you've now got me thinking of how to disguise a fin so it can be sneaked in with a normal load.

Just say it's a charcuterie plate.

remery said..
Just say it's a charcuterie plate.

No , it's a BIG Knife

Can it be chromed ? Alloy castings get chromed . Then anodised . ? Black chrome ? Cutter plating ? Ceramic ? What other plating options are there ?
And ,
What about casting in glass infused resin ? Should be strong enough .
Cos , you need more to think about

I'd like to see some more results from double anodised fins before I go to the trouble of setting up my own anodising. I don't care at all about appearance just smoothness and the toughness of the oxide layer.

Not much time spent this weekend but tried sanding the new 'pox' and seems I've introduced new pitting. 20mins at 1200 grit didn't budge it. Old pitting is now much more pronounced/deeper thanks I think to the caustic bath. Based on that, will try and avoid caustic from now on. So went and got a high-powered ultrasonic cleaning kit from Altronics (Jaycar sell same kit)...for those outside Australia this was the original project www.siliconchip.com.au/Issue/2020/September/Advertising+Index Seemed to be the best way to go as can fiddle with power, make own tank, self calibrates, cheaper etc.

Got the ultrasonic cleaning electronics all completed and started working on cleaning bath....knew I had an unused stainless roasting tray lying around which didn't fit in oven for some reason which meant it might fit a FF28. Spent way too long finding this only to find it was about 10mm short on one corner. Damm Fangy fin, the gift that keeps on giv'n!

Was about to chuck it (the tin, not fin) in the vice and get to it with a hammer to get that extra 10mm when thought better (seems nice tray after all) and started making another custom cleaning tank from some freebie dumpster dive acrylic I'd scored whilst scrounging for some abrasion resistant polycarb for that other project. I hate acrylic as it cracks, polycarb rules as can't break it, but midway through that process there seemed to be a breath of wind so went to do what all this is about and go sailing.

Plan will be to ultrasonic clean in bath of Methylated spirits for starters (or other solvent since getting a water reaction)...since the 'crud' is heavy should be able to let it settle after each clean to reuse majority of solvent. The ultrasonic transducer that came with the kit is optimised for about 4litres of fluid which is the other justification for custom tank. (aside: can further optimise electronics by changing the transformer windings so acoustic impedance matches electric impedance so spent some time 3D printing winding machine to make this easier as is painful process hand winding transformer. ..hopefully will not have to rewind this thing...which is why in photo its mounted weird)

Hopefully this helps remove the sanding goo quicker. Whether it helps with the end objective remains to be seen..

For the other suggestions like chroming, the problem is cost...have tried HVOF..at least I tried to get my old subcontractor to try but they won't even look at it for a price Fangman would give you a lifetime supply of disposable fins for. Cold spray might be good future option but will be outside most user abilities.

Anodising 'seems' to give a good outcome of cheap (roughly $100) to set up a basic and simple anodising system which you can then use forever) and very good wear resistance. If you have a few Fangy fins then its not much investment compared to all the other gear. The trick seems to be in the details of how to best go about the process.

Also going to revisit CNC'ing these from solid billet to avoid 99.999% of all these issues. Will try dumpster diving scrap and new. Billet for a big FF28 will/should be roughly $250, machine cost...not much if you do yourself but will try and get some quotes from my old contacts.


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To add to Flex's post ( fine work with ultrasonic bath there BTW Flex) I have been mucking around with current density and acidity. My feeling is that regardless of whether its silicon, silica, magnesium or whatever in the aluminium it's a pain to anodise. The electropolish is good for blasting off big mobs of oxide and that's about it. The investment in phosphoric acid is not justified for something that a bit of Gumption and elbow grease does just as well.
High current and high % acid baths do more damage than good. The surface will anodise in places where the aluminium is of high purity, but wherever there is a spot rich in other alloying material in/near the aluminium surface, the current and acid just blast a hole. With time the pits gets deeper and do not seem to start anodising to any degree. The high current flow also heats the bath, so the sulphuric acid gets more aggressive with time. As proof I now have a fin that looks like the surface of the moon.
I am currently trying 'low and slow' approach. I guess I am down to about 15% Sulphuric acid. The current density is very low, for example 2-4 amps on a FF18, but I run it for about 8 hours. This seems to inhibit the pitting and so far I am getting consistently anodised surfaces. There are still issues with high silicon spots not anodising, but the results are good enough for me to keep playing around with this low and slow approach.
The really exciting bit is that Flex has done a shedload of work on the CNC option using a high quality billet that we should be able to anodise easily. The costs appear to be a fraction of what I was quoted a few years ago, but it seems, while still $, a high precision super tough FF made locally might be within reach.

Was about to do data dump of todays efforts when saw your post. Thankfully Fangman and I have worked out how to digitally communicate using a coke can and string method so a perfect fitting 3D printed "Flex" gasket is trivial exercise. Whether it works it of course subject to testing. Will try and model what you are saying..

Haha Stretch I read your post and thought that is so far up Flex's alley he has probably already done it! And voila, scroll down one post and Flex gaskets are born.

Another day, and another day without wind so had to resort to playing with the Fangy Fin again. It really should be in the running for gift of the year as this thing just keeps on giving. I'd be hard pressed to decide between a ball, some cardboard and hot glue or a Fangy fin for long term entertainment. My kids are getting bigger so its a Fangy fin for me now....I have a Netflix account too but I don't think I've used it in months thanks to this thing. Was really not gonna post anything until made some decent progress....however..some of you are obviously very bored from lack of wind...

Today: Started resanding the FF24, (anodised once) with the idea to do a light sand and anodise again to replicate the success of my first FF22 attempt. Failed, the porosity was really bad, way way worse than the native fin and I really lost motivation....why spend all this time sanding only to get a result that is way worse than when you started. Whilst sanding was thinking of how to go about actually making a supersonic cold spray device when it occurred to me haven't tried something basic. Hopefully others have tried and will stop me before doing this if its not a good idea. (I already know its a good idea and nobody has tried but putting it out there)

I'd had enough of all this sanding and porosity after just 5 fins (no clue how fangman has done 300+ of these things) so ordered some nice fresh billet to cut a nice fin from scratch. Fangman and I had made some progress speaking digitally enough that we could communicate between ourselves and to the outside world. I managed to convince someone to agree to bring Fangman's love child into the real world using a CNC and eliminate 99% of all this sanding/trying to get a surface finish BS/time wasting. No doubt there will be some other issues arising but they will be trivial compared to this current saga.

Simultaneously to all that, I thought bead blasting the cast fins to seal/close/hide the porosity prior to anodising might be a good plan. I'd spent 10 years in previous life perfecting this process so probably should give it a try before abandoning the cast. Motivated again, I aimed to have three fins ready for bead blasting tomorrow as the CNC machine is just a few yards from my bead blaster of choice. First fin,the new Skunk works Fangman special cast FF18V4, exactly the same as the CNC one so can compare the orange to apple but at least exactly the same same size. Have finished it to a rushed maybe 400 Grit, 2nd fin, a FF24 anodised with low desmut, resanded (looks like ****) at 1200 then 800 and then lost interest, FF28 (just looks like ****..but you would too if you went through what it went through). Me thinks bead blast will bash surface of all three so you won't be able to tell them apart.

To close the day off, I'd read that brake cleaning fluid gets rid of silicates and silicon so I got myself some and applied it to the freshly sanded skunkworks cast FF18V4. Not one sign of black goo coming out. Like zero...of anything. So chucked fin in a warm (50degC) bath of soapy water and hit it with ultrasonics. I'd calibrated this thing to a tank of methylated spirits so maybe the power xfer was a bit out with water. I fiddled around with position of fin in bath and it made a massive difference to acoustic power applied. From almost zero to overload. I measured the current from battery and got a max of 2.5amps at around 13.X volts when fin was in optimal position. Assuming electronics are around 90% efficient that's about 30W good vibrations into the bath. (the electronics limit the power to 36W best case for a 40W transducer so 30W is probably a reasonable max)....regardless still did bugger all as far as getting that black goo out.

Not many bubbles compared to methylated spirits and didn't want to leave in tank so pulled it out but was surprised to see 'blast marks' coming out of the porosity adjacent to where the ultrasonic transducer was. These are in the metal and can't be rubbed off. Damm, more sanding.

In the same photo you can see the porosity...its never ending with one almost bullet hole size, I hit this thing with 80 grit flapper disc till it now bears no resemblance to Fangmans original intended shape and the effort was completely pointless. (oddly the opposite side has almost no porosity which seems to be the case in all fins I've played with, note to self: is porosity only on one side? and same side for all fins)

Tomorrows mission, get the CNC loaded and bead blast the hell out of 3 various buggered up Fangy fins to see if it makes the slightest difference. Luckily I can find the almen intensity if needed but thinking this process will either do nothing or large improvement.

From memory we always did an almen intensity of 7 but can't remember if it was A or C. (It might sound impressive but the Almen is how much a piece of metal of thickness A= 0.051" or C=0.094" deflects when you blast one side with whatever you've got. The more intensity (faster or heavier) the more the material deflects due to cold working just one side. Its vaguely similar to anodising in that it hardens surface but in this application I am hoping it will clean out/mash the porosity into surrounding material to give a uniform surface to anodise. If this fails can still try shot peening or sandblasting...showing how much joy just a single Fangy fin can bring.

Some more thinking ......
If CNC ing the fin , I like stretchys idea of the flange being a seperate part . Being accurately machined , the fin could nicely slide down into the flange . This would save a lot of money in the thickness of the billet . The flange could be made out of a tough plastic , ( polyethylene) , that can be easily shaped to the bottom of the board .
Whilst being CNC'd make all fins box universal .
Discuss , and get onto it chaps .

Imax1 said..
I like stretchys idea of the flange being a seperate part . Being accurately machined , the fin could nicely slide down into the flange . This would save a lot of money in the thickness of the billet . The flange could be made out of a tough plastic , ( polyethylene) , that can be easily shaped to the bottom of the board .
Whilst being CNC'd make all fins box universal .
Discuss , and get onto it chaps .

This sounds like a great idea, but the reason fangy fins can be "box universal", is that the fin is "seated", by the flange not the box. A separate flange would have to be securely fixed to fin and be strong enough to take the loads. Not insurmountable, but needs to be taken into account.

Flex, you are having way too much fun. Your lateral thinking, problem solving and tech skills are impressive and entertaining even for someone who is an absolute tech newbie. Now what on earth is a bead blaster? Sounds like something from Star Wars.

Windxtasy said.. Now what on earth is a bead blaster? Sounds like something from Star Wars.

Nah, more like Red Dwarf, or Hitchikers Guide to the Galaxy

What flavour was the pie ?