The basic idea is to fix a template of the shape desired to the table of the lathe, then slide a tool holder along the table, with a tracer pin following the template and a cutting tool shaping the work.
This photo show the tool in use. Note the tool block is held firmly against the table, but can be slid around to follow the template. One important point for my holder is that it can be angled into the work to make sharp corners, where conventional duplicators only allow the tool to move perpendicular to the work
I made two tool holders, one holds a round nose tool which gives a smoother finish, but cant get into sharp corners, and a square nose tool for the corners. Each tool has a follower that must be exactly the same profile as the tool. This ensures that the part is cut exactly to match the template.
The block is simply an aluminum block of a handy size. The hole for the tool can be made by clamping the block to the lathe slide and drilling in place. This assures the tool will be exactly on center of the work. The hole for the tracer pin needs to be at a height to match the template. Drill and tap the blocks for set screws to hold the pins in place.
It is important to keep the projection of the tool from the block as short as possible. If its to far out the leverage on the block will increase making it harder to hold the block.
I made both the tool and the tracer pin from round stock, both cut to identical shapes. The tool is then cut off half way to make a cutting edge. Use drill rod (or Silver Steel as the English call it). Harden and temper the tool, but you can leave the tracer soft, unless you plan to make thousands of parts with it.
The template is held to the table with a simple aluminum strip with a slight rebate cut along one edge to align the template. The allen screws are used to lock the T nuts to the table, the brass thumb screw holds the template in place.
I made this template from brass, but even plastic will wotk, and is easier to shape.
When you start a part place the template on the table and adjust the lathe X travel so the tool is cutting to the correct diameter. Its nice to have the end of the template made to the size of the raw stock. Just hold the tool against that part of the template and adjust the slide until the cutting tool is just touching the work. If your part had large cuts it might be wise to make a rough pass with the template adjusted closer to the front, makeing a lighter cut. You could then increase the cut depth is a few passes until the part is to finish size.Return to main page