How to Make a Quick-Change Tool Post – Part 1

I have a metal lathe.

I’ll just let that fact sink in for a minute

Impressed?

It’s a relatively small Chinese lathe sold by Harbor Freight long ago and purchased by me from Craigslist a while back.

I’ve had a lot of fun learning how to use it, and now it’s time to start putting my little machine shop to work: that’s right, it’s time to start making parts and tools to use in my machine shop.

The biggest shortcoming of my lathe is the tool post (the part that holds the cutters).
Tool Post

It’s a standard design, with four sides that can each hold a cutter, and in theory you can rotate the holder to bring each of those cutters to the workpiece as needed. The problem is that cutters have different thicknesses, and they must be shimmed by various amounts to place the cutting tip at the correct height (exactly aligned with the center axis of the workpiece).

Finding and placing the shims is a pain, and I am rarely able to get the height just right.

So I decided to make a new tool post that could be quickly and easily adjusted.

I decided the best approach would be to start with the concept of a sliding/locking dovetail, and figure out the rest as I went.

First order of business: a big chunk of metal…

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Tool Post

Tool Post
Check.

Then I drilled a hole through the center to accommodate the locking bolt and roughed out the cylindrical hub on the bottom.
Quick-Change Tool post

I significantly misused my boring head to bring the cylinder to its final diameter and smoothness.
Quick-Change Tool post

I marked, drilled, and bored out a hole horizontally through the block to fit a piston that would lock the dovetail.
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Then I went over the the lathe to make the piston itself.
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Then I drilled a smaller hole near the back of the tool holder (the opposite end from where the dovetail and piston would be). This is where I would place the cam that would move the piston and lock the dovetail.
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To make the cam, I started with a shaft that fit in the newly drilled hole and marked it where it crossed the hole for the piston.
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Then I placed a piece of a washer between the shaft and one of the teeth of the lathe chuck to set it off-center and turned on the lath and cut passes between the marks on the shaft until the cutter was removing material all the way around the shaft.
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Now I had a shaft with a cam (a camshaft) to move the piston.
I put the camshaft into place and them set the piston in the hole.
I rotated the camshaft until the piston was at its lowest point and then scribed a line.
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Then I shortened the piston to this line so that it would be flush with the surface with the cam in its low position and protruding slightly with the cam in the opposite position.
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Coming soon: Part 2 – The dovetail, the tool holders, and the camshaft handle