Butt-Joint Bolstering

[sequoiaranger]

For those of you who cut-and-paste in 3D styrene, the weakest joint is the "butt-joint", where the two interfaces have no interlocking sections, no pin-and-sockets, etc. This is the easiest bond to break, too. So if this joint is going to be strong, it is best to bolster the joint.

"Hollow" joints, like wing section to wing section, where only the thin, outside layer of the wing is being joined, is most easily done with "tabs", like with vac-forms. A small section of sheet plastic is glued half-in, half sticking out to one face of the joint, and then the other face is slipped on over it (glue being applied, of course)

"Solid" butt joints have a bit more inherent strength, having more gripping surface for the glue, but it can "sheer" or part if bending forces are applied. I have had most success with small lengths of steel tubing (being inherently strong and virtually impossible to bend), but even "safety pins" sections will help. Here is a setup for my latest Me-2262:



There are small, matching holes in the joint area where the wing will attach. Notice you don't have to have much depth, but you do have to be accurate with the placement so that there is no offset to the surface of the joint.



First, you should align the parts you want fused up EXACTLY, then mark a line (pen, pencil) across the fusion line.



Next, carefully gouge a small indentation in the plastic to be drilled with the end of an Exacto knife or something to "start" the hole. Then drill in a short ways, making sure the hole diameter fits the supporrting rod you will use. Of course, do the same to both sides, making sure the distance from the top is the same on both sides. Insert the small bit of rod in one side (with some sticking out, of course), and then glue the two faces together. You will hopefully end up with something that looks like the second picture! And...it will be strong!

[PR19_Kit]

I know JUSTwhat you mean!

I'm in the middle of building my PR19b, like the one already featured here but with even LONGER wings (there's a surprise....  ) and humunguous engines.

It uses a vacform wing from a Rareplanes TR-1 attached to a semi-standard Matchbox Meteor NF14 fuselage. Of course the bits touch where they will and need lots of trimming and filing to match but that still doesn't give the joint any strength so I added a semi-spar made from three layers of 30 thou styrene which passes through holes in the wing root that are sized to ensure it's a tight and accurate fit. The top surfaces of the spar are filed to give the correct anhedral angle and the notch in the underside of each end of the spar butts up against the Meteor landing gear bays that are recessed into the underside of the vacfiorm wings to locate the wings fore and aft. Then I used slow drying super-glue all over the spar and the root of the wings and clamped it all together, using lengths of tape tightened to top and bottom of the fuselage to get the anhedral correct.

It's like concrete now and after the inevitable PSR work around the roots it all came out pretty well.

You can also see the flat spars that pass through the fin that support the joint for the TR-1 tailplanes, not quite as critical as they only have to support their own weight in this case, not that of the whole model.

[Gondor]

I must admit that when I saw the topic I thought for a moment I was on the wrong forum..... 

I used spars for my Meteor F2 as I cut out the engines and later fitted them under the wing so the outer wing surfaces were even less connected than a butt joint.





Gondor

[Weaver]

I agree with everything Craig's posted about pinned joints. Some extra points to consider:

1. Another way of getting the holes to line up perfectly is to fit the pins to one half of the joint, then put blobs of paint on the ends of the pins and offer them up to the other half. That way they mark exactly where their corresponding holes should go.

2. Use a slightly smaller drill bit than the one you think you need, looking at the pins. Drill bits, particularly tiny, bendy modelling drill bits, tend to flex and wobble and unless you've got a very elaborate set up, you'll be doing the drilling free-hand, not with a drill stand and jig. This means that you've a fair chance of ending up with conical holes that are wider and looser than is ideal if you use the same size drill as the pins, whereas if you use a smaller one, the holes are a tight fit. Of course if you don't conicalise the holes, you can always take them out a size.

3. When drilling the holes, remember to think about their direction as well as their position: if you drill them in the right place but at an angle, then you'll end up giving, for instance, a wing or tailplane the wrong dihedral. The upside is that if you're using fairly fine rod/wire for the pins, you can often recover this mistake by simply bending it at the joint line.

[sequoiaranger]

>Another way of getting the holes to line up perfectly is to fit the pins to one half of the joint, then put blobs of paint on the ends of the pins and offer them up to the other half. That way they mark exactly where their corresponding holes should go.<

I have done that, both successfully and UN-successfully. There is a danger in that where the paint hits MAY not be where they need to be to line up the joint properly when the gap is closed. You may be holding the other part just far enough away to be offset and not know it---I speak from bitter experience here!

>Use a slightly smaller drill bit than the one you think you need, looking at the pins.<

Good idea, generally. Luckily styrene and (especially liquid) glue is our friend here. If the hole is a scosh too small for the pin, some liquid glue will likely soften the hole so that the pin will fit in anyway--be careful of a slight "bulge" (in this particular case) where the pin goes in the hole, in order to limit any gap caused by the bulge.

>When drilling the holes, remember to think about their direction as well as their position: if you drill them in the right place but at an angle, then you'll end up giving, for instance, a wing or tailplane the wrong dihedral.<

Yes--that is also the possible "drawback" of the "paint the rod ends" paradigm. You may START the rod in the right place, but a slightly-slanted rod could cause a slight offset by the time the two parts are joined.

>The upside is that if you're using fairly fine rod/wire for the pins, you can often recover this mistake by simply bending it at the joint line.<

Be careful, here! The whole point of the "bolstering" is to PREVENT bending. If you can bend it INTO place, then you might be able to inadvertently bend it OUT. Ideally, a bolstered wing joint, for instance, should be strong enough to grasp at the wing tip and still hold the model up without bending or breaking anything, despite the leverage of the weight of the rest of the plane.

Actual wing spars, like Gondor so aptly demonstrated, are VERY STRONG (why they use them on real aircraft!) but often require a bit more "engineering" to make sure the dihedral is a proper angle and symmetrical on both sides.

[Mossie]

One problem I have with butt joins is very thin parts like vertical tails.  When these are very thin they often have a tiny locating pin that is prone to snapping & once you bust the tail off, it comes off again & again.

I've tried drilling these to accept a metal or plastic pin, but the thin material makes it very difficult to firstly to drill the part & secondly it's difficult to find a pin that's thin and strong enough to do the job.  Any tips?

[rickshaw]

On my long-wing Canberra PR.9 prototype I used a length of brass strip about 1mm thick and about 10mm wide.  It was IIRC about 12 inches long.  I had hoped, as it was in front of the wheels to have helped to add to the nose weight but even so, along with a fair bit of lead weight in the nose, the model still ended up a tail sitter.    The wing joint though is rock-solid with a spar like that and quite a bit of superglue to hold it position. 

[PR19_Kit]

I've tried drilling these to accept a metal or plastic pin, but the thin material makes it very difficult to firstly to drill the part & secondly it's difficult to find a pin that's thin and strong enough to do the job.  Any tips?

This is a constant problem with airliner wheelsets. At 1/144 they end up stupidly thin if moulded in the proper scale, and Revell are only to prone to doing that, plus they have a designer who's never built a model in his life and insists on you fitting the nose leg BEFORE you do anything else! This means you have to build the whole model with the nose leg sticking out and it never lasts. I've lost count of the various 767s I've built that have had to have the nose legs repaired before the model's even finished.

I found that a 0.5 mm drill and 10 amp fuse wire do the job OK when the whole lot is superglued into place. It's filddly to centre the drill and you must be very careful keeping it alignment but the same method should work with thin tail surfaces, plus you only have to be hyper-accurate in one plane.

[Mossie]

Thanks Kit, I'll get hold of some 10amp fuse wire, I've got the drill bits.  It's the alignment I find the biggest problem with, even in just the one plane!  Despite starting with tiny drill bits to get centre on, I still often end up with an off centre hole & the pin often breaks the surface and I end up with slight bulge.  I think I'll have to invest in a small vice, doing things single handed doesn't help.

[Weaver]

>Another way of getting the holes to line up perfectly is to fit the pins to one half of the joint, then put blobs of paint on the ends of the pins and offer them up to the other half. That way they mark exactly where their corresponding holes should go.<

I have done that, both successfully and UN-succesfully. There is a danger in that where the paint hits MAY not be where they need to be to line up the joint properly when the gap is closed. You may be holding the other part just far enough away to be offset and not know it---I speak from bitter experience here!

Fair comment. One way around that is to fit short "marking pins" to one side that only just protrude enough make a mark, but which let the plastic parts get as close as possible, thus making it easier to line up. Then once you've got your holes, you replace them with the proper long pins. Of course, you have to damn sure you can get the short pins out again, both tightness and grip-wise (i.e. having enough protruding to get hold of).

>The upside is that if you're using fairly fine rod/wire for the pins, you can often recover this mistake by simply bending it at the joint line.<

Be careful, here! The whole point of the "bolstering" is to PREVENT bending. If you can bend it INTO place, then you might be able to inadvertently bend it OUT. Ideally, a bolstered wing joint, for instance, should be strong enough to grasp at the wing tip and still hold the model up without bending or breaking anything, despite the leverage of the weight of the rest of the plane.

What I meant was to bend it BEFORE you glue it, i.e. you fit the pins, fit the tailplane (or whatever), check it's angle, bend the pins to suite, then dismantle it again and glue it. If there's a danger of the pins moving after bending, i.e the bent pin might "spin around", then glue the pins into one side first before bending.

[mkhulu]

Gents , thanks so much for these valuable tips    

[NARSES2]

One way around that is to fit short "marking pins" to one side that only just protrude enough make a mark, but which let the plastic parts get as close as possible, thus making it easier to line up. Then once you've got your holes, you replace them with the proper long pins. Of course, you have to damn sure you can get the short pins out again, both tightness and grip-wise (i.e. having enough protruding to get hold of).

Done that a few times myself and it worked for me. I have real problems measuring and lining things up accurately. A large part of it is my eyesight even with lenses as thick as mine, but part of it is, if I'm honest, inherent sloppiness 

[sequoiaranger]

>I've tried drilling these to accept a metal or plastic pin, but the thin material makes it very difficult to firstly to drill the part & secondly it's difficult to find a pin that's thin and strong enough to do the job.  Any tips?<

Guitar string is both thin and strong, and comes in many sizes (Cello string, anybody??). Yes it flexes in very long segments, but in short segments is does not. Also, for, say hollow tailplanes, you can put a protuding locating/strengthening "pin" in both ends of the hollow that will line up with its counterparts.

If you can find a source for "surgical stainless steel tubing", there are the tiniest diameters available that are also EXCELLENT for gun barrels--the tubes are PERFECTLY round and straight, there is no "ridge" of two-half moldings, and interior wall thickness is consistent. I got my "stash" forty years ago from a friend, so I cannot give you a source for these, but they are precious and VERY useful---you have to have a rotary corundum "cutter" (like a Moto-tool) to cut it, however. Luckily, I do.

You might also consider plastic "tabs". I have a Moto-tool (ABSOLUTELY INVALUABLE!) with tiny little burrs that can gouge out tiny "slots" in solid surfaces to put in tabs.

[Joe C-P]

This technique is also an excellent idea for helicopter rotors. I built a resin 1/48 H03S, and there was no way the blades would have stayed glued with just flat-joined glue surfaces. I marked centers, drilled holes and used thick brass wire to support the blades.