Here are some pictures of the areas where I'm getting some failures. I have the Precision Cut Kits laser cut B-24 Don Smith. The failures are where the 1/8 inch laser cut fuse formers (plywood) are attached to the 1/4 inch balsa keel. The clean joints are with Elmer's and the dark residue is from Titebond. Frankly at this point I'm not against even taking a lot of time and using epoxy or am I adding too much weight? Most blogs say that they use epoxy only where there are areas of high stress or fuel in the area. And since this isn't in areas where you would see it anyway, I don't mind going back to Titebond.

Thanks

Tally Ho<br type="_moz" />

I also forgot to tell you that during construction I would place the former onto the keel, weight it down, clamp it straight and then dab some glue at the 90 degree intersection. I wouldn't put any glue down first then put the former on the glue, just dry, make sure everything was straight then add glue.

Tally Ho<br type="_moz" />

I'm sorry to hear about that David,

First, those places the parts came loose need to be cleaned so the new glue will stick to the wood and not to the old glue residue, pliers or hobby knife are very useful, not to over do it just reveal some wood.

Now trying to think why its happening, maybe its that you put it first in that cup and then apply it with the pencil this is something I never did, for me it was a little drop from the bottle nozzle and spread it with a Q-tip, thats why I started that thread how to apply aliphatics, I couldnt get the bottle in every corner.
once the glue is out of the bottle its starting to cure and kick in at the first place its in contact with.
anyway its good to run a dry practice run with closed bottle and a Q-tip over the place first.
I also did those tests like seamus did earlier on scrap wood to find the right method of work with the aliphatics.

Alex

Thanks for the input Alex. I personally think that the Elmer's maybe good in areas of no stress. You can see by the pictures that the 1/4 inch stringers are of hardwood and when you try to bend them to the contours of the fuse that must surely put some stress on the former joint at the keel. It's not a major problem just a nagging one. I clean off the broken joint and dab some epoxy there and this seems to work just fine. I've only had about 10 or 12 separated joints and this isn't much when you see the amount of joints the complete fuse takes with stringers and such. I'm even contemplating making my own hardwood stringers. The ones in the kit are not long enough so you have to use 2 in some places. I can go to Lowe's and get some poplar wood in 8 foot lengths and use my table saw and planer or router table to make some 8 foot 1/4 inch stringers or what ever I need. Then I might soak the stringers in water and try to bend them to the contour of whatever I'm doing and hope that when they dry they will be in the contour I want. I've seen that Norm Abrams on The New Yankee Workshop use steam to bend wood to some pretty drastic contours.

Tally Ho



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Personally I'm kind of scared putting wood into water as it should be trail and error process but if you do this tell how to.
edit: deleted the story about quarry.

Alex

Sorry for taking it out of subject, I'll be glad to learn how you will resolve that at the end, i never thought you could drill those square holes with the simple tools you can have at home.
Lets get back to the B-24.

Alex

I'm thinking that is has something to do with the gluing technique.

Current state: If I understand your technique (and I may not - so correct me if I'm working on the wrong assumption), you first dry-fit the pieces. Once all of the pieces are positioned as you want them (square &amp; true) them you apply glue to the intersections of the wood, effectively creating a fillet out of glue. A fillet's primary function is to create a mechanical restriction limiting lateral movement of the pieces of wood. Same as applying a hot glue to a joint. Very little or no absorption of glue into either piece of wood. Depending on the tightness of the fit some or very little glue will flow into the joint. IMHO there is no bond between the fibers of the two pieces of wood.

Others have shown that the strength of a glued joint is based on the amount of adhesive that is absorb into the two wood component's fibers. The two pieces of wood that your working with are lite ply of the former which has a fairly hard surface and a porous end. The keel is of balsa that should readily absorb glue through its sides as well as its end (but not an issue here).

AR glues aren't readily absorbed into the sides of ply but they do absorb into the sides of balsa. Maybe Titebond wicks into the lite ply (and its end) more readily than Elmer's glue. That may be why it held better.

If this were problem I would dip a cotton swab into the AR and cover the end grain of the notches in the formers with AR. Before it dried too long I would clean the notches with a wet paper towel or swab. This would allow the AR to absorb into the end grain of the lite ply leaving exposed dried glue. Others modelers have shown that surfacing wood end grain with AR provides an excellent glue anchor when the piece is finally glued with additional wet glue. I would mark the locations of the notches on the keel with a pencil. I'd pull or slide the keel away from the former and add wet AR inside the pencil marks, reposition the keel, and reclamp the keel &amp; former at this joint. I would NOT try to do all of the joints at one time.

For a completely different approach that does not require repositioning after getting the former and keel aligned - how about using thin or maybe medium CA? CA wicks very quickly into the joint, up into end fibers as well as into the surface of the balsa keel.

pic 1 - glue as fillet only
pic 2 - glue absorbed into end as well as fillet

Yes,
Maybe on the places got separated to work with med CA.
I think the ungluing have something to do with the parts edges are burned from the laser cutter, i used to sand it to get to the unburned wood.

Alex

I've sanded the laser cut edges too - just have to be so careful to not take anything but the ash. Kinda smells too. I bought a handful of emory boards from my local grocery store (finger nail files) for this. The ones I got are like Popsicle sticks with 2 different grits of paper.

Cheers,

Great input. I will put this knowledge to work on my project. Thanks.

Tally Ho<br type="_moz" />

Looking good David and it will all come together. I don't know if someone has already mentioned this and maybe I over looked it. I believe all the Don Smith large bomber fuse are built in halves like yours. At least the B-29 I was building many years ago was done this way. I had the same problem and joined the bulhead halves with a small balsa strip to keep the glue joint from separating off the balsa spare. This will a least give it some additional ridgidity when you apply the fuse sheeting. It's gonna be a sweet model when you get it done.

Now I will need some input as to the strength of the servos that I'll need for this kind of build. How many oz/in should I be using for the Fowler Flaps, ailerons, rudders, elevators and steering?

Tally Ho<br type="_moz" />

David,

Personally I would put in 100in/oz metal gear servos for all the control surfaces. Your not going to be doing any knife edge or torque rolls so these should provide plenty of holding power. I would do a little investigating and see what others have done with similar size/weight models before you make your choices.

(2) Elevator for a total of 200in/oz
(2) For rudders
(2) for ailerons
(4) For the large fowler flaps (2) each flap
(4) standard throttle
(1) 70-80in/oz on the nose gear (metal gear)
(1) standard on the gear and sequencing door valves (if your using them)


You may be able to get away with less, but why take the chance with an investment like this.

Something came up in my weird mind. I don't see a lot of inspection covers or bays over the servo areas. Are servos so iron clad these days that you can install them and forget them? Or are they mounted is such a way that if there is a problem, in an emergency, you can get to them?

Tally Ho<br type="_moz" />

IMHO servo screw inspection needs to be part of every pre-flight check list. There's gotta be a hatch or cover of some kind that provides you with access to the servo.

I couldn't agree more.

What's the difference between metal gears and karbonite gears in a servo?

Tally Ho<br type="_moz" />

To quote ServoCity's website:

<span style="font-size: small;"><span style="font-family: Arial;">"<span>There are two things that you need to know about metal gears in servos.First, they offer much greater strength than their nylon or karbonite counter parts.If your application experiences many jolts and heavy vibration, metal gears are usually the way to go. Second, metal gears wear much faster than their nylon or karbonite counter parts.Although stronger, metal gears will develop a certain amount of play in the gears over time.How much depends on how much load is placed on the servo and the cycle time.If your application needs precision over a period of time we highly recommend using nylon or even better, karbonite gears."

</span><span>"Karbonite" gears are four times stronger than our standard nylon gears and offer virtually ZERO wear; even after 250,000 cycles when tested! The result, you get better control with KARBONITE gear technology.

HTH</span></span></span>

Well it's been a while since I've been here. The fuse carcass is pretty much finished. The blocks of balsa are going to be next to be attached. I've been working on the stab and rudders for now. And it's true. Nothing is hard when you have the tools to do it. I've been very lucky to have some machine tools to work with. I've noticed that some builders will add a 1/16 inch sheet of balsa on the movable part of the rudder. I mounted the leading edge of the movable rudder in my Bridgeport mill and milled a 1/16 inch trough (0.075 in. deep) down the middle so instead of a butt fitting, I had kind of mortise and tennon fit. Really strong. On the other side of the movable rudder leading edge, I mounted it also in the mill and used my raised panel bit from my woodworking stuff and rounded over the front edge. And you have to do it only half way on one side then round over the opposite side only half way. Then when I was done I discovered a major faux pas. I made the edges mirror images of each other. NOT. When you look on a full size 24, they are duplicates. Most likely so a damaged right rudder can be replaced with a good left rudder if needed, And you don't have to modify anything. Well I hope the judges don't notice. It should fly just fine. The delay has been my Mom. At 92 she's been getting a little dementia but still fairly healthy body wise. Well she was forgetting to eat and last Monday almost passed out on me. So my sisters and me have been attending to her and making sure she eats. And sometimes she can irritate me when she says, "David, God willing if you live this long, you'll look and remember just like me!!!" RATS.

Tally Ho<br type="_moz" />