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  1. #1
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    20$ kiln. Can it do the trick?

    I recently purchased a kiln from a yard sale. Plugged it in it works. It's old tho, and the thermometer is broken and none digital.
    My questions are: if I get a new thermcouple or switch to a digital control will this work, is it worth it? If it needs a digital control, what is involved?
    I can post pics if that will help with ideas

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    Re: 20$ kiln. Can it do the trick?

    Pics would probably be a good idea.

    Without knowing you or your background it's difficult to advise what to do, but for most folk with reasonable technical ability, it should certainly be possible to bypass any existing controls and make up a control box that will digitally control the temperature of your oven.

    If you put a power socket on the control box instead of hard-wiring it to the oven, it can be used for temperature control of other stuff too.

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    Re: 20$ kiln. Can it do the trick?

    Pics

    [IMG][/IMG]






  4. #4
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    Re: 20$ kiln. Can it do the trick?

    Think for o1 and high carbon steel I need anything more complicated? I've made my own knives from o1, files and spring steel in a BBQ "forge". I just figure this would give me more certainty of the finished steel than going non magnetic. I'm a plumber by trade so I am technically capable enough to get a toilet work.
    Last edited by EPM; 06-05-17 at 09:57 PM.

  5. #5
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    Re: 20$ kiln. Can it do the trick?

    Give it a try.
    Looks like it should be OK.

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    Re: 20$ kiln. Can it do the trick?

    It looks like the knob on the left is a variable power knob.

    If so, it's a case of using it to set the power and reading off the temperature: it's effectively manual control and it'll take a long time to settle at temperature.

    Do you know whether it's just the thermocouple that's goosed, just the gauge, or potentially both?

    I assume you've plugged it in, powered it up and checked it gets hot, albeit you don't know how hot?

    I'd be inclined to get a new thermocouple, along with a connector block, some thermocouple cable and a miniature plug, plus a hand-held pyrometer, and run it as originally intended to start with. If you then decide you want to run with PID control (which will give full-power during the heat-up and eliminate all the faffing about trying to adjust the temperature), you can add it.

    As you are way out beyond the Western edge of civilization, it's not easy to come up with appropriate sources, but rogersdini on ebay are in Ontario and look like they'll have everything you'll need.

    http://www.ebay.co.uk/itm/K-Thermoco...zc1zW9RmFd-1Gg

    I have been using DM6801A pyrometers lately*

    http://www.ebay.co.uk/itm/Portable-D...EAAOSwnHZYZwIu

    Once you have the temperature measurement, you probably need to start playing. Switch on and turn the power dial to maximum. Take temperature and time readings as it heats. Initially, the temperature will rise fast and you may need to take readings every few seconds. As the temperature increases, the rate-of-rise will reduce and, one-minute or even five-minute intervals might be appropriate as it approaches the top end of the working range. Once it's just a little hotter than you'll ever want to run it, start making adjustments to the power knob until it's stable at the temperature you want. This is very unlikely to be a quick job.

    Once it's stable at the desired temperature, do whatever you'd do to safely load a workpiece (probably power off at the wall unless there's a door interlock) and stick in a suitably-knife-sized piece of scrap steel. Power up the oven, take one-minute readings and see how long it takes to return to temperature. Do not touch the knob at any point during this.

    Once you are happy you have all the timings, leave the control knob alone and power off at the wall. Leave it to cool overnight.

    Still without touching the control knob, power up and note the times/temperatures as it heats up. It will be slower this time because it is on the power setting you found appropriate for holding temperature, rather than full power. Note the temperature it settles at and compare it to the temperature on the previous run.

    You will then have the information needed to decide whether it does what you need, whether it can be made to do what you need, or whether it's of no use to you.

    If the repeatability is good enough and you can live with the heating time, great.

    If either the temperature is not repeatable enough or the heating time with less-than-full power is longer than you can live with (but it's acceptable on full power), and there is nothing else obviously wrong, upgrading to PID control should give you something you can live with.

    If it won't get hot enough within a reasonable timescale on full power, then it's not for you.



    *I had been using TM902C pyrometers, also from ebay, until recently. I had bought perhaps 20 TM902Cs over maybe 5 years and they had all been great: I have access to a calibrator at work and they were as accurate as any of the big-name instruments costing over ten times the price from 0 to 1370 degC, even the ones that said 800 degC on the front. Then I bought ten TM902Cs in late 2015, put them on the calibrator and found they were fine to around 800 degC but then started showing an error that increased with increasing temperature. I can't remember whether they read high or low, but they were all pretty consistent and the discrepancy was 80 degC at 1370 degC (either reading 1290 at 1370 degC or reading 1370 at 1290 degC, but I can't remember which).

    The "bad" TM902Cs look slightly different to the "good" ones when placed side-by-side, but the differences are not obvious enough to show in the photos on an ebay listing. I also don't know whether I just got a bad batch or whether there has been a manufacturing change and they are all "bad" now.

    I stopped recommending the TM902C after that. It's a shame because the TM902Cs come with a glass-fibre-insulated thermocouple that's good to about 400 degC and flexible enough to shut in an oven door for checking tempering temperatures. The DM6801A comes with a PVC-insulated thermocouple that's probably only good to a little above the boiling point of water.

  7. #7
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    Re: 20$ kiln. Can it do the trick?

    Thanks for the thorough step by step guide. That makes sense to me. The kiln does turn on and heat up. I will order the new thermocouple then and find a way to test the heat/ time efficiency. I wasn't sure how to test viability. Thank you Timgunn

 

 

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