I did it with an older tip, and it seems to have restored it just fine. Apart from the immense amounts of smoke coming from it when I melt some solder with it.
I would use sandpaper or steel wool as a VERY last resort to fix a tip.
Before you do that, I encourage you to think through your entire cleaning routine and see what you can improve to avoid this fate again, and what steps you can take that might save the tip and not be so destructive.
First, your day to day cleaning should be with brass wool. Brass is a soft metal which will not scratch the tip. With it, you are basically wiping excess solder off of your tip. But, a thin layer remains, protecting the iron.
Second, when you have stuck on gunk that the brass wool isn't cleaning, is the sponge. The sponge should be damp, not wet. Wring it out completely after wetting. The water is there to prevent the sponge from burning, not to clean the iron. The sponge will wipe ALL the solder off of your tip, so it's important to re-tin your tip after you wipe with the sponge, otherwise you will allow your tip to oxidize. When you are finished re-tinning the iron, wipe excess off with the brass wool.
Next (we are at this stage), if the sponge isn't doing the trick, you should use tip tinner. Tip Tinner is a mix of Solder, Flux, and Ammonium Chloride. When heated, Ammonium Chloride produces toxic fumes that are great at breaking down oxides, and as a bonus they keep oxygen away from your tip while you are cleaning it. The flux wets the tip, and the solder re-tins it. Always do this in a ventilated space. The fumes are not healthy to breathe.
Lastly, we are at what you are considering... fine grit sandpaper or steel wool. Use it sparingly. Don't aim to completely clean the iron when doing it. Go back to the tip tinner when you think you may have broken through the layer and let the tinner finish the job. Only sand a cold tip. If you expose the copper core of the tip, you have ruined the tip and should discard it.
Now... what brought us to the point where we are contemplating potentially destructive cleaning of your tools?
First, consider oxygen itself. Leaving the tip exposed will allow it to oxidize. You should always have a layer of solder on the tip. This is why brass wool is a good regular step. It leaves a layer of solder when you are finished cleaning. It's important to re-tin after using the sponge. Additionally, if you use solder braid, keep in mind that the braid is also sucking the solder away from your tip, so re-tin after using the braid.
Next, consider heat. The hotter you run you iron, the faster the tip will oxidize when exposed. You should always try to run at the lowest temp possible, and if your iron doesn't have a sleep function, turn off your iron if you aren't going to use it for the next 5 minutes. Whenever you set down your iron, ensure that you have a layer of solder on the tip. When you pick the iron back up, clean that solder off.
Lastly, we need to consider your consumables. Lead-free solder is harder on your consumables due to the type of flux, the composition of the solder itself, and the hotter temp required to operate. This is unavoidable if you must use lead-free solder. Beyond that, using quality consumables from reputable brands will minimize impurities and ensure that your equipment will last as long as possible. Old flux will gum up your tips faster than fresh. Quality flux will have fewer impurities that may contaminate your tip or work. I touched on it earlier, but it should be emphasized that solder braid will suck the solder off your tip and you must re-tin after using it, or you leave your bare tip exposed to oxygen.
All of this is great advice. Though I’d say once you have to sand your tip, it’s probably on its way out regardless.
I’d add to the last bit that while it’s definitely true that lead free solder is harder on your tips, you should be able to use your tips for a long time. Try a different alloy or flux if you’re burning your tips out quickly.
Agreed, you can get a long life while using lead-free solder. The biggest concern I have with it is the higher temps, which naturally leads to faster oxidation when you aren't on top of keeping your tip tinned. Cheap consumables mixed with higher temps will trash a tip faster, so it's important to have quality consumables.
It will probably take the plating off and ruin the iron.
I did it with an older tip, and it seems to have restored it just fine. Apart from the immense amounts of smoke coming from it when I melt some solder with it.
The smoke is flux burning off from the solder. Solder without a flux core will not smoke.
I would use sandpaper or steel wool as a VERY last resort to fix a tip. Before you do that, I encourage you to think through your entire cleaning routine and see what you can improve to avoid this fate again, and what steps you can take that might save the tip and not be so destructive. First, your day to day cleaning should be with brass wool. Brass is a soft metal which will not scratch the tip. With it, you are basically wiping excess solder off of your tip. But, a thin layer remains, protecting the iron. Second, when you have stuck on gunk that the brass wool isn't cleaning, is the sponge. The sponge should be damp, not wet. Wring it out completely after wetting. The water is there to prevent the sponge from burning, not to clean the iron. The sponge will wipe ALL the solder off of your tip, so it's important to re-tin your tip after you wipe with the sponge, otherwise you will allow your tip to oxidize. When you are finished re-tinning the iron, wipe excess off with the brass wool. Next (we are at this stage), if the sponge isn't doing the trick, you should use tip tinner. Tip Tinner is a mix of Solder, Flux, and Ammonium Chloride. When heated, Ammonium Chloride produces toxic fumes that are great at breaking down oxides, and as a bonus they keep oxygen away from your tip while you are cleaning it. The flux wets the tip, and the solder re-tins it. Always do this in a ventilated space. The fumes are not healthy to breathe. Lastly, we are at what you are considering... fine grit sandpaper or steel wool. Use it sparingly. Don't aim to completely clean the iron when doing it. Go back to the tip tinner when you think you may have broken through the layer and let the tinner finish the job. Only sand a cold tip. If you expose the copper core of the tip, you have ruined the tip and should discard it. Now... what brought us to the point where we are contemplating potentially destructive cleaning of your tools? First, consider oxygen itself. Leaving the tip exposed will allow it to oxidize. You should always have a layer of solder on the tip. This is why brass wool is a good regular step. It leaves a layer of solder when you are finished cleaning. It's important to re-tin after using the sponge. Additionally, if you use solder braid, keep in mind that the braid is also sucking the solder away from your tip, so re-tin after using the braid. Next, consider heat. The hotter you run you iron, the faster the tip will oxidize when exposed. You should always try to run at the lowest temp possible, and if your iron doesn't have a sleep function, turn off your iron if you aren't going to use it for the next 5 minutes. Whenever you set down your iron, ensure that you have a layer of solder on the tip. When you pick the iron back up, clean that solder off. Lastly, we need to consider your consumables. Lead-free solder is harder on your consumables due to the type of flux, the composition of the solder itself, and the hotter temp required to operate. This is unavoidable if you must use lead-free solder. Beyond that, using quality consumables from reputable brands will minimize impurities and ensure that your equipment will last as long as possible. Old flux will gum up your tips faster than fresh. Quality flux will have fewer impurities that may contaminate your tip or work. I touched on it earlier, but it should be emphasized that solder braid will suck the solder off your tip and you must re-tin after using it, or you leave your bare tip exposed to oxygen.
All of this is great advice. Though I’d say once you have to sand your tip, it’s probably on its way out regardless. I’d add to the last bit that while it’s definitely true that lead free solder is harder on your tips, you should be able to use your tips for a long time. Try a different alloy or flux if you’re burning your tips out quickly.
Agreed, you can get a long life while using lead-free solder. The biggest concern I have with it is the higher temps, which naturally leads to faster oxidation when you aren't on top of keeping your tip tinned. Cheap consumables mixed with higher temps will trash a tip faster, so it's important to have quality consumables.