The mini metal lathe had quite some run-out in the 3-jaw chuck, so I thought to try to truing using a grinding stone and a dremel. I just need some custom mount for the dremel and a custom ring to apply pressure to all the 3 jaws in the chuck, so I thought it could be done using 3D printed parts, why not 😉 !!!!
So using a CAD software the mount and pressure ring were done and 3d printed using 90% infill and ABS blue filament. At the end of the document you have the STL files, in case that you can use it in your lathe.
After, i need to make an extension for the grinding round stone because the length of the shaft was short. So I used a brass solid rod and drill a hole to fit the grinding stone and in the other end reduce the diameter for the dremel chuck. I cut the shaft of the grinding stone and glue it to the brass extension using super-glue.
Before assembling everything, I apply some blue marker to the inside of the chuck jaws so I could visually see when all the surface has been trued. Then I use a slow speed in the lathe and a high speed in the dremel with different rotation direction, and slowly work my way through all the length of the jaws.
The end result looked very good but I discover the quality of these Chinese 3-jaw chucks. To check the precision I used HSS drills of different sizes and I discover that the run-out vary randomly with the diameter of the drill, and I think that the precision of the run-out depends of the inner spiral metal part that adjusts the jaws, which it is made probably of a not so good precision :(. So far I will have to live with it, and in the future I may invest in a better quality chuck.