Skinning General

How to deal with the ally skinning

Skinning General

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Skinning General

Postby MBN Downunder » Tue Jan 08, 2013 12:16 am

Hello all,
Just a couple of comments on the skinning of the Lanc model. I'm no means an expert, but have though a lot about how the skin panels have been designed to fit.
I am up to about issue 103, where a whole bunch of A4 sheets of aluminium and templates are provided for wings and fuselage. My skills are improving as I go along, which doesn't make for a consistent standard of finish, but you need to look closely to pick faults.
The ply frame is very well cut and generally fits together very well. When it comes to the skin however, particularly where curves need to be made, panels are fixed by hand in slightly variable positions. This results in the need to adjust the skin panel shape/size to fit against panels that have already been fitted. I ended up having to shave about 2.5mm off the side of one piece to fit the edge of the wing frame after accumulating minor errors fitting earlier panels. The end result is fine though, as I now carefully match rivet lines to the frames and stringers before applying the rivets.
I am hopeful that, when I get to the starboard rear fuselage skin, I will be able to cut the skin panel to suit my door position. I moved my door one frame forward from where the standard instructions say it goes, after research and advice convinced me that Hachette had put the door in the wrong place.
Just at the moment, my model components and unstarted issues are all packed carefully in a large suitcase, so I can't get any photos or look up details. Here in NSW, Australia, we are facing a very high bushfire danger today and I live in the countryside. We have all our important belongings (including the Lanc) packed up ready for a rapid evacuation in case this becomes necessary. Hopefully in a few days the danger will have passed and I can unpack everything and start building again.
No signature yet - can't think of anything suitably witty. Will work on it!!!
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Re: Skinning General

Postby Mark » Sat Jan 12, 2013 9:28 pm

I hope the fire risk passes uneventfully. I have to admit, I'm still in two minds about whether to skin or not. However, my Lanc has stalled, so I'm in no rush to decide. I'll look forward to seeing how yours turns out.
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Mark

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Re: Skinning General

Postby baby_astons » Sat Jan 12, 2013 9:39 pm

you'll need to rebuild the engines then mark if it's all stalled??
building:DB5~E-Type~Testarossa~Aston Vantage V12~Millennium Falcon

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Re: Skinning General

Postby Mark » Sat Jan 12, 2013 9:54 pm

Groan.........
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Re: Skinning General

Postby MBN Downunder » Mon Jan 14, 2013 9:22 am

We escaped the NSW fires, thankfully, but suffered a few very hot, windy, scary days. The hot weather has moved to the north of NSW and today, several homes were lost to fires near a town called Coonabarabran (now that's a mouthful).
I have unpacked enough of the Lanc to keep building - a good activity when too hot to go outdoors.
I am continuing with the skinning and discovering more as I go. I think it vital to get the skin right, as this is what is most obvious in the final model. I will be skinning most of the Lanc, but might leave some sections off so you can peer inside.
I have discovered very small variations/irregularities in the frame build - either the dimension of the ply cuts or my assembly. The result is that the skin sections won't fit perfectly if cut exactly as per the templates. They are very close, but I found that small adjustments (generally less than 1mm) before cutting the aluminium give me a perfect fit.
I work progressively, following the sequence recommended, measuring each new piece carefully against the section/s just attached. The old adage "measure twice, cut once" certainly applies, although I find I am measuring 3 times at least!
After trying different methods, I find the recommended technique works best. Using a sharp hobby knife/scalpel with a metal ruler provides perfectly straight lines. I mark up the template with a very sharp pencil for any adjustments to the basic template pattern before cutting along the lines. It is hard to return the ruler to exactly the same position against a cut already started, so it's best to position the ruler, holding it firmly while running the knife along a number of times. More runs with moderate pressure is better than trying to do it quickly with high pressure. 3 or 4 runs along each straight edge is enough to release the card template piece and place score lines in the metal underneath. The card and metal sheet are held together with a few pieces of sticky tape. I then use the card cutout to do a final check of fit before the final metal cut. Another 4 or so runs along each line directly on the metal (having removed the card) are enough to score the metal enough to break out the piece. You just need to flex the metal sheet back and forth along each scored line until the metal gives way (a classic fatigue failure!). This gives a lovely straight edge that just needs a little smoothing with wet and dry or a file.
I sand and clean the underside before rivet marking, as per instructions. I expect this helps the paint adhere better. I am now much more careful about placement of rivet lines than when I started. I try to make sure that the rivet lines continue across adjoining skin sections (following the frames and stringers underneath). I find I need to measure carefully and mark with my sharp pencil each rivet line, using the frame and previous rivet lines as guides. Then the rivets go on quickly and accurately. You quickly get your eye in as to how far to place the metal straight edge from the pencil line to get the rivets exactly along the line.
I am using contact cement - applied thinly to both surfaces then allowed to dry. Despite what it says somewhere in the instructions, once the skin is brought into contact with the frame, it is stuck fast and can't be moved to adjust position. Hence it is important to get it accurately positioned first. I do a couple of dry practices before applying the glue, and I work the skin by hand so that its profile matches the frame as closely as I can manage.
This all makes for very slow progress, but I think this will pay dividends in the end. I have almost finished the underside of the starboard wing (issue 104) and am much happier with the end result compared with the port wing done some time ago.
I was a bit disappointed to find the instructions in issue 104 (steps 5 and 14) show the skin protruding 1mm past the ply frame along the aileron gap. I don't recall this instruction when applying the corresponding panels to the port wing (issue 103) and I decided to make the skin flush with the frame. Means I will probably end up with a different gap (port and starboard) at the leading edge of the aileron when finally assembled. If you haven't done issue 103 yet, take note!
I also found it much easier to cut the notches for the aileron hinges and drill the holes (look in issue 111, step 15) before gluing the skin panels onto the wing. I would also recommend fixing on the flap (2 tiny nuts/bolts) before attaching the adjacent skins - makes the job a bit less impossible!
I will have to figure out how to upload photos to demonstrate what I mean!
No signature yet - can't think of anything suitably witty. Will work on it!!!
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Re: Skinning General

Postby Mark » Tue Jan 15, 2013 5:19 pm

Lots of sound advice there. Thanks for making such an informative post. K on the way :D
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Mark

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Re: Skinning General

Postby MBN Downunder » Wed Apr 10, 2013 1:50 am

A few more "discoveries" on skinning, which might be helpful to those who have yet to get to this point.

I found the templates supplied were pretty accurate, but I always double checked them by careful measurement on the model. Cutting a fraction large then filing back carefully is better than ending up with a piece that is too small.

I had earlier moved the door one frame forward to its correct location. Cutting the hole for the crew access door in the rear starboard fuselage skin was easy enough. You need to measure up carefully (recommend at least three times) and draw the new position accurately on the template. Note that the template supplied is reversed (ie the outside surface is on the back!). So you need to swap your measurements left/right when marking up.

I used a sharp hard pencil to draw the rivet lines on the inside, matching the position of frames and stringers. Then easy to run the rivet wheel down the line.

The real Lanc rivets seem mostly flush to the outside surface, while the wheel produces "round head" rivets. I found that use of the back of a spoon carefully on the rivets, using a rolling movement with light to moderate pressure, flattened them out enough to look more realistic while still being visible. You don't want them completely flat or they will disappear under the paint coats. Practice first on a piece of scrap.

I spent a lot of time shaping each piece by hand to fit as close as I could make it before attempting the gluing. This reduces the risk of sections of skin popping off the frame later.

The instructions recommend contact glue. This is applied to both surfaces, left to dry, then joined together. It produces a very strong bond, but has the disadvantage of not being adjustable once brought together. The adhesive grads instantly! I have been using a new glue, sold in Australia as Tarzans Grip Mega Bond. This requires clamping (rubber bands are ok), but gives a few minutes for precise adjustment of skin position.
No signature yet - can't think of anything suitably witty. Will work on it!!!
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