Following an injury I've had to start doing lat pull-downs instead of pull ups.

I've been using the cable machine but there seems to be too large jumps between weights for gradual progression, so I thought about doing them with the lever machine instead, allowing to increase weights more gradually.

This is what i mean:

http://www.exrx.net/WeightExercises/LatissimusDorsi/LVFrontPulldown.html

Does anybody here do pulldowns using this machine, and if so how do you find it? I just see little mention of them being done this way, even with a google search. Seems to be the same range of motion as cable machine...just after some opinions.

(my injury, exertion headache, is brought on by pull-ups but not pull-downs for some reason, I'm hoping to gain strength at this movement with gradual progression so that when I eventually get back to pull-ups, I'll be better)

Cheers.

Yes, I think the leverage type machines are pretty good.

I use a similar machine from time to time. It's the Hammer-Strength Front Pulldown machine. It's a different movement from the traditional pulldown on a cable machine. Actually feels a bit more like a high row than a pulldown (although I know they also make a specific High Row machine which is different again).

If it allows you to train without any strain to your injury, then I'd say you are good to go.

But ultimately, the only thing which is going to help you get better at pullups/chinups is to work at those.
Pulldowns/machines don't really help a great deal with pullups/chinups IMO because they involve a different recuitment pattern. So the only way to get better at those is to do those.