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Duplicating bridges with my
3-D Carver
© Frank Ford, 5/8/98; Photos by FF, 5/7/98

Here's my little machine:

It has a sliding table that moves in two dimensions, and a carriage that moves up and down with a stylus and cutter. I can guide the stylus over a pattern as I move the table around, and duplicate any small object with real precision.

The cutter is driven by an air turbine at 40,000 rpm. This turbine is no where near as heavy or loud as a router, and at that speed the cutter hardly "pulls" at all.

I made the machine around these very heavy duty Thomson Ball Bushing units:

Each unit is rated to handle a working load of 600 pounds and moves effortlessly on ball bearings. They are so precisely made that there is no looseness or play at all! (The only negative thing I can say about these bearings is that they are expensive.)

The simplicity of this design is that I didn't have to machine anything with precision. (That's what I need because I'm no machinist!) All I needed was to have the stylus and cutter move over identical paths, so I didn't even have to make sure that the bearing slides were exactly perpendicular. As long as the stylus and cutter are rigidly held on their carriage, everything else falls neatly into place.

Here's the machine from the back:

Here, I have the vertical carriage balanced with a lead weight hanging from the ball bearing pulleys. As I guide the stylus over my pattern I have to exert very little effort to make contact. Even if I bump the stylus really hard the cutter doesn't dig in because the bearing units are so rigid.

Each horizontal bearing slide has a 1/4" thick steel top to increase the mass and stability as I move the slides around.



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