about 660C - so a small problem existed. The enclosure was going to have to be very well insulated and to achieve this I used a combination of ceramic fire brick, ceramic blanket and high temperature adhesive. To fuse glass you don't just turn on the heat full power and sit back. You have to increase the temperature slowly and more importantly reduce the temperature slowly to prevent thermal shock of the glass. To control this process I used an Altec PC 410 multi-program multi-step industrial temperature controller connected to a K-type thermocouple.

I hope you enjoy the series of videos and images I have included to describe my Kiln building project. Please if anyone has any questions or comments please feel free to get in touch and I will be more than happy to try and help.

Please remember if you attempt to build any type of kiln the resulting temperatures can be extremely dangerous and could result in serious injury. Not to mention the use of mains electricity in high current applications.

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Step 1: Initial Look at the Enclosure & Temperature Controller

I have link to a video here which show the enclosure before I started to line it with insulation and also a look at the Altec PC 410 industrial heating controller.
My initial though was to line the enclosure with large bricks. However, these subsequently became difficult and expensive to get hold of. I found a supplier of standard size ceramic insulation bricks in Bristol and the guy did me a great deal with all the bricks and high temperature adhesive coming to under £100 cash - bargain !

(All the bricks, fire blanket and adhesive obtained from Paul at Complete Fire Protection (CFP) Bristol)

Video of initial look at enclosure and temperature controller :

Step 2: Enclosure Now Lined With Brick & Fire Blanket ...

After getting my hands on the ceramic fire insulation brick and ceramic fire blanket I set about lining the lower half of the box. So the box is initially lines with the blanket and then subsequently lined with the brick.

In order to make as much space as possible I cut the bricks down from the stock depth of 75mm to 50mm. The bricks can be cut using a standard hand saw. Do this outside as they create a massive amount of dust while cutting and I am sure you don't want to be breathing the dust. I made a simple wooden jig (see video) to get all the brick a consistent depth.

The bricks and blanket are all secured in place using a high temperature adhesive.

Video of lines enclosure :

Step 3: Construction of the Control Box

This section again features a video showing the completed control box that will drive the heating element.

Essentially the control box consists of the Altec temperature controller driven with a K-type thermocouple. The Altec then drives a 40A solid state relay which switches power to the heating element.

I have not added too many words here because I think the video covers things :

Step 4: The Construction of the Enclosure Lid

One of the most challenging aspects of building the kiln was construction of the lid section. I decided early on I wanted the heating element in the lid as this apparently would produce the best finish for the glass.

I decided to make the lid insulation from an array of the same ceramic fire brick used to line the lower enclosure. In order to hold everything together I went to a local metal supplier and got them to make me four corner brackets plus to long and two short straight sections and also cut a thin stop plate. The brackets and straight section were all cut from 2mm mild steel and the top plate from 1mm mild steel. The corner brackets and straight sections I drilled and screwed together around the brick secured with self thread cutting screws. The resultant lid is very sturdy if not a little on the heavy side. I also fitted a handle to the front which luckily came attached to the original enclosure obtained from work.

Step 5: Choice of Heater and Mistakes Made

Ok, so now I had a fire brick lid all held together with mild steel and a handle - what I needed now was a heater. Having looked at commercial kilns I decided I needed a heater capable of delivering about 2.5KW of heat. Quite a few of kilns I had looked at used an inexpensive heating element which is essentially a coil of resistive wire which is rated at a give power at a given voltage. The element I initially chose was rated at 2.5KW at 220V AC (see the image attached).

I ordered the heater from China and it was <£5 .....

The heater looked good on arrival and I proceeded to chase out a channel in the fire brick lid with a Dremel and an abrasive tool. If you are going to chase out this ceramic brick DO NOT use a fluted metal cutting bit the brick although soft will blunt the cutting tool in about two minutes rendering useless - I found out the hard way. Use an abrasive grinding bit which works really well. The element was pinned into place using pins made from a slightly thicker version of the same resistive wire - so just about 2cm of wire with a short ninety degree bend at one end.

So I installed the element with feed wires through the lid to the top side. I plonked the lid onto the lower enclosure and connected it directly to the mains.

Sure enough the element heated up to a cherry red hot and the temperature measured by the thermocouple started to rise.

OK - two major problems became apparent :

1. No matter how much you pin the element in place it expands a great deal when it heats up. The element then sags as large hanging loops under the force of gravity. In my case the loops were hanging down some 15cm into the lower enclosure and even when the power is removed and the heater cools the heater only contracts slightly leaving the loops to flap about - it just didn't feel right to me and I wasn't happy with the heater solution.

2. The heater caused the chamber to climb rapidly in temperature until it reached about 300C where the rate of increase slowed. By about 550C the temperature was rising painfully slowly at maybe 1C/minute and was clearly not going to reach 800C in any sort of reasonable time. At this point I had taken delivery of a mains power meter. Attaching the power meter showed my heating element was actually only delivering about 1.2KW and NOT the specified 2.5KW as the supplier had stated ! I think the supplier was just selling 'an' element as various powers hoping that someone didn't check - well I did, complained and got a full refund :)

So the bottom line was I decided to ditch the first heating element and rethink the entire heating problem.

Step 6: Final Choice of Heater and Lid Construction

After ditching the first heating element I set about looking for another solution. After lots of research and surfing I picked up another bargain but this time it was a winner !

I found a supplier selling 400W 240V bar style heating elements. These still use a coil of resistive wire but contained within a high temperature glass tube and capped off with ceramic end caps with screw bolt style terminals. I picked up ten elements brand new and boxed for £13 (the lot) delivered from the UK - happy days ! After the low power issue with the first element the first thing I did was pop one of the new elements on the power meter and was happy to get a reading of ~426W.

The plan was to stack eight elements in parallel to give a total power of ~3.2KW

I used two sections of 25mm steel angle iron to support the eight elements. Steel is not a very good conductor of electricity and even worse when hot. So I faced the steel angle with 10mm strips of copper plate to act as bus bars to conduct power efficiently to the heating elements. Each bus bar is then connected up through the lid using 2.5mm copper wire terminated with a ceramic connector block.

To fuse glass you need a temperature of about 800C and copper melts at 1085C. So I figured even if the top of the enclosure was 100-150C hotter than the temperature probe as long as I didn't go any hotter than about 850C the copper would be fine - this has proved to be the case with no issues to report.

Step 7: Finished Kiln and Some Temperature Data

Without adding too many words here is a short video showing the finished Kiln :

The lid is now attached with rear hinges and the heater has been fitted. The underside of the lid has been lined with more ceramic fire blanket mainly to stop metal oxide from falling into the glass chamber during heating.

The Altec temperature controller has an automatic tuning mode which learns the characteristics of the chamber and then automatically updates the control loop PIC parameters. This worked extremely well and after calibration the temperature matches the set point to within +/-1C and even when the sequence is put into hold mode the temperature only overshoots by 1C for about ten seconds - very impressive I thought.

Step 8: Temperature Results From the Kiln

One of the first things I did was to run the kiln at full power and record the temperature at one minute intervals up to 820C and then kill the power and measure the natural fall in temperature again at one minute intervals.

I then plotted the results - this data allows me to work out the maximum rate of heating / cooling at any point on the firing sequence to subsequently optimise the design of the glass firing sequence programmed into the Altec PID controller.

Step 9: First Result From the Kiln .....

Here is the first result from the kiln .....

The pendant on the left came from the microwave kiln I had been using and the pendant on the right from the new traditional kiln which has been the subject of this article.

The right hand pendant show much better shape, colour and no trapped air bubbles :)

Step 10: Conclusion .....

I have had a lot of fun building this kiln and have learned many new skills.

I realise that there is not a huge amount of construction detail in this article so if anyone has got this far and wants to know more about any aspect of the project please feel free to contact me.

One piece of advice I will give ....... when a top loading kiln is at 820C DON'T lift the lid and shove your head in to have a look at the work inside - bad idea, just a thought !

5 People Made This Project!

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91 Discussions

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krumly

Question 5 months ago

Dave -

Nice kiln. I've built both a fiber, propane-fired forge and crucible furnace. I would like to build a fiber electric furnace for investment burnout and heat treating. The heat treating part of the deal requires precise PID temp control up to 1315C/2400F. I was thinking of quartz halogen short-wave IR tubes because of their high heat output and quick cycling, but am concerned about them in such a hot furnace environment. Of biggest concern might be how to protect the connection ends from burning up.

Do you happen to know the max temp the elements you used in your kiln are rated for? Funny how those elements are so easy to source inexpensively on Ebay in the UK, but not in the US.

Chris Krumm

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dtrewrenkrumly

Answer 5 months ago

Hello Chris,
Yes, this was the part I most scratched my head over. Many of the elements come fitted with cables which are not going to take the heat. My kiln was for glass and so only needed to hit around 850C mark and so I could use copper as a wire conductor. My solution was to encase the heater element end connections in fire wool - this is also the solution many commercial glass fusing units seem to adopt. The heaters I used had stainless screw terminals in ceramic end caps and so can handle the high temperature. Some elements have a spring loaded terminal but I didn't think that would be up to the job. I am not sure exactly what the temperature rating of the elements is but after many firings I have had no failures.

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progcont

5 months ago

Hi
I am also a fuser and glass distorter in that I change shapes of existing glass. However I was interested in where you got hold of the heating elements was that UK or china perhaps if you can remember you could let me know an e mail address Thanks and great project.
Mike Hare

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dtrewrenprogcont

Reply 5 months ago

Hello Mike,
Unfortunately, I don't have the exact source of the elements I used as I bought them as a one off job lot from eBay. However, there are lots of similar elements on eBay. I went for 400W elements so that I could reach about 4kW of power and have enough individual elements to spread the heat output. I also went for an element with a bolt type terminal at each end as I was planning on mounting the elements into a bus bar. If you do a search on "Quartz heating elements" you will find loads of options to suit your design.

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RoaldR1

7 months ago

Hi Dave.
I have a Hobbyceram kiln that needs a controller.
Is it possible to attach the PC410 controller to this one?
Regard Roald

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dtrewrenRoaldR1

Reply 7 months ago

Hello Roald,
Absolutely, there should be no problem coupling the PC410 to your kiln. The PC410 will need a K-type thermocouple (there may already be one fitted to the kiln). You will also need a way for the PC410 to switch the heater - if you look at my Instructable you can see I used a solid state relay which will be more than adequate. Once you have everything hooked up you need to put the PC410 into it's self calibration mode whereby it will take the kiln temperature up to a preset point (I chose 400C) and then it will heat and cool the kiln about this temperature a few times. Once self calibration is complete you are done and can start using the kiln with firing programs.
Fire away if you have further questions.

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GrahamA45

Question 10 months ago

Hello Dave. I live in country Australia, about 500km from the nearest main population centre.

I became interested in glass a couple of years ago and, like you, found the cost of kilns

formidable - A$ 3,000 or so for what seemed right for me - so decided in a self-build, which has topped out at around $700.

Although there are a lot of examples on the internet, your clearly explained project was my main inspiration, which has prompted me to request your help in programming the PC410 controller.
As a layperson I find the operating manual almost incomprehensible and what I can find on the internet, including YouTube, almost as bad.

What I need is a detailed, basic language, step-by-step explantion of what buttons to push in what sequence to enter a simple fusing/slumping program - e.g.

(Celsius) 1. 150 per hour to 620 - hold 40 mins: 2. 150 p/h to 675 - hold 40 mins: 3. Fast to 860 - hold 12 mins: 4. Fast to 515 - hold 40 mins: 5. 65 p/h to 370 - hold 2 mins: 6. Off :

7. Save program.

Once I have that under control I imagine I can program pretty well whatever I can dream up.



Out of interest my device is a “clamshell” design, as I am no longer young and placing delicate arrangements down into a confined space does not apeal. Internal measurements
are 350 x 350 x 200mm. Externals 495 x 495 x 300mm. Insulation is 50mm Morgan Ceramics rigid Superwool (highly efficient and FBS1- probably safest available). Protective sheathing is 20mm Plaster of Paris mixed with 300%
by volume Perlite and reinforced with small guage chicken-wire. Framing 2 x 25 x 30mm steel angle. Element is (about) 2600W of Kanthal wire wound onto old quartz heater bars. Havent run flat out because dont know how to set
controller, but reached 400C in 6 minutes and am hoping will be adequate.

If you can help with my request I will be extremely gratefull. If not, hopefully someone else will pick up on it, otherwise I’ll have to wait untill next trip to the city and keep
fingers crossed.

Regards, Graham.

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dtrewrenGrahamA45

Answer 10 months ago

Hello Graham,


Sorry for
the delay, had some time today to look at the controller programming. Hopefully
this format will be ok – written in Word and posted into Instructables.


First thing
to say is that the format of the menu system for the PC410 may not be in line
with the manual. My PC410 controller has custom firmware for BGA work and so
only some of the menu items are present and some are pre-set.

The sequence of events I use is as follows:

  • -Basic parameter setup
  • -Auto-tuning sequence
  • -Firing sequences

Basic Parameter setup.

The operational parameter list is accessed by pressing and holding the PAR/SET key for three seconds. For my controller the first parameter that appears is PROG. My controller displays the following list. Each parameter is accessed by a subsequent press of the PAR/SET key (manual section 7.5).

PROG
TUNE (off)
PROP (PID controller proportional component)
Int.t (Integral Time)
dEr.t (Derivative Time)
H c.t (Heat cycle Time)
Loc (Config password 808)
SPH (Setpoint High limit, I set to 1000)
SPL (Setpoint Low limit, I set to 0)
H PL (Max output power, set to 100.0)
Snbp (0)
OfSt (0)
CF (Centigrade / Fahrenheit – I set to C)
Addr (Default)
bAud (default)

Set those in bold

My controller is pre-set for a K-type thermocouple and can’t be changed – yours maybe different. So look for a parameter in the list called “Sn” – see software configuration section 8 of the manual. I assume you also are using a K-type thermocouple and so need to set this parameter to “CAtc” if available.

The parameters listed above SPH and SPL are important to set up as you can only use a set point temperature between these two limits.

Auto-tuning sequence
The controller uses a PID algorithm to achieve stable temperature. A PID is notoriously tricky to configure but fortunately the PC410 has an automatic tuning algorithm which makes setting the control loop really simple.

I used the following steps:

  • -Set the SPH and SPL as described above
  • -Use the up and down arrow buttons to configure a sensible mid-temperature set point, I chose a value of 400. The general full fuse temperature for glass is about 800C so 400 sits in the middle.
  • -Press and hold the PAR/SET key to enter the config menu. Press PAR/SET until you see “tunE”. Use the up down arrow key to select ON. The controller will now start auto-tuning and you will notice the heater switch on full power. Temperature will climb at full rate until 400C is reached. The controller will overshoot a few degrees and the heater will switch off. The temperature will fall to under 400 and the heater will switch back on. Again the temperature will exceed 400 and then fall below. All the time the set-point on the display will alternate between the temperature and the “tune” indicator. Once this cycle has completed the heater will switch off and “tune” is no longer displayed – that’s it tuning complete. The controller has now learned the thermal characteristics of your kiln and automatically configured the PID control loop.

Firing sequences
The PC410 can store ten, eight stage firing sequences (I think). Each sequence consists of multiple sets of three parameters:

  • -Ramp in degrees per minute / second
  • -Target setpoint in degrees
  • -Dwell time in minutes (mine is in seconds)
See manual section 12.2
So for your sequence you would program the following:

  • -Select the program you want to store using the PTN key, I start with zero.
  • -Press the SET/PROG key and you will see the first parameter r1 or ramp rate one. This parameter is little confusing as it is configured as (degrees/minute degrees/second). You need 150 degrees/hour which is 150/3600 ~ 0.04 degrees second. This is an approximation and will give you 0.04 x 3600 = 144 degrees per hour but it is not that important. So r1 is set to 0.04
  • -Press PAR/SET to see the next parameter Target Setpoint L1 in your case set to 620
  • -Press PAR/SET again to get Dwell time d1 in your case set to 40x60 = 2400. My controller sets the Dwell in seconds not minutes as shown in the manual, yours maybe be different.
Your remaining parameters are, using PAR/SET to select:

  • -r2 150/3600 ~ 0.04 degrees/second
  • -L2 675
  • -d2 40x60 = 2400 (assuming seconds)
  • -r3 STEP (reduce rate to zero and one more down arrow click) STEP tells the controller to achieve the next set point as fast as possible with no ramp.
  • -L3 860
  • -d3 12x60 = 720 (assuming seconds)
  • -r4 STEP (as fast as possible)
  • -L4 515
  • -d4 40x60 = 2400 (assuming seconds)
  • -r5 65/3600 ~ 0.02 degrees/second
  • -L5 370
  • -d5 2x60 = 120 (assuming seconds)
  • -r6 End (reduce rate to zero and then two more down arrow clicks)

To start a firing sequence just select the sequence number using PTN key and then press RUN/PROG. The display will tell you the current temperature, set point and program step.

The most important part is to get your controller tuned otherwise everything else won’t make much sense.

I hope this helps, if you have questions please fire away and I can refine the detail if confusing.

Cheers,

Dave
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GrahamA45dtrewren

Reply 9 months ago

Thank you Dave,
I now realise that I couldn't see the forest because of all the trees. From your detailed and simple directions on setting and programming the controller I now appreciate how amazingly capable the device actually is, and is and how few of its capabilities I really need to access. The manufacturers marketing people could do worse than employing you to write an "Idiots Guide".
I've now successfully entered and run several programs and thrown out my tranquillisers.
My kiln well, uses little "juice" and seems to distribute heat nice and evenly. The design allows excellent access for positioning materials, element wound around recycled quartz rods function well as heat source and "Superwool" insulation and perlite/plaster cladding panels hold heat well - internal temps 830C, external temp 110C. Only downside is the "clamshell" doesn't allow rapid dumping of heat, which means extended cooling and annealing times or propping it open and risking stress fractures .
All up, a project I'm proud of and which now works, thanks to your help.
Graham.l

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dtrewrenGrahamA45

Reply 9 months ago

Hi Graham,
That is great news, very pleased you git everything working. If you have any other questions please fire away (excuse the pun),

Cheers,
Dave

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dtrewrenGrahamA45

Answer 10 months ago

Hello Graham,

Good to hear from you and great build- your kiln looks the business.
No problem with help on the controller, I will remind myself how to program the PC 410 and get back to you this week. The first thing you need to do is set the PC 410 to characterise your kiln's thermal properties. There is a special test mode you can initiate whereby the controller automatically increases/decreases the kiln temperature in order to "learn" your kiln's unique thermal profile. Once this has been completed the controller should be able to hold your kiln at a particular temperature to within a degree (it is very stable and accurate).

I will be aback soon.
Cheers,
Dave

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GrahamA45dtrewren

Reply 10 months ago

Thanks Dave,
You’re going to be a lifesaver (maybe that should be sanity-saver). I suppose that with your technical background this sort of stuff is as simple as breathing.
I like to think that although only basically educated I’m reasonably smart, but this issue has put strain on that evaluation
I hope you have a pleasant and rewarding Christmas break.
Graham

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sfonts

Question 9 months ago on Step 6

Hello,

Where did you buy those "quartz heating elements"?

Best regards,
s. fonts

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dtrewrensfonts

Answer 9 months ago

Hi there,
I picked up a job lot of the elements from eBay for about £5 each. There are lots of similar types of element available like:
https://www.ebay.co.uk/itm/AC-220V-400W-Quartz-Hea...

Depends of the dimensions of your kiln and lid design - I designed my lid around the elements I managed to find.

Best regards,
Dave

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Lesle5

Question 1 year ago on Introduction

Hi Dave, great kiln you have made for your daughter.

I have been Glass fusing for about 10 years now using an old ceramic kiln with a glass controller fitted. We have now made our own kiln using a stainless steel case we had made by a friend and my son an electrician has fitted elements to the lid, supplied by midland elements and lined the kiln with superwool fibre board 50mm thick, we are using the sentry express controller from the old kiln.

it’s only been put in situ today but not commissioned yet.and we are a bit concerned about the weight of the lid. We plan on fitting heavy duty gas struts but although a lot of commercial kilns have gas struts fitted we are a bit concerned, that the heat might make the lid lift. Do you know if they use different gas struts on commercial kilns ?

Thanks

Lesley

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Lesle5Lesle5

Answer 1 year ago

Thank you Dave
We have the kiln running now it was a bit scary on the first fire with the binders burning off,black smoke and soot but its gone now after a couple of test fires
It seems to be getting pretty hot outside though we clamped the lid tight last night and it still got hot
Waiting to fit some latches to hold the lid down and get a tighter close,maybe that will help
Thanks for the reply I’ll see how hot it gets once it’s closed tight
Lesley

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dtrewrenLesle5

Answer 1 year ago

Hello Lesley,

Sorry for the delay, I was on holiday.

I think standard gas struts would be fine. The outside temperature of my kiln to the sides is only about 70C and even on the top only hits about 120C. I doubt there are
special struts used on kilns for home use.

Let me know how you get on.

Cheers,

Dave

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gaberenz

Question 1 year ago on Step 3

Hi Dave, awesome inscrutable! Im going to attempt to upgrade my small gas kiln in a couple weeks, and I had a question about the voltage. If im running this off a 120v, 15A outlet instead, which internal pieces would I need to change in order to run it without electrical issues. My element will be different, and requires 12A... is the initial breaker switch the only thing that has to change? Any advice is much appreciated.

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dtrewrengaberenz

Answer 1 year ago

Hello,

If you are running from a 120v outlet rated at 15A you will only be able to a total power of approximately (120 x 15) = 1800w. If you want to support more power than this you will need multiple power outlets. The internal breaker I used was rated at 20A. This was to protect against a malfunction or short circuit. The current 20A breaker should be ok for your 15A outlet. I think the main issue is whether you have enough available power to generate the heating required. How big is your kiln going to be ?

Regards,

Dave

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dtrewren

1 year ago

Hello jlcurve,

Nice work !

I was planning on writing a C# GUI to control the Altec but never got around to it. I generally found that once I had my favourite firing profiles set up I didn't really change anything. However, having the temperature curve per firing would have been nice. I will take a look at your interface.

Maybe you should do a quite Instructable ?

Cheers,

Dave