Infrared Thermometers - which is good to measure temp of Aluminum plate?

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I weld 2 mm aluminum and want a thermometer to measure the temp of the work PRIOR to welding and also  maybe the temperature of a weld after heat treating a weld seam.Are the cheap IR thermometers any good?  What is a good welder's choice for measuring metal temp.Thanks, J.
Reply:You get what you pay for. I have an off brand, a Fluke, and ALCO, (most accurate) and Sears Craftsman branded. None of these read within about 50 degrees of one another when reading cylinder temperatures of exhaust manifolds. I've never used any to measure welding temperature. The ALCO unit consistently reads within three degrees of a precision contact thermometer at the same area. I have no idea where you would purchase one of these as mine is about 20 years old.SlobPurveyor of intimate unparalleled knowledge of nothing about everything.Oh yeah, also an unabashed internet "Troll" too.....
Reply:I wouldn't use a cheap IR on reflective aluminum.It will read really low.If I were going to do aluminum that needed preheat I would get a surface contact thermometer.old Miller spectrum 625 Lincoln SP-135 T, CO2+0.025 wireMiller model 250 and WP-18V torchCraftsman 100amp AC/DC and WP-17V torchCentury 115-004 HF arc stabilizerHome made 4 transformer spot welderHome made alternator welder
Reply:Yes it will read low. That is not to say one could not come up with a formula.An explanation as to why it does not read properly was offered in another thread. I don't care to look for it though.
Reply:Emissivity of the substrate is the reason for the low readings of a non contact thermometer.SlobPurveyor of intimate unparalleled knowledge of nothing about everything.Oh yeah, also an unabashed internet "Troll" too.....
Reply:My Extech has a adjustment for emissivity. Great. The problem is that it doesn't give any real info on how to adjust it. I guess I'll have to calibrate it myself one of these days and see.Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply:Originally Posted by irish fixitMy Extech has a adjustment for emissivity. Great. The problem is that it doesn't give any real info on how to adjust it. I guess I'll have to calibrate it myself one of these days and see.
Reply:As others have said they are not accurate on bright metals.  At work we take the temps of stainless process pipe on a regular basis.  We spray paint spots of flat black paint as targets and get believable numbers.  I know that will not help what you are trying to accomplish but I thought I would throw that out.DanManipulator Of Metal
Reply:If I want accuracy, I use temp crayons.ChrisAuction Addict
Reply:+1 on tempil sticks...you can get them within a few degrees of whatever temperature you need.KevKevin / Machine_Punk from The Aerodrome Studio - Lincoln PowerMIG 210 MP - Meco N Midget w/custom welding station - Vintage Victor 100Current Projects: The Aerodrome Studio
Reply:A weird question. How did you guys come to know the readings were off?I don't remember the particulars, I was welding some aluminum rims and picked up on the ir being off. Is the ir so north and south that it can't be made use of? Does it really matter if it reads 100f lower? Is it kind of like an oven whose dial does not match actual temperature? You just adjust.
Reply:Originally Posted by SlobTake a flat black piece of construction paper and let is soak in the midday sun for about an hour with a remote bulb capillary tube thermometer under the sheet. Adjust your non contact thermometer for a close reading of what the bulb thermometer displays and you will be very close. Should you not have access to a remote bulb thermometer, a long "spike" type thermometer will be close in indication and definitely close enough for handguns and hand grenades. Emissivity of a material is a measure of it's reflectance to an equal sample which is black.
Reply:I read or heard somewhere that for critical work infrared heat guns aren't accurate enough. Tempil sticks are much more accurate and pretty much fool proof.
Reply:I bought one from Nubee on e-bay for something like $20.00. It has adjustable emissivity and a laser sight etc. Reads to 932 degrees F. I wanted to try them out. It seems to read consistently enough for what we are doing. We set the emissivity by comparing  with a contact thermometer and once set it worked consistently enough for our purpose. However we are measuring on the same piece all the time at a temperature(shell mould pattern) between 500 to 650 degrees. As to how accurate it is I can't say. In our application we are maintaining relative temperature more than specific temperature so accuracy is not paramount. Nubee supplied a chart for relative emissivity of various materials but the surface finish will change the emissivity. From the chart: Oxidized iron 0.7, steel and iron 0.80, oxidized steel 0.70-0.90. You see the difficulty. I think it might be useful to recheck you temperature after you have dialed it in by comparing to a contact thermometer but unless you deal with stuff the identical surface prep,as we do, I wouldn't trust it on its own without the initial comparison on every new item.If you research even the well known name brands they have downloadable emissivity charts but they are really only a general reference. Many of these cheap IR thermometers are marketed to the culinary trade to measure the temperature of meat. It is a poor strategy in my view because the surface temperature does not guarantee the internal temperature so you steak may not be as well done as you might think.---Meltedmetal
Reply:Originally Posted by DanD78As others have said they are not accurate on bright metals.  At work we take the temps of stainless process pipe on a regular basis.  We spray paint spots of flat black paint as targets and get believable numbers.  I know that will not help what you are trying to accomplish but I thought I would throw that out.Dan