After the hinge locations are marked and the aileron it drilled and cut for the torque rods it's time to dig out/cut the slots for the CA hinges. A little background for anyone who doesn't know what “CA hinges” are. They are basically a piece of plastic sandwiched between two sheets that can be bonded with CA adhesive. The installation of CA hinges requires a slot cut in both sides of the material to be hinged. The hinge is inserted in both side and then CA adhesive it wicked into the hinge. The CA will use capillary action to be pulled all the way down the hinge and it will bond with the wood it is inserted in to. After the CA sets the hinge material can still be flexed, this hinging the surface. A couple of quick notes about CA hinges. First, CA hinges are a “one time only” material. Meaning that you can't put CA adhesive on just part of the hinge, you much do the entire hinge at one time. This means that you must have the hinge inserted properly in both sides of the hinge before you apply the CA. I won't go into what happens if it's not, but trust me that's not fun. Second, when you cut your slot for the hinge to be inserted into you also need to drill a hole in the center of the hinge. This allows the CA it pull all the way to the end of the hinge by way of capillary action.
Ok, now for cutting the hinge slots. One of the best tools that you can own is the [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXK263&P=ML]Great Planes Slot Machine[/link] . What's sad about this tool is that you only use it for about 5 minutes on a plane you are working on. That's about how long it will take you to cut all the hinge slots on a plane with this tool. If you are going to use CA hinges in your builds this is probably one of the best $20 you can ever spend. For the sake of this build, and for those who haven't purchased a Slot Machine, I'll describe how to cut hinge slots without the Slot Machine as well as how to do it with one.
First, the hard way. Manually cutting the slot. This isn't hard to do, it just takes some time to get them all cut. When we cut the slots we want to cut the slot just “thick” enough for the hinge to slip into, but there needs to be resistance when you insert the hinge. The reason is that you want the hinge to be in contact with the wood on all sides so that it is bonded to the wood. If it's not the hinge will pull out in flight, and it doesn't take too much to imagine what the results will be if that happens. It's really hard to describe how to cut this slot using a hobby knife. You really “just do it”. Take a look at pictures #1- #5 and you should get an idea on how to do it. I'll try to describe it if I can. I start by first using the tip of the knife to score the line where I will cut. I will do this several times going a little deeper each time. I will then start at one side of the marked area and push the knife in all the way to the hilt, then pull it out and move over and push it in again. Keep doing this until you are at the opposite end of the marked area. Picture #4 shows something that I like to do that helps clear the slot and make it just about the right width for the hinges. I will insert the knife on one end of the area and then I will work it back up the slot with the “dull” side of the blade, meaning the backside of the knife. This will clean the slot out and get it ready for the hinge. After you have the slot cleaned out and the hinge will snugly fit into it we need to drill a hole in the center of the hinge line (picture #6). I use a 1/16” drill bit and drill all the way thorough the trailing edge. Although it doesn't seem like it would be, this hole is very important. I ensures that the CA adhesive will wick all the to the back of the hinge. Without the hole it becomes an “iffy” guess if the CA will work all the way back. Once again, it's better safe than sorry. So take the extra minute it takes to drill the hole. After the hole is drilled stick the hinge in the slot, we're done with this slot. Wasn't that easy? Sure it was, and you only have 15 more to go!
I do want to point out one very important safely note. Never ever pull the knife towards you or your hand. Remember that balsa is a very soft wood and won't always stop a knife blade that has slipped. I know that saying this seem like I'm saying the obvious, but sometimes it's really easy to concentrate on your work and not pay attention to where the knife it going. I learned when I was 13 years old building a plastic model. I had a knife slip while I was pulling to towards me and it went into my left hand. It made a 4” long 1/2” deep cut that took 25 stitches to close. Since then I have always made sure that I know where the blade is going to go if it slips, or more importantly I know where it WILL NOT go! Please take the time to think about it while you are working.
Ok, now we did it the hard way, so let's do it the easy way. I can't say this enough, get a [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXK263&P=ML]Great Planes Slot Machine[/link] . Before you ask, no I'm not getting kickbacks (I wish I was
) from Great Planes for advertising. This is one of the best tools that I've seen in awhile. If you are going to do much building it really is worth the $20 if you plan on using CA hinges. Ok, so how do we use it? As with anything else that we do when building, you need to practice on scrap wood first. Trust me on this one. If you grab the Slot Machine for the first time and try to start cutting slots in the trailing edge you WILL be building new wing because the trailing edge is screwed up. It can chew through a lot of soft balsa wood in a heartbeat. So get some scrap balsa (hey, another good reason to save all that scrap wood from the kit!) and practice. Keep practicing until you can accurately put the blade on a marked line and cut the slot without cutting anything outside of the line. It's well worth the practice, because once you get the hang of it you can cut all 16 slots in the wing in the same time it takes you to cut one slot using a hobby knife. Pictures #8, #9, and #10 to show cutting the slot. The only real advice I do give is don't force the tool, just a little pressure and feed it as it cuts. If you force the too, especially in harder wood, you'll wind up bending or breaking the blades. When you order the tool you may want to pick up a couple sets of replacement blades. Murphy's law will kick in. If you buy the blades you'll probably never need them, but if you don't buy them then you will break a blade for sure because you don't have a replacement.
After you have the slot cut, just like cutting them manually, you'll need to drill a hole in the center of the slot (picture #11). After you finished stick the hinge in and move on to the rest of the wing (picture #12)
Cutting the hinge slots on the trailing edge of the wing you'll need to cut the slots in the ailerons themselves. There's nothing too much different in cutting these than there was cutting them on the trailing edges. The only thing I would point out is that you'll want to take a little bit of extra care with the slot machine so that it doesn't “jump” or “wander” off of the tip of the bevel. Other than that it's pretty much the same as doing the trailing edge. If you feel a bit edgy or nervous about cutting them you should take a few minutes and practice first. Get some scrap balsa and sand a bevel onto it so you can practice on. Once you feel comfortable after practicing go ahead and cut the slots.
Next we'll be putting the ailerons on the wing and trimming the tips off.
Pictures
1. Cutting the hinge slot with a hobby knife.
2. Cutting the hinge slot with a hobby knife.
3. Cutting the hinge slot with a hobby knife.
4. Cutting the hinge slot with a hobby knife.
5. Cutting the hinge slot with a hobby knife.
6. Using a 1/16” drill bit to drill a hole in the middle of the hinge line.
7. Completed cutting the hinge slot and ready for the next one.
8. Cutting the hinge slot with the Great Planes Slot Machine.
9. Cutting the hinge slot with the Great Planes Slot Machine.
10.Cutting the hinge slot with the Great Planes Slot Machine.
11. Using a 1/16” drill bit to drill a hole in the middle of the hinge line.
12. Completed cutting the hinge slot. Only 15 more to go!!!
Until next time
Ken