im riding fixed at the moment on a shimano deore hub.
all i did was remove the free wheel and weld the bearings up inside. give it a grind down and slot it back on. you have a fixed where you can change the chain line really easily. deore rear hubs are about £12 here, then get some old cassettes from your local bike shop and space out your cog.
i guess the difficult bit is building the hub onto a rim, but if you use an old rim and spokes then its good wheel building practice i rekon.

anyone else done this sort of thing?

And you ride this brakeless? You have more balls than I. I've build a SS in this fashion but not a fixie. Doesn't the freewheel just screw on? I would worry about either the weld breaking or the freewheel spinning off. You should look at the surly product that replaces the freewheel and offers a lockring. Put a brake on that thing so you will be also onelessScar as well.

https://www.surlybikes.com/parts/fixxer_pop.html for the Surly Fixxer.

Or just a proper track hub.

If I understand correctly, sounds like a similar hack to this:
https://www.63xc.com/mathieson/cheaphub.htm

Seems if you can braze the innards solid, you'd have pretty much the same thing as the Surly Fixxer.

I'm betting a new track hub costs less than a welder.

No doubt about that.

This idea has me thinking, however. I found a old forgotten Shimano freehub in the junkbox yesterday. Never taken a freehub apart. I've got a torch setup, may give it a try.

i suppose its only worth it if you have a welder allready or can borrow one.

I was following Sheldon's example: I've made fixed conversion by brazing the cassette freehub body. It's an old Shimano 7 speed. I've took the freehub out, soaked it in degreaser, dried it, and a friend of mine brazed it. I am riding that bike as a commuter/beater since 2013 with no problems at all (unscrewing), even the bearing cup is still OK (I was afraid that during the brazing will loose it's hardness).
Taking apart the freehub mechanism is tricky, requires special tool. simply soaking it in degreaser and then drying is simpler. I think that welding could cause small deformities, brazing will not. That's why I chose brazing over welding.
I recommend you my method, if you want cheap fixed gear conversion. Chainline adjusment is very easy too. I rarely make skid stops, and run a front brake.

This might be the winner. I think twelve was the oldest zombie before. I'm pretty sure fourteen years is the new record. Congrats.

And reviving FIVE old threads on the same subject too? Yep, winner.

How do you know all those original posters from 10+ years ago weren't still waiting on advice before welding up their hubs? Maybe this guy's providing a valuable service.

And smoking an 8-ball of crack every day is good for you!