Hasegawa Fw 190S Conversion

[LSP_Kevin]

Well folks, I decided to have another bite at the cherry, since I couldn't think of any other parts to practise with, and these gear doors are the parts I actually want to replicate. I took Dan's advice and rigged up a two-part mould based loosely on his drawing, and all was going swimmingly until it came time to separate the two halves of the mould. Despite using mould release agent this time, they still stuck together! Here's the mould, with the kit part ensconced firmly inside the pink block:





Obviously I was going to need to cut the part out..again...but decided that if I could find the original join, perhaps the two parts might pry apart relatively easily once I'd cut through the outer edge. Thankfully, that's pretty much what happened:



Note the lower part of the mould half on the left however. You can see how the silicone has found its way under the part, effectively trapping it inside. I've trimmed all this away, which isn't easy with this RTV stuff! I've poured some resin now, and will know in about 30 minutes whether this has actually worked or not. At this stage, I'd be happy with just an improvement over last time! My gut feeling though is that I'll be reverting to the original kit gear doors for this build, or begging for new-tool spares in the Traders Forum!

Stay tuned...

Kev

[LSP_Kevin]

Thanks for your input Steve. I bought my own box of generic Lego bricks for this exercise, as I'd already read warnings similar to your own. They're certainly very handy!

Well, here's the result of Round 2:



Success! The only problem is, the part is really quite bendy. I know this can happen due to incorrectly mixed resin, but I'm reasonably sure I got that right (being a newbie though, I'm not prepared to guarantee it). The Procast resin requires a 1:1 mix ratio, but I have no idea how much tolerance it has for slight imbalances. I'm more concerned that this bendiness might be a result of the product's 6-month shelf-life. I bought this stuff in January, and it's almost exactly 6 months old now. Could that be the problem?

In any case, I'm pleased just to have a whole part, and in reasonable nick too. The bendiness won't actually matter for these particular parts, as they're not load-bearing and will just hang off the undercarriage legs. Since I still have to make another one for the other leg, I guess we'll see if I get the same result.

Kev

[A.Wolf Grant]

Perseverance wins out in the end - this just exemplifies what these forums are about ... advice, help and encouragement.

 

Grant

[LSP_Kevin]

Perseverance wins out in the end - this just exemplifies what these forums are about ... advice, help and encouragement.

 

Grant

 

Thanks Grant. I'm happy to report that the bendiness has substantially subsided overnight, though the part is still hardly rock-solid. But I can certainly work with it. Lesson learned: when the tin says demould after 1-3 hours, wait for 3, not 1!

 

Kev

[LSP_Kevin]

Thanks again Dan! The 16-hour cure time explains everything. The part is still a little flexible, but not unusably so. It's probably stiffer than the original plastic part actually.

I used some canola-based kitchen spray as a release agent. I sprayed some into a sheet of aluminium foil and then used a brush to transfer it to the mould. I'm still not sure whether it was the product or my application that was insufficient. Since I don't have any vaseline on hand, I'll try it again anyway, but perhaps spray it on this time. I'm actually thinking of giving Steve's one-part mould technique a try, as while the two-part mould did work, the produced part is far from perfect. Looks OK in a front-on comparison:



But from the right angle you can see some issues created by what I suspect is the mould tearing slightly when trying to separate the two halves:



There are also some thickness issues due to the part lifting slightly (which caused the aforementioned flow of RTV under the part):



So, while this is definitely a step in the right direction, I'd have to class it as a failure ultimately, in that I don't think I could actually use this part. I just hope I can get two acceptable parts moulded before I run out of RTV!

Kev

[LSP_Kevin]

Hope that makes sense.

 

Actually mate, now that I've had a good look at your instructions, I have to say I'm still a bit confused about how to approach the one-piece mould. I'm pretty sure I've figured out where my second try at the two-part mould went wrong, so I might give it one more try (no guarantees it'll come out any better though). I'm still interested in giving your method a go though.

 

When you removed the clay bed from the first pour did your master come loose?

 

Yeah, that's pretty much what happened. There was a bit of lift at one end, and combined with the sub-optimal release agent, the result was a bit of mould distortion and some RTV creep. I think if I try your method of ensuring the part stays put after the first pour, I might finally get the result I'm after. Or not. One thing's for sure, if somebody already made these parts, I'd buy them in a heartbeat! I certainly have a new-found respect for the guys who do resin casting, and the work that's involved (and that doesn't even include making the masters!).

 

Kev

[LSP_Ray]

Hmmm....I think you made one of the same mistakes I made when creating a RTV mold. Mold release agent is really for helping to remove parts from the mold. It does not work too good for the second half of the RTV material; in other words, for between RTV and RTV.

[LSP_Kevin]

Hmmm....I think you made one of the same mistakes I made when creating a RTV mold. Mold release agent is really for helping to remove parts from the mold. It does not work too good for the second half of the RTV material; in other words, for between RTV and RTV.

 

You're probably right Ray; but that begs the question: what does?

 

Kev

[Bruce]

vaseline petroleum jelly works great as separator for RTV two part molds. use a Qtip and wipe the vaseline all over the RTV parts of the first half of the mold and then pour the second part.

 

you first mold might not be a loss. I often pour one mold then cut it open part way down so it opens like a clam shell. when I pour the resin is simply use a rubberband to hold the mold together.

 

Bruce

[D.B. Andrus]

You're probably right Ray; but that begs the question: what does?

 

Kev

 

Kevin

 

This is the release product I have used for years:

 

http://www.smooth-on...1226/index.html

 

HTH,

 

D.B.

[LSP_Kevin]

Thanks for the ideas, tips and advice fellas - I really appreciate them! In an effort to push forward, and in the true spirit of learning by doing, I've had another go. I'd already put the mould box together and laid down the clay before reading Dan's advice about a bigger mould box. I used more and smaller key holes though, but they didn't work out so well (not sure why, but the RTV didn't fill them properly).

Anyway, the result represents one step forward accompanied by one step back:



The mould has captured the part properly with no lifting or slippage, but as you can see from the photo, with the wide end of the mould now being, correctly, much thinner than the previous one, the resin failed to make it all the way down there during pouring. There's an air vent at that point, but it's not particularly large due to the thinness of the part in that area. At least I can reuse the mould without having to make another one - finally! Would I get away with pouring some resin from both ends?

Kev

[D Bellis]

You'll probably trap air in the mold if you pour from both ends.

 

Try squeezing the mold with your fingers while the resin is flowing through it. Maybe that'll help push it along.

 

FWIW, I always try to make a large 'sump' areas at the top of the fill & vent holes. This makes sure there is at least some reserve resin as it flows through the mold. Also, keep pouring until the resin fills the vent sump(s). This guarantees that the resin has passed through the entire mold.

 

HTH,

D

[D Bellis]

If I may, I'd also like to suggest making molds for a long, thin parts vertically. Again, this helps gravity force the resin through the mold:

 

By the looks of the alignment bumps, they had air trapped in them when the second half of the mold was poured. It helps to use a stick to dribble small amounts of the RTV into tight areas such as those bumps before pouring the remainder over it.

 

This also works for pouring resin into molds that habitually have air bubbles in small areas: quickly dribble a little resin into the problem area, close up the mold and pour into the fill sump.

 

HTH,

D

Edited June 20, 2012 by D Bellis

[LSP_Kevin]

Thanks D, good advice. It addresses a couple of related issues I'm having, both of which probably contributed to this round's result. Firstly, I have no real way of telling how far the resin has proceeded along the mould. For the first pour, I could see some resin coming up the far air vent, so it seemed all was well in that regard. This time however, I didn't see that, but I couldn't get any more resin to pour into the mould, I think partly due to the opening of the pour hole being too narrow. I'll try to cut a wider opening out of the RTV. Of course, if I had a trapped air bubble up the end that wasn't venting for some reason, that probably isn't going to help, so I may have to consider widening the far air vent too, or at least the junction between it and the part (which is exceedingly small, and may in fact not be very effective at all).

 

I'll have another go tonight and report back.

 

Kev

[LSP_Kevin]

If I may, I'd also like to suggest making molds for a long, thin parts vertically. Again, this helps gravity force the resin through the mold:

 

HTH,

D

 

Yeah, thanks again mate. I was beginning to come to that conclusion myself, but your diagram really makes it clear how to go about it. I'm going to make do for this particular gear door, but since I need to make a starboard one too, I'll give your modified approach a shot. I guess I just had the misfortune of needing to start with something that's not so straightforward for a beginner. I certainly appreciate all the help and advice though! (And I probably should have spun off a new thread in the Tips forum, to be honest.)

 

Kev