Sunday, May 23, 2010

The Compound

While installing the toolpost on the lathe, I took the compound apart for the first time.

The compound is a part of the lathe that the tool holder sits on. It can swivel to allow a tool to present a more suitable cutting edge to the work. A screw mechanism allows the compound to be advanced and short tapers turned.

The compound is pretty simple. When the compound is swiveled, it is locked in place by 2 bolts. When tightened, they drive 2 angled steel pins into the hub on which the compound rotates. The pins lock the position by friction and draw the compound down against the carriage by their geometry.

Much to my horror, a previous owner had made an exciting enhancement. He had apparently lost the angled pins. Instead of making more, he turned points on two steel bolts. The points dug into the hub, gouging divots. The divots will prevent the compound from locking up at the right position, or may cause the compound to move unexpectedly. Horrible. I find it extra frustrating since it took only a few minutes to make replacement pins.

Here are the bolts that damaged the hub and the proper replacement pins I made.

I replaced these bolts with common hardware store bolts and turned a 'dog point' on each as per the originals.

Now a couple of pics of the hub showing the damage.

After getting a lot of good advice from the HSM on how to fix the hub, I won a far better casting on ebay for a very good price. That's good because I'm getting pretty tired of fixing abuse.

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