Casting Gears At Home

Automatic doors and gates are great, except when they fail, which seems to be about every three days in our experience. [MAD WHEEL] had just such a failure, with a plastic gear being the culprit. Rather than buy a new drive unit, they set about casting a replacement in metal.

The video is light on instructions and heavy on progressive rock, and may be a little difficult to follow for beginners. The process begins by gluing the original plastic part back together, and filling in the gaps with epoxy putty. A mould is then created by setting the gear in a gelatine/glycerine mixture. This mould is then filled with wax to create a wax copy of the original part. The wax gear is fitted with cylindrical stems to act as runners for molten metal, and then a plaster mould is made around the wax positive. Two plaster moulds are made, which are placed in an oven to melt out the wax.

The aim was to cast a replacement part in aluminium. The first attempt failed, with the aluminium cooling too rapidly. This meant fine details like the gear teeth simply didn’t cast properly, creating a useless metal blob. On the second attempt, the plaster mould was heated first, and this kept things hot enough to allow the aluminium to fill in the finer details. With that done, it was a simple matter of some post-processing to remove the runners, clean up the gear teeth and refine the shape of the gear on the lathe.

The resulting part does its job well, meshing properly with the other gears in the drivetrain and moving the gate effectively. Many in the comments have stated that the original gear being plastic was likely as a safety measure, to strip out in the event the gate is jammed. While this may be true, it’s a far more robust design practice to instead use a breakable plastic key rather than breaking an entire gear in the event of a problem.

Casting is quite accessible to the dedicated home maker. It’s a great way to make custom metal parts once you’ve learned the fundamentals! Video after the break.

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Casting CNC Parts In Aluminium

When it comes to machining, particularly in metal, rigidity is everything. [Tailortech] had a homebuilt CNC machine with a spindle held in place by a plastic bracket. This just wasn’t up to the job, so the decision was made to cast a replacement.

[Tailortech] decided to use the lost PLA process – a popular choice amongst the maker crowd. The spindle holder was first sketched out, then modeled in Fusion 3D 360. This was then printed in PLA slightly oversized to account for shrinkage in the casting process.

The PLA part was then used to make a plaster mold. [Tailortech] explains the process, and how to avoid common pitfalls that can lead to problems. It’s important to properly heat the mold once the plaster has set to remove moisture, but care must be taken to avoid cracking or wall calcination. It’s then necessary to slowly heat the mold to even higher temperatures to melt out the PLA prior to casting. With the mold completed, it can be filled with molten aluminium to produce the final part. When it’s cooled off, it’s then machined to final tolerances and installed on the machine.

Lost PLA casting is a versatile process, and goes to show that not everything has to be CNC machined out of billet to do the job. It’s also readily accessible to any maker with a furnace and a 3D printer. If you’ve got a casting project of your own, be sure to let us know. Video after the break.

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And So Castings Made Of (Kinetic) Sand . . . Turn Out Pretty Well, Actually

That kinetic sand stuff is pretty cool. It’s soft, it builds motor skills, and outside of sprinkling it on carpet, it’s not messy. If you don’t know, it’s 98% sand and 2% polydimethylsiloxane, which is a major component of Silly Putty, and according to a certain yellow and red clown, it’s safe enough to put in chicken nuggets. [Chris]’s wife bought him some, probably because she wanted to see him play around with something that isn’t potentially deadly for a change. In the course of researching its magical properties, he found out that it doesn’t really have a thermal breakdown point, per se. At high enough temperatures, It vitrifies like a sand castle in a mushroom cloud. Between this property and its malleability, [Chris] thought he’d have a reasonable substitute for founding sand. As you can see in his latest experiment, he was right. As a bonus, he managed to turn the benign into the dangerous.

[Chris] had never cast aluminium before, so he decided to start small by making an offset cam for a rotary broach. He packed some magic sand in a wax paper cup and shoved the cam in to make the negative. Then he cut down some aluminium rod and put it in a graphite crucible. He stuck his DC arc welder’s electrode down into the crucible and cranked it up to 50A. That wasn’t enough, so he went to 110. The crucible was soon glowing orange. He carefully poured the molten aluminium into the mold. Make the jump to see how it panned out.

Spoiler alert: there’s no cussin’ this time!

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