When it comes to metal working, 3 jaw chucks are perhaps the most common clamping device utilised by the hobby machinist. Usually supplied in the scroll type, 3 jaw chucks allow for manual positioning to ensure adequate clamping of irregular shaped material. In order to keep the chuck jaws performing at their optimum and retain their machining accuracy it is essential to clean them on a regular basis. The process detailed below should enable you to keep your 3 jaw chuck well maintained and increase its life expectancy.
Freeing the chuck from the lathe
Before you can begin the task of maintaining your 3 jaw chuck, you must of course free it from the lathe. Be sure that you have unplugged the lathe at the mains or isolated it from any other power source. Next, insert a socket into the jaws and then clamp it tightly, before attaching a Tommy Bar to the socket. Now, use a metallic soft faced hammer to strike the Tommy Bar, remembering that the chuck must go in a counter clockwise direction in order to loosen it from the lathe spindle. Whilst a wooden or rubber hammer may work, a metallic hammer will deliver a sharper shock to the Tommy Bar and thus chuck, increasing the chances of freeing it.
In the event you do not have a suitable socket and Tommy Bar then you can use a large Hex Key or Allen Key instead. If the chuck will not loosen after a few strikes then try using a bigger hammer and also a thicker Tommy Bar if you have one.
Once you have loosened the chuck enough to twist it by hand, it is a good idea to unclamp the socket and remove it from the jaws to allow yourself more space to manoeuvre and reduce the chances of dropping and damaging the chuck. At this stage you could place some form of protective material in the floor, just in case the chuck does slip from your grasp – a thick blanket or wooden board should do the trick.
Preparing the chuck
It is important to have a suitable space to lay your 3 jaw chuck on whilst you work on it. You can either lay some paper towel on the surface of your work bench, or some lint free cloth if you have any handy. Once you have laid the chuck on the workbench you can use another piece of the lint free cloth or the paper towel to remove any oil and dirt that is on the outer surface of the chuck.
Removing the jaws
You can now begin unwinding the jaws from the chuck by inserting the chuck key in the jaw scroll socket and turning counter clockwise. Do this stage of the process in a slow and steady motion so that you can keep an eye on the jaws as you do so. This will allow you to spot any areas where the jaws seem to be tight in the chuck.
As the jaws get to the end of the scroll, take a firm hold of the number one jaw and pull it gently out of the chuck. Now do the same with number two jaw, followed by number three jaw.
Cleaning the jaws
With the jaws removed, you can now use an old toothbrush to give each one a good clean, removing any debris. Be sure to do this on another area of the workbench where none of the removed material will end up on the other jaws or chuck itself. You may even wish to do it over your rubbish bin to reduce the tidying up time later on.
If you have a fairly old chuck then it could be that there is some staining and even pitting on the jaws. This is not something to worry about too much and is unlikely to affect the accuracy of your machining. Whilst it can be tempting to try polishing away the stains, you are likely to do more harm than good. Just concentrate on cleaning the slots and the teeth to allow for smooth operation.
Cleaning the chuck and scroll
With the jaws cleaned, you can now concentrate on tidying up the chuck and the chuck scroll. Be sure not to use any cleaning fluid on the chuck – you can however use a little silicon spray if required. Use your toothbrush to remove any gunge or material from the thread in the centre of the chuck that attaches to the lathe.
Next you should focus on cleaning out the thread of the scroll. This can be done by cutting a piece of softwood so that it will fit in between the scroll. Position the scroll so that the beginning of the thread is located at the slot for jaw one, then push your shaped piece of wood into the scroll. You can now turn the scroll using the chuck key and the wood will collect any dirt and debris. Only turn the scroll a small distance, before removing the piece of wood and giving it a wipe, then repeat the process.
Although it may take some time to complete this stage of the process, it will leave your 3 jaw chuck in excellent operational condition. You may even decide to repeat this step, using a slightly different shaped piece of wood, just to clean up any spots of gunge that you missed on the first time around.
With the cleaning done, all that is left it to reassemble the chuck. Begin by inserting jaw one into its slot and then tightening the scroll until you feel the jaw begin to move inwards. Now repeat the process and insert the jaws into slot one and two. Remember that each jaw is numbered and must be replaced in the right slot, due to the fact it was specifically shaped for it. Putting the jaws back in the wrong slots could have a detrimental impact on the machining accuracy. In the unlikely event that you notice the jaws sticking as you wind them back in, you should take them back out and give both them and the scroll another clean.