C3 Mini-Lathe Metalworking Beginners

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7x12 mini lathe in fetching blue!

Mini-lathe torque - gear changes


The standard 7x12 mini-lathe is a wonderful tool. Like all wonderful things, we do like to make custom modifications to improve an already useful tool.

As you progress in your lathe ownership, you will want to cut bigger and bigger jobs. Eventually you might decide that the mini-lathe is no longer for you, and that you will buy a bigger lathe. Good luck to you!

However, there is no escaping the fact that the standard mini-lathe is a little lacking in low end grunt. At the same time, the maximum speed is rather high, and only used on finishing the occasional polishing job. At the same time if we added a huge motor to the mini-lathe, we would have problems. We would have loads of torque, but the structure of the lathe would not be able to handle it. Things would bend. It is a bit like trying to put a F1 engine in a mini - you would be able to do it, but the chassis really won't handle the power too well.

Now, it occurred to me that a small increase in either power or torque would be of benefit. Perhaps an extra 10 per cent or so. Not a vast improvement, but enough to make working a little more comfortable in certain situations.

This idea occurred to me at about the same time I broke my mini-lathe. The mini-lathe is powered by a 300W electric motor, which is controlled by a PWM (pulse width modulation) controller. A small gear on the motor is linked via a belt to a bigger gear on the lathe spindle. Thus the speed of the motor is geared down making the mini-lathe spindle turn more slowly than the motor.

This gear is made from cheap low quality plastic. Over some over zealous beginner mistakes, the woodruff key which hold this gear to the motor shaft disintegrated leaving the motor spinning and the gear not turning.

This gear has 18 or 19 teeth. I sought a replacement. On visiting the website of the supplier RS - http://rswww.com I found a range of metal pulleys with the same pitch as the mini-lathe original motor pulley. However, I selected one with only 14 teeth. The metal gear was much better made than the original on the mini-lathe. I did need to drill it out to the correct bore and insert a set screw.

On the mini-lathe spindle, the big pulley gear has 45 teeth. So the original reduction was 2.5. With my new gear I get a reduction of 3.2. Further gears inside the headstock reduce this further before you reach the spindle , but I think my modification with a smaller motor pulley will reduce speeds on the lathe by maybe 20%. Hopefully this means the torque is increased by 20%.

The increase isn't really enough to increase the chances of you breaking anything on the lathe, but it certainly makes life more comfortable. I recommend any mini-lathe owner replace the plastic motor pulley with a metal one with a smaller tooth count.

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