The first part of this project uses basic lathe techniques - tried-and-true techniques you pick up when you take the Metal Lathe SBU class at the shop. Put to awesome effect!
Step 1: Tools and Materials
- Cutting tools with interchangeable carbide cutting points
- Center drills for the lathe
- Drill bits (larger than 1/2" - I chose one the size of my desired inner diameter, or ring size, for the ring.)
- 1 1/8" diam free-machining brass *careful, "free machining" means it has lead in it. DON'T WEAR THIS MATERIAL!*
Step 2: Boring the Center Hole
The first thing I did was insert the cutting tool in the holder, then adjusted the height in the holder so the point of the cutting tool is JUST below the center line. Which you should know, really, if you're already at a project-making stage on the lathe.
Then I faced the end of my material - fed the cutting tool across the butt end of it to remove maybe .010" - a very light cut to even the surface (no picture, sorry.)
Next, I chucked a substantial center drill into the end stock of the lathe, and advanced it into the material. Look for my speeds and feeds calculator on Instructables to decide how fast to spin your material in relation to the drill bit size. The idea is that we'll pre-drill a hole with this sturdy, self-piloting bit, then open the hole with a drill bit the size of our desired inner diameter.
As you can see!
To be totally clear, we'll be left with a slightly *small* inner diameter because a) the bit isn't quite the right size and b) we want to leave some material which will be removed during the sanding and polishing stages at the end.
Step 3: Cutting the Outer Diameter
I bring the cutter point to the butt edge of the stock. It should be perpendicular to the spinning material and also just below the center line. I'm not a very experienced machinist but I noticed that the cutter cuts "across" the point, in a way; the cut really ends as the far end of the point passes by. In other words, the cutting point isn't really a single, sharp point like a needle. So I advanced the cutting edge into my material *just a little* to call that the very end of a cut. The point is *just* biting into the butt edge. Then I set the digital readout to X = 0 and Z = 0.
I run the cutter very lightly down the length of the material - 0.010" - to even the surface. Remember that we started at 1 1/8" (1.125") diameter, then we removed something like 0.010" So we're left with 1.115". Any advances in on the X axis represents something *subtracted* from the *radius* of the material. To remove material, plan on taking away maybe 0.020 each pass. Slow and steady. I made sure my material was spinning at the right rate (Speeds and Feeds charts!) I also used the auto-feed on the cutter, which was itself moving at the correct speed. *whew*
So just to get a good concept of constructing your ring:
- Start with the inside diameter - the size of the ring. You'll drill out that size (a little smaller, actually.) 0.732"
- Divide that size in half, to have the radius of the ring size. 0.366"
- then determine how "thick" you want the ring to be. 0.08" perhaps. Think of your ring as the "radius of the ring size PLUS 0.08" " Total = 0.446"
- So now, when you move in with your cutter, think:
" I started with 1.115" diam of clean material; that's 0.5575" in radius. I want to be LEFT WITH a ring that's 0.446" in radius. So I'll move in 1.115" - 0.446" on the X axis - that's 0.669" "
You with me? Thinking this way will get you THIS MUCH CLOSER to CNC, too.