Effective finishing work: Medical Manufacturing

Continuing the theme of my previous two columns, presented here are additional tips and tricks for effectively performing finish work.

■ If you have a bunch of parts to be sanded at a particular angle, you can mark witness lines on the table of the belt sander to guide your roughing work. This visual cue keeps you from drifting too far from your intended angle. You can clamp a guide to the table, but that destroys one spot on the bench.

■ Use a thin masking plate when you are working with intersecting linear finish lines. This produces a crisp demarcation line between the two intersecting finishes. Be sure to use a plate of the same material to avoid contamination.

Courtesy of All images: T. Lipton

One of the guiltiest parties in the shop with regard to contamination is the dirty little wire brush on a bench grinder or buffer.

These brass laps were applied to a bearing bore (far right) and the OD of a gage (front, center). The lapping compound is diamond paste. The laps are applied at 100 to 300 rpm and stroked axially over the part length to produce a 30° to 45° crosshatch pattern.

■ Mark the materials you use abrasives on and segregate them from the other discs. I have seen some beautiful jobs ruined by a contaminated sanding disc or even a dirty wire brush. When in doubt, use a new disc. One of the guiltiest parties in the shop with regard to contamination is the dirty little wire brush on the bench grinder or buffer. It spreads its corrosive disease on everything it touches. You may have the best intentions, but this wheel is almost always contaminated with steel, rust and grease.

■ Cylindrical laps for OD and ID work are easy to make and produce fantastic results. The results are controllable down to microinches if necessary. The laps need to be made accurately, but, with a little effort, results that cannot be attained any other way are possible.

■ Dress a surface grinder wheel at a slight angle for peripheral roughing work. The edge will break down fast, exposing sharp grains for fast stock removal. Redress the wheel for fine finish work. For roughing, use an aggressive DOC and step-over as much as the wheel will tolerate without complaint. The abrasive grains must break down to continue the cutting action. If they are babied and allowed to glaze over, all your effort just turns into heat. Abrasives should be thought of as little cutting tools, much like those applied on a lathe or milling machine. Properly applied, the chips from abrasive tools look similar to those from cutting tools under high magnification.

Although not an efficient material-removal method, side-wheel grinding is sometimes necessary.