Homemade 4-jaw lathe chuck and faceplate
New headstockI wanted to try making a wooden four-jaw chuck for my lathe. My plan all along was that the four jaw chuck would be permanently attached to a drive shaft, which I'd swap into the lathe when I needed to use the chuck.
But I wanted this drive shaft to be a bit thicker to have more support for bowl turning, so I used some 16 mm polished steel rod that I had lying around.
This meant I needed bigger bearing blocks. I also wanted to switch to hanger bolts to mount them. With those changes, I needed the mounting holes to be further apart. The easiest solution was to just make another headstock for the lathe.
The "hanger bolts" have a wood screw thread on one end and a machine thread on the other. I jammed two nuts against each other on the end of the bolt and used a nut driver in a drill to drive them in.
I used the same method for shaping the pulley as last time, with the V-belt first riding on the unshaped lower step pulley. I had to make some blocks to clamp on either end of the shaft to keep it from sliding side-to-side.
Making the four jaw chuckI used my BigPrint program to print a 1:1 template of the main part of the chuck, and cut it out of Baltic birch plywood.
A piece of threaded rod will go into each of the four slots. This needs to go in fairly precisely. So I made a drilling guide that fits in the slot to help guide the drill. I drilled 15/64" holes for the 1/4" threaded rod (the holes are slightly smaller than the threaded rod).
I used a nail as the pin. Usually when I do this, the holes end up not quite through the center, so I orient it so the misalignment is in the same direction on both parts. But this time, I got the hole in the shaft unusually centered. I expanded the hole in the wooden part a bit so the pin could go through the center of it.
I ground a point on the end of the pin (which is just a cut-off nail), then used a piece of wood and a hammer to drive the pin through both parts. The point on the end helps to align the parts as it goes through.
I sized the holes so that the 1/4" threaded rod fit tightly in the holes in the chuck, but to make extra sure they wouldn't pull out, I also put wood glue in the holes and on the threads. Wood glue doesn't stick very well to the metal, but it will stick to the wood and form threads that mesh with those of the threaded rod.
I expanded the hole in the guide block to 1/4" and then used it to help guide the threaded rod in straight.
I was very careful to get these very precise.
Here drilling the holes, 17/64" in size to provide a tiny bit of clearance with the 1/4" threaded rod. I marked the locations by scoring with the jaws of my callipers, then punched a divot using an awl. The point of the Forstner bit naturally follows the divot.
The jaws need to have a sort of "dovetail" cut into the inside of them. I figured the best way to cut that was on the lathe. I made some spacers to allow me to tighten the jaws while they are still moved all the way out.
In fact, this whole chuck is kind of scary unsafe. If the threaded rods come loose, or the nuts become undone, part of the chuck would just go flying. Staying out of the plane of rotation of the chuck, and/or using a face shield would be advisable.
Having turned these jaws on the chuck itself, it automatically compensates for any wobble that the main body of the chuck may have, provided I always put them back in the same slots. So I numbered the jaws and slots to make that easier.
The idea of these jaws is that they clamp onto a dovetail that is turned onto the bottom of a workpiece. But to turn the dovetail on the bottom in the first place, a raw blank first needs to be mounted on a faceplate with screws.
So before I could try out this chuck, I needed to make a faceplate.
Making a faceplateMaking the faceplate was very similar to making the chuck, but simpler.
I started by drawing two circles on a scrap of Baltic birch plywood. I like to draw arcs from the edges to work out how close to the edge I can draw a circle.
A normal faceplate is detached from the lathe when mounting the blank. But with this faceplate, the entire drive shaft and pulley is removed, and that pulley gets in the way. Screws at an angle make it easier to get the screwdriver in.
I had about 8 mm of gap on the shaft. To avoid having the shaft move side-to-side, I needed to make a spacer to go in this space. I measured the gap, cut a piece of wood to that thickness on the table saw, then made a spacer and cut it in half.