When I assembled a few ARF's years ago, the hinges were always either the flat plastic or round plastic hinges.

So now I'm about to assemble the Alpha 40 ARF... and it's got those CA hinges.

There are a few aspects of the hinge attachment process that are a little unclear to me (at least it sounds unclear in the Alpha40 instructions)...

1) the T-Pins: What is the purpose of these during hinge attachment? The instructions say to pierce the hinges "through the center" with the T-Pins before inserting the hinges. But the hinges have rectangular holes in their centers. There is nothing for the T-Pin to stick into. And what is the purpose of the T-Pins? From the way it's described, they don't appear to temporarily hold the hinges in place in any way or serve any purpose.

2) wicking of CA: About how many drops of CA do you normally end up putting on a single hinge? ... that's not a point of confusion for me necessarily but would be nice to have an idea before doing it.

Obviously the T-Pins have some purpose, so I'll feel silly once someone enlightens me about that, but as yet I don't see what they're for or what exactly to stick them into.

Cheers

T pins are inserted in the ca hinge to ensure it's centered between the surfaces before you apply the glue.

http://www.rcuniverse.com/magazine/a...?article_id=55

Well I'll tell you how I do it, others may have different methods....

I use two T-Pins on the larger hinges and this can work if there is a hole in the middle of the hinge, although none of the models I've used CA hinges on have that. I also open up a small area in the wood near the center of the hinge area on the fixed and movable surfaces to allow the CA to penetrate better. This can be done with a small drill bit.

Put the two pins in at the hinge center line where it will flex. Put the hinges into one or the other surface first (I prefer to do the fixed surface) then slide the moving surfact onto the hinges. The T-Pins will go right in the middle providing just a bit of clearance for control movement, as well as let you make sure the hinge is centered and straight.

Then I run the CA down the T-Pins to the hinges. This makes it easy to only run CA on the hinges and not get it all over the surfaces. I just run a couple of drops initially, when it soaks in I run a few more drops. Keep running CA a few drops at a time into the hinges until it no longer wicks into the hinge/wood. Grab the T-Pins with a pair of plyers, give 'em a quick twist and pull them out. If done before the CA sets up with that last application, it fills the holes created by the T-Pins and eliminates any raised area of CA that might have accumulated around the pins.

Let 'em dry good, give them a few flexes to get rid of that bit of surface CA at the flex point and make sure they work. Then you're ready to seal the hinge gaps.

Works for me....

Thanks a lot. Your descriptions cleared this up 100% for me, which is really good, because you only get one chance with CA glue and hinges of this type.

So using two T-Pins when you have the hole in the hinge will not only keep it centered in the slot but also keep it straight. I'll do it that way.

The instructions say to take the T-Pins out and close the gap before dropping in the CA, but if you have materials for sealing the gaps, then leaving them in has advantages for applying the CA.

Thanks this is very helpful

p.s. I included a pic of the hinge and how it has the rectangular hole. Clearly using only one T-Pin in the center (as the instructions say) would not work with these... hence the confusion.

If you feel the need to do it at all, then they're actually wanting you to put the pin through the centerline of the hinge. Anywhere will do. The centerline would be where the hinge bends. The idea is to keep the hinge from moving into the slot on one side farther than the other side as the two parts being hinged are pushed together. In actual practice, the hinges often have nowhere to go in lots of slots. Put hinges in those slots and how many slots are left? And in most slots, they're held very tightly in one of the two slots that hinge is going into. It doesn't take but one or two assemblies to get the picture and work out a safe way to just stick'em in and go. For example, ailerons on most 40 and 60 size ARFs are solid wood. I stick the hinges in there first. Some won't even go halfway. If they do, kewl. If not, the slot gets cut just deep enough for half. You actually need to inspect all the slots on an ARF for centering and for slots that are in at an angle. In the last year, I've not assembled an ARF that didn't have slanted or off center slots. So checking them for holding the hinge tight enough for assembly isn't really a hardship.

I've also penciled a line on each hinge flat at it's centerline. It helps show if the sucker has been pushed one way or the other. Doing this awhile has taught me that step is about useless, as is the pin deal. For me at least.


More than one. Depends on the size of the hinge actually. On the last 60size, I hit each one with two drops (the bottle was putting out big drops) all along one side of the wing. Flipped the sucker and went down the other side with two each. You will get a feel for how much almost right away. The first couple ought to be sucked into the slot right away. And truth is, one drop spreads out very well. You want to do both sides without pause. 2nd side probably doesn't need as much because CA has tremendous penetration power, but it's cheap and almost no weight.

BTW, you really need to keep overflow in mind. Bottles are a pain to dispense from. Just turning them up to dispense can spit some drops. Lots of LHS have squeezy-bulb dispensers. They're like eyedroppers only one piece and some kind of vinyl. They work excellently well.

If you get runs with CA, Acetone wipes the runs off with no sweat. Well, no sweat within a few minutes. Slight effort after awhile.

Also, right after you've run the CA along all the hinges, it's a good idea to flex the surface. Push it together as you flex because you don't want to pull on the hinges, just to establish where they're going to bend. I wait a minute or two just for the heck of it.

I got no idea why this does what it does, but MinnFlyer mentioned it was good to do so I tried it. It does seem to help a couple of things. The hinges won't be stiff like some can be. And they seem to last longer. Since starting to do it, every hinge I've had the good/bad fortune to autopsy has been supple and none showed any cracking. I've only ever had one instance of CA hinges failing, however. They looked cheap when I installed them. Looked like shiny vinyl. So who knows for sure.

I use the two-pin method too, to keep the hinges centered and straight. I leave the pins in when I CA the hinges to leave a very tiny gap so you get good hinge flex. When I've not done this (left a tiny gap with the pins), I've had some very tight hinges. I also flex the hinges afterwards to help loosen them up, and give a good tug to be sure they are secure. To get the pins out, you give them a twist to break the CA bond, and then they pull out easily.

One set of instructions I had said to hit each side of the hinge with 4 drops of thin CA, so that's what I usually do (maybe it's overkill). I've found that you can tell when you adding too much when you see the CA just start to drip instead of wick into the hinge & wood. Usually the second side seems to need less CA since a lot has already soaked through from the first side.

Thanks guys. There is a lot of vital info here. I'll leave the pins in and do the flexing right after the CA. I've had an arf before with preinstalled surfaces where the hinges were really stiff. I don't want that to happen with this plane.

If I need to remove any excess CA, I've got CA debonder handy as well.

Thanks again. Got the ARF a few days ago and I've been putting off getting this assembly started because I've been unsure about the hinges. It's a really good quality plane for a trainer otherwise, so nice to know that I'll be able to make sure the surfaces move really smoothly and easily (while still being good and strong).

I would add, I remove the pins prior to using the CA because it can puddle around the pin and make a little mound of CA when removed later. I don't like these when I seal the gap with covering. No real need for the pin after the hinge is in place on the center line, and everything is ready to glue.

A couple more suggestions. Take a new (sharp Crayon ) and draw a line on both sides of the hinge in the middle, parallel to the airlon, etc for 2 reasons: the wax keeps the ca from penetrating the hinge somewhat so it stays flexable at the joint, and it gives you a visual to make sure you have the hinge deep enough ( basically doing the same thing as the t pins). Number 2 suggestion, and most important ( Don't ask me how I know) before you use the CA glue ...turn the wing, etc. over and make SURE all the hinges are in their respective slots, specially on multi hinge surfaces. Those buggers have a way of slipping past /under the slot when you're trying to get 4 or 5 in at the same time, and its virtually IMPOSSIBLE to work one in after the fact. ( line it up , drop the drops, flip it on its back to wick from the other side, and THERE IT IS, 4 like they're supposed to be and 1 sticking out!!!!I hate cutting off a rudder, etc and reslotting because I didn't check BOTH SIDES!!
Mike

Thanks for all responses. I read through them all a second time to make sure I'm not missing anything.

A few people mentioned sealing the hinge line with covering. The Alpha40 instructions don't say to do this, but I understand that it is good for airflow (and maybe also for avoiding flutter). I don't have any extra covering of the right color. I suppose I could do this later (even after having done some flying)?

Also relating to the hinge sealing/gaps, the Alpha40 instructions does say to push the control surface all the way against the trailing edge after removing the pins and before adding CA (the control surface edges are slightly beveled of course). Does generously flexing the surface down (to drop in the CA) not ensure that there will be enough flexing in the hinge line (without deliberately leaving a larger gap)?

As for the hole in the centers of the hinge slots. I was thinking I'd make sure not to drill them any deeper than half of the length of the rectangular hole in the CA hinges. I figure that would be good since the hinges already have slightly less surface area because of the rectangular hole.

One last thing about this process that makes me a little curious is the time that elapses between doing the drops on one side and then the other. By the time you get to dropping CA into the other side, is the CA not already fully hardened making the hinges non-absorbing? I'm just seeking a better understanding of the physics of this.

Thanks for all the input

Sealing isn't automatically required. If a hinge gap is slight, you really won't see much benefit. If the hinge gap is sloppy, you really need to seal. Experience will teach you what's tight enough and what's too wide. The gap basically reduces the effectiveness of the surface. Some gaps influence flutter. The ideal is to hinge the surface to almost touch and no extra work would be needed. As you do more hinging you work out the techniques to do that. BTW, there are a number of ways to seal the gap, with covering and with tapes etc. Search on "hinge gap". We got lots of information already posted and hashed out completely.

Removing the pins just before adding the CA is a good technique. Sometimes the pins cause a gap. Sometimes pressing the surface to close the hinge gap causes the pins to dent the balsa. They've served their purpose once the surfaces are pushed together, so they're not doing anything for you. As for ".. generously flexing the surface down (to drop in the CA)", don't get too generous. All you want to do is make it easy to get the CA in there. "Generous" may lever the hinge line into gapping. You're developing techniques here. Take a dry run or two to see how much flexing works so the CA applicator can reach.

The holes in the hinge slots is a debatable technique. The idea is to provide a sinkhole for the CA to use to get everywhere it needs to go. The slots themselves overlap the sides of the hinges don't they? CA is going to suck right down the sides with it's amazing penetration capability. I haven't drilled those holes after doing it the first time. And you especially don't need them when the hinge flats themselves have a slot that does exactly the same function. Save yourself some unnecessary work. Forget about those holes. But if you're going to do it, then drill them deeper than the slots in the hinge, because the slots are already providing a sinkhole twice as deep as your plan, but not all the way down.

Already hardened? Depends on the brand you use, it's age, the wood's absorption, atmospheric pressure temperature and how we hold our mouths. And whether or not somebody's talking to us while we're trying to get this simple task accomplished.

CA kicks off when the anti-catalyst in it gets separated enough from the two active components and those to have a clear shot at each other. We mix two part epoxy, and as soon as the two parts touch they start linking up. With CA, the two parts are mixed with a third. They're all together in the bottle and in the drops. When the CA starts thinning out, the two parts that lock on to each other have lots better opportunity to get together. So if the CA is still wet enough from the application on one side, that damp stuff hasn't kicked yet. And if it had kicked really quick, then good chance it didn't get completely around the other side. PH also deals with the anti-catalyst, but bottom line is, if the CA is still damp from adequate application, it's not kicked yet.

You may find that 3 drops on one side work great but that the other only needs 1. Sometimes you can tell by watching the absorption. The 2nd side really shouldn't need as much as the 1st.

BTW, you really don't need a lot of drops, honest. Some of those slots go completely through wing or stab or fin trailing edges. A couple of years ago, I autopsied a newbie's plane to show him how to look for why it crashed, and to teach him why it's a good idea to check ARF glue joints when you're assembling the suckers. I pulled the covering off the TE of the wing and it looked like a couple of bottles of CA in there. He'd wanted the hinges to not come out and had dropped 5-6 drops on each side. And he said a couple took of hinges "a lot of CA". He wasn't kidding.

The good ones learn from their experiences.

I hadn't thought of that I guess that's why they put the rectangular hole there in the first place.

Thanks da Rock. I think I feel comfortable about doing this now.

Hi again,
I noticed that I've got one less CA hinge than required (maybe I misplaced it, dunno). So I've ordered a pack of Great Planes brand CA hinges. They should arrive in a couple of days.

The new ones are the exact same size/shape, but they do NOT have the rectangular hole in them.

I've started prepping, but I have not yet CA'd any hinges in place, so I wanted to ask, given a choice, would you rather use CA hinges with or without the rectangular hole?

As da Rock said, the rectangular hole does serve a purpose, but of course you do then have less hinge holding the surface attached. I suppose too that there would be a difference in freedom of flexing?? There are subtle pros and cons I guess.

I've re-attached the pic of the CA hinges that I have currently for reference...

Thanks for any thoughts on this

As you have mentioned, the slot has a purpose. How important that is would be open to debate.

After you've accumulated some experience it will be clearer to you how minor most of the details are that have to do with gluing. I've found that as long as I get at least 2 drops of CA on one side and one on the other, every style of CA hinge I've used becomes one with the wood. What I've found depends on my judgement of "2 drops" etc, and won't work for everyone. And it might depend on which brands of CA I've used in the past. But bottom line, is that most techniques match up to the user/developer, but can work for others. And I've found that every quality CA hinge has worked excellently well. Those with the slot and those without.

About the only detail I've found to matter with CA hinges is that the ones that look like slick plastic are to be avoided. Every other type I've seen has a textured look on both sides and has glued perfectly and has lasted as long as I've had the model without failing.

Here's a picture of a model of mine that probably stesses the hinges the most of any I fly often. It was built in the fall of 2005. No hint of failures. But you can bet, it and when there is the opportunity to autopsy it, I'll check how the hinges held. It's the best way to build that experience that helps making these decisions down the road.

The rectangular hole does two things...

- It aids in wicking in the CA
- It lets the control surface move more easily

It does the latter, because there will be slightly less material full of CA to "bend" when the hinge moves.

The drawback to this is that the hinge is slightly weaker, but that difference may not be very important given the overal strength of the material used.... it is far more likely that you'll rip the wing out before you put enough force on the CA hinge to break it.

I've always left the pins in too, but never thought to run the CA down the pins. Great tip. That's if I can get the damn bottle turned upside down and the tip on the pin before it runs out on the wing somewhere [:@]!

Thanks for the input. So I'll decide on which one I'd rather use... sounds like both would be great and I guess the Alpha40 has light wing loading anyway.

I received the new hinges today. They are not the same shape as I had thought... they do not taper in on the ends nearly as much, which means they will have even more surface area to bond with the wood.

Here's a pic of them side by side. The new Great Planes hinge is on the right...