1:72 Boeing V-44 Quad Tilt Rotor

[kitnut617]

Gob-Smacked   ----- again 

[Captain Canada]

Great work on this one !

[jalles]

I really wanted to have four-bladed rotors for this build. Unfortunately I only have two V-22 kits and I didn't want to buy another one just for the four additional blades. After watching the success of sandiego89 casting his pegasus engines for his STOL C-130 I thought I'd finally give casting some parts a try.

I think these blades may have been a poor choice to cut my teeth at resin casting.  The short story is it wound up being a major pain to get usable blades out of the mold. The blades are long and thin and getting resin to fill the whole cavity is difficult. Here's a pile of failures:

1:72 Quad Tilt Rotor by Jason Alles, on Flickr

Out of all of my attempts I think one blade turned out flawlessly. Luckily there were a few more that could be cleaned up and made to work and now I finally have four extra blades. I printed out a new hub and things are finally looking up:

1:72 Quad Tilt Rotor by Jason Alles, on Flickr

The other part I was missing were main gear wheels. I wanted to have four wheeled main undercarriage and after looking through my donor kits the only two candidates were a KC-135 or Revell's old 80's whify B-2. Unfortunately the wheels of both looked too big for the V-44. But after taking a second look, the front wheels from the B-2 looked to be the right size. The problem there is they're only two of them and I need eight. After my limited success casting blades, I decided to try casting some wheels.

I went with a two part mold and the results were much better, with almost all the wheels being usable:

1:72 Quad Tilt Rotor by Jason Alles, on Flickr

Work on the actual V-44 has been confined to just PSR, which has taken longer than I thought it would:

1:72 Quad Tilt Rotor by Jason Alles, on Flickr

[PR19_Kit]

That's looking more and more awesome the further you get into it.   

The rotors, with your cast blades, is especially noteworthy. 

[kitnut617]

I've had the same problem with some blades I've tried to cast for my F-82s. However a tip I was given that might help (I haven't tried it yet) is to do it with a close fitting frame around the blade, if you look how some of the aftermarket guys do it you'll see what I mean.

[Captain Canada]

Wow you're doing it all ! Great stuff.

[sandiego89]

Looking great, glad I could give you some inspiration to try casting. I tried and failed with some long thin casting attempts (B-36 bomb bay doors in 1/72) but it is fun to experiment. Agree in thinking the resin does have a hard time getting to some thin parts of the mold. Fatter shapes seem to allow better flow and fill.

Dave

[Dizzyfugu]

That's looking very good! 

[Old Wombat]

Would holes at the bottom of the mould help? Somewhere for the air to escape as the resin flows down?

[jalles]

Thanks for the kind words guys!

I've had the same problem with some blades I've tried to cast for my F-82s. However a tip I was given that might help (I haven't tried it yet) is to do it with a close fitting frame around the blade, if you look how some of the aftermarket guys do it you'll see what I mean.

Yeah, I've been studying my aftermarket resin pieces, although I'm not sure I understand exactly what you mean by making a close fitting frame around the blade. I have no idea how they cast such small/thin parts. Either their resin is much lower viscosity than mine or they have a vacuum chamber.

Would holes at the bottom of the mould help? Somewhere for the air to escape as the resin flows down?

I do think some sort of venting would have helped. Unfortunately my decision to make a one part mold precluded doing that, if I was doing it again I'd make a two part mold with venting.

[kerick]

In difficult spots I've heard people apply resin with a brush before putting the mold halves together.

[kitnut617]

Yeah, I've been studying my aftermarket resin pieces, although I'm not sure I understand exactly what you mean by making a close fitting frame around the blade.

OK, say your blade is 3mm at it's thickest, tapering down to say.25mm, if you make a close fitting frame which is thicker than the thickest part of the blade, say 5mm, it's supposed to help with the casting. What I was told anyway ---

Pic of what I'm trying to say;

Spinner end 3mm, blade tip .25mm, side bits (the frame) 5mm and the pour block at the top 5mm thick or thicker

[jalles]

Yeah, I've been studying my aftermarket resin pieces, although I'm not sure I understand exactly what you mean by making a close fitting frame around the blade.

OK, say your blade is 3mm at it's thickest, tapering down to say.25mm, if you make a close fitting frame which is thicker than the thickest part of the blade, say 5mm, it's supposed to help with the casting. What I was told anyway ---

Pic of what I'm trying to say;

Spinner end 3mm, blade tip .25mm, side bits (the frame) 5mm and the pour block at the top 5mm thick or thicker

Ahh...okay, I see what you're saying. Having someway for air to escape would be very beneficial, knowing what I know now I probably would have done something like this. Curious about why the frame needs to be thicker than the part?

[kitnut617]

Curious about why the frame needs to be thicker than the part?

Not sure there Jason, but I think it's something to do with more resin volume

[rickshaw]

There are several methods to get a good casting, most are borrowed from metal casting.

You've discovered the use of air vents to allow air to escape from the bottom of a  mould, easily.

Other methods are a little more complex.  Centrifugal casting is one such.  You can use smaller air vents and basically you have a larger reservoir area at the top of the casting and you then spin the mould to force the resin to the lower extremities.  This means you need a slightly longer fluid casting time but the spinning motion can consist of some string around the mould, held in your hand and spun over your head.  Some people use old gramophone motors, some use electric motors to produce the same result.

Another and easier method would be pressure casting.  Using a disposable syringe and large diameter needle, you basically force it down the mould from the neck and "inject' the resin, from the bottom up. withdrawing as you inject to fill the mould up.   You then have to throw the syringe and needle away, as it's a one shot affair and you have filled it up with resin, which is irremovable.