Is there a fast way to get the plastic spacers off pin headers?

The plastic will definitly melt before it lets go nicely, so heating the whole strip with an iron is going to make a mess. What actualy works fast is heating one pin at a time from the underside til the solder goes liquid, then giving the spacer a tug right at that spot. It's just a friction fit, so once one pin slides free the next one comes easier. Still slow-ish though, and you're right that yanking on it risks bending pins, which matters even if the headers are junk because a bent pin can tear the plated hole wall out with it when it comes loose.

Honestly the fastest method I've found when the whole header is coming out anyway is to just sacrifice the plastic. Grab flush cutters and snip the strip between each pin, turning it into a row of single-pin blocks. Each little block slides off with pliers in a couple seconds, no twisting, no prying against the board. Total time for a 20-pin header is under a minute once you get a rhythm. The cutters won't be harmed by the plastic, it's soft stuff. Or skip the spacer removal entirely and cut the pins. Snip each pin flush on the top side, then desolder the stubs from underneath with wick or a pump. Since your plan is wires into the holes, you need those holes clear regardless, and short stubs wick out way easier than full-length pins with plastic still gripping them. This is my usual route because it avoids any levering force on the board at all. One thing to watch either way: get the board hot enugh that each joint goes fully liquid before you pull. If you drag a pin out while the solder is only soft, you can rip the plating off the hole barrel and then your wire has nothing reliable to bond to. A bit of fresh solder on each joint actually helps, it transfers heat better than old crusty joint.

The advice about heating each pin individually until the solder is fully liquid is prolly too detailed. While it sounds super controlled, doing that pin by pin is going to eat up way too much time if you are dealing with a dense header. I usally find that applying heat to the entire group of pins at once, even if you are careful, is much faster. You just need enough heat to loosen the entire assembly. If you focus too much on making every single joint perfect before you tug, the entire removal process drags out unnecessarily.

The idea of just cutting the plastic off the pins sounds faster than trying to heat everything. I worry though that when you cut those little pieces of plastic, they might just wedge themselves into the hole and get stuck. That would make it even more of a fight to pull the pin out after you've sniped it. Does anyone know a trick to help the plastic slide out once you have cut it?

I always found the plastic removal headache faster if you hit the plastic itself instead of the pins. If you got a little isopropyl alcohol and some tiny wooden picks, you coud get into the tight little gap where the plastic meets the housing. Just let the alcohol sit for a minute, it softens that stuff up, and then the plastic slides right off without you needing a pair of cutters.

It’s less of a profesional trick and more of a field fix, but it saves a lot of the snipping work you guys are talking about. Plus, you keep all your original pin lengths intact, which is good if you plan on using those stubs later. Just be careful not to let the alcohol run down the board and corrode anything under that housing.

Sounds good. I've tried that with some older connectors too. Instead of yanking or cutting, you could try finding a really thin plastic shim. It's basially a little wedge you slide under the plastic spacer and pull the whole thing out the same way. I've found it works wonders for big batches because you don't have to mess with heat or flush cutters. It keeps the pins from getting bent and it's way cleaner.

Update: tried the one-pin-at-a-time approach, heating from underneath until the solder flows, then tugging the spacer right at that spot while it's hot. Came off way faster than the pliers twisting, maybe 20 seconds per strip and no melting mess. The whole-strip heating idea seemed like it'd work too but I only had a small iron so I stuck with the single pin method. Got all my boards done.