Dearth of Machining Posts

I think I finally understand why I'm primarily writing electronics and programming posts rather than machining posts (despite the fact that this blog is entitled The Tiny Machine Shop): Well, ok, it's not simple enough for a single statement. It's.... complicated.

For starters I haven't been able to spend as much time as I like out in my shop. It sounds awfully cliche to say this, but work's been a bear. (And sadly, I haven't been doing machining at work much, either. Such is life.)

But more to the point, I haven't been doing any big projects recently. The machining and metalworking I've been doing has been a whole string of small things that don't make for good storytelling. A mandrel here, some sheet metal there, way too many toy repairs for the kids... it's a lot of job shopping and not a lot of project work.

(As a quick aside, I say job shopping with a great deal of respect, and in no way compare project work and job shop work with anything but complete parity. If you ever find yourself thinking otherwise, one of the best treatises on this is the Echoes from the Oil Country series of books published by Lindsay Publications. An even better one is to try it for a while!)

I'll share one story, though: When I first got into home shop machining, I proved the old adage over and over: If the only tool you have is a hammer, every job looks like a nail. I had a lathe and later added a mill. Great tools. I've still got them. But my early approach to every job was to use one, the other, or both tools. I'd crank out parts with acceptable tolerances of +/- 1/16" with a +/- 0.001" tolerance and a far better surface finish than the job required. Think I'm bragging? I'm not. It's actually a self-deprecating remark. The tradeoff, of course, was that I could take hours cranking out a part that should've taken me about fifteen minutes... if I'd thought in terms other than lathe and mill. Great looking stuff, but it was like watching the grass grow... while the glacier approaches... and the paint dries...

Over the years my list of tools has grown. A drill press and bench grinder were very early additions, along with an ever growing assortment of files, hammers, vises, screw drivers, hex wrenches, calipers, micrometers, indicators, etc. Then one day my wife bought me a scroll saw. A scroll saw? Yeah, a scroll saw. I was a little surprised, but I endeavored to get the most out of it that I could. I got a book on scrolling, picked up some good blades, and had at it.

(Another aside: If you intend to pick up scrolling, get good blades. This bears repeating: GET GOOD BLADES. I got mine from Mike's Workshop. He sells Flying Dutchman blades. The difference between the blades you pick up off the rack in the store and a high quality blade is night and day. More on this in a sec...)

Within a few months I broke the thing. More accurately, I broke the blade clamps: the things that hold the blade on the saw. Rather than let myself wallow in pity for too long, I took it as a challenge and made new blade holders, only this time I made them better, and made them so they'd hold jeweler's saw blades as well as scroll saw blades. It was a good move, and was what finally launched me into how I use my scroll saw now. Because it was this change that finally hammered home a key point: Scroll saws can cut wood, plastic, and metal.

Mmmmm... Metal. Now that is sexy. So I took the same techniques people use for scrolling wood and tried making parts in the shop. Here's what I wound up with:

For 2D work I draw the part in CAD and print 1:1 on the printer. All drill holes get crosshairs, all cut lines get the finest line my printer will print. All bend lines get lighter or dashed lines, same width. The drawing gets adhered to the metal with 3M Super 77 adhesive. Spray the drawing with adhesive and let it dry until it's tacky. Then stick it on the metal. This lets it peel off easily afterward without a lot of cleanup.

I tend to cut the part on the saw first. I wear a magnifying headset when working with metal on the saw. Pick a blade that lets you take the cuts you need. Jeweler's blades are great for really intricate work, but it's easy to wear them out if you push them. Unless I'm doing very fine work I tend to reach for the blades I got from Mike. I don't know if Flying Dutchman makes blades specifically for cutting metal, but if you choose your tooth count to match your material, it really does cut just as smooth as butter.

I use a cutting lube when cutting metal on the scroll saw. My wife's a jeweler so I beg, borrow, or steal her Riolube, which is made for jeweler's saw blades. Great stuff. I keep a cake of the stuff by the scroll saw and just touch it to the blade every now and then to keep it cutting clean.

Be aware of the kerf (thickness) of the blade, and keep the kerf on the correct side of the line. I tend to leave a little extra (a little being up to 0.010" at the most) on the free side of the line so I can file down to the line afterward. File to the line and move to the drill press.

I pre-punch my holes with a scribe under a 30x loupe (hey, I used to do a lot of 4x5 view camera photography, so I have one handy). If they don't come out dead-on, I'll drift them until they do line up with the crosshairs on the drawing. Then comes the prick punch, which sets the hole. Then comes the center punch that actually sets the right angle on the punched hole to match the angle on the drill bit. At that point it's ok to drill the holes on the drill press.

Once the part's cut and the holes are drilled, it's a simple matter of pulling off the drawing, deburring all the holes, chamfering all the edges, and cleaning things up nice and pretty. If it's a part that will show, I'll put a nice surface on it. (Ok, I tend to put a good surface on practically everything I make... for that everything still looks like a nail.)

In the end I can very quickly make fairly complex parts that are good to +/- 0.005" or so. (Tolerances get looser as my speed goes up.) This is how almost all the sheet metal work on my first robot was done, and it's how the motor mounts on my first ROV were done as well. Despite having CNC tooling available, this is often the first technique I'll turn to when prototyping a new part or simply knocking something out to get the jobs moving through my shop and out the door.

Tom