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Homemade precision wax iron

post #1 of 18
Thread Starter 

When I started waxing my own skis last year, I was too cheap to buy a proper wax iron, so I dug up my mom's 1950's vintage GE non-steam, solid baseplate clothing iron and used that.  It worked....well, sort of.  The mechanical thermostat has a wide "dead-band", making the temperature cycle up and down over a 20 deg C range.  I set it so that, at its hottest, it just melted the wax, but then at its coolest, it didn't melt properly, making it a pain to use.  I was afraid to set it hotter for fear of damaging the bases.

 

The other day I was rummaging around in my basement and came across that old iron, and I thought this year I'd better buy a proper one.  Then the proverbial "light bulb" came on....  Why toss out my poor derelict GE iron?  Why not bring it out of the dark ages and into the computer age?!!

 

Out of my years of accumulated gizmos, I dug up a thermocouple and a PID process controller (that's short for proportional-integral-differential, in case there are any other engineering geeks out there :-)  I opened up the iron, removed the original mechanical thermostat, and installed the thermocouple so that it could feel the temperature of the baseplate from inside.  Here is the result:

 

 

On the right is the original power cord, and on the left, poking out through the hole left by removing a light bulb that used to be there, is the lead from the thermocouple.

 

Then I assembled the process controller and its associated power relay and an outlet box so that it would use the signal from the thermocouple to control the iron.

 

 

I didn't have an enclosure handy, so I just attached everything to a piece of wood for now.

 

Now for the test....does it work?  Well, in a word, yes!  In fact, it works incredibly well.  Here is a picture of the iron holding a temperature of exactly 100 deg C with less than +/- 0.5 deg C variation.  The green numbers on the controller are the thermocouple temperature and the orange numbers are the setpoint.  The thermometer I put on the sole of the iron confirms the temperature read by the thermocouple.

 

 

That sure beats +/- 10 deg C with the mechanical thermostat.

 

Of course, the real test will be to see how it performs when waxing skis.  That's coming soon, I just have to clean up the mess in my basement so I have room to work :-)

 

Cheers,

    Robert

post #2 of 18

All you really need to do is just pay a little attention to the wax and any iron will do.  If it's smoking it's too damn hot.  If it isn't melting it's too damn cold.  I used a $12.00 KMart iron from about 1980 until two years ago.  It even had the steam holes on it. Made no difference in the functionality and wax still ended up smooth and even enough.   About 10 years ago the knob that sticks out to slide up and down broke off in my boot bag so I had to stick something in that slot to turn it on or adjust the temps.  Two years ago Vistman sent me a Swix iron.  I do like it better, but it isn't at all necessary.  It does work much better for ironing patches on my kid's Cub Scout uniform though..biggrin.gif  I still have that old KMart iron stashed in a pile of stuff somewhere.

post #3 of 18
Quote:
Originally Posted by renenkel View Post

 

Out of my years of accumulated gizmos, I dug up a thermocouple and a PID process controller

 

 

 

Truly deserving of the word "awesome".   icon14.gificon14.gif

post #4 of 18

renenkel,

 

That's awesome.  I love reusing things.  My kids call  the basement "The Laboratory" because I'm always Frankensteining things back to life.  On top of that, you have great accuracy.

 

Ken

post #5 of 18

Trying to imagine a load that would throw that thing off - I don't think he'll get much oscillation, even with high heat capacity waxes.  

 

And the baseplate itself will low-pass filter temp noise  so sprinkling water on the baseplate  or a bad contact in the heater coil shouldn't cause any untoward behavior from the differential term.

post #6 of 18

ahhh, a true story of either a geek, an environmentalist (for recycling) or just sad ....

 

I'll presume your keeping fine toys around for possible use in the future a sign of environmentalism .... I'd venture to guess it's more accurate than most irons on the market.  Very nice

post #7 of 18

That's pretty cool. 

Why are you using a proportional controller with a relay?  It seems like you could just stuff an arduino and a relay inside the iron. 

That might be my next project.

 

BK

post #8 of 18
Thread Starter 

P.S.  I imagine this one (Swix T71 WC iron) http://www.swixsport.com/eway/default.aspx?pid=278&trg=MainPage_6117&MainContent_6179=6117:0:24,2743&MainPage_6117=6138:68591::0:6118:2:::0:0 has a similar kind of controller inside, and it claims 1 deg C deviation.  It's rather more expensive than my homebrew version, ranging from $350 online to $600 in local shops.  On the other hand, I'm sure it's a lot more robust and convenient, not being attached via umbilical cord to a bunch of Rube Goldberg apparatus.  But for the price of mine ($0.00 for mom's iron and garbage-picked electronics), I think I can learn to live with it smile.gif
 

post #9 of 18
Thread Starter 
Quote:
Originally Posted by Bode Klammer View Post

That's pretty cool. 

Why are you using a proportional controller with a relay?  It seems like you could just stuff an arduino and a relay inside the iron. 

That might be my next project.

 

BK


Thanks.  I just used what I had lying around.  (It's actually a solid-state relay.  The controller sort of pulse-width modulates it to get the proportional effect.)

 

That would be cool if you could put everything inside.  Heat might be a problem though.  You'd have to insulate the electronics well somehow.  Do post pictures if you build it!

 

Robert

post #10 of 18
Thread Starter 
Quote:
Originally Posted by renenkel View PostOut of my years of accumulated gizmos, I dug up a thermocouple and a PID process controller
Originally Posted by cantunamunch View PostTruly deserving of the word "awesome".   icon14.gificon14.gif

 

Thanks smile.gif  Most of the stuff I've accumulated came out of the university dumpsters when I was a grad student.  Amazing how much good stuff gets thrown out.

post #11 of 18
You ought to post this on the hack a day website.
post #12 of 18

another good one

post #13 of 18

Does the PID allow you to supply current incrementally, rather than on/off?

Hats off!  Great project.

post #14 of 18
Thread Starter 
Quote:
Originally Posted by incognito View PostDoes the PID allow you to supply current incrementally, rather than on/off?

Hats off!  Great project.

Thanks!  I think this controller does have a continuous output available, but you'd need an appropriate power device to make use if it.  The output I'm using is pulse-width modulated, so it cycles on/off at a fast rate, with the on/off time ratio controlling the heat.  This works with the solid state relay I'm using, and for a heating load, I'd think the effect is pretty close to what an actual continuous control of the voltage would accomplish.

post #15 of 18
Thread Starter 
Quote:
Originally Posted by cantunamunch View PostTrying to imagine a load that would throw that thing off - I don't think he'll get much oscillation, even with high heat capacity waxes.  

And the baseplate itself will low-pass filter temp noise  so sprinkling water on the baseplate  or a bad contact in the heater coil shouldn't cause any untoward behavior from the differential term.

 

I finally got around to actually waxing some skis with the iron.  The temperature doesn't stay nearly as steady when you actually apply the iron to the ski and start waxing.  Surprisingly, the temperature doesn't drop, but actually increases to about 10 deg C over the setpoint, and then it drops back down and stays steady at the setpoint. Sounds like the "untoward behaviour" cantunamunch proposed.  The controller does have parameters that can be set to tune the behaviour.  When I get a chance, I'll try playing with those and see if I can improve things.  For example, I could try turning off or reducing the I (integral) and D (differential) components of the response, and relying more on the P (proportional) one.  That'll probably cause slightly more fluctuation with a steady load, but might reduce the overshoot when applying the iron to the ski.

 

Another idea is adding a thick aluminum plate to the base of the iron to provide more thermal inertia.

post #16 of 18
Quote:
Originally Posted by renenkel View Post

 

Another idea is adding a thick aluminum plate to the base of the iron to provide more thermal inertia.

 

 

The more higher end irons have very thick plates.  Let us know how it goes.

post #17 of 18

Keep the P as is, definitely reduce the I (integral) component, keep the differential one as-is for now, maybe with a slight increase later.    

 

Leave the iron base alone, it's already quite thick enough on those old irons.     A thicker base  can only introduce more droop at this point.

post #18 of 18
Quote:
Originally Posted by renenkel View Post

Thanks!  I think this controller does have a continuous output available, but you'd need an appropriate power device to make use if it.  The output I'm using is pulse-width modulated, so it cycles on/off at a fast rate, with the on/off time ratio controlling the heat.  This works with the solid state relay I'm using, and for a heating load, I'd think the effect is pretty close to what an actual continuous control of the voltage would accomplish.

Way cool.  I have the Toko T14, and I don't think I have any advantage over your home project.  And you have way more bragging rights beercheer.gif

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