a couple of weeks back realised that my chain slipping was due to loose cones on XT hub giving 4or5mm or so of play on axle

took apart replaced bearings/packed with grease and tightened so just spin nicely and same when QR done up
20miles later loose again – not as much but still means will need to adjust and to be honest wouldn’t expect to take cone spanners on a ride

normal operator error or some other problem?

XTs have a habbit of doing this from new, mine did anyway. Answer was a full strip and rebuild. Been fine for 2 years now. Quite a few others on here with the same issue.

On cup ‘n’ cone rear hubs (and just for consistency fronts too), I always rebuild the hub when new and Loctite together the drive-side cone and locknut at the correct axle protrusion (I find it’s always the inaccessible drive-side cone that comes loose). Adjustment is only then ever made on non-drive side/disc side cones.

What tucker said pretty much. I get the drive side really really tight so that it can’t come loose. You need to get the otherside tight too. Trickier without overloading the bearings but doable if you take your time. I found the trick was to have it ever so slightly too loose before tightening the outer nut against the cone.

Oh, before you do that, check they aren’t knackered. I had some that I thought were coming loose but they were just developing play as the bearing races had gone.

Hold axle by centre section in a vice & tighten the drive side cup/cone together as much as possible. Should stay put.

To adjust I always mount the wheel on the outside of the non-drive-side drop-out, with the skewer done up tight.

Before you go mad with the vice etc…..

Check the freehub body’s on tight. On shimano hubs the freehub’s screwed onto the rest of the hub with a fine thread, if this isn’t tight then it’ll appear that the cones are always badly out no matter how much you adjust them.

To check, remove the axle, insert a 10mm allen key in from drive side and tighen!

Bet this is the problem.

14mm hex key for the newer XT hubs.

That was part of the problem on mine – the freehub retaining bolt worked loose and locked up the bearings completely. At the same time, the hub had side to side play since the freehub contains the bearing race but was no longer tight on the hub body.

some good advice – done plenty of cup and cone bearing over years and usually get right (other than chasing errant ballbearings around the floor) – checked races all ok and replaced balls in case had been damaged but didn’t check the freehub at all so will look at that – did up drive side tight but probably not that tight – but didn’t bother to loctite – will do that thanks to all