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Making Chips

November 17, 2014

To cut metal, the most basic tools are the drill press and band saw. The use of a drill is obvious, but a band saw can easily be used to nibble at edges, and cut pretty much anything you can fit on it. Some might prefer a jig saw, but 9mm/.45ACP. Doesn’t make too much difference. I’ve been told you can finish an AR lower on a drill press, you don’t need a mill, but it’s harder and longer. There are designs out there for a lower that is made of plate metal, an ideal project for a press and saw.

band saw

Level one would also include a welder. Welding is stronger and easier than bolts, and looks a bit nicer on top. Gas will let you do some cutting as well, without buying two machines, but has some disadvantages, like being slower. It’s very versatile however, and the bead and puddle management you learn will also be useful with other welding techniques. I’ve been told by some people stick and gas welding are going the way of the dodo, but every welding truck out here has an oxy-acetylene rig as well as the electric welder, and most of those are capable of stick welding. Welding deserves it’s own post, probably by a welder(any volunteers?), but you need to be able to cut, drill, and assemble metal with reasonable accuracy, for which you don’t need machine tools for on a basic level.

Almost all of the stuff we do on CNC machines these days were done on manual machines in the past. Time was the limiting factor, and some stuff was done differently until CNC machines made it worth the time and effort. Manual machines are also still very useful for modifications and repairs—by the time a CNC operator has a part set up, tools set up, and program written, a lot of operations can be set up, done, and torn down on a manual. Even in the age of Star Trek replicators, there will likely be a Bridgeport around the corner from the warp core for those times when just tapping a new hole will be enough.

A variety of companies make small bench top mills and lathes, some of them can actually be useful. For machining, the two big points are vibration and flexing—an accurate tool won’t do either. This generally means mass, and lots of it. Even small machines will have thick, heavy parts, and “bench top” machines can weigh hundreds of pounds. Most of the small cheap machines are made in China, so quality can vary. The manual Sherline machines can be a good buy for starters, but for most work, will be a bit small and slow. Sherline is also one of the companies blurring the line, since their machines can be had in CNC versions. It’d take a while to make an AR lower on it, but most of it could be done.

AR lowers are a good example of how not to design something for making at home—the magazine well has nice sharp inside corners that you can’t just mill out with the same tool as the rest. Big shops use a process called broaching to finish out the well. This requires a specialized machine and special tooling that you’re not going to have at home, or at most hackerspaces. It can be worked around, but will be a pain.

Most of the smaller machines in the bench top size can be modified to be CNC, but quality varies. Larger manual machines can be modified too, but aren’t nearly as good as real CNC designs. Part of this is machine geometry—hand cranks are a different beast than motors, and are placed differently. The other part is the “motion control” that actually moves things. The smaller and the cheaper machines use stepper motors, which are limited in torque, and aren’t controlled the same way.

I’ll let someone else explain the difference:

http://www.amci.com/tutorials/tutorials-stepper-vs-servo.asp

We can get to Tormach and similar machines at this point, which offer actual CNC control, though I’ve heard complaints the stepper drives are rather slow, and servos are expensive. You can get servo machines in the price range however, but I have had little luck finding many with a whole lot of features. If you look carefully, you can find good deals on higher end machines, but keep in mind you still have to ship it, and since most of the machines are well above five thousand pounds, they’re generally out of reach of 5K forklifts and LTL shipping, which means flat beds and more or less hiring a whole truck, which is rather pricy.

The next level is to buy a real CNC machine, like a Haas or Mazak. While a Tormach with bells and whistles can be had for $12-25 grand, real machines start well used in the upper part of that range, and go up, bigger or fancier machines can be a million a piece new. If you can afford it, it would be the king of the hackerspace, but are really only needed when you’re running the machine 16+ hours a day in production, and making heavy cuts in hard alloys.

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14 Comments
  1. Mike B permalink

    Done several lowers on a Sherline…Just need to re-clamp to move the piece, since the working area is limited

  2. Boon Vickerson is out there permalink

    I volunteer to do an essay on the practical use of welding, aka metal joining and fusion, within the scope of your narrative.

    As a side note, forge welding is a very useful, much forgotten method of metal joining. Thermite welding has its place. So too is the various brazing processes, quite few of which depending on joint design can be accomplished in a furnace, forge, or open heat sources if a torch is not feasible. And a properly designed braze joint using various braze alloys suitable to the parent metal has strength near that of fusion welds.

    Basic heat treating and hardening, and the effects on weldments in the heat effected zones is good info to understand also.

    I believe there is a practical and holistic imperative for incorporating metal joining with the new fabbing movement.

  3. Boon Vickerson is out there permalink

    As wonderful as cnc and cad systems are, for all the amazing things which can be fabricated using them, there is something they don’t do, and that is creating the knowlege and skill of hand craft work.
    I’m not in any fashion disparaging cnc, in fact I think it has made life better in many ways.
    But cnc doesn’t require the craftsamship of hand work, and much of the art and ways of production pre cnc are becoming forgotten or lost in time.

    I’m a child of handcraft. I think both systems of manufacture must become symbiotic at least on the small scale.

  4. The hand craft work has moved offshore for the most part due to labor costs, and the lack of people willing to spend the 10,000 hours necessary to learn a skill in the US.

    I work in a area tht all there is, is hand crafting. Admittedly skilled workers who take pride in their work are as scarce as they are in the US, there are plenty of slap dash cowboy machine shops running pre ww2 Japanese equipment.

    • Worked about ten years ago in a screw machine shop. Some of the machines dated from the 20s, a couple still had war production order plaques on them from WWII. Even single spindle machines can be competitive with CNC still, if you know what you’re doing.

      Part of what a hacker space does is turn some of this into more of a hobby for now, and you can get people to learn it that way rather than as a living, and then you have some slightly skilled people you can build on when the world cuts you off.

  5. Lapua permalink

    Ok….bear with me here guys…..this is gonna sound nutso.

    So the problem is broaching the mag well. Crazy ol’ me thought “why don’t you split the receiver right down the middle…..machine both halves….drive alignment dowels into them and securely epoxy them together with hardware for good measure. Apparently Lotus BONDS their aluminum chasses together because aluminum bonds very well and they get higher strength bonds than welds without the loss of temper. The buffer tube ring could be another attachable part.

    Now I got even more evil. A half AR receiver is in no way, shape, or form a “firearm”. There is no manufacturing process known to man that can turn it into one. Doesn’t matter if two of them are sitting in a box together.

    Can’t one make these half receivers and buffer tube ring kits and sell them with no trouble at all? End user bonds and bolts the halves together instantly creating a firearm out of three pieces that are, in no way, a firearm?

    Am I nuts?

    • For the most part, no. It’s probably quite reasonable to do it that way, but be wary of half a receiver not being a “firearm” according to the ATF, IIRC the old Car15 lowers were molded in two pieces, then welded together. One of the beefs the ATF had was that the molding took place in a different building than the license, it some some sort of constructive possession type thing. Manufacturing in two pieces is a good idea though, even just welding it together shouldn’t be too hard on it.

      • Lapua permalink

        My concern is that they would just consider BOTH pieces to be a firearm. Now, this creates a hilarious problem for some ATF anal-retender if a kit were sold with two serialized “firearms”. They must have unique numbers…..but so must the finished firearm. Which serial number is it???

        I actually found several sites where someone has already tried this…or at least posted examples. Some really interesting designs including one that was mostly sections of square plate.

        While novel receiver ideas are great, the biggest issue I see is having piles of receivers and no rifled barrels to put on them. So far I haven’t seen any good examples of viable home or small-shop built machines for producing them.

      • Barrels are the tricky part. From the research I did a few months back, it’s tricky, is more art than science, and can take years to get a machine up and running right, with an operator that can produce good barrels reliably.

  6. I have a bunch of 3D printed tools I am uploading around the web. You want to share them?

    Here is the first one.

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