Re: Is a 3D printing option available yet

Gary M1EGI

I've been playing around a little with 3D printed horns for a while with limited success, but the link below might hold the key to getting good performance from them.

I have wrote an article for CQ-TV about the subject, this was was published in Scatterpoint April 2018. 
The next issue of CQ-TV should feature a follow-up article in relation to the above link, again this will be shared with Scatterpoint.

73s Gary M1EGI

On Tue, 11 Dec 2018 at 11:30, Neil Smith G4DBN <neil@...> wrote:
I've seen some half-decent work at the right sort of scale (but for
non-radio end uses) in aluminium and bronze using a PLA print which is
made over-size, embedded in an investment-casting mix, baked in a kiln
to burn off the PLA (like the lost-wax method) then embedded in a
sand-cast drag and cope with a narrow sprue and gate and tall, wide
risers to get a fast melt flow with good pressure. The surface finish
depends a lot on the fluidity of the melt, also you need to spread some
exothermic compound on the top of the risers to keep them molten so
there is a reservoir of liquid metal to prevent voids forming in the
cast. Where you need a really good surface, eg for a waveguide flange
(or the top of a piston) they sometimes use a cold-plate embedded in the
cast. From what I've seen, the finish is sort-of OK, good enough for
waveguide bends and tapers to 24GHz-ish, but making a thin cast for a
large feedhorn would be challenging.

It is a marriage of Bronze-Age tech with additive machining.  You still
need to fettle the finished object and machine any critical surfaces.
Laser-sintered metal powder prints look promising, but that is serious
industrial tech.

Metal casting at home from 3D prints is simple enough, but it isn't
exactly kitchen-table work, even if you use an electric pottery kiln for
the burn-off and melt.

Neil G4DBN

On 11/12/2018 10:20, Chris Bartram G4DGU wrote:
> Hello Dave,
> There's been quite a lot of work on this reported professionally over
> the last couple of years. Although it seems possible to go down that
> route, the consensus seems to be that current materials which can be
> 3-d printed a) aren't conductive enough to be a replacement, and b)
> the 3-d printing processes usually available don't result in good
> enough surface finishes - particularly at the higher frequencies.
> Summarising this. It might currently be possible to use 3-d printing
> for low-performance items, but it would probably need some further
> work, such as plating the conductive surfaces, to achieve the
> potential which the technology could offer for microwave assemblies.
> 73
> Chris G4DGU

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