My drill bit has stuck in the chuck of my dewalt sds chuck ,have tried wd40 but still stuck

It depends to where you want to apply your lubricant.
If you want to lubricate the chuck with the sds drill bit you simply add some cheap grease on the drill bit and the drill bit will slide easily on the chuck. On the other hand if you want to lubricate the sds drill machine then there is a special type super grease that you can buy from Dewalt in order to do so. Also since in order the super grease to be needed this means that you have used the drill a lot then also is needed to change o-rings, brushes and so on. So usually you have to ask for a service center to do it since they know how to do it properly and using the right kit.

Can not see what model you have. Is it a keyless chuck or an SDS chuck? With a keyless chuck hold the machine in a vice by the drill bit. now tap the chuck with a hammer or pin punch & hammer. DONOT hit the chuck on the jaws gut on the rim around them. I have had success using this method. If it is an SDS type chuck pull the chuck cap up as far as possible along the bit them if there are any ring springs you will have to try remove them then slide the sleeve up the bit, now you should be able to remove any steel balls. If the bit does not come out now hold bit in vice as before and tap on tool holder.

There is supposed to be grease on the chuck end of SDS+ and SDS Max bits. Actually, you should put a little lightweight grease on the end of the bit every time you put one in your drill. If you, or noone who has ever used the drill, have ever done this, it is possible internal grease is leaking out of the drill and it should not. There are seals to prevent internal grease from getting out of the transmission and striker mechanisms. If you are loosing internal grease, these seals should be checked.

If debris enters the chuck it may no longer turn for adjustment. Spray plenty of wd40 into chuck and allow plenty of time for oil to do its magic. Hold chuck/drill pointing down and turn drill in both directions to clean out debris. If chuck is too far gone, remove the center screw (backwards thread) and remove the chuck(threaded on). Replace the chuck with new generic part from Lowes (about $25.).

Try wrapping a cloth around the chuck while unscrewing it by hand. This may give just enough grip to undo it.

This is an SDS chuck and uses ball in tapered slots to hold the bit - if the inside of the chuck is dirty (dust+grease) it will not operate correctly. Use a cleaning degreaser spray and wash the inside out whilst moving the chuck outer body up and down. Try your SDS bits in it and if it works okay - spray some WD40 in it and then keep clean and re lubricate it regularly after use - hope this helps

Put some WD40 into chuck and wait a few minutes. Open the chuck as you would do when normally removing the drill while at the same smartly tapping the back of the drill.Alternatively try to grip the broken drill bit with a long nose pliers to extract it. A strong magnet might also pull the bit out.

Youcan only use standard drill bits with the use of a chuck attachment with the SDS type bayonet. These hammer drills use an SDS type drill bit which just pushes into the fitted chuck and are released by pulling back on the lock mechanism on the chuck.

the rubber cap in the sds chuck nose is only snap tight try to remove and dismantle the retractable locking pins.

tap it lightly with a ball pin hammer, if that dosnt shake it out try opening it and useing something to push it through