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Jan 13, 2020, 01:54 AM
Registered User
tspeer's Avatar
Quote:
Originally Posted by springer
...
I too have pondered printing plugs, but smoothing the surfaces tedium has prevented me so far. I am tempted to cut a piece of pvc pipe into a tapered fuse half (right and left identical) as a test, though.
There's an epoxy that is specially made for smoothing 3D printed articles.

However, even without any extra treatment, 3D printing is my favorite way to make vacuum forming plugs. I use disposable styrene plates, and they show every detail of the print.

I wonder if one can vacuum form foam at, say, 1 mm thickness.
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Jan 13, 2020, 06:54 AM
Obviously I'm a "Minus Member"
buzzltyr's Avatar
Quote:
Originally Posted by tspeer
I have cases of 6 mm MPF. How difficult is it to slice to 3 mm with a hot wire?
Don't know if it will help, but here's Keith Sparks' method of cutting thin sheets of foam: https://www.youtube.com/watch?time_c...&v=cCS8FzBKxNM
Jan 13, 2020, 08:26 AM
gpw
gpw
“There’s no place like Foam”
gpw's Avatar
We’ve been modeling since 1955 , flew the first electric RC in our area in 1972 , and it was a Foamie ( Superstar) , and since then we’ve built a few foamies out of anything we could find … The game was "using what was available to make planes" … Modeling … Part of which is materials acquisition… So we’re always eyes open to find that odd piece of salvage foam that May become a plane or part of … Packaging foam comes in so many varieties and shapes and weights we had to STOP collecting it as it was so easy to get, and the hanger is only so big ( hot wire is a necessity for harvesting foam ) .
Food trays , we’ve made a few planes out of those … https://www.rcgroups.com/forums/show...ne-say-it-fast Got a new Foam EZ made of chicken trays , ready to fly ...

The other foam boards/sheets/ rolls boards are "where you find them" , all are different and present a new challenge to modeling … We currently have 2 boxes of 4mm Epp that’s so light it may not make a plane , certainly not without some creative bracing , and that should be EPP too to take advantage of the materials extreme flexibility and crashworthiness. The challenge of Modeling … make something from what you can find … Cardboard works too, as well as coroplast ( sign material) …
For heavier materials , just make the plane BIGGER …
Last edited by gpw; Jan 13, 2020 at 08:35 AM.
Jan 13, 2020, 08:40 AM
gpw
gpw
“There’s no place like Foam”
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And a word to the wise … or foamie' addicted. When you find a foam you like , best stock up on it . just saying , I still have 16 sheets of Blucor left , in great shape … 8 of the old pink and even a couple Green …All waiting for their chance to Fly …
Latest blog entry: Lost plans
Jan 13, 2020, 09:39 AM
treefinder
springer's Avatar
Quote:
Originally Posted by tspeer
There's an epoxy that is specially made for smoothing 3D printed articles.

However, even without any extra treatment, 3D printing is my favorite way to make vacuum forming plugs. I use disposable styrene plates, and they show every detail of the print.

I wonder if one can vacuum form foam at, say, 1 mm thickness.
Wow! That I a deep draw! What temps did you use???
Jan 13, 2020, 09:45 AM
treefinder
springer's Avatar
Quote:
Originally Posted by gpw
And a word to the wise … or foamie' addicted. When you find a foam you like , best stock up on it . just saying , I still have 16 sheets of Blucor left , in great shape … 8 of the old pink and even a couple Green …All waiting for their chance to Fly …
Well spoke, old man, we had a foamie breakfast last thursday, and the topic came up that with scratchbuilt foamies, EVERYTHING is raw material!

The specific item shown was the bunch of water balloons fixture that has like 30 1mm ID plastic tubes - perfect for control wire guides!
Jan 13, 2020, 10:46 AM
Registered User
tspeer's Avatar
Quote:
Originally Posted by springer
Wow! That I a deep draw! What temps did you use???
I don't know what the temp was. I have an electric hot plate, and plywood holders for the plastic. I wave the holder over the hot plate until the plastic wrinkles, smooths, and sags. Then I plop it on the vacuum box. I don't have any photos of the holder, but here's a pic of the vacuum box.

The photo shows another deep draw, this one for a Big Pink Beaver cowling.

Getting back on the topic of modeling with foam, what I do is vacuum form an inner skin over the printed mold. Then I glue strips of foam to the skin and dress the foam while it is supported by the mold. For a shape like this, I use narrow strips applied in a spiral - like building an igloo. The outer skin can be either styrene skin vacuum formed over the foam or something else. I haven't done it, but I could use glass on the mold for the inner skin and/or glass for the outer skin. Or newspaper/brownpaper & Titebond II. As you can imagine, using a plastic plate results in a very thin molding that won't hold its shape. But adding a foam core results in a light shell with adequate stiffness.

The cowling mold is the most plastic I've ever printed in one piece. It has a conical inner hole that eliminates the need for supports and acts as a plenum chamber. The fill was printed at 15%, IIRC, and it still ended up being quite a chunk. Notice the array of small holes around the periphery of the inlet that ensured the vacuum would draw the plastic around the inet lip. 3D printing is so good for implementing details like these.

I'm still working on finding a suitable glue for bonding the foam to the styrene skin. I've tried 3M77 - messy and doesn't bond all that well. Beacon Foam-Tac is hard to apply to large areas. Epoxy won't hold the strips in place on the mold as they are applied. I have some water-based contact cement that is sold in DIY stores for attaching laminates to counter tops, and I'll probably try that next.
Last edited by tspeer; Jan 13, 2020 at 10:56 AM.
Jan 13, 2020, 11:22 AM
treefinder
springer's Avatar
Michaels sells a "tacky glue" that may be an aliphatic resin that I use for paper to foam repairs, gluing unattached edges, etc that may work for you. Do you fill the printing grooves or just run it as printed? Perhaps I'm too finicky about the plug surfaces....

It just dawned on me that you are forming a dense styrene plate, not a foam plate! Still an amazingly deep draw. I've not had that kind of luck forming plates. It would be interesting to try forming the foam plate, then the dense plate over it. Just what I need, more projects!
Jan 13, 2020, 12:01 PM
Retired CAD guy
birdofplay's Avatar
You will no doubt find that FOAM is much more difficult to achieve the RIGHT TEMP.

It's insulating itself from getting the SAME TEMP on both sides.
And about the time it sags it also is just about to LIQUIFY and totally fail !

Let us know if you figure out how to regulate that .
Jan 13, 2020, 03:19 PM
gpw
gpw
“There’s no place like Foam”
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Just saying , 2 liter bottles shrink nicely around a form without much heat ( heat gun) Made a lot of canopies that way …


Foam seems to respond(soften) well to boiling water … 212F ( 100C )
Latest blog entry: Lost plans
Jan 13, 2020, 04:20 PM
treefinder
springer's Avatar
Ha! Well spoke again! I just finished turning a cowl plug in basswood for the SuperTwin latest incarnation, but am out of the 1 liter bottles that fit that size plug. Time for some pop!
Jan 13, 2020, 06:50 PM
Space Coast USA
hoppy's Avatar
Quote:
Originally Posted by Cheesehead
After being offered some 3mm Depron for almost $3 a square foot, I think we're done with the era of cheap and easy foam. Pro-Formance is expensive and terrible, and foamboard is heavy and loses its' strength if skinned.

Which leaves us where we started: skinning extruded polystyrene, mostly.

I'd like to cut some very small (22" wingspan or smaller) models from XPS and cover them in something so they're not quite so fragile. Do I want doculam, mylar, or something else entirely? Should I just cut slices and make my own depron? Or should I pay the piper and accept that this stuff costs more than myrrh?
Try a meat market that uses foam trays. Some are quite large. The foam is thin and stiff. I got a bunch several years ago for free.
Paper covering to increase stiffness-strength. https://www.rcgroups.com/forums/show...ighlight=paper
Jan 13, 2020, 08:03 PM
Scratch builder
I hot wire $$$tree foam similar to the vid above but my wire is much thinner at .015. (SIG braided control line) I make 2mm (.078) thick sheets. This method makes sheets that are "good one side". Sanding the hot wired side makes a passable finish. I make sheeted wings and fuselages with traditional ribs and "guillows" type formers cut at the full 3/16 thickness.

Any thickness less than the original is possible by simply choosing the desired shims between the table and the wire. Drills and even nails are easy to use.
Jan 14, 2020, 12:40 AM
Ego varius quis.
Cheesehead's Avatar
Thread OP
On the subject of depron vaccuforming:

This guy builds huge scale indoor warbirds and seems to have it figured out.

I'm told that the unprocessed foam forms molds much better. Commercial foam plate production is pretty much a vaccuforming machine, so it stands to reason this should work, too.

Adding "ribs" to the foam for rigidity is also a viable option for 3D molding.
Jan 14, 2020, 02:56 AM
Registered User
tspeer's Avatar
Quote:
Originally Posted by springer
...Do you fill the printing grooves or just run it as printed? Perhaps I'm too finicky about the plug surfaces....
It depends on what I'm doing. I may wet sand the plug if I'm concerned about the grooves. IIRC, I did some sanding of the cowling plug, but not very much. I didn't sand the flap skin mold, because the whole point of it was to mold corrugations on the bottom side. However, the leading edge and the top skins came out smooth. I've not tried to do anything with a printed mold where the cosmetics would be important.

I'm only forming cheap plastic plates from Dollar Tree. If I don't like what I see, I'll toss it and work on the plug! The deep draws do end up paper thin.

BTW, the pink foam flap with styrene skin turned out as light as balsa trailing edge stock of the same size. I then wrapped it with bond paper/Titebond II, paint, and 1.5 mil laminating film.


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