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01/31/2018
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Converting A Manual Jeweler’s Rolling Mill To Automatic

We recently posted a video on our YouTube Channel of some new tools we're adding to the work are at the shop.


A comment was made on that video requesting an in-depth explanation of how we had replaced the lever arm on our manual rolling mill with a geared electric motor. While not precisely complex, the process of converting a manual rolling mill to automatic / electric isn't exactly simple either. You need to take into careful consideration the power / torque requirements, the control scheme, and how you intend to attach the motor to the mill itself.

Let's begin with selecting a motor. We chose a Bodine Electric NSH-54RL brushed DC gear motor. Bodine manufacture(d) these motors in a range of different specifications, mainly changing the rated speed, torque, and gear ratios. The one we used for our rolling mill conversion is a 115 volt model rated at 1.2 amps (peak), producing 1/8 horse power. In the video explanation of our conversion, there is a slight error in reference to the motor's gear ratio. In the video, we stated that it is a 10:1 gearing ratio - in reality it is a 30:1. The motor is rated at 1725 rpm, reduced to 57rpm by the right angle gear box. All of the above stated specifications make this motor ideal for powering a rolling mill. The 75 inch-pounds of torque it generates means that anything inserted into the rollers is virtually guaranteed to come out the other side without binding, and it's maximum speed of no-more-than 1 rotation per second means the newly thinner piece won't be shot out the other side at unmanageable speeds.

The control scheme for the motor comes next. Any given motor is going to need a power supply of some kind, preferably one that allows a reasonable degree of control over the motor's speed. Every mill / motor combination is going to require it's own control solution, so chose accordingly. The controller we chose for our motor is a Bodine Electric BSH-200 DC Motor Controller (Part # 431-00037). We chose it because it allows easy control over the motor's speed, but also over its direction if properly wired. Because our motor is a DC gear motor, it's actually wired in a 5-wire configuration with the green wire going to ground / earth, the black and red wires going to the motor armature, and the white and brown wires going to the motor field circuit. When wired to the controller with matching colors, the motor spins one way. When wired with the red and black wires reversed, it spins the other.

Lastly, the motor's output shaft needs to be coupled to the mill's input shaft. In our case, this was straightforward on the surface. The mill has a 22mm diameter square-keyed input shaft. The motor has a 16mm diameter square-keyed input shaft. We designed a simple coupler for these in McNeal's excellent modeling software Rhinoceros. While we can cast just about anything in gold or silver, we weren't quite so comfortable with casting stainless steel. Instead, we had the coupler fabricated from black stainless steel by Shapeways. We've included a parametric version of the coupler here. It's provided as an OpenSCAD model. Simply change the relevant numbers in the script window for the diameter of your mill's input shaft and your motor's output shaft. OpenSCAD will do the rest, and the resulting STL file can be uploaded to Shapeways for production, or printed on any 3D printer you'd like.

We're more than thrilled with the performance of our new rolling mill. It cuts the job time down on any from-scratch fabrication job by a considerable amount. We even used it to produce the flat-stock for making the gold baskets in our follow up video to this article's accompaniment here. We'd love to hear your feedback on this one, and of course we're happy to answer any question. Just leave them below in the comments.

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