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Over the past week, I had a couple of nights free to get some machining done on the Quadruped. Initially I had to clean the edges of the waterjet cut parts, and eliminate the connecting bits. After that, filing some corners into sharp edges where parts fit together. Plenty of drilling and tapping was next in order, as the design is held together mainly with screws. For the body and one leg, so far I’ve had to drill and tap a little over 50 holes to keep it all together, all without breaking a tap. (This is my first project that involved tapping screw holes)

For those who are just venturing into machining, tapping small holes such as 2-56 is nowhere near as hard as it sounds, and horror stories of broken taps ruining parts can be easily avoided if you take your time and do everything carefully.

Here are a few hints for easily tapping small holes that I found useful:
(experienced machinists can skip on ahead)

• Make sure your pilot hole is drilled perpendicular to the surface, and free from metal chips before tapping
• Use lubrication. I used WD-40, although there are specialty tapping fluids available
• Use a tapping block to ensure the tap is perpendicular to the part’s surface, and cocentric with the pilot hole. You can easily make one by drilling a hole the size of your tap’s shank into any firm material large enough to keep the tap straight. I don’t recommend using wood, metal is the best choice.  Unfortunately, wood was all I had available and I found it absorbed the WD-40, and the tap did bring some sawdust off.
• Make sure your part is firmly held in place so that it’s easy to keep the tapping block firmly on the surface. For thin parts, using a vise is a very good idea.
• Make sure that you back off a quarter of a turn often while tapping, when you feel increased resistance. This will break the forming chips and keep them from clogging your tap. I usually did three half twists forward, then one half twist back and it seemed to flow nicely
• Keep in mind how deep you have to tap. Typically twice the width of the screw you are using should be enough to properly secure your part. Just me mindful of the type of tap you are using, since a plug tap will have to go a bit deeper than this, and a taper tap will have to go much deeper.
• Clean the tap often. The chips will build up and stick, especially with the use of lubricants.
• Wikipedia has more information on tapping, and if you look around there is a lot of wisdom floating around on the net, but hopefully I have brought some of the best points togethor here

After all the finishing, drilling and tapping, I finally put the parts togethor to form a leg. Although there is still a lot of work to go in boring the holes to seat shaft bearings, making the shafts, boring holes to fit gear hubs, making more holes to mount various sensors, pins, cable guides, etc, it’s starting to finally come togethor. So far it looks really good, and I don’t think I will need any major changes to the design before I send out to get the parts for the other three legs waterjet cut.