Go and visit your local high school. Will definitely have a kiln in the art room and may have one in Technology block for heat treatment of steel. ( older ones were removed due to asbestos lining). The process of normalising metals/alloys is pretty common as is quenching where you heat and cool quickly to get different properties. Normalising (specific to material and other alloys present) is very dependent on temp and time and being held for too long /too high a temp will promote grain growth and reduce hardness properties. The reason no one likes to plate/chrome/anodise cast aluminium is the porosity which is a product both of sand casting and the urge to keep production moving. Diecast which injects molten alloy under pressure gives a much better finish due to the quality of the steel mould vs sand mould and the more universal cooling rate before the mould opens. Diecast also tend to be much finer products ( Matchbox cars) but the newer car alloy heads are pressure cast vs old Holden red 6 cast steel in sand moulds.
Fascinating discussion. I would be surprised if anodising would produce a significantly harder surface than some epoxy paint which could be blocked and recoated. Not all epoxy paints will have the same hardness and hardness is reduced when blocked back. Let's now start a discussion on painting ??.

Not sure hardness is the ultimate goal here. Cheap, easy to make your own designs, strong, looking nice and abrasion resistant are probably my top wishes in no particular order. Whilst I don't plan on buying a Taber abraser anytime soon the local substitute is doing some dredging in sand or limestone or just cruising the weed and seeing which coating holds up best. My personal interest is just scientific curiosity and playing around. Volumes are small, based on this thread of 5years+ I think Fangman has made approx 400 fins?? or about 80 per year or about 1 1/2 per week. Knowing roughly the cost of casting, what he's flogging them for and the amount of effort in finishing them, I'd be surprised if he could afford a pack of Weetbix for his efforts, he'd certainly be way better off just working as checkout chick at Macca's... so die cast not really an option unless this whole thing goes viral on tiktok or whatever its called.

CNC option is of course intriguing, especially if can get a cheap CNC router to do the work. One issue is the giant flange on a Fangy (which is one of its big benefits), if trying to machine out of a solid billet it adds twice the material cost and almost twice machining time/cost..this becomes crazy price if you want good material. Most Fangy's are about 43mm wide which means 50mm material requirement. (this a huge benefit for cast fins as you only pay material for what you want) Enter the possible solution which many have suggested but so far no execution. Make the load bearing bit out of Al but the flange separate, since the flange bit will be in compression it is perfect application for 3D printing. Also doubles as a board saver. Requires moving the mount more forward which according to Fangman may 'give better upwind ability and stiffen the feel' . This drops the Al material requirement thickness to 20mm or 25mm plus a corresponding reduction in machining time. The 3D print cost is almost negligible and is replaceable/recyclable. Anyway, playing around with both options at present,. (Edit, yes, sure I can hang out at the high school using their kiln but not sure my kids would think its cool me hanging around for 10 hrs and the teachers/QHSE would freak when making all the super heated steam when trying to quench this bad boy)

Maybe a Multi Conic base?

Flex2 said..
Well, built and fired up the Bunnings special Fangy Fin Furnace only to be told by Windxtasy yesterday, "why don't you just use my kiln?" Arg! At least have backup plan now, Didn't quite finish the control electrics today but a short test run seems to suggest it might work. In theory should be able to reach 1300 degC. Reality, like wind forecasts, might be substantially different. Need to slowly dry and cure the bricks/mortar over a few days plus there's a pile of wind com'n so will be a while before actually cooking a fin. Most expensive part of the build was the steel to make the frame to hold the door. So far cost is $200 AUD for everything (bricks, mortar, element, thermocouple, controller, high temp wires, SSR, porcelain terminal blocks, steel)....coulda saved and not bought so much high temp wire, bought 10m for $25 when really only need <0.5m

Your kiln looks very professional, and the cost of materials is unbelievably low compared to what it would cost to buy a kiln.
Now I know who to come to when I want a bigger one.

you could take the concept a step further and further reduce the Aluminium required further and still keep the entire 3D printed bit in compression by doing something like attached. You would probably just hand carve this Al tip with the angle grinder. Same as before blue is Aluminium and grey the 3D print. The threaded bar is 6mm. The cost would be <$20 for everything...would it be strong enough for windsurfing? No clue but cheap enough to find out the hard way.

Back to CNC. I suppose it would be cost prohibitive to cast a fin finished with CNC? Integral clamping blocks could be added to the casting of the fin if needed and hand removed after CNC machining. It would obviously minimise the amount of metal that needs to be removed and the finishing time needed. Along with with the benefit of much greater accuracy of the fin profile.

from my experience with stainless leading edges, a dissimilarity in leading edge material will lead to a step, as the softer stuff wears away faster. In this case it will cause a weed grabber half way down the fin.
That's why my stainless now covers the whole leading edge. Earlier attempts with it part of the way, ran into trouble.
Even with the stainless almost 5mm wide, the fibre glass wears away faster behind it, requiring regular bogging up.

decrepit said..
from my experience with stainless leading edges, a dissimilarity in leading edge material will lead to a step, as the softer stuff wears away faster. In this case it will cause a weed grabber half way down the fin.
That's why my stainless now covers the whole leading edge. Earlier attempts with it part of the way, ran into trouble.
Even with the stainless almost 5mm wide, the fibre glass wears away faster behind it, requiring regular bogging up.

maybe if the metal portion of the fin is stepped behind the 3d printed part it would allow for erosion of the softer 3d part

Its a good idea Waricle..originally I thought making the leading edge all print and using 2mm bike spokes (first two images) but is way more complicated...your concept is simpler. 6mm threaded rod at normal tuttle angles gives allows the leading edge made out of 12x32mm flat bar. (last two images) Small enough to shape with the angle grinder. (this is FF21). Roughly Al and print cost is $6 ea.

Speak with Decrep as I think thats what he uses to paint his boards with

Well, bit of a fail. Started drying out the oven slowly...word of caution for others, AAC bricks are initially conductive (probably because Bunnings store them in the rain) which means you can't earth the frame and you also get a nice shock if you try and feel how warm the bricks are. This effect wears off once the bricks dry out and you can then earth the frame. At 540degC the outside of the bricks was about 60 degC so to further insulate and add a bit more safety I added a layer of 25mm Isowool and cased it in cement fibre. The controller could easily hold the temp within 2 degC without the blanket and within 1 deg with the wool blanket. Since the drying process took quite some time, been sailing etc, I'd forgotten I put cast FF18 fin in for original photo...oops. Was planning to do the real heat treatment today so opened oven up to find the attached. Obviously either my thermocouple is not reading correctly or material isn't as stated, probably the former. Was planning on using a junk fin Fangman had donated for first test but seem to have sacrificed a good fin..oh well.

Well, that has sorted out the porosity nicely.

Could be a hot shortness issue?

Flex2 said..
Well, bit of a fail. Started drying out the oven slowly...word of caution for others, AAC bricks are initially conductive (probably because Bunnings store them in the rain) which means you can't earth the frame and you also get a nice shock if you try and feel how warm the bricks are. This effect wears off once the bricks dry out and you can then earth the frame. At 540degC the outside of the bricks was about 60 degC so to further insulate and add a bit more safety I added a layer of 25mm Isowool and cased it in cement fibre. The controller could easily hold the temp within 2 degC without the blanket and within 1 deg with the wool blanket. Since the drying process took quite some time, been sailing etc, I'd forgotten I put cast FF18 fin in for original photo...oops. Was planning to do the real heat treatment today so opened oven up to find the attached. Obviously either my thermocouple is not reading correctly or material isn't as stated, probably the former. Was planning on using a junk fin Fangman had donated for first test but seem to have sacrificed a good fin..oh well.

And here I was thinking the Fangys were indestructible..

YP1 said..
Sheesh & Fangy thought I was tuff on his fins, makes me a pussy

Yes I am afraid both you and I have well and truly lost any chance at a top spot on the Demolition Derby leaderboard Tricky.