Or is this best done at a LBS

Ditch the SFN and get one of these instead

http://www.chainreactioncycles.com/Models.aspx?ModelID=911

buy the tool, it can be done with a hammer, but its a PITA and never quite goes in straight.

It's pretty easy to f&*k it up, but then again it's a pretty easy thing to do. Straight is more important than depth, so lots of little taps rather than a couple of big wallops and "oooops…" Mind you, it takes a bit of a whack to get them started.

Reading that back, that's not the best advice that's ever been handed out.

Hope head doctor is the biggest peice of crap i've ever purchased and with mountain biking kit that is some achievement.

Use a long bolt and top cap with a raised stem as a guide.

Tip: if using a hammer, screw a bolt into it first!

Bit of a long winded way of doing it but it works well.
Get a threaded bar longer than your steerer and the same size* as your SFN with a couple of nuts locked against each other at one end with a big washer. Put threaded bar through steerer, washer and locknuts at the bottom, thread SFN on the top untill it butts up to the steerer then use a spanner to 'wind' the SFN down into the steerer.
I'm probably not explaining this very well am I?
Like I said its a bit slow but better than using a hammer as you're less likely to mess it up. As a bonus you can use the threaded bar and washers as a headset press too also if you don't have a spare SFN handy you can use this to tension the stem and bearings (and remove before riding obviously)

*i dunno what the proper term is

Oh and continuing the theme of re-using stuff, head doctors (or certainly the similar design cheapo one I had) can be used as a bearing puller to get those external BB bearings out of their cups – with 3 hands a load of wooden spacers and lots of swearing aswell of course 🙂 but for actually tensioning your headset they can be fiddly buggers

Thanks folks. I think I'll try DONK's idea. Cheers

just hit it with a hammer & then a screwdriver to straighten it up when it goes wonky.

15mm copper pipe offcut used as a drift (hit it with hammer) for me, the more you do with the same bit of pipe the better it gets as the end moulds to shape.

I asked this a few weeks ago and bought the tool, glad I did, so easy to use

Tracey