I don’t need no nanny

In the recent “From the Safety Files” column (Poor design contributes to an eye injury,” July 9 issue), the safety expert says that a “rental center employee should also have provided an owner’s manual and safety documentation with the mower.” So hopefully the next grocery cart I use will come with proper documentation to keep me safe. He also says, “Better training might have taught the renter to let go of the lever that kept the mower operating.” This is another classic case of trying to blame someone or some manufacturer for operator incompetence. So I guess that wood chipper I am going to rent better come with a full Kevlar body suit and maybe even some .pdf operating files so I can refer to them on my Blackberry during operation.

James Kurk

The next time you are in a grocery store, read the warnings on the grocery cart. They are there because of accidents and serious injuries involving grocery carts. If you were to compare the design of the earliest grocery carts to those available today, you would see they are much different. Carts today have far fewer, if any, pinch points and their center of gravity has been moved toward the front wheels. So you see, grocery carts do come with proper documentation.

Most machines, equipment, and accessories from rental companies are dangerous if not used properly or if the equipment is not maintained properly. In most cases, the equipment is being rented by week-end warriors who only have a general idea how to use them. Without proper training, or if the equipment has not been properly maintained, it could cause accidents and serious injuries. That is why OSHA requires all employees be properly trained in the jobs they do and the equipment they use, and that includes wood chippers.

I see you work for a medical firm. Do you think your company would condone a heart specialist using one of your products without the in-depth training your company offers? And don’t say this is a stretch. It is no more a stretch than the comparisons you are using. Picture the heart surgeon having to refer to a Blackberry for step three of the installation process in the middle of an operation to implant a heart valve. — Lanny Berke

Who goosed the moose?
Though a recent Backtalk article (“Bird + Plane = Possible disaster,” June 18) cited two wildlife experts, you still managed to make the common error of calling the bird a “Canadian” goose. No such bird exists. The Canada goose is named for a person and not the country. Therefore it is always a Canada goose or Canada geese.

Ralph Heady

Our online bird expert, Lisa Shea says: The vast majority of English-speaking people call the goose that is large and has a black head -— Branta canadensis — a Canadian Goose. However, the name given it by early English settlers was Canada Goose.

Remember, the official name for any bird is its Latin name. So the “real” name for this creature is Branta canadensis. That’s because the bird probably has 200 different names in 200 different languages, based on its colors, its sounds, its habitat, or any of a hundred other reasons. The Latin name is the same around the world for that bird.

So it’s true that at one point in time Branta canadensis was called a Canada Goose because it was often seen flying toward Canada and living there. And over the years, the name has changed to become Canadian Goose in English. Just as people in the 1600s used to call pumpkins “Pompions” and vegetables “potherbs,” we have changed what we typically call the Branta canadensis to Canadian Goose.

DDM for antiques?
My hobby is restoring antique vehicles and sometimes I need parts that are simply not available. Often these parts are cosmetic, but they can also be functional and structural. I have been reading a bit about stereolithography and believe it might let me make one-off parts after I get a computer file describing the part from some sort of digitizer. Cosmetic parts could be almost any material, but functional and structural parts would likely have to be metal, and perhaps high strength. From what I have learned, we are close to being able to do this, but not quite yet. Would you comment on this and direct me to some other reading that would help my understanding?

Tim W. Elder

Your quest for replacement antique parts is shared by the Dept. of Defense as it tries to extend the life of weapon systems, as well as by auto aficionados who want to maintain rare automobiles for which replacement parts aren’t available. In both cases no tooling or even drawings for replacement parts exist. There are two ways to get there, after, of course, a laser or optical scan is made of the worn or broken part and converted to a CAD solid model in .STL format.

First, the model can be reproduced in a plastic pattern that is used to make a mold for conventional sand or investment casting. The plastic pattern can be fabricated by one of several additive manufacturing methods, including laser sintering, fused-deposition modeling, stereolithography, and 3D printing. Several service centers are available to produce such patterns, and some of them have connections with foundries which can make the casting. (Go to JayLeno’s Garage at http://www.jaylenosgarage.com/video/video_player.shtml?vid=944641 to see a demonstration of the scanning and fused-deposition modeling to produce the pattern.)

Second, the part can be produced from a CAD solid model directly in metal by additive manufacturing processes such as laser sintering, E-Beam, or 3D printing and sintering. Again, service centers (fewer in number than for plastic parts) can make parts in metal. A wider variety of alloys is available by laser sintering than by 3D printing and sintering.

A third approach actually exists, and that is to print the sand mold directly by 3D printing. No pattern is required, and cores and molds can be printed together. This approach is popular at DoD, which has several 3DPrinter installations that turn out replacement parts. In addition, the process is used extensively by many OEMs with short-run production requirements. My company has a contract shop to make such molds.

The best approach depends on part loading (strength required), tolerances, and finish desired. If you would like to discuss your application further, my contact information follows. — Howard A. Kuhn, Ph.D., PE Director of R&D, The Ex One Co. LLC, howard.kuhn@exone.com