Had a busy workweek away from home, and by Saturday morning, the itch to make some chips on the lathe is strong. Since I’ve just received the movements, I have yet to start on the watchcase project so I need to find something simple.
I looked around the project room and found a waste piece of brass hex stock that I had from my first keychain project (on a Unimat!). I remembered that I wanted to build a vertical incense holder for the longest time to be added to my incense box from India. This is as simple as lathe work is concerned. The hex was chucked in a three-jaw, drilled for the incense, and random cuts made to form a miniature vase. Then a light filing and sanding complete the piece.
Satisfied with the product, I started to look for the next victim. This one is a bit eccentric. I have been building the CNC stepper drivers and PC to run the Sherline Mill. Despite the mill being in Imperial units, I will be running the CNC in Metric. Not sure what I was thinking at the time, but I bought a 10mm edge finder to keep everything metric. This presented an obvious issue with the toolholders on the Sherline (Imperial). I must have figured that I can just turn down the shank to 3/8″ to fit the endmill holder I have – 3/8″ is 9.525mm so just a trim of 0.475mm is needed.
Well, it was a cheap eBay purchase, why not give it a go? Turns out (pun!), the hardest part of all of this is the chucking. The four-jaw chuck is critical to center the shank and a dial indicator was key to confirm concentricity. After much adjustment, I managed to get to it within a thou (0.001″) which was good enough for its use. Now comes the next hardest part – I’ve never worked on steel! I figured the standard carbide cutter is enough and geared down the lathe to its slowest speed. Hope for the best?! The first pass surprised me with ease, but I knew something was not quite right. There was some chatter and the end farthest away from the chuck clearly showed some minor deflection. I thought this would happen since the piece was thin and hard and blamed it on the large radius of the carbide. I then switched the cutter with a small radius (thread) cutter and tried again, this time with slightly better results. Then it hit me, I needed lubrication! Of all the good YouTube makers, I’ve never seen anyone that didn’t brush on a nice coat of cutting fluid on their steel pieces. How dumb of me!
Fast forward and I got the piece within a thou or two of the final dimensions. To get down and smooth, I filed the piece gently with extra cutting fluid to remove the small filings. Feeling it with my fingers, I still don’t think it is smooth enough. I had some fine sandpaper, but they just get clogged so easily and are a pain to hold flush to the piece. I then remember that I have two sets of ceramic sharpening sticks (for my kitchen knives). The ceramic sticks worked wonderfully, smoothing out any tool marks and allowing the shaft to fit firmly into the 3/8″ toolholder.
Results! The edge finder was chucked to the mill and the dial indicator found less than three thou of run-out. I was a bit disappointed but I figured it will be good enough for most of my projects and perhaps not so bad in actual use. I then trialed it a few times and found the repeatability is within 0.2-0.3 of a thou! That should be more than enough!