Designing A 360 Degree All Metal Hinge

Looking for a 360 degree hinge that had no slop was harder than [Mr. LeMieux] thought it would be. Add to the fact it had to be made completely out of metal with no plastic components — and basically fireproof. He was coming up blank.

You see, [Mr. LeMieux] is casting metal components, and needed a hinge to close two halves of a mold. When he couldn’t find anything commercially available, he decided to design his own. Using aluminum, he machined the two halves with an interlocking mechanism between the two. Essentially, it’s a 3-bar linkage, but if he stopped there, it would have too much slop. So he actually designed in two fixed gears that roll over each other — this ensures the hinge stays perfectly smooth throughout its entire range of movement — it’s actually quite ingenious.

Though we gotta admit, we’re only seeing about 355 degrees of rotation…

Interested in metal casting? Why not build your own casting furnace?

[via r/metalworking]

38 thoughts on “Designing A 360 Degree All Metal Hinge

    1. Its not opening to 360 Deg as the wood holding the hinge fouls. The hinge clearly allows for 360 Deg, opening albeit with a translation.

      Use of cheap COTS gears to constrain the moment is clever, although, I must admit I visualise how it’d be used in a casting mold.

      1. Pour the metal in one side, pause, turn it over, pour the metal in the other side, pause; open mold and extract the sprue; repeat. The molds themselves can be for fishing components, or balls for shotguns/slingshots.

    1. The teeth are only there to stop the mentioned slop, and are not doing any load. And it’s a hinge to open a mold, by hand, so how big a use and wear do you think that has? If kept dry and not tossed across the room I would project it’ll be OK for at least 5 to 8 decades.

    1. It’s because it can go flat to flat barring other stops.. The first time I saw this type of hinge was when they started touting the 2 in 1 folding laptops. Specifically the HP Spectre 360 in my case and is relatives.

      I’m curious what he’s molding.

  1. I’m just curious as to what reason there is that a single large diameter hinge pin wouldn’t have done the trick. This doesn’t appear to be providing any special offset in rotation as far as I can tell. Certainly nothing in his post that alludes to it. Something I’m missing here?

    1. That was my thought too. Does it need to be temperature resistant? Or water resistant? What kind of tolerances are necessary and what specific benefit does this design convey that requires the smooth opening operation? It’s a very nice build but I don’t follow the end use requirements that necessitate it?

      1. That is what the gear is for, so that doesn’t happen.

        The hinge needs to be all-metal and fireproof because we are pouring liquid lead or bismuth to cast the shapes. The mold heats up with use. As to why, it’s zooming out and min/maxing the entire project. I set a retail price of $49.95 for this. I’m making a lot of them. Gotta work backwards and find solutions that are cost effective. To start off with a large enough piece of billet bar to make a scissor hinge like what you are thinking about, you end up spending a lot of your budget just for the metal. Then you have to machine away 50-75% of it to end up with a working mechanism. You have to flip the part three times (back, front, side), and then assemble it.
        With this design you still flip the part three times and assemble it, but even including the extra hinge parts, it costs half as much. Then there is the time savings on the expensive to run milling machines. Less machining needed = cheaper. The hinge parts will be EDM cut out of stainless or titanium, not milled. This is just for the first ones.

        Plus it just looks cool.

        1. Agreed, it does look rather cool.

          Could not get your link to open but this link worked for me:

          It looks like the articulation is important? It needs to close “flat”, basically?

          Wait. EDM? Why not waterjet or laser cut the hinge parts? Seems like a slow and expensive approach, especially if you are making these in quantity. I could see a few mostly minor ways to improve this design in production.

          Could you make these out of aluminum instead, for more cost / weight savings? Lead and bismuth are well below the melting point of aluminum. What about ceramic or metal sleeve bearings? Seems like less machining to do.

          I like it overall. How easy is it to clean out spilled and solidified lead from the gear teeth though?

          1. Yeah, it needs to close flat, so the two stubby alignment pins line up with their holes on the other half, to line everything up.

            I tried laser and waterjet. The bevel/kerf left by the beams on the 1/8″ thick hinge links is random and uneven to the point the long 1″ pins don’t slide in. I would have to go in and drill/ream out the holes. I’d rather not do that. And the gears are 1/4″ thick. I don’t know a laser/waterjet that can cut that thick and leave you with working gear teeth. I could probably go thinner, but this looks cool.

            The wire EDM might be slow cutting, but it allows you to cut a lot of these at a time. You can stack and bolt a 10″ stack of 1/8″ metal plates together, and slice through all of them in one go. Making a ton of parts real quick and with great tolerances/finishes. Basically ready to install right off the machine, no extra work.

          2. EDM gives you tolerances the others can not that’s why IMHO. faster with water yup, but at the end of the day if you need it to fit nicely use a wire and do it right once.

  2. Well done on building it yourself, with thinner handles it would really fold flush at the the back. However there is nothing new about this mechanism. My 11 year old glass shower-cubicle panels have this mechanism in them (with helical gears to reduce ‘slop’ even further). They are still working as new even with daily use.

  3. While it’s an extremely neat design, I don’t understand why you need full 360° rotation, if it’s just to open the mould enough to remove the cast balls. As for getting alignment between the two halves, would it not be sufficient to have a “normal” knuckle + pin joint at the hinge, then a pin + slot near the handle?

    1. Well, one reason to open all the way like that might be to put molds on the other side of the plates. That way after you’d cast your first side of bullets, and flipped it, and cast your second side of bullets; you could open the molds on one side and close the molds on the other side, and have the bullets you just cast on the outside, and two rows of mold ready for casting.

      You could sure cast a lot of them in a hurry with a lead melting production pot and a multiplex mold like that.

  4. Working in telecom, we use products from Erico and others whose purpose is to firmly close a mold for exothermic welding processes like bonding to copper bars and rods. The ‘handles’ are simple cantilevered clamps that bring the two halves of a mold together and lock closed. They can be had on ebay, used, for under $30USD. All you’d need to do is provide the mold. Oh, and since the mold is removable, different molds for other forms could be made to use the same handles.

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