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…

IMAG0269Tool Post

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.
IMAG0592

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.
IMAG0595

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.
IMAG0609

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

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7 thoughts on “How to Make a Quick-Change Tool Post – Part 1

  1. ooo very exciting. Looks really good.
    Your lathe looks similar to ours, though we had a quick change tool post with it – definitely a super useful addition!
    One question: I had been told that 3 jaw chucks don’t like anything that isn’t round (unless they are independent jaw ones – which I think are quite rare?). Could be worth checking, as I think it can affect the accuracy of the chuck…
    What was the metal you are using? looks to finish really well.
    Thanks for sharing.
    B.

    • Thanks!
      I’m working with cold-rolled Steel, I’ve really been enjoying it.

      I’m sure accuracy is affected somewhat by offsetting the workpiece in a 3-jaw chuck, but since I still had 2 surfaces referencing against the jaws, I figured it would be acceptable, and it was.

      I need a 4-jaw chuck, but I’ve actually even used the 3-jaw on a square workpiece before to bring one end down to a cylinder, and then flipped the workpiece around to shape the rest of it with the round end in the chuck. It worked very well.

      In my experience I’ve found that “ideal” and “correct” have similar usefulness to “precision“.

      Thanks,
      ~Andrew

      • Hi Andrew. Agree with you about going with what works. I din’t mean that there would be precision during the actual operation.. The way I understood it, and I might well be wrong, was that it might prematurely wear the 3 jaw chuck, such that when you use it in future operations – say to turn down one face so it is exactly concentric to the one being gripped, or to centre drill a hole in the exact middle… The kinds of things a 3jaw can do reasonably accurately and very quickly – but would take a load of setup on an independent 4 jaw chuck.

    • I see what you’re saying. In terms of premature wear on the chuck, its important to make sure all teeth are engaged in the workpiece to that pressure is evenly distributed, but I don’t misuse my chuck often enough to be too worried about this.
      The biggest downside of using non-round workpieces in a 3-jaw chuck is that you have to remove a lot of metal to get down to the right shape. And, because the workpiece is not in constant contact with the cutter, you have to run at a lower speed/feed rate.
      But it works in a pinch, and even if I also had an independent jaw chuck, I would probably still use the same technique to create a cam, because it’s much easier than switching the chuck.

  2. Pingback: How to Make a Quick-Change Tool Post – Part 2 | GarageSandals

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