Calibrating the Covering Iron

[jiott]

The Polyfiber Covering book tells you how to calibrate your iron using a 1/2" thick stack of paper towels, a thermometer and heat conductive grease. I did this and marked the dial on my iron, but later decided this method was too slow and cumbersome to periodically check the calibration. The thermometer is slow reacting and only gives you an average of the iron temp as it cycles on and off with the thermostat. So I went and bought one of those infrared instant read temp guns from Radio Shack which is much quicker and easier to use (and I suspect more accurate). Polyfiber states this is also an acceptable method in their book.

I discovered something I am curious about and wonder how others deal with this: The temp gun reads instantly and shows you the full temperature range as the iron temp control cycles. When I set the iron to the 350 degree calibration mark I had made with the old fashioned thermometer & paper towels I was blown away by what showed on the gun-it cycled from a low of about 285 to a high of 405 degrees. Now Polyfiber tells you that anything over about 375 is dangerous and will actually start to relax the fabric tension and damage the fibers. This high end really spooked me and also the low end where I would not be getting near enough heat for proper tension.

Maybe my iron is too cheap and a better quality one would hold a tighter temperature cycle range. Anyway, I have been using this iron but I watch the little light on the iron that tells you when it is cycling on and off and I only apply it to the fabric after it has been on for about 8 seconds and then remove it after another 5 seconds, to try and avoid the two temperature extremes. If I had never got the temp gun and stayed with the thermometer calibration method I would never have known about these extremes!

Am I being too anal about this? What have the rest of you been doing? Maybe if you move the iron around on the fabric slow enough and cover the area several times the low end is not a problem. Also maybe the high end is not a problem because it only lasts for a few seconds and that is not enough time to transfer that much heat to the fabric.

Jim

[t j]

When I calibrated my iron I used the candy thermometer and let the iron set on the paper towel stack through several on/off cycles to capture the maximum temp it was reaching.

I found that on my iron there was a little slop in the temperature control dial. I had to turn the dial in the same direction to the temperature mark that I had turned it when that mark was determined during calibration. That is, I always turned the dial up to calibrate a mark and then when using it I always turned the dial up to the temperature mark, never down to that mark from a higher temperature. Did that make sense?

[Jerrytex]

I tried the laser thermometer. It gave readings as you mentioned, all over the place. I think it's due to the reflective silver bottom of the iron. I had good luck using a thermo couple like the one attached in the link. I would place the probe in a small stack of paper towels and I would constantly check the temp because I too was worried about over heating.

http://www.sears.com/shc/s/p_10153_1...&blockType=G11

I found one of these at sears for $19.00 clearance. The one I bought went to 500 degrees.

[Wiley]

You're not being too anal at all, in my opinion. We also ended up buying an infrared thermometer to calibrate our iron, and believe it was a great investment. It sped things up and provided peace of mind. We originally had two large irons which we planned to use to speed things up on the tightening, plus one small one for the tight areas. With one of our large irons not only did we find a wide range of temperatures as the unit cycled through, but also found hot spots on the iron, as well.

Some of the temps peaked well over what might damage the fabric when other areas were about the temperature we wanted, plus temperature peaks varied from one cycle to the next, and as you noted, with just a bulb thermometer we may not have known. Needless to say, we didn't use that iron. The other iron produced a fairly consistent temperature and we just spot checked it whenever we first turned it on, after it had been through a complete cycle. Multiple passes with a good iron will hopefully heat the fabric throughout the temperature range as it cycles and provide even tension. Thermal mass of the fabric is minimal so the heat transfer happens quickly.

As an aside, we found the little hobby iron to be the most accurate and generally kept the temperature within about 5-10 degrees of what we had set, while our large iron varied about 25 degrees when it cycled, topping out at the desired temp.

A shiny surface can throw off the readings with an IR thermometer. One of our large irons had a dark, teflon-type coating and posed no problem, and the hobby iron base was black. With the other iron we could get an accurate reading by putting a scrap piece of fabric on it and shooting the temp of the fabric with the iron in contact with it.

Once the fabric work was done, the IR thermometer was still useful for checking temps in the shop and paint booth prior to painting, or you can look for hot or cold spots in the house, calibrate your oven, check the HVAC for even heating/cooling...fun tool.

[jtpitkin06]

When I bought an iron for the shop I thought a cheap one would be fine as I certainly didn't need power steam, shot of mist, auto shut off, or other fancy functions. I just needed an iron. After checking el cheapo with the ACS thermometer I found the temps were wild variations up and down with a 50 degree swing. That would never work.

That's when I grabbed the one from the house and checked it. The fancy iron would hold temps within 10 degrees.

The one from the house was getting a bit tired in the steamer function, so it made its new home in the shop. I got a new fancy iron for the laundry room which really pleased my wife.

The $10 cheapo found its way back to the Wal-mart return desk.

Net Result... you might have to check a few irons to find one that will hold temps in a close range.

My hobby iron is a Century product. The electionic temp control is super accurate. I you don't have one of these, put it on your must have list for covering. The size and angle of the shoe makes it perfect for reaching around tubing and flanges. I think it is an essential covering tool. The slightly curved bottom is great for smoothing down those little pinked tabs on finish tapes.

JP

[Geowitz]

Yeah, as others have said I don't think you're being too picky at all. I had the same problem and ended up using the nicer one from the house as John did. My wife hates to iron anyways. It kept temps within a range of about 30 degrees during its cycle. I used a laser thermometer that I borrowed and checked it constantly trying to make sure temps ran from about 330 to 360 at the center where it was hottest. As long as your close to 350 without going too far over with the iron you will shrink it plenty enough and the actual fabric temp will never exceed 350, so long as you keep the iron moving at all times. I ironed a lot of times at the 350 shrink stage to ensure that all of my fabric eventually saw the 350 at the center of the iron. Actually it was kind of relaxing.

You may have localized spots in your fabric that were over heated. Only you can make that judgement call, but it sounds like you might be good with the technique you applied to avoid the extremes. I had the same problem with my first cheapo iron. Temps from 320 to over 400 depending on where you checked the temp. I ended up recovering both wings as described above to calm my anxiety over it.

[Dorsal]

I agree with John, you're not being too careful. I melted a hole in my fabric from an overshoot which was pretty much limited to initial heating of my iron. Once heated it worked well and I made sure to keep it moving.

[jiott]

Thanks for all the good comments. I think I should probably go buy a better iron that holds a tighter temp range. You are right about the Century hobby iron; its a great little iron that hold an accurate temperature. My large iron (el cheapo) does have a dark grey teflon bottom, so I think the temp gun is giving accurate readings.

Jim