UKH

I’ve noticed that the quick release skewers on the wheels of my wife’s mtb have worked loose a few times, despite me following the usual method of adjusting the tightness and then folding the lever down. I’m pretty sure I’m doing this bit right. When I checked this again, no matter how tight I get the lever, it’s possible to to turn the skewer by hand by rotating the quick release lever once it’s been folded down tight. I assume this isn’t normal? Hopefully this makes sense.
I tried cleaning the surfaces of the quick release mechanism and of the frame / forks to no avail. Could the radial ridges in the quick release washer or on the fork have worn a bit smooth?

It’s possible that this happens when there is too much axle projecting beyond the lock nuts relative to the width of the frame drop-out. Is it possible the axle is off centre? Does one side project more than the other? You can create more space by removing the little centring springs, these are not essential and may have become fouled up which can cause these types of issues.

Edit: An angle grinder to an over long axle could be a fix but I can’t discount your QR is just a bit rubbish (though this would be unusual).

Thanks. The springs looked ok when I checked earlier, but I’ll check the projection of the axle. 
We’re away on holiday so I have limited tools with me, so I think we’ll have to leave the biking this time. Don’t want to risk a wheel falling off. I tried ordering some new skewers to be delivered to our holiday accommodation but a Wiggle / Yodel comedy double act means that they will probably arrive after we’ve gone back home.

Seems an odd thing, but the radial ridges really shouldn't have much effect on how tight you can get the QR. The wheel won't be able to turn it and the lawyer tabs on the ends of the forks should stop the wheel coming out if it's tight.

Only thing I can think of is that the QR has stretched over time and the nut is now hitting the end of the thread and won't go any tighter, but I assume that's not happening, or you would have said.

You haven't somehow lost anything off the spindle, such that it is now wider than the drop-outs? Unlikely, especially if it's both wheels, but just thinking out loud.

One plan might be to do the QR up and then turn it clockwise to tighten it up further - see if the nut on the other end is trying to turn when you do this.

I’ve tried this and I can turn the QR a certain amount until it’s hand tight, and no further. The nut on the other end isn’t turning. At this point the QR lever is too tight to lever out by hand and I have to rotate it a quarter of a turn before I can lever it out in the normal way. 

if it’s almost tight as is, then ditching the wee springs will add an extra 1mm each side which I’d expect will fix the problem albeit without the convenience of the springs doing their job.

Thanks everyone. I checked that the axle isn’t projecting beyond the dropouts - it isn’t. But I think I might have found the problem. When the quick release lever is pressed, during the last mm or so of movement it actually starts to loosen off again. I assume this is wear somewhere in the camming action.

Despite various Wiggle / Yodel cock-ups I managed to get some new steel quick release skewers delivered today which has fixed the problem.