Title says it, pretty much - I've a crank (drive side with chainrings) where the cap threads are stripped. This is an older square-axle crank. Since my Park tool won't thread into the cap threads, I can't use it to remove the crank from the axle. I need some "brute-force-and-awkwardness" way to pry the crank off the axle without damaging the bottom bracket or the chainrings. Any ideas?

Thanks!

Crank caps? Do you mean the threads for the extractor on the crank arm?

This is one of my favorite problem cases.

Two ideas:

-get a gear/wheel puller. Depending how the arms of the puller fit between the arms of the crank, this one can work beautifully. The pullers of this size are a bit pricey, so maybe you can borrow one from a friend who does lots of car repair work. BTW, do NOT pull on the chainring; pull on the spider itself. Not all pullers can get a grip on all spiders however.

-loosen the spindle bolt a turn or so. Then go for a short ride. Maybe a couple of miles. This might loosen the arm enough. This one might distort the hole in your crankarm, but then it is toast anyway with stripped threads. Don't take the bolt all the way out, btw, since the arm might just fall off.

Still no good? Then beat the snot out of the arm with a heavy hammer. Try to get some penetrating oil down in there as well as you can. Beat it some more. Go inside, have a fight with your loved ones. Come back out and beat it some more.

Sounds like a plan!

Early in my learning curve and before I had the proper tools, I was able to carefully wedge a crank set off using a straight claw hammer.

you could use a gear puller, but you can bend your crank. why are you taking your crank off?

I had the same problem a few weeks back on a Peugeot I rescued. After giving the the crank a good soaking with WD40 and leaving it for a while to do its stuff I got a punch with quite a broad head and carefully tapped the crank off from the none drive side.
I placed a rag down in the "v" of the frame to prevent the punch scratching the paintwork. If you are careful and keep turning the chainring to spread the force and also hit as close to the spindle as possible it shouldn't take to much to knock it off the taper..... Worked for me!

You don't have to destroy it! In fact, you can use it again if you want.

Find a socket that just fits inside the square of the crank arm.

Put the socket on a cement floor.

Place the bike over the socket so the socket is inside the square of the crank arm. Have someone hold the bike.

With a flat punch and a BFH (big f@cking hammer), hammer on the crank arm as close as you can to the bottom bracket. Put a big flat washer between the punch and the crank arm to protect the soft metal.

Took me 2 wacks to get it off last time I did it.