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Re: Soldering irons [was Re: gEDA-user: Free Dog meetings at MIT starting this September!]

On Aug 23, 2004, at 11:40 PM, Charles Lepple wrote:
Please remember that this is my understanding of what's going on in a
Metcal gained by lab heresay; I might always be confused about some
detail or another . . . .
The techical details sound right... or maybe someone gave the same sales pitch at my lab :-)
Well...nobody comes to my lab to give sales pitches, but the details ring true with what I see on the bench. I have an older, high-end Weller iron (I don't recall the model number, the one with the digital temp display) and putting it side-by-side with the Metcal I can say my observed behavior matches that description.

A Metcal will give you the same amount of heat whether you are heating a QFP lead or a wad of 12 gauge wires (unless you reach the wattage limit for that particular tip). With a slightly less sophisticated temperature-controlled iron, you may have to boost the temperature setting slightly if there is a lot of thermal mass to whatever you are soldering.
Yes. The problem there, though, is that the thermal mass of whatever you're soldering affects things much more with pretty much any other make of iron. With the Weller irons, it seems they're depending on having a larger thermal mass in the tip than what it's designed to solder...because all that heat diffuses into what you're soldering, and it takes so long for it to be replenished by the heating element.

The Metcal tips, on the other hand, seem to have very little thermal mass...the heat being pumped into the joint being soldered was generated pretty much "on demand".

It's interesting to strap a Type K thermocouple to the tip of an iron and run it into a chart recorder while you're soldering. If you look at the temperature profile of an older technology iron, you'll see the temperature bouncing around quite a bit as you solder, and drop very low when you solder something big. I tried this the first time I got my Weller iron's tip *stuck* to the center conductor of an SO-239 connector...the tip temperature dropped below the melting point of the solder and took a good twenty seconds to come back up so it could be dislodged.

These crazy Metcal irons, however, just don't care. It's amazing what they can do.


Dave McGuire "...it's a matter of how tightly
Cape Coral, FL you pull the zip-tie." -Nadine Miller