zippo

I like experimenting with different materials and would like to post a few questions regarding some materials I'm currently playing with.

I'm lazy and hate spending hours cutting multiple ribs. I recently bought 20 sheets of 6mm thick depron. It is designed for use under floor heating insulation and cost about £25. The sheets are 4ft by 3ft. Its in a not very attractive black colour (if black is a colour). My first question - what is the best glue to use to stick the depron to balsa?

Secondly .. over in the UK we are just getting to hear about foaming Urethane wood glues. The spec's sound interesting and it seems that it could be a useful product for modeling purposes. Has anybody used this stuff who could express an opinion?

Finally, there is a thin flat glass re-enforced sheet coming available, which is being experimented with over here as a covering material. There is a description of the product on http://www.mrmodels.co.uk . Has anyone used this material in anger?

Thanks for your time!

zippo

Sorry the URL should be http://www.mickreevesmodels.co.uk.

ProfLooney

Hi Zippo yes we have used urethane glues here for a long time now. they are great for sheeting foam core wings and for laminating ply and balsa. you just have to put a paper thin layer over whatever you want to laminate and add the other piece and weight it down. when cured (abt 12 hrs) you wont get them apart without ripping the wood or foam apart. it also sands as easy as balsa and better than reg whit glue or CA thus you wont groove your balsa when you are trying to sand a joint that has been glued with it.

Joe

Al Stein

Wow, I didn't realize that Mick Reeves was still active in world competition -- Love those Sopwiths!!

Anyway, on the Depron question... it sounds like the part you don't like is the shaping of individual ribs -- wouldn't you still have to do that with Depron ribs just like you do with balsa ribs? I know the following doesn't answer your question, but it's food for thought...

I did build two airplanes in the last few years with individually cut ribs and each time I feel dumber about having done it that way. My usual process is to make a couple of templates, stack enough blanks for all my ribs plus a spare or two, and shape them all together. That usually takes me an hour or so including production of the templates and the resulting ribs match to within a few thousandths of an inch. It's very fast and easy compared to cutting individal ribs.

So, that's my sidetrack on the issues. The real point is to enjoy the trip, whichever way you go!

zippo

Al

At the moment its nothing more than a 'plank' type wing, so all the ribs are the same. I've made a simple jig of two rib template stuck together at the le and te with 6mm balsa. I've then cut the depron foam sheet so that I can feed it up through the jig and then hot wire cut all around. I've knocked out 20 or so ribs in about 15 mins. The ribs are 300mm long NACA0020 section which is gives quite a thick section - for a fun fly. With the foam being so cheap, its represents a good cost saving over balsa .. and soo much quicker. (told you I was lazy).

The foam ribs are going to be cap'ed using 1/16 x 1/4 sheeting; which really stiffen's them up. The only prob is what glue to use. PVA doesn't seem to work too well and I'm not certain about foam safe CA as I've never had much luck with it.

I don't need great accuracy in this instance - in the UK we call it a bodge job!

balsaman

For glueing the foam to balsa use the foaming polyuathane glue. Put a wee amount on the ribs, wet the sheeting just a tad and stick it on. Weigh it down as it cures because its foams up and will push the parts apart if not clamped or weighed down. The water is because the glue needs water to cure. If the stuff you are glueing is dry the glue never cures. People who live in more humid climates don't have this problem.

Eric

zippo

Balsaman

Thanks for that info .. dampness/humidity is not a problem where I live (the UK)! I will have to go and buy some of this foaming glue and give it a try.

One of my main problems is that some of my models in storage have got everso damp - I have a couple of aircraft that have green mold growing on exposed wood! - I think I have discovered a new strain that loves castor oil and balsawood.

Strangly the worse affected model is a VMAR T-34, which isn't balsa - rather it seems to be made out of some wood that fruit baskets are made out of. Perhaps the mold came in from China? I know that the US customs are really hot on importing fruit/veg and possibly molds ... better not say too much ... they might ban VMAR kits from being imported into the USA because of this! (thinking about it - that might not be a bad idea).

Me thinks - Must get a heater in the garage.

Regards

zippo

Balsaman

Many apologies .. I just assume that most people who reply to my questions come from the US of A. Just noticed that you live in Canada. Sorry, I just jump to the wrong conclusion sometimes

Regards

balsaman

Hey I have seen the fruit basket wood in the Vmar kits. It's kind of like a laminate or veneer of some sort eh? Sorry I am straying off topic here.

Eric

Al Stein

Zippo -- that sounds like a good method. Do you use a little cutting bow for that or just a wing-panel length one? I think I may just give your way a try.

An interesting project that I was intending for this winter was a big aerobatic plane (I think it's a 99" CAP, but I haven't looked at the "recipe" for a while) which has swept, tapered wings (dual tapered some would say). The instructions for it involve setting up foam sheet blanks spaced out at rib stations along a half-span and cutting them as though it were a solid block of foam to get the individual tapered ribs. Pretty close relative to your technique.

I just don't seem to have time to do all of the experiments and building projects I'd like to.

Steve Lewin

I usually use aliphatics for gluing depron to itself or to wood. IIRC that's what Dave Smith recommends for his models which have foam ribs.

If you're in a hurry you'll probably find that the foam-safe CA works o.k. but, however humid it is where you are (about same as me I guess ), you'll find it works a lot better if you dampen the foam. CA too needs moisture to set (that's why it's so irritatingly good at sticking skin).

I've never tried the epoxy sheet and, at those prices, I don't think I will be trying it anytime soon.

Steve

zippo

Al

Don't laugh .. but I'm using what can only be described as a kiddie's foam cutting bow. Its made of plastic and has a cutting width of about 3". It cost about £1 from a local craft shop.

I connect it to a whopping bench PSU that can deliver upto 18amps - bit of an overkill really. But it does the job and what more can you ask.

Steve

Do you mean the super or ordinary type of Aliphatic?

Regards

Steve Lewin

Mostly I use plain aliphatic wood glues for Depron/foam to wood (and most other things). Titebond II is my current favourite as it sets fairly fast and it's reasonably waterproof when cured.

Steve

Al Stein

The bow fronm the craft shop sounds good -- I'll have to see if they have them here. For £1 or so, it's worth just buying it, but if I don't find it I think I will make one.

I have a power supply that I put together from pieces of other things. It's got a 24 volt AC isolated power source adjusted by a big ol' variac. I'd like it better if it had an ammeter as well -- I figure that any length wire (of the same guage) should heat to the same temperature if it has the same current flowing through. Does that sound right? Anybody?