Injection Molder/Research Development

Integrated Frame

Narrow Steel Rod, Drilled Aluminium Block design

See Rick Sparber's modified Gingery system. Steel rods can easily be salvaged from (sadly abundant) broken-down inkjet printers from scrap yards. If a thick plate/ingot of aluminium cannot be found, a barrel/chamber can be cast out of small scraps of aluminium (pending a 3D-printed form for ideal shape).

Thick Steel Rod and Pipe design

Dave Hakkens has put together an initial prototype for an all-steel injection moulder. A solid design using a wide square-tube frame and a long piece of 30mm steel rod for the piston, this thing would not be easy to transport.

Drill Stand Accessory

Having recently got hold of a cheap power drill stand from LIDL (£13, brand 'Powerfix') that could be used to kickstart development of this, by focusing on designing a modular piston & chamber system that could be mounted in any such drill press, instead of one integrated into a frame like the Gingery design, I have been looking into options: 4ndy (talk) 21:57, 3 December 2014 (CET)

Limitation: the drill only traverses up to 60mm vertically when the lever is swung, though the whole carriage can be positioned anywhere on the top half-or-so of a 500mm post. Consequently, the piston should only need to press up to 60mm in order to inject the plastic, so a short & wide barrel is needed, rather than the long, narrow option of Gingery's steel rod in a drilled-out aluminium block.

Possible resulting problem: the piston will need a much higher force on it in order to deliver the same pressure out the nozzle, and hoop stress on a pipe used for the barrel may be an issue (need verification from those who have tested this before). Will the 4mmx20mm steel bar lever in this stand provide enough leverage to press such a piston down without warping? Moments: the press-bar mounting point is 80mm from the pivot/fulcrum, the handle extends 260mm beyond that, for a total of up to 340mm leverage distance.

Wide-barrel design

Standardised Parts design

Drive an aluminium compressor piston down a 1½ inch steel pipe, with a bespoke con-rod made out of whatever (a wooden board should do here for compressive strength, but steel plate or rod is preferable), use a 1½" to ½" reducer nipple and tap a corresponding threaded hole into the mould gate for a perfect seal between nozzle & plates.

Problem: a 1½" BSP pipe is supposed to have a 'nominal' diameter of 40mm. Does this mean inside diameter, and how close do they actually come? Will a 40mm piston have a loose fit or interference fit, and so do we need a larger/smaller piston with silicone o-rings to seal it properly? Why do we still use imperial pipe sizes when everything else is already metric??

Reusing Unintended Parts design

Just get an old stainless steel medical syringe and stick a heat-sink on it. Done. Piston is guaranteed to fit the barrel perfectly.

Problem: will the wall thickness be too thin and cause a split? We need to know necessary injection pressure for small moulds for this.

I am seriously considering getting a cheap second-hand one of these right now to start adapting.

Mould plates

Though cylinder pressure is unknown, clamping force for plates in commercial machines is commonly given as requiring a few tons. For lost-PLA cast aluminium plates, the top end of the plates could have smooth/threaded holes through each side to clamp them together with a pair of hexagonal-cap bolts, while the work-piece vice of the drill stand can hold the bottom end. This itself may be unnecessary, as this video shows a drill stand vice providing sufficient clamping force for small moulds. The bolts would make good locating pins however, making it easier to align the plates.