Some of my upcoming projects need some small parts machined on my lathe. The standard 3 and 4 jaw chucks that I have just don’t hold small parts well. The other day I broke down and ordered an inexpensive Chinese collet chuck and a set of 5C collets to go with the chuck. Since there are many different chuck mounting methods for lathes the adapter plate to mount the chuck to the lathe has to be ordered separately. These plates are partially finished. They will mount on the lathe spindle but have to be machined to fit the chuck.
In the picture above is the collet chuck as it came out of the box except I put one of the collets into the chuck.
There is two reasons the adapter plates come blank. One is that there are a lot of different chuck mounting configurations. Also by machining the adapter on the lathe it is going to be used on guarantees that it will run true on that lathe.
In this picture the blank adapter is mounted on the lathe ready to be machined.
In this picture I have turned the adapter plate so that the raised part will just fit inside the back of the collet chuck. This centers the chuck with the lathe and must fit without any slop. To do this you have to sneak up on the correct size by taking a very small amount off and test fitting the chuck until it fits. One thing you have to be aware of is the adapter plate will be warmer than the chuck from the machining. This makes the adapter bigger than it should be to fit the colder chuck. Probably the best way to deal with this is to warm the chuck until it is slightly warmer than the adapter. This way when they are the same temperature the fit will be tight. I like to take the final amount of material off using a file on the rotating part. This gives a smoother finish and lets you round off the sharp corner. If you don’t do this the fit may end up being too loose as the sharp corner and rough finish can fool you into thinking more material needs to be removed.
The adapter is attached to the chuck with three Allen head cap screws. In this picture the adapter is mounted on a rotary table on the milling machine. The three mounting holes have been drilled. To align the drill with the holes in the chuck I placed the collet chuck on the plate and put a rod in the drill chuck and aligned the mill table until the rod just fit down one of the bolt holes.
Here is the final result with the chuck mounted on the lathe. I have yet to measure the run out but I did a test cut on this brass rod and it ran well. One last thing to do. The mounting screws stick out the back of the adapter plate a little bit. I want to shorten them so they don’t stick out to eliminate a possible snagging hazard.