Monday, January 11, 2016

When You Need a Long Hex Key

A friend of mind needs a long one to reach down inside an AR handguard to adjust a gas block. Have you ever tried to find a 12" long hex? We couldn't either, so we made one.

  • A spare key of the right size (5/64" in this case) 
  • A piece of music wire of 5/32" diameter*. To get the length, measure from the gas block to the front of the handguard, add an inch or two as suits you, then another few for the handle. 
  • A center punch & hammer 
  • Propane torch 
  • Some solder 
  • A drill press (unless you're steady enough to do it with a hand drill) 
  • Either a drill press vise or some other way to hold the wire steady. (I clamp the drill press vise in the workbench vise for the filing and marking) 
*Yes, a larger diameter -- as long as it'll fit -- will be easier, as you'll have more leeway for the hole to be a bit off-center.

Step One: Use the torch to normalize** an inch or so of one end of the wire. If it's mild steel, you can skip this. If it's something like the music wire I used, you HAVE to do this before drilling, or you'll wind up with destroyed bits and no hole.

**Strictly speaking, 'annealing' involves getting the piece up to suitable temperature, holding it there for a couple of minutes (in the case of something small), and then cooling it down very slowly to get it as soft as possible. 'Normalizing' means to get it hot -- a low red will do -- let it cool to dark, repeat that a couple of times, then let it cool to ambient temperature. It won't get it as 'soft' as annealing, but it's much easier to do and it'll be enough to do the job.

Step Two: Square-off one end of the wire. The easiest way is to clamp it in the drill press vise (which usually has cuts milled in the jaws to allow better holding of shapes other than flat) with just a tiny length of it sticking up. Take a file and file that exposed bit down; the jaws should help you square it off nicely.

Step Three: Use the punch to mark the exact center(or as close as you can get), to give the drill bit a place to start.

Step Four: Take the vise to the drill press. In this case I used a 3/32" bit, which is just a touch larger diameter than the hex key. You want as little slop as possible in the fit when drilling stuff like this,

I set the press on the slowest speed it has, then drilled with light pressure, just enough to make sure the hole is centered. If it's off, or too far off, now's the time to take it back to the vise and file it square and start over.

If it's good, put some lube in the hole, and proceed to drill with light pressure. Pull the bit back up regularly both to clear chips and to add a bit more oil.*** Continue until the hole's as deep as you need. I went with 1/2" here.

***Much like with guns, any oil is better than none; it both lubes the surfaces and helps chips flow up the flutes on the bit. If you're going to do much drilling in metal, it'd be worth it to find a bottle of actual cutting oil.

Step Five: When the hole's deep enough, try the hex key in it to make sure of depth and see if it sit in straight. When it will, figure how much of the hex key to cut off (1" in my case). You can either cut it with a rotary tool and a cutoff wheel if you've got one, or do it fast & dirty by clamping that length in the vise, grabbing the rest and bending it until it snaps off. These things are hard, and the small ones break easily.

Step Six: Clean the hole in the rod and the piece of hex. It doesn't matter if it's dish soap and water, brake cleaner or whatever else, just as long as it gets rid of every trace of oil. It's amazing how little it takes to screw up a solder joint.

Step Seven: Solder it in place.
  1. Clamp the rod upright in the vise with a couple of inches exposed.
  2. Put some flux on the bottom of the hex piece and work it into the hole.
  3. Cut off a couple of pieces of solder, in this case about 3/4" or so total in short pieces, and push it into the hole.
  4. Set the hex piece into the top of the hole.
  5. Start heating the rod a little below the bottom of the hole.
  6. As the solder melts, the hex will sink into the hole. I wanted the solder to fill in all the way to the top, and the first time it wasn't, so I lifted the hex out with pliers, added another piece of solder, and heated again.
  7. Do NOT push the hex into the hole; it'll act like a pump rod and may well pump molten solder out. This is Bad. 
  8. Let it sink in, give it a few seconds to make sure the bottom of the hex gets hot enough for the solder to grab, then remove the heat. Right now is the time to make sure everything is straight; while the solder is still molten you can push things around a bit if needed. 
  9. Let it cool. If you did everything right, that hex will be locked in; if you didn't (probably having left a trace of oil), it may slip out. If that happens, clean the hex again, flux, and heat it in again.

Step Eight: Make the handle. Clamp the other end in the vise, heat at the appropriate spot until it's a low-to-medium red, grab it with a big pair of pliers, and bend. Let it cool.

That's it. At that point you can clean it all off thoroughly, if there's any roughness on the end of the handle you can file or sand it smooth, and it's ready to use.

The finished product. 

The Difference Between Solder and Flux
General-purpose solder used to be a mix of lead and tin, the tin both lowering the melting point and making it flow a bit better. Now the stuff is almost always tin with a low percentage (usually around 3%, I believe) of silver. It's non-toxic, and will hold well, but I've found it's more sensitive to oil or other contaminants than the lead stuff.

Flux definitely helps by doing several things: cit helps clean the surfaces, masks them from the atmosphere to prevent scale (mostly in high-temperature situations), and helps the solder flow.

The stuff can be found everywhere from Wally World to auto parts and hardware stores. Some solder comes with flux, some you have to buy it separately.

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