doorknob

3 Articles

Making A Metal Hand Doorknob

September 24, 2021 by 23 Comments

Regular doorknobs are widely reviled for their bare simplicity, but by and large society has so many other problems that it never really comes up in day to day conversation. Fear not, however, for [Matthew] has created something altogether more special: a doorknob in the shape of his own outstretched hand.

The build was inspired by a similar doorknob at the WNDR museum in Chicago, and its one you can recreate yourself, too. It’s achieved through a multi-stage mold making process. [Matthew]’s first step was to make a flexible mold of his hand using Perfect Mold alginate material to do so.

Once solidified, [Matthew’s] hand was removed and the mold filled with wax. The wax duplicate of [Matthew]’s hand was then used to create an investment plaster mold for casting metal. Vents were added in the end of each fingertip in the mold to allow molten metal to effectively fill the entire cavity.

Once the investment mold was solid and dry, the wax was melted out and it was ready for casting. A propane furnace was used to melt the casting metal and fill the mold using a simple gravity casting method. [Matthew] ended up making two hands, one in aluminium and one in copper. Some cleanup with grinders and a wire wheel, and a replica of [Matthew]’s hand was in his hands!

The finished piece looks great attached to a door knob, and we’re sure it’s quite satisfying shaking hands with your hefty metal self every time you open the door. It bears noting that the same techniques can be used with 3D printing, too! If you pull off your own great home casting project, be sure to drop us a line. Video after the break.

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Homebrew Doorknob Caps For High-Voltage Fun

February 19, 2021 by 15 Comments

Mouser and Digi-Key are great for servicing most needs, and the range of parts they offer is frankly bewildering. But given the breadth of the hardware hacking community’s interests, few companies could afford to be the answer to everyone’s needs.

That’s especially true for the esoteric parts needed when one’s hobby involves high voltages and homemade lasers, like [Les Wright]. He recently came up with a DIY doorknob capacitor design that makes the hard-to-source high-voltage caps much easier to obtain. We’ve seen [Les] use these caps in his transversely excited atmospheric (TEA) lasers, a simple design that uses high-voltage discharge across a long, narrow channel filled with either room air or nitrogen. The big ceramic caps are needed for the HV supply, and while [Les] has a bunch, they’re hard to come by online. He tried a follow-up using plain radial-lead ceramic capacitors, and while the laser worked, he did get some flashover between the capacitor leads.

[Les]’s solution was to dunk the chunky caps in acetone for a week or so to remove their epoxy covering. Once denuded, the leads were bent into a more axial configuration and soldered to brass machine screws. The dielectric slug is then put in a small section of plastic tubing and potted in epoxy resin with the bolts protruding from each end. The result is hard to distinguish from a genuine doorknob cap; the video below shows the build process as well as some testing.

Hats off to [Les] for taking pity on those of us who want to replicate his work but find ourselves without these essentials. It’s nice to know there’s a way to make unobtanium parts when you need them.

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No Doorknobs Needed For This Nitrogen Laser Build

December 26, 2020 by 15 Comments

Sometimes the decision to tackle a project or not can boil down to sourcing parts. Not everything is as close as a Digi-Key or Mouser order, and relying on the availability of surplus parts from eBay or other such markets can be difficult. Knowing if and when a substitute will work for an exotic part can sometimes be a project all on its own.

Building lasers is a great example of this, and [Les Wright] recently looked at substitutes for hard-to-find “doorknob” capacitors for his transversely excited atmospheric lasers. We took at his homebrew TEA lasers recently, which rely on a high voltage supply and very rapid switching to get nitrogen gas to lase. His design uses surplus doorknob caps, big chunky parts rated for very high voltages but also with very low parasitic inductance, which makes them perfect for the triggering circuit.

[Les] tried to substitute cheaper and easier-to-find ceramic power caps with radial wire leads rather than threaded lugs. With a nominal 40-kV rating, one would expect these chunky blue caps to tolerate the 17-kV power supply, but as he suspected, the distance between the leads was short enough to result in flashover arcing. Turning down the pressure in the spark gap chamber helped reduce the flashover and prove that these caps won’t spoil the carefully engineered inductive properties of the trigger. Check out the video below for more details.

Thanks to [Les] for following up on this and making sure everyone can replicate his designs. That’s one of the things we love about this community — true hackers always try to find a way around problems, even when it’s just finding alternates for unobtanium parts.

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