Why does my soldering iron do this?

I'm trying to do some soldering on my bass guts (250k pots and 22awg wire for reference). I have a solder station iron with digital control with the temperature set at 380F and I'm using rosin core solder.

What happens is the solder will initially flow ok, but then whatever is deposited just won't re-melt even though I'm making the part super hot. It happens often enough to discourage soldering. I'm afraid I'm going to cook parts, plus it looks like a hack job. I stopped after one cap and a short tail of wire on the tone pot. 

What am I doing or not doing to cause this frustration? If you see no other products or techniques mentioned above, expect I'm not doing/using as I'm not an experienced solder guy.

Thanks for help 

In reply to akamcfly :

Soldering 101: Your first step should be to clean the iron's tip on a damp sponge or paper towel. Next, each of the parts to be soldered need "tinned" - that's where you heat up the wire/part, then allow solder to flow into/onto it. After that, you can put the two parts together, heat them up & allow more solder to wick between them to form a bond. Make sure you don't allow any movement while the solder cools. 
 

I've not experienced the problem you're having, and I've never used an iron with adjustable temperature, but the larger the part, the more heat required - either through longer contact with the iron, or(I suppose) higher temps.
 

I have a handful of irons, most are the smaller handheld "wand" style(50-watt iirc). Those don't really put out enough heat for something the size of a potentiometer case(which functions as a heat-sink), so I break out the soldering gun for something like that.

I've seen this a few times with solder that has either been sitting for a while or some of the newer (reduced lead) formulas of solder.

My son and I had this problem recently, and switching to a bigger tip helped.  Not sure why because it sure seemed like the part was getting hot.

We run our Hakko soldering stations at 550f or so if i remember right.  I'll check in a bit.  May just be too cold. 

triumph7 said:

I've seen this a few times with solder that has either been sitting for a while or some of the newer (reduced lead) formulas of solder.

Lead free solder needs a lot more temperature - exactly what solder blend are you using?

Your temp seems too low. 600F is what we normally do. If your iron's tip is oxidizing then that layer can form a barrier and either create a big temp drop or dork up the wicking / bonding chemistry.

Just don't see the need for temperature control on a soldering iron.

 The purpose is to melt the solder.

I have used a lot of different irons and became quite proficient.

The switch was the only control unless it was fire heated.

Way too cold. 650f or higher. I'm probably around 720f. If you have steel wool, a wire brush or even some sandpaper make sure to clean the tip until shiny again. Clean the tip with a damp sponge as needed while working. If it's RoHS solder it can be a real pain to work with. Tends to oxidize the tip 10x faster than leaded. When you're done soldering tin the tip before you turn the iron off. Keeps it from oxidizing.

Tip temp is way too low.  Should be in the 650+ range.  Size of the tip matters too.  A long thin tip will require a higher tip temp to start as the workpiece will suck the heat out of it quickly and the heating element in the handle will take some time to reheat it.  A short, fat tip will hold the heat much better.

Thanks all. I'm going to jack the heat when I get home and try it out. The solder is lead free "60/40" rosin core. I have also ordered some flux and a solder sucker. Theyll be here Monday. 

If you don't do a lot of soldering I recommend spending a little more for 63/37 eutectic solder. My experience is that it more easily achieves satisfactory results even with poor technique. 

oldopelguy said:

If you don't do a lot of soldering I recommend spending a little more for 63/37 eutectic solder. My experience is that it more easily achieves satisfactory results even with poor technique. 

Well I have poor technique down pat. 

I learned my display is set in those pesky French units. I was at 380C or 716 in freedom units. i bumped up to 450 or 842F and it was a lot more forgiving. i may drop to 400/750 with a fatter tip as suggested and see how it goes. Thanks again, all. 

iceracer said:

Just don't see the need for temperature control on a soldering iron.

It looked cool what with the big blue box power supply and DRO. It sucked me right in. Plus it heats up in a hurry. 

If anyone is still seeking out  traditional lead/tin solder, look for stained glass window supplies. I got a fat roll at Hobby Lobby.

oldopelguy said:

 63/37 eutectic solder.

I haven't found any locally yet, but the local electronics places keep bankers' hours. I did change to a slightly larger, chisel shaped tip on the iron and set the temperature to 400C. It made a very positive difference in the quality of the joints. I did a bunch more this afternoon with much less ugliness. Successful enough.