Phil dropped by to have a look at my lathe, because I am unable to make a clean cut unless I take at least 0.005" off at a time. Since it's often useful to take off 0.0005" I was clearly not doing well. We decided that the problem was excessive play in the carriage of the lathe - the bit that carries the tool and moves along the work.
I found a plan on the web that offered a solution within the range of my abilities, so I bought the plan. Phil gave me a gift to get me started: enough bearing bronze to make the part I needed. He even cut it into rough slices on his big bandsaw.
I went to work on the bronze using my mill, making the two large faces flat and parallel. I was using a fly cutter to rough out the parts, and since the face was not flat to start, I was sort of "cutting uphill," taking a cut that got deeper as it went along. I was trying to limit my cut to 0.020" on any pass.
Phil later advised me that 0.020" was too big a bite for my little mill. I had gotten that number from a YouTube video from a teacher I trust, but of course, he has a big, heavy Bridgeport mill that is designed for heavy work. But, things seemed to be going well with my cuts, right until the time when the mill decided it was done cutting for a while! By then, I had two slices that were flat and parallel, but still too thick:
I knew exactly what had happened to my mill. That model is notorious for the plastic gear in the mill head. It eventually strips, wears out, or shatters. I was actually excited that it happened, because there's a permanent fix that also makes the mill better in every way, and I had been looking for an excuse to buy it from Little Machine Shop.
The repair kit converts the mill from gear drive to belt drive, making it much quieter, and also expanding the speed range of the spindle. It arrived late yesterday, and I was very pleased with the quality of the parts:
I did have a laugh at the indication in the instructions that the upgrade could be made in 10 to 15 minutes. I needed more than that just to understand the 29 steps in the instructions! All in, it took about an hour for me to make the change.
First job was to dismantle the mill. There's a special wrench included with the mill to get the spindle nut off so you can reach the plastic gear.
When I got inside I could see the failure mode of the existing gear. It was not, as I first suspected, sheared or broken. Instead, it just plain wore out. The plastic gear is spun by a metal gear on the motor, and every time I used the mill, it shaved a bit more of the plastic away, until it finally didn't mesh at all. The pile of plastic shavings on the housing and in the cover told the story:
No need for step-by-step photos, since the process is well documented elsewhere. Here's the mill, with repairs completed and ready to work.
As a test, I milled the surface of an aluminum block, and all worked perfectly. Well worth the time and money! After the Thanksgiving holiday is done, I'll get back to work on that bronze, and make my lathe better too.
While Phil was at Grant St., he looked around and said, "If I had this much space, I'd have a Bridgeport in here in a heartbeat." Well, there's a concept! Kind of a big step for a beginner, though. Just for fun, I grabbed a picture of a Bridgeport mill off the web, and matched it in scale to a mill like mine. It's bigger!
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