Something stirs in the Undergrowth

[pre65]

Like it Mark.

I once planned to make a turntable plinth with similar materials.

[Paul Barker]

£10/kg Iron powder looks better value. Would that be good enough?

[IslandPink]

I think it would Paul . I just had a very slight fear of rust but I think with the powder encapsulated in resin, and possibly a thin coat of varnish at the end it oughn't to be a problem. The mesh size sounds alright ... not sure if the Smooth-On product is any finer ? - their iron powder is about £17 per Kg, so I suspect it's not any more special.

I can understand ( maybe ) the reason why you didn't go ahead with the plinth , Phil ? - the cost would be frightening, as the resin itself is not cheap.
I ended up paying £100 for the whole lot, the low-shrinkage Shore 30 hardness silicone and the Smooth-cast 325 resin were each almost as much as the metal powder.

[IslandPink]

OK so I've been having a go at the molding operation today. Done the faffy job of preparing the mold box and fastening the fins in there for replication. The base for this is a piece of 9mm birch ply, which I covered with aluminium foil, using photo-mounting ( spray ) adhesive.
So I aligned two good ( rapid-prototype ) spare fins from the first effort ( after fettling them to clean up all sides/edges ) onto the foil, marking with OHP pen. Then I drilled through-holes in two places ( each fin ) through the foil and ply ( countersunk heads on underside ) ; then marked and drilled the fins in the right places with a smaller drill to act as the guide 'core' for the screw to go in.
Meanwhile I also cut the bottom out of a 0.8 litre sandwich box ; this was then tacked to the foil with the spray-mount , and once vaguely secure, I went around the lower edge with a holt-melt gun and sealed ( almost ) all round, to hold in the silicone.
Then I screwed-in the two fins nice and tight to the foil. This is where I am on the picture below.

I also put in a couple of extra make-up pieces of 9mm ply in the sides of the box with hot-melt just before mixing and pouring the Silicone . This was a very good idea, as the amount of silicone ( Mold-Star 30 ) was limited.

Now I've mixed and poured in all of the 2-part silicone and it's just right on the brim of the box so all of the fins and their two 4mm stubs are well submerged in that . Just need to leave it now for several hours. I just had a check and all looks OK after about an hour - the silicone is just staring to stiffen vs. how it was when mixing.

[IslandPink]

Just took the base plate off the mold and had a check how firmly the fins were stuck in the silicone. Not too bad - I gave the first one a bit of help with a ( clean) araldite spatula to free it up along both sides, then screwed the plywood back on to that fin with the two screws and was able to pull it out without much persuation. The mold cavity looks very good. I'll do the other one later .

Should be OK to do the casting one evening this week.

[IslandPink]

First go at casting here. Polyurethane resin and bronze powder, mix is 33% 'A', 33% B, 33% bronze powder by volume. I thought the working time was 20mins, but luckily while stirring the combined mix I noticed 2.5 mins on the back of one of the bottles After that I got the mixture poured into the mold cavities damned sharpish . I rather over-filled the things just to make sure it ran out fully to the (thin) ends, so I'll have some work to do, filing down the top edges to the correct height & cleaning up - not sure how easy that will be ....

[IslandPink]

First two fins are very good - successful job. Dense, and quite dead when tapped, so non-resonant . More rigid than the ABS ones for sure. Will need to do some fettling work to tidy up the top edge, but might cast another two today or tomorrow. Colour is a sort of shitty brown, so I might get some blue paint & spray them to look like the others - but perhaps a shade darker. Will check in the car shop this afternoon.

[IslandPink]

Got some dark blue paint from the car shop.

Cast two more fins this evening .
Off on hol now for a week

[IslandPink]

New kit of parts , see below.
The fins are actually blue, they look nothing like the pic
I did some of the tricky mitring work, hole drilling & turning today at Hywel's place.
ps. the fins are fully fettled and finished. No further fin-fettling foreseen

[IslandPink]

Still out there making sense :
http://www.labjc.com/?p=3468
Very interesting to read what he says about Dub ...
...and great comments about speaker design & the compromises .

[IslandPink]

Mr. Snouty was out & about today ....

[IslandPink]

Haven't taken any pics, but Horn No.2 is now 3/4 assembled. Despite the effort to make things as accurate as possible, the fit on assembly so far is still 1 to 2mm out in some critical places, so I think I need to do a bit of fettling of the final side piece to get everying together nicely. At least I've finished putting the new bike together now.

[IslandPink]

Couple of quick pics of the horn in a natural environment , just before I nip off to Yorkshire for the weekend.
Haven't had chance to play the second one yet - too much on.
Not exactly 'Living Voice : Vox Olympian' levels of finish, but it'll do for me !

[pre65]

Looks pretty shoddy to me.

Well done.

[andrew Ivimey]

The books go in the front and you can put a vase of flowers on top. When screwed to the wall it makes a nice talking point.

Ver'nice!