Getting Started on a Design

You finally have that product specification completed and can begin designing the gearbox. The gears, you will quickly find, are the easy part; especially if you have access to modern software and good information on the interface connections. I was over twenty years into my career when they took my drafting board away and made me learn Computer Aided Drafting [CAD]. Once I overcame my unfortunate tendency to delete my files, it really reduced the time required to get a design roughed out for cost estimating and pricing, topics we will get to next. The computerized design process is quicker because you do not have to wrestle with a huge piece of paper and continually sharpen pencils and verify that your corners are square. If you were a good designer on paper, you were a better designer on the screen. Computers did not improve the results of the un-organized or sloppy draftsman, however, Regular readers of this blog will know that I advocate maintaining a “book of knowledge” with guidance on all the things you need to “look up” during the design process. I began mine as an apprentice back in 1971 and it was invaluable in keeping up with my design backlog over the years. I also follow the same procedure that I was taught in the days of 2H, 4H, and 6H pencils. First line on the screen is a dotted centerline for the output shaft. All the other “envelop” dimensions then get added so I know how much room I have to work with. Nothing is more frustrating that working out a great set of gears than finding out they will not fit in the space available. Understand your “constraints” before you put too much effort into the gear design. The same with the input and output shafts; make sure you have a shaft diameter that will transmit the load and has room for adequate bearings. This is a place were that “book of knowledge” shines. Consider it your “playbook” where you keep track of bearing arrangements that “work” with gears of the type and proportions typical of your shop. Designing is not inventing; you may need to vary the size of the “wheel” for your situation but it will still be round.