March 2012 / Volume 64 / Issue 3|
Primer on the 'king of machines'
By Tom Lipton
The manual lathe is the cornerstone of any machine shop because almost all shop workers find themselves working on one when they start. The manual lathe has been called the “king of machines,” for good reason. Some can be enormous; you can bet that if you need a forklift and a ladder to put a tool bit in the machine, some fun is bound to happen.
Courtesy of T. Lipton
Anyone who has spent time on a modern lathe would immediately recognize all the design features of Henry Maudslay’s revolutionary screw-cutting lathe, which he built around 1800. It is one of the oldest machines in which the look and features have not changed much since its invention. Joseph Whitworth, another famous Englishman, added the compound rest, significantly transforming the original design into the modern engine lathe.
I started on a lathe in high school. At the time I was disappointed; I wanted to be assigned to the welding section because I had been welding for some time and was eager to demonstrate my skills.
The school had four Rockwell 9 " or 10 " manual lathes on one side of the shop. These lathes had the old rocker-style tool posts, quick-change threading gearboxes and taper attachments that took a little head work to figure out. The funny part is I somehow spent the entire semester on the lathes. I learned a tremendous amount and enjoyed the work immensely.
My first project was a stylish aluminum meat tenderizer, a definite must have for every kitchen or crime scene. The project involved straight and taper turning, threading and knurling.
Like almost all high school machines, the corners of the compound rest on our lathe were hammered to death from running them into the spinning chuck jaws. The shop teacher fabricated aluminum blocks and glued or screwed them to the compound, enabling them to serve as sacrificial beating blocks for lathe newbies. Take note, this improvement increases a lathe’s resale value. Among the first items used-machinery shoppers look at are the condition of the ways and the corner of the compound. A clean, crisp corner on the compound is usually an indicator of a gentle life.
A few years later I got my first lathe, a 1915 Prentice with a 9 " swing. It had a flat leather belt that made a unique tick-tick-tick sound as the joint in the belt passed over the sheaves. It came with a huge stack of change gears for threading. If you want to learn to run a lathe, start on one that’s old and loose. When you can produce parts on that type of machine, you will be a superstar on a tight, modern machine. It took me a week to figure out how the clever little planetary back gear setup worked.
The guy I was working for “offered” to let me store it for him while he was going through a divorce. After a couple years, I bought it for $300, which was a huge sum because I was only making $3 an hour working part-time.
A funny thing happened with that old lathe that took me years to get over. One day the cross-feed screw just gave up the fight. It had been getting pretty crunchy, so its demise wasn’t totally unexpected. I took the slide apart and looked at the remains of the screw. It was fine at the ends, but the center section was obliterated.
I decided to make a new screw and nut on another lathe. I carefully measured the screw and nut, and decided to upgrade and make a stainless steel screw. I even remember the thread: 7⁄16 -20. After a few evenings of fussing around, I had my new lead screw and cool bronze lead screw nut. I was extremely proud of my downright cheapness and felt a head-swelling self-sufficiency about this time.
I put everything back together and got a big surprise when I went to spin the cross-feed handle. The thread was supposed to be a left-hand one but I made a screw with a right-hand thread. Once I realized my mistake, the visual difference in the screw was obvious. Whoops!
I didn’t feel like taking the machine apart again and making a whole new lead screw and nut, so, head still swollen with pride, I left it in and started using it—big mistake. It took a bit to get used to the weird backward direction, which should have been my first clue I was headed for trouble. But after a while, it was second nature.
The real problems started when I began working in a machine shop. I must have gouged a zillion parts before I unlearned the right-hand lead screw.
The moral of the story: Don’t learn anything the wrong way just because it is easy; you never know when you might have to unlearn it. CTEAbout the Author: Tom Lipton is a career metalworker who has worked at various job shops that produce parts for the consumer product development, laboratory equipment, medical services and custom machinery design industries. He has received six U.S. patents and lives in Alamo, Calif. Lipton’s column is adapted from information in his book “Metalworking Sink or Swim: Tips and Tricks for Machinists, Welders, and Fabricators,” published by Industrial Press Inc., New York. The publisher can be reached by calling (888) 528-7852 or visiting www.industrialpress.com. By indicating the code CTE-2012 when ordering, CTE readers will receive a 20 percent discount off the book’s list price of $44.95.
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