24 June 2011

Knurler Part I

Since most flashlights are knurled, one thing I'm going to need is a knurler. Like many machine tools, you can go out and buy one. Or, for about 1/10th the cost in materials, you can make one. If you've read this blog before, you know I generally prefer the cheaper option. And, it's good machining practice.

Normally, parts are cut from rough stock on a bandsaw. I don't have one of those, so out comes the angle grinder with a cutoff wheel.

This is steel flatstock from Home Lowes. The only reason I'm using Home Lowes metal is I already had this from some forgotten project like 8 years ago before I knew how poor quality Home Lowes steel is. There are at least two real metal suppliers here in Boise, like lumberyards only for machinists and welders. One of them was closed without warning the first time I wanted metal, and I never bothered to go back. Gem State Metals is where I go now, and even though most metal suppliers like to deal in $1,000+ orders from real shops, they are so tolerant of individuals buying $50 at a time that the guy actually gave me a tour of the place today. Thumbs up.

Once I have my parts rough cut, I clamped them together and ground the ends so they're all about the same length. Tolerance is not critical here.

Then I begin layout. I'm following some plans that someone posted online. I'm making some minor alterations, however.

The stock surface is coated with a blue dye, then I set my calipers to the dimensions specified in the plan and then use the jaws of the caliper to scratch lines. Places for holes to be drilled are dented with a centerpunch so the drill bit starts on center and doesn't skate around.

This hole has been started with a spotting drill, a short stubby stiff drill that will start a straight hole for the normal drill bit to follow.

The plans said to stack and drill, but I think it was a mistake in my case. The first one was drilled perfectly but the deeper I went, the more my drill bit wandered -- my drill press vise isn't the best and my drill table flexes a little. The locations of the holes were not critical, however, so everything should still work ok.

This part was fun. The plans call for half-rounds in the edges of the pieces, so I just clamped them side-by-side and drilled one hole in the middle where they met. Each piece got half a hole.

Swarf mountain.

Then I deviated from the plans. I don't like how many bolts are holding the thing together. There are 2 extra bolts top and bottom that I assume the author added to stiffen the assembly. My scrap steel is already thicker and wider than the plans, so needs less stiffening. Still, just to be safe, I decided to give ears to the upper and lower pivot points to keep the arms from bowing out under pressure.

Here's one ear ready for a trial fit...

Yep, fits nice. A close fit so there is no slop but not so tight it binds.
Finished pivot point.

I used 12L14 "leaded" steel for these pivot points. Man, that stuff cuts so nice and easy. No drama. It costs a little more than regular mild steel, but the extra money is worth it for a newbie. If you're curious, here are some of the prices I've paid for metal. These are all per inch of 1/2" round stock:

6061-T6 aluminum: $0.08 (mild steel is about the same)
12L14 Steel: $0.12
303 Stainless Steel: $0.33
Tool steel: $0.36
416 Stainless Steel: $0.50
C360 Brass: $0.67 (spendy!!)

Of course, the price goes up with diameter. The 3" aluminum I made the Jetta alternator pulley with is $3/inch! So as you can imagine, 3 feet of metal stock (depending on the metal and the diameter) probably costs more than 8 board feet of nice lumber for woodworking. I still think metalworking is way cooler though. ;)

Here you can see how the arms fit into the grooves, with the ears securing the sides of the arms.

This is as far as I got as it got late and I need to buy some bolts from the hardware store. But wait, you say, you have a threadcutting lathe, you can make your own bolts! Well, yes, I can, but hardware store bolts are actually cheaper than the metal stock I'd use to make my own! The whole "economy of scale" thing.

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