Hi all yet again with another question. This has NOT been a first time for me, but I am finally wanting to find out why my dope feels like it has to 'lift' at most joints on my models. I will best describe my problem, as I have kept forgetting to take pictures. My models that I have used dope on, both Sig Supercoat and Randolph Non-Tautening Butyrate, have had tendencies to pull up/lift from my joints. These are the wing to fuselage as well as the horizontal stabilizer, and only slightly once on the vertical stabilizer/rudder. Also this has occurred on both the top and bottom of the aforementioned surfaces. When drying or dry, it creates a 'hollow spot' in the corners of the surfaces. Up till now, I have been trimming this excess waste/material away and reapplying dope again and sometimes it happens again very little or not at all. I was wondering if it has something to do with a chemical reaction of the glue I am using. I have been up until now using yellow carpenters glue and as of late, Gorilla white wood glue for my builds. Or could this be possibly from having excess dope sitting in the 'corners', drying or gassing off. I would like to have this figured out for my next build, which will be quite a way from now as I will be starting to build next week. If you may have any suggestions, tips, or whatever, I am open to anything. If you would like more info, please ask and I will gladly try to supply the required information. Thank you.

No fillets. I have not gone there yet. But, the first plane I had noticed this on, after the build and before doping, I had run a nice clean line of the yellow carpenters glue in the corners as a 'fillet'. I had not done this on the past 2 aircraft I built and still had the problem.

The dope has been appled usually 2 - 3 days after the last of the gluing is done. I will be trying fillets this time by way of Bob Smith Industries 15 minute epoxy. I also have a supply of the 5 minute stuff from the dollar store, but think that the 15 minute stuff would work better as I have read. Thank you for the help and input.

I have found that dope does not adhere to yellow or white glue well. Putting the 15 minute epoxy should help, most will recommended mixing it with micro-balloons. Don't try for an elaborate filet though, Super-Fil works much better. After it dries rough it up a bit with 320 or so sandpaper and use brushed on nitrate for the first few coats.  

Yes. Since my first bout with the 'carpenters glue' fillets, I had not ever done that again. As soon as I put my wings or horizontal stabilizer in I have used a damp cloth with water to remove any excess glue from the area. I have not since used any fillets, just square 90 degree corners, which is apparently another no-no. So, without any of the mentioned products on hand or locally, would just a epoxy fillet work, or do I NEED to add another material? I will get this and figure it out one day.

    Do a search for threads with my name and fillets and see how I do it with finish cure epoxy and micro balloons. I use Bob Smith Industries 20  minute finish cure epoxy Great Planes micro balloon. You don't need to mix much. I think for a typical .35 size model I mix 1/4ounce of each component in one of those graduated mixing cups, and then add micro balloons a little at a time until it gets to a cake icing consistency. it will probably fill up the mixing cup by this time. Then apply the mixture with your favorite tool to make the fillet as big or as small as you want. If I am covering the wings with iron on  material, I cover the wings first and take the covering up to about 1/8" to 3/16" from the fuselage side, and overlap the edge of the covering with the mixture. Adding the micro balloons really slows down the curing time so take your time. When you have them looking like you want, stop there and wait until the mixture starts to kick off and get thick. Then you can dip your finger in alcohol and drag out the edges until they disappear into the two surfaces. I have never had to sand these type of fillets and have never had any kind of paint  lift or blister off of them. The epoxy mixture also has the advantage of filling small gaps and voids and adds strength to the wing/fuse or stab/fuse joint. Also great for filling and fairing in canopies, cowlings, what ever. Very light, and if you need to sand anything it sands well also.
   Good lick and have fun,
   Dan McEntee

Prep the corner so there is no contamination. If you are spraying the dope, do not spray directly into the corners, spray one surface, then spray the other and the overspray will cover the joint OK. If brushing, do the wing surface up to the joint, then they fuselage down to the joint. Allow a little time for the first surface to set up before going to the next. A bit of practice and you should have no problem.

For some reason some of the pictures do not appear. I'll add them below in another post

I like fillets made from micro-balloons mixed with 30-minute epoxy. They've held up well without any dope lifting from them or any crash damage in multiple earthly encounters. I've posted some of my techniques before, but here's the current project, showing most steps.

1) This is the amount I mixed for one 11”+ wing fillet. There was too much left over this time. I used a piece of wood or a tongue depressor to mix this thoroughly. I spread it out on foil to slow the set-up time. When I use a cup, I have to use the graduation marks and when the epoxy is mixed, I pour it onto a foil-lined paper plate anyway.

2) After mixing the epoxy, I pour on a large amount of micro-balloons and mix in. I do this repeatedly, until no more will mix in. It absorbs an unexpected amount of these to get that cake-frosting consistency mentioned above.

3) This is one of the roots to be filletted. If there is more gap, the slurry will help fill it at some weight gain.

4) Here I tape off a root area before applying the epoxy/micro-balloon mix. Space depends on your choice of fillet radius.

5) This is the mix, and these are applicators. I either use the radius given or sand the tip to a different radius.

6) Here is the fillet material just after application (I didn’t take a picture during application, because I was , uh, busy). While it’s still wet, I pull the tape off and scrape off any splatter with the edge of a #11 exacto blade.

7) This is the initial result.

8 ) After removing the tape, I fine-tune the shape, not expecting it to fully retain this curve. However, I want the width and radius to remain as constant as possible. This is also the chance to feather the edges, where the thickness of the masking tape raised the edge thickness of the fillet. I have to be careful here not to do this too soon, but not too late either, since the stick can lift or rough up the material. Some use water, fingers, or acetone to help shape later. Wet fingers for me have not given the uniform thickness I want.

9) When one fillet is pre-contoured as shown, I brace the plane in this position, with the new fillet at the lowest point, facing downward. That way the fillet material does not puccle in the middle and loose its width.

10) After a few hours the fillet may be sanded. This is the initial sanding (using appropriate size dowel wrapped in, say, #320 wet emery paper and with Dupont PrepSol. Dry Garnet paper of higher roughness may also be used, as I did on this particular one. I took this picture to show that my fillet lost some of its uniformity while setting.  I sand the fillet until it is this light color and uniformly smooth, being careful to protect the doped adjacent surfaces. I often re-apply masking tape along the edges and sand into it when finishing, to feather the edges. I’m often less successful than I’d like and have to, if it’s worth it, fill the edge areas with white primer (Brodak) or some other sanding sealer. My skills have apparently diminished. Anyway, the surface is then free of the waxiness and rough enough to help dope to adhere.

11) Here’s a photo of initial sanding, with the low spots showing dark.

12) Here’s another way to help ensure that dope doesn’t lift. This picture shows my first clear dope application to the fillet. I use clear first, because it has no pigments to get in the way of adhesion. I only dope up to and including a part not exceeding ¼ the width of the fillet on each side. That way these areas can dry and shrink for a while, before any more dope is applied.. After this a steady-handed modeler can run a narrow, non-overlapping bit down the center. If not, then just apply to one edge, with minimum overlap and let dry for an hour, before doing the same to the other edge. This way the dope shrinks in small areas of minimum curvature. After this, I put still highly thinned (50/50+) dope down the center with overlap. I repeat this procedure, until I have a sheen and then wet sand with , say, #380-400 just to roughen the surface for pigmented dope or...whatever.

13) Here’s another initial application.

14 –16) Last three. show fillets after a brushed and sprayed coat of gold underlay. I agree about spraying, ESPECIALLY since I use the PreVol spray cannisters, which spray a narrow band, not too consistently; don’t spray directly at the fillet, unless you have a deft touch or a very fine spray. I brushed mine on first in places, using the partial coverage technique mentioned above. Then I sprayed, letting the edge of the spray area overlap the fillet. I also sprayed from one side of the fillet and went on to other fillets or parts of the plane, before returning to spray from the other side. After a day or so, I sprayed clear over the entire plane so that the next coat would have the best possible adhesion.

I PRESUME that this application will be as successful as the others.

SK

Two quick points:

First, I'm currently using epoxy mixed with microballoons.  I do what's been mentioned already, except that I squeeze out equal amounts of epoxy into separate containers, mix microballoons into each, and then mix the two.  I do this to give myself the most working time.

Second, Serge is showing phenolic microballoons.  They're a red-brown color.  Glass microballoons are white.  As far as I know there's no structural difference, but if you have some of each, a pinch or two of phenolic microballoons in a mix that's otherwise all glass microballons gets you something that looks kinda-sorta balsa-like.  Plus, if you put all the phenolic microballoons into just one part of your mix (see my first comment) then you can tell when you've got both parts well mixed (it can take longer than you think).

http://www.aircraftspruce.com/
order the small packages since this stuff is pretty lightweight.  You can add a small quantity of cotton flocking with the microballoons to make it thicken up much more readily...although there is a small weight penalty for this.

Phil

  A lot of guys use Super-Fil, I think it is, with good results. I think Sparky uses it and you know how much he builds! But some of us don't get to build like that, and purchasing a separate product that may go bad sitting on the shelf before you use it all isn't too appealing. We all use 30 minute epoxy, and the 20 minute finish cure epoxy has many uses also, among them the fillet method. It just gives another option, and the materials can be had locally in many cases. It's easy to learn and easy to use. this is one of the threads/subject that needs to be pinned at the top of the section so it is easy to find. I've lost count on the number of times the question has been asked about using spackling compound for fillets. Worst possible material to use!
   Good luck and have fun,
   Dan McEntee
 

See the thread on leather fillets for the solution I think best. Accurate radius, lightweight, easy to do, and absolutely absorbant of dope or whatever finish you choose. Buy the radius you want and you get consistent fillets.