In my last post I covered making a duplicate of my Hendey’s spindle threads in preparation of fitting a four jaw chuck. I needed a piece to make a back plate out of and Gill came to the rescue by providing a back plate from a worn out chuck he doesn’t use. It was around 6″ in diameter and had a 1.5×8 threaded hole in the middle. I started off by reducing the outside diameter of it down to a little larger than my needed diameter of 4.75″.
The back plate is made of cast iron. This is my first time maching cast iron. I found that it turned well but made a huge mess. With steel you get chips or strings of steel when turning it. Cast iron makes tiny chips and a lot of dust in contrast. I ended up clamping a piece of flashing to deflect the stream of small chips and started removing material.
Next, I started boring out the inside in another first on my lathe. Boring is interesting since you can’t see the tool cutting compared to normal cuts on the outside. Luckily, I wasn’t boring into a blind hole and could let the lathe feed the tool out the back of the plate.
Here’s another view of the boring.
Once I’d finished boring to the minor diameter of the threads, I removed the step on the back plate.
Next, I started threading the inside of the hole. I made multiple passes, cutting deeper each time, until the thread crests started getting small. From that point I alternated taking a light pass and trying to fit my plug.
Once the plug just started to thread in I knew I was close. I took another pass and found that the plug would thread in tightly. So, I took one last pass followed by a spring pass and tried the plug again. Perfect!
Now that the plug fit, I flipped the back plate over and bored out the inside some. This is required because the spindle has a generous radius as it transitions from the threaded section to the surface the back plate sits against. I also took a pass to clean up the back of the backplate. Finally, I put a small chamfer on the inside and outside of the back surface.
To see how I’d done, I removed my three jaw chuck and threaded on the back plate. It fit well.
Now that the back plate is on the spindle, like it will be when put on the chuck, I finished machining the outside and front surfaces. I made sure to leave a small area untouched next to the spindle because I didn’t want to risk hitting it. This small step isn’t a problem because of the hole in the center of the chuck.
The last step is to put some threaded holes into it so I can attach it to the four jaw chuck. To start this, I positioned the back plate in the chuck and used a transfer punch to mark the hole locations.
Then it was down to Gill’s to use his mill to actually drill and tap the holes. Note the use of the “don’t mess up Gill’s table” aluminum plate. Better safe than sorry.
The holes were located, center drilled, through drilled, chamfered, and hand tapped using the mill to keep the tap straight.
Here’s the finally finished back plate!
I returned home, put the back plate on the chuck, and installed it on the lathe. Success!
So far all I’ve done is turned the lathe on with the four jaw chuck installed but I plan to make use of it in the future for a project.