Thread Tools
Jan 10, 2020, 07:31 AM
Ego varius quis.
Cheesehead's Avatar
Thread OP
Discussion

Building with foam post-Depron?


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?
Sign up now
to remove ads between posts
Jan 10, 2020, 08:11 AM
Build more, websurf less
FlyingW's Avatar
Brown wrapping paper works well to cover regular white styrofoam. Apply like wallpaper using a 50-50 mixture of Titebond-II and water. Do in small pieces on opposite sides to prevent warping. Very lightweight.
Jan 10, 2020, 11:57 AM
Registered User
Tzicul's Avatar
Quote:
Originally Posted by FlyingW
Brown wrapping paper works well to cover regular white styrofoam. Apply like wallpaper using a 50-50 mixture of Titebond-II and water. Do in small pieces on opposite sides to prevent warping. Very lightweight.
I just tried to do this and I've had two problems. One is that the glue disn't hold to the polystyrene, it was a white, water based glue for wood, it was the cheapest and maybe I can find a better one. There is a special one for polystirene, but it is rather expensive. The second problem is kind of problematic, because the final weight is around 450-460 grams/sqm. Which is close to what I can already buy as is and the price is close to Flite test foam board. But way heavier, as FT foam is something like 380 gr/sqm. And this is a big problem because all my planes needs a lot of lead on the plane nose to properly balace ir. So, beside the fact that the plane is heavier than it could be, I had to add some extra lead. So, even if a new glue wil work, I think I will stick with FT foam board. Even if it is like 50% more expensive here, in Romania. Shipping, custom duties, VAT and everything. You know, Europe What I used is brown paper @80gr/sqm times two 160gr/sqm, 5mm thick polystyrene @180 gr/sqm and the rest was the glue.

Sent from my H8216 using Tapatalk
Jan 10, 2020, 12:33 PM
Ego varius quis.
Cheesehead's Avatar
Thread OP
Quote:
Originally Posted by Tzicul
I just tried to do this and I've had two problems. One is that the glue disn't hold to the polystyrene, it was a white, water based glue for wood, it was the cheapest and maybe I can find a better one. There is a special one for polystirene, but it is rather expensive. The second problem is kind of problematic, because the final weight is around 450-460 grams/sqm. Which is close to what I can already buy as is and the price is close to Flite test foam board. But way heavier, as FT foam is something like 380 gr/sqm. And this is a big problem because all my planes needs a lot of lead on the plane nose to properly balace ir. So, beside the fact that the plane is heavier than it could be, I had to add some extra lead. So, even if a new glue wil work, I think I will stick with FT foam board. Even if it is like 50% more expensive here, in Romania. Shipping, custom duties, VAT and everything. You know, Europe What I used is brown paper @80gr/sqm times two 160gr/sqm, 5mm thick polystyrene @180 gr/sqm and the rest was the glue.

Sent from my H8216 using Tapatalk
Agreed. From what I can tell, you're better off just using 3/4oz fiberglass.

Unfortunately, using fiberglass on a wing core 8mm thick is a bit tricky.
Jan 10, 2020, 02:01 PM
An itch?. Scratch build.
eflightray's Avatar
There's this amazing stuff I heard of, I think it's called 'balsa-wood'.

Worth trying

.
Jan 11, 2020, 03:49 AM
Ego varius quis.
Cheesehead's Avatar
Thread OP
Quote:
Originally Posted by eflightray
There's this amazing stuff I heard of, I think it's called 'balsa-wood'.

Worth trying

.
These days, it's more expensive than Depron. I remember when you could get a pile of cheap balsa for $5 at the hobby store, but it's no longer 1996.
Jan 11, 2020, 12:07 PM
treefinder
springer's Avatar
Cheesehead, To your first question, how about this: a 17sheet box of A grade Model Plane Foam costs $40, plus $22 flat rate shipping to WI, which gives $.45 per square foot delivered cost for 6mm foam (24x48 inch sheets - Actual dimensions are more like 23.75x 47.25" ) The difference between nominal and actual is a combination of process variation at the manufacturer, and the fact that I trim the long dimension and the box to get it under 48" and avoid an "extra handling" penalty of about $15/box from the shippers. Order it at modelplanefoam.com Also, browse the gallery and you will see all the various types of planes folk have built with MPF.

As far as stiffening and adding rash resistance, I frequently use colored packing tape as a poor man's monokote. I have a local dollar store that sells 8 colors for a buck a roll. Check around your area. It's also available online, of course. If you can't find the colors, you can paint the MPF with water based paints and apply clear tape after. While the tape adds a lot of stiffness and durability, colors are limited, so using the newsprint/paper or Bunn style coffee filters with either Titebond ll wood glue, Minwax Polycrylic or water based urethane varnish will give a surface that's durable and paintable with most anything your can think of. There is a whole thread dedicated to the paper technique here on scratchbuilts, you can search for it.

Extra note to Tzicul, regular Aliphatic resin white glue probably doesn't have the "tack" to work well with paper on Styrene foam. That's why we use Titebond wood glue here in US. Look in your local hardware store for wood glue with high initial tack. I wouldn't know any brand names in Romania, but I'm sure there are equivalents to Titebond.
Jan 11, 2020, 03:54 PM
Ego varius quis.
Cheesehead's Avatar
Thread OP
Quote:
Originally Posted by springer
Cheesehead, To your first question, how about this: a 17sheet box of A grade Model Plane Foam costs $40, plus $22 flat rate shipping to WI, which gives $.45 per square foot delivered cost for 6mm foam (24x48 inch sheets - Actual dimensions are more like 23.75x 47.25" )
If you had 3mm, I'd buy it. 6mm is unsuitable.

As for the coatings, tape adds a lot of weight for the amount of strength added, and polyurethane isn't great either. Doculam is popular with the indoor balsa crowd because it's light and dirt cheap, but it also adheres low enough you can use it on styrofoam without melting it. Paper and fiberglass resin is a popular combination that's less fussy than actual fiberglass and is substantially cheaper than Polycrylic.

https://www.flitetest.com/articles/s...roof-foam-core

I might look into whatever they use to make paper plates. I have access to a large (if crude) 3D printer, and I never get hand-rolled airfoils right - better to vaccuform the whole thing.
Jan 11, 2020, 09:47 PM
treefinder
springer's Avatar
You might be surprised, I have convinced several guys who thought they just had to have 3mm that 6mm works just fine once the design accommodates it.

The trick with tape is to get the cheapest you can find -dollar store. The cheap stuff is thinner/lighter than good 3M tape, and works just as well for our purpose.

I dont know about WI, but around here glassing resin (epoxy, since less expensive polyester eats foam) is more than twice as expensive as polycrylic or wbpu.

Just did some checking and realize you are into the micro stuff, so 6mm would require very different techniques. I happen to have some of the foam plate stuff, got end of a roll from MPF mfr. Who also makes foam plates, trays, etc. It is about I mm thick, has a pronounced curl (they extrude it onto a roll, cure it, then unroll and vac form the plates). I haven't had a lot of luck with it. It has a noticeable skin (integral, not added) and tends to kink when i try to flatten or shape it. I have considered vac forming planes but not got around to making the plugs. Too many planes, too little time!
Last edited by springer; Jan 11, 2020 at 10:02 PM.
Jan 12, 2020, 12:53 AM
Registered User
tspeer's Avatar
I have cases of 6 mm MPF. How difficult is it to slice to 3 mm with a hot wire?
Jan 12, 2020, 03:01 PM
Ego varius quis.
Cheesehead's Avatar
Thread OP
Quote:
Originally Posted by springer
You might be surprised, I have convinced several guys who thought they just had to have 3mm that 6mm works just fine once the design accommodates it.
I'm building indoor stuff, so weight is very important.

>
Quote:
Originally Posted by springer

I dont know about WI, but around here glassing resin (epoxy, since less expensive polyester eats foam) is more than twice as expensive as polycrylic or wbpu.
Polycrylic is $10/half pint. Apparently it's much cheaper if you buy it by the quart. That said, I'll pay another few dollars for strength to weight.



Quote:
Originally Posted by springer
It is about I mm thick, has a pronounced curl (they extrude it onto a roll, cure it, then unroll and vac form the plates). I haven't had a lot of luck with it. It has a noticeable skin (integral, not added) and tends to kink when i try to flatten or shape it. I have considered vac forming planes but not got around to making the plugs. Too many planes, too little time!
I've been considering the use of a 3D printer to make vaccuform molds.
Jan 12, 2020, 03:37 PM
treefinder
springer'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?
I haven't tried, but some have. My only experience with ripping sheets thinner was with EEP blocks using a gravity feed hotwire. (That didn't sound right, I Weighted the sheet and let gravity pull it through the wire. ) the results were pretty consistent, though I was cutting about 10mm sheets . If I were to do MPF, I would work with the 10-12" widths I did with EEP. Trying to slice a full width sheet would i think be really hard to get consistent thickness across the width. I have hot wire cut sheets to size for the international boxes, and it cuts clean and straight if one moves the wire at consistent speed. I still have the setup, i think so may try it and post results.
Jan 12, 2020, 03:47 PM
treefinder
springer's Avatar
Quote:
Originally Posted by Cheesehead
I'm building indoor stuff, so weight is very important.

>

Polycrylic is $10/half pint. Apparently it's much cheaper if you buy it by the quart. That said, I'll pay another few dollars for strength to weight.





I've been considering the use of a 3D printer to make vaccuform molds.
I saw that your interests are all micro, yep different parameters. If you are interested, I will send you a few pieces of the plate stock and some 3mm samples. PM me an address. (I looked into 3mm last year, and got a sample run, but it all had corrugations - not dead flat, so ok for skinning but not profiles. Not enough market for the minimum order required)

The half pint is the killer. Last I checked a quart was $13 or so and I think I paid $10 for Valspar wbpu qt. A couple months ago. The quart will last me over a year on the around 1 meter span birds I typically build.

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.
Jan 12, 2020, 04:14 PM
Ego varius quis.
Cheesehead's Avatar
Thread OP
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.
I'm curious if the stuff smooths out if you vaccuform it. I could take a shot.
Jan 12, 2020, 05:07 PM
treefinder
springer's Avatar
I expect it would, pm me and I will send some 10x14 " pieces


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Article Building With Foam - A beginners guide to building model airplanes with foam FLYWINGFAN Foamies (Kits) 14 Oct 11, 2016 03:29 PM
Discussion Built Up Foam Board / Depron Questions (Heinkel 100 build log) The_Red_Baron Scale Kit/Scratch Built 6 Aug 06, 2016 01:26 PM
Discussion Built up foam board / depron Heinkel 100 build The_Red_Baron Foamies (Scratchbuilt) 4 Aug 05, 2016 06:30 AM
Build Log 2m Boeing 757-200 depron + blue foam scratch build RCExplorerUK Foamies (Scratchbuilt) 2 Aug 01, 2016 08:32 AM