elmo said..
The problem is finding off the shelf fins which can handle seriously heavy weed. There are some.

The next fun part is places like Albany can absolutely destroy a leading edge within 4 hours and @ $300 a pop you just grimace a lot when you see your nice fin munted.

As the largest fin we use in these areas are generally about 23cm, 3D printing gives a good idea on fin performance without big expense as a piece of G10 to suit is +$100 just for material let alone + the days worth of machining on a CNC Router then the cleanup after.

Flex's been using PET G successfully, PC would be a better option, but more expensive and can be a pain without a heated chamber Flex has a Bamboo labs printer which I think is ok , mine (Ender 6) struggles a bit with PC.

Elmo, you need slip on covers over a G10 dummy fin or carbon posts. As they wear simply unclip & replace, you could even change length, angle & foil shape in seconds?? thank me later ??

This thread wasn't intended to be all about fins but there is some significant gains to be had by making fins that can warp or change shape. 3D printing with TPU (Thermo Poly Urethane) is an ideal medium to make fins that can adapt to different situations. It is a nearly indestructible filament. I am no expert on any of this but this video and a long winded version linked in description detailing the motivation behind the idea attempts to show potential of all this. The first few tests certainly felt there were significant improvements over same profiled stiff fins

So have you tried it yet???

decrepit said..
So have you tried it yet???

Not yet, off the water at the moment. Brother-in-law is test pilot new time it blows.

Printed a bunch of wave fins and slotbox thruster fins in abs, Asa, and Petg. Working really well.

Need to optimize tool paths and print parameters to get the right strength and flex.

Also print futures to slot box adapters to enable using readily available futures base fins in my slot box wave boards.

fangman said..
Very cool.
I did have a universal tuttle box and core modelled, with the thought of slipping different skin-foils over the top and held in place with a grub screw or similar.(there is probably a better way) The idea being the core with all the fixings and strengtheners and resin only has to be made once, and the cheap skin-foils printed as required. If the skin can be printed in plain PETG and it is reasonably durable, I will revisit this approach, so please keep us posted on how it wears/flexes/etc.

THATS VERY CLEVER!!! and cool

My take is yes, the print doing quite a lot. The combo of print + filler is like cement with reinforcement. (Yes, I tried making a cement/plaster of Paris fin but so far pushing cement through small holes is trickier than you would think) If you watched the foam filled fin vid you can see just a few percent infil increases strength from easy to break to indestructible. There is no doubt some optimal combo depending on desired result. Abrasion resistance is also way better than you would think...try sanding Al, then PETG then TPU to get an idea. Done 800+km in full weed with PETG/TPU and wear is better than Al for sure. Early days..too many ideas

Petg is best finished by wet sanding which avoids the melting and clogging problems you might otherwise experience

fangman said..
Very cool.
I did have a universal tuttle box and core modelled, with the thought of slipping different skin-foils over the top and held in place with a grub screw or similar.(there is probably a better way) The idea being the core with all the fixings and strengtheners and resin only has to be made once, and the cheap skin-foils printed as required. If the skin can be printed in plain PETG and it is reasonably durable, I will revisit this approach, so please keep us posted on how it wears/flexes/etc.

Brilliant minds think alike . I designed this a few weeks back.
I wondered if you could machine a Tuttle like this out of aluminium. I made it 3 piece so that you can insert the two ends in the fin and then use the middle piece to force them apart and engage with lugs in the fin shell. The hole is just to put your finger in to insert/remove.

Jetlag, the obvious suggestion would be to 3d print your mech instead of machining out of Al. It 'should' be strong enough filled with epoxy, certainly if used with a flanged fin, but certainly cheap to at least test your concept.

Paducah, there is no ratio for the expanding foam I used. You just mix it 50/50 then used a syringe to inject it. There is about 1 minute working time which can be increased to 2 mins or so by chilling the goo and parts first. You are right the amount of expansion you get is inversely proportional to the infil %. With 2% infil probably getting close to the claimed 35Kg P/U density. Your question motivated me to recheck some calcs.

Attached is pic of the samples I tested and weighed at the time (hand written #'s). You will notice the 4% infil weighs less than the 3% (I just remeasured using two different scales, the more accurate resolution scale shows them at 25.9g and 24.9g respectively). This is because I tried to fill as many samples using one mix and due to the short working time didn't measure and inject the same amount of goo into each sample. I also held my thumb over the inject holes till the foam reached all areas (the advantage of using transparent filament). You will see the higher infill percent I had to drill additional inject holes to fill as the foam couldn't expand far enough.

One concept I haven't tried is putting a vacuum on to help the foam expand faster/further/less density. Possibly could reduce foam density further??

The yellow text is the amount of PETG the slicer calculates is used. The first # is the Bambu calculation and the second (in brackets) is Prusa Slicer. Here you can see a clear bug in the Bambu slicer (the one I used to print). The Bambu calcs show almost exactly the same amount of PETG for 3,4,5% infil which is clearly wrong. In hindsight I should have weighed the samples before filling them. It also doesn't really highlight what density the foam actually achieved is. Certainly the 3% is the only sample that clearly shows more dense foam. But for sure the 15% has the highest density but the numbers don't show that.However, 4% infill sample shows that a strong result can be achieved that is lightweight. In the video at time stamp 1:30 the 4% slightly imploded on the lever test (10Kg load) but the 5% survived.

The main objective was to see if one could make a board using this technique and appears the infill required to get a strong result is around 4-5%. Assuming you can get the foam to expand enough to get close to 35Kg density, means a 100 litre board would use 3.5Kg foam (cost $105 for 4 litres). A board printed at 4% infill and 1mm wall thickness should use 7.88Kg of PETG filament (cost $181 AUD using Bambu refill PETG). Actual consumption would be higher as would need alignment/strengthening carbon rod stringers to join sections and solid epoxy filled areas around fin/straps and mast. If allow +1.1kg +$50 for this, a board should weigh about 12.5Kg and cost $336 cheaper than what I paid $350 2nd hand for it).

I realise this too heavy as my 2nd hand iSonic 97 weighs 6.9Kg and new boards are sub 6Kg. Where it starts to get interesting is using foaming filaments (i.e. foaming ASA) which have print densities 0.46 ~ 0.97 g/cm? with almost same mechanical properties. If use a mid range density of 0.75 the filament requirement is now 5.5Kg for 100litre board weight of 9Kg (or theoretical achievable minimum 6.8kg). The downside is cost of material is about three times higher and non translucent....or so I thought....

Turns out there is a simple hack to make your own DIY foaming PETG filament. Anyone with a 3D printer will know that filament absorbs moisture and after a while won't print very well. This is because the moisture turns to steam when printing. So the recommendation is to always dry your filament before using. One bright spark who goes by RCHacker decided to do the opposite and soak his PETG filament in a bucket of water overnight then print. He achieved nice foaming PETG with expansion ratio of 1.54 (which means with some tweaking of flow rates in theory could reduce a PETG print mass by 1.54). Can't find anyone else remotely playing around with this idea so a spool of transparent PETG has just been submerged.

Jetlag said..

fangman said..
Very cool.
I did have a universal tuttle box and core modelled, with the thought of slipping different skin-foils over the top and held in place with a grub screw or similar.(there is probably a better way) The idea being the core with all the fixings and strengtheners and resin only has to be made once, and the cheap skin-foils printed as required. If the skin can be printed in plain PETG and it is reasonably durable, I will revisit this approach, so please keep us posted on how it wears/flexes/etc.

Brilliant minds think alike . I designed this a few weeks back.
I wondered if you could machine a Tuttle like this out of aluminium. I made it 3 piece so that you can insert the two ends in the fin and then use the middle piece to force them apart and engage with lugs in the fin shell. The hole is just to put your finger in to insert/remove.

This is way more elegant than mine. I will post it when I can access the file again. Rather cleverly I fed my laptop into the seat mechanism on the plane home. The seat won and now my laptop resembles a silver salad bowl... doh.

Put the popcorn away Ross, bit of an anti climax. Soaked clear transparent PETG overnight as per RCHacker, printed small test piece with thinest wall possible with 0.4mm nozzle which is 0.34mm. Could not measure any WT difference in dry vs soaked but soaked print was a little rattier. Should have been closer to 0.52mm. Soaking another brand of PETG non transparent PETG and asked RCHacker what PETG he used.

Printed 4% infill test pieces with thin walls to reduce 3d printed mass as much as possible, the soaked sample came out 0.2 grams lighter. I tried dropping the flow rate 10% (the middle sample with 0.85 on it which is of course lighter as less material) then did a vacuum vs non vac fill. Max vac I could put on was -320mmHg as the 3D print leaks. Thought I injected 3.5ml into each sample but by mass I put 1gram more into the non vac filled. Regardless result was opposite expected. The non vac almost filled the whole cavity (3.5ml if expands the claimed x25 should fill all the void), the vac sample filled a lot less but more importantly all the integrity of foam gone with voids everywhere.

Attached pics (Blue is dry PETG, clear is soaked, first number is Slicer weight prediction, 2nd # is actual unfilled mass and 3rd # is filled mass.

Flex2 said..
Put the popcorn away Ross, bit of an anti climax. Soaked clear transparent PETG overnight as per RCHacker, printed small test piece with thinest wall possible with 0.4mm nozzle which is 0.34mm. Could not measure any WT difference in dry vs soaked but soaked print was a little rattier. Should have been closer to 0.52mm. Soaking another brand of PETG non transparent PETG and asked RCHacker what PETG he used.

Printed 4% infill test pieces with thin walls to reduce 3d printed mass as much as possible, the soaked sample came out 0.2 grams lighter. I tried dropping the flow rate 10% (the middle sample with 0.85 on it which is of course lighter as less material) then did a vacuum vs non vac fill. Max vac I could put on was -320mmHg as the 3D print leaks. Thought I injected 3.5ml into each sample but by mass I put 1gram more into the non vac filled. Regardless result was opposite expected. The non vac almost filled the whole cavity (3.5ml if expands the claimed x25 should fill all the void), the vac sample filled a lot less but more importantly all the integrity of foam gone with voids everywhere.

Attached pics (Blue is dry PETG, clear is soaked, first number is Slicer weight prediction, 2nd # is actual unfilled mass and 3rd # is filled mass.

So does that mean the low pressure generated penetrated the surface of the resin foam and removed the air from there too?
Oh and too late with the popcorn. Ate that in anticipation.

I just print fins in solid petg (100% fill)

I did a bunch of break tests to optimize my tooling paths and print parameters; ending up at a higher temp I ended up with fins that are working quite well for my application (wave fins and thrusters). PETG is quite ductile and not easy to break if done right. With larger sized they can be a bit too soft, so working with solid Asa on those to get a stiffer flex.