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Build Log
Lavochkin La-7 1:48
Since I had been inactive for too long, I decied to build a Lakov... Lachok... Lavok, well a russian plane.
They called it the LosAngeles 7 (dunno why...) and I picked it out because it was the cheapest 1:48 set I could find on e-Bay. I am gonna try to mould Depron quite a bit more detailed, than I usually do. So I also bought some plaster. The plan is to form a positive and a negative form from the plastic parts, heat them up in the oven (the forms) and then just sandwich a piece of foam in between. Hopefully I need no vakuum or continous heat for this. Looking at the set, I am seriously considering using the canopy parts, the rotor and the spinner from the set. But I guess the prop would just not create enough wind. |
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Last edited by JustAHuman; May 08, 2021 at 08:45 AM.
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Watching with much interest...
Several years ago I bought the plaster, some plastic model kits, etc., but never got past the wishful thinking stage. Forget using the kit prop, spinner and canopy - polystyrene is way too heavy, and the prop is probably useless for actual propulsion. If you can't find an off-the-shelf prop of the right size (say, from a micro-quad), then mold one from .005" or .010" garolite (fiberglass sheet from McMaster Carr or other suppliers). For the canopy, you can probably use the original as a plug to plunge mold one from .005" laminating film (though you have to be careful not to melt the original). I like to 3D print my canopy plugs, but used to carve/sand them out of balsa in the old days. Vacuforming works better, but plunge molding isn't too hard, and doesn't require any special equipment. And for a spinner, turn one from balsa or dense foam (blue, pink, purple or green foam, depending on what your local home improvement store carries). At this scale, it takes literally seconds to make one using a Dremel or drill press and a piece of sandpaper. Mike C. |
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Been thinking of building a smaller version of this subject myself maybe 24", just about 5 minutes ago. Alfa has a smallish molded depron version too, although they're custom order. I think the Juergen S method should work at this size, where he heats the foam sheet clamped in a frame, and plunges it over the plastic parts making half fuselage shells. He posted a video of it with a heating device and slide rail setup. Avoiding the setup hassle, I would just clamp my heat gun to the bench a few feet off the floor, heat the foam in a frame, and drop it over the plastic parts. Molded more canopies than I can count that way. Making the frame just a bit larger than the perimeter of the fuselage shells (or in my case canopy molds) works, if you're not using vacuum to pull the foam inward at the bottom of the mold.
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Thread OP
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Thanks for the infos.
Step two after attaining the raw materials was to get the wire cutter working, so I could make myself 1mm Depron-sheets. Funny thing about the whole setup is, that I tried it just like that before and only got it working for one cut off a tiny styrofoam block. The only thing I changed this time, is that I took a very big LiPo from an old laptop as the energy-source. So I guess the last time the NiCd-pack I used back then though:"OK, I'll give you one..." Next up, testing how plaster and plastic interact and if I can use vegetable oil as a separating agent. |
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Last edited by JustAHuman; May 10, 2021 at 09:59 AM.
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Thread OP
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I have cut some Depron.
The slack wire is less of a problem than I would have thought. But look at the pic below, it is not a very flat cut. My guess is that the feed rate my hands provide isn't constant enough. Anyways, it's good enough. Next step, as promised: PLASTER. |
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Last edited by JustAHuman; May 10, 2021 at 12:45 PM.
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Never did any foam wire cutting, but it reminds me of a 6v lantern battery we had with a piece of nichrome wire in the 6th grade. Cut through paper really well, with a bit of smoke.
Wasting good sheet supply to get a good mold has always irked me, so I'd try testing with the low dollar thin foam plates that some have had success with. Using the plastic fuse shells as is avoids going through the plaster mold making process. Aluminized duct tape was a good discovery, as it easily tolerates heat from the heat gun without loosening. Instead of molding plastic like the canopy below, tape foam sheet to the mold frame and try heating it with heat gun. Heat might have to be applied from below the foam sheet at an angle so the heat raises upward, or it can blow through the foam. I've had to do the same thing with plastic sheet. The method won't hurt the plastic fuse shells, so it's worth a try. I've done up to about 7-1/2" length with plastic (last canopy) which is where things start to become difficult. I'd like to think foam could work better. Seems possibly worth a try as it's fast and easy. |
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Neat idea, but I have the aspiration to recreate the model with all its details this time around.
With rivets and all the bells and whistles. So, I see no way around plaster (since I don't have a 3D printer). Speaking of the devil: I snipped of a part of the frame and put it into a joghurt-cup with plaster. Before putting it in, I wiped the thing with some vegetable-oil. Lets see if I can get it out, once its dryed, and how good the detail is (there is a number on the little square in the corner, lets hope it gets diplayed). Adressing your concern: I dont see myself using the 3mm Depron which I cut anytime soon, so it's not wasting it. Also, it's pretty easy for me to get more, and at around 6 bucks for a 70x100cm sheet, it might even be cheaper than buying plates. Edit: Well, it dryed pretty fast, and I am pretty content with the result. I could remove the plastic part pretty easily and the resolution is good enough. Next step, trying with actual parts. |
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Last edited by JustAHuman; May 10, 2021 at 03:05 PM.
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So... I cut apart a cream container, mixed up some plaster and wiped the fuselage halves down with some veg-oil. So far, I have removed the first half from the mould and I am pretty happy with the result. There are some air-bubbles, but all in all it worked out about a well as I had hoped.
I am especially happy with the vegetable-oil working as intended, as it was pretty easy to get the plastic out of the dryed plaster. |
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When I mentioned wasting material, I was referring to purchased thin depron sheet that can be expensive. That would be the advantage of cutting your own sheet for sure. I imagine the plan is to fill the bubbles, or is it even necessary? Not sure what plaster you're using, but I've used enough 20 minute Easy Sand to fill the average home, over the years. Wouldn't be much waiting time for molds to cure. Always wanted to try this, but I can't get over the price they want for the large scale plastic kits. I remember buying them as a kid in the 70s, when they were cheap. I think you made a good pick with the LA7, which is a good flying r/c airframe from what I've seen. I disregard comments from those who are terrorized by tapered wing tip stalls as if all tapered wing aircraft are stall demons, as it's only an issue when a model is too heavy.
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Quote:
Are you sealing the mould before you apply the foam? Ditto on the plastic model kits. I shudder to think about the cost today compared to what I paid for Monogram, Revell, MPC, Tamiya and Testors back 'in the day'. |
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It's joint compound, so probably the same thing. I've never molded foam yet. All my molding is plunging plastic over sanded primer balsa molds. The heated plastic is not hot enough to damage the grey automotive primer, so I've haven't used any release compounds on the molds. My memory of the larger scale plastic aircraft kits was maybe $10, at the high end. I used to buy model cars for $2 to $5. We used to build extra cars using the spare option engine and wheel parts, using the parts tree as a frame. They looked like the Humongous car on the Road Warrior.
Was just looking at 1/24 scale aircraft on Ebay. I think the LA7 was a good choice. All I'm seeing is over modeled stuff and at around $100 or more. If I were to put loot into a project like this, it doesn't need to be a ME109, FW190, P51, P47 or some other common subject I've already built. |
Last edited by AntiArf; May 10, 2021 at 09:10 PM.
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I was pretty happy, when I discovered that I could buy big sheets of Depron at the local architect-students shop. Remember, I am not American. So no dollar-store foam for me.
I also remember buying Revell-kits for a lot less, then they want for it now. Thats why I am trying this with a LaMunchkin instead of a FockeWulf or Mustang. The plaster is gypsum [CaSO4·2H2O] (Gips in german). Managed to make a core out of plaster, but of course the tail broke off and disintegrated. I will have to make it more solid next time. Anyways: I tried to cast today and you can admire the results below. I did not fill up the bubble holes, since I first want to see at least some result before I go improving details. First go around I set the temperature to 130°C (which is the correct way to measure heat...), but the depron would not really do much, so I cranked it up to 250° (still Celsius) and that was too hot, as you can see on the two strips of deformed foam. So I waited a bit and that kinda worked. Put the plug on top and let it sit for a while. Conclusions: This should work, but there needs to be excess of material all around , or else it gets sucked into the form. (See nose of the fuse) Ideal temperature is somewhere between 130° and 250° and some sort of seperating agent is needed, as the foam peels bits of plaster off the form otherwise. Being the cheap-skate that I am, I am gonna try vegetable-oil for this again. Will give this another try tomorrow, I think. |
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Last edited by JustAHuman; May 11, 2021 at 06:14 AM.
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