SAvannah kit 2 comming home tomorrow :)

[Marty_d]

You'd think with a critical piece like that where you're bolting / riveting through at least 3 layers, they wouldn't try to hole match but instead just have the holes on the steel piece and leave it up to the builder to align that and drill through.

[IBob]

It is an absolutely critical piece, both in terms of location and structural strength.

The holes line up accurately and without difficulty. 

Check the pics I posted.

[rmorton]

23 hours ago, IBob said:

If a door won't shut, you can try slamming it progressively harder. Or you can look to see why.

 

I think the welds and some deformation from the welding certainly produce difficulties in the fit. With mine it is only the four holes, almost as it it slipped in the jib when drilling

[rmorton]

13 hours ago, IBob said:

It is an absolutely critical piece, both in terms of location and structural strength.

The holes line up accurately and without difficulty. 

Check the pics I posted.

So I sent the pictures to the agent and his rather brief reply was there is no choice but to redial the holes. I will confirm this with him tomorrow and then ask a welder at work to close up the badly aligned holes before drilling the new. Is this a stainless steel piece do you know? 

 

I agree with Marty on the critical areas it might be better if they drilled undersize pilot holes that we can then drill out to suit. Generally the fit and finish is remarkably good when you consider all the bending and stretching some of the parts have to go through. Mind you this is the only kit I have built so can't compare. 

[IBob]

Rmorton, I have a suggestion for you before you start moving holes at such a critical location:

 

Take an accurate pattern of the holes from the steel part: to do this you will need stiff paper/thin card, cut into a 'C' to fit round the part. Then see how the holes of this pattern line up with the holes in the fuse side.

 

I suggest this because my own initial difficulty with these parts had nothing to do with the position of the bolt and rivet holes (which, like yours, would not line up). The reason was that the steel part was fouling the sides of the rectangular hole in the fuse side. Once I remedied that (as per the pics) the parts fitted quite easily.

Edited January 11, 2021 by IBob

[IBob]

And PS to the above. Why it is a really bad idea to be moving holes, effectively moving the steel part at this location:

1. It houses and mounts the undercarriage, and so defines the angle of the undercarriage sits at.

2. It is the attachment point for the wing struts, so any small movement will affect wing dihedral.

[rmorton]

1 hour ago, IBob said:

And PS to the above. Why it is a really bad idea to be moving holes, effectively moving the steel part at this location:

1. It houses and mounts the undercarriage, and so defines the angle of the undercarriage sits at.

2. It is the attachment point for the wing struts, so any small movement will affect wing dihedral.

Thanks Bob, I will give that a try, particularly the interference between the welds and the outer skin. I will also try to discuss this with the agentry phone as emails are all too easy to miss understand. The oddity is overmuch that the four front holes and t

two of the three rivet holes align reasonably well (they are podgerable) It would be useful to know some check dimensions between holes. I tried to compare the position of my holes relative to the bolt tube with some photos on here and there does seem to be a difference. Ill let you know what I find

 

[rmorton]

Finally after a week back at work, much reflection on the wise words and pictures from Ibob and others on FB, I took a cardboard template and proved the holes weren't a million miles apart. I started by using the awl to align the different layers then cleaned the holes out with a slow drill of the right diameter. Then with reference to Ibob's photo I started to identify where the welds caught on the U channel. First I filed back the welds where this was safe to do so and then trimmed the end of the U channel and outer fuselage skin to allow space for the bracket welds. I think there is still a small bit to come off the end of the U channel and then the rest should align. One remaining problem is the two shims that go between the bracket and the sides of the U channel. The front one will go in and there is space to spare, but the back one wont fit. Is it ok to put this on the inside of the fuselage or even use it only on the front face of the bracket ie have two at the front and non at the back. If they are only shims then the second option seems to be ok ?

[IBob]

Rmorton, my experience of the Savannah build was that 99.99% of it went together as per the manual and diagrams, and for the other 0.01% I never reached for the drill: when you open holes with a drill, you risk shifting the alignment of the parts and also weakening the join.

 

As suggested earlier, you do however need properly fitted, polished, tapered podgers, and where a part needs working into place, you usually need at least 2 of them (so that you can walk them along or round a series of holes). They need to fit properly to align the holes without damaging them, and they need to be polished so that they do not bind in the hole. They are easily bought as awls, or made from cheap pin punches, sanded to a taper then polished with fine emery.

 

There is also an order of podgering/clekoing for some parts: try to attach them in one order, they will not go, try them from the opposite side or end and they come together. So where something will not come together, it is worth trying different orders of podgering/clekoing.

 

Where I trimmed metal (and there was almost none of this) it was only where it could be done without weakening the part or the join. So, for instance, any internal corners were made with a drill to reduce the possibility of cracking.

 

..................................................................................................

 

My main suggestion to you is to resist the urge to change the design when faced with a problem:

 

So, don't move the holes mounting the steel undercarriage and strut brackets; instead, find out why they won't fit and how that can be remedied.

 

And now, don't move the two shims between the brackets and the channel (which are also riveted into the channel, and so are more than shims): keep working at it to get them where the design calls for them to be.

[rmorton]

The awls work well and as you say there is usually a cause for the misfit. On one side this was one of the legs in the channel was warped and blocked the correct positioning of the bracket, plus the welds binding on the skin and end of the U channel. The other side took more time to figure out. Similar issues with the bracket as well as the top plate of the bracket welds were too high. 

 

I have been very wary of edge distances with rivets and notice there are a few places where the holes are very close to the edge, I assume thatches locations are non critical. Another annoyance is the black stuff will often prevent a rivet going in even when the holes align first time. 

[IBob]

I didn't use the black stuff, I sprayed a primer.

However, for another build I would definitely reconsider the black stuff.

The Australians apply it with a small self-wetting roller (can't remember the name, but there will be references to it here somewhere, the black stuff goes in the handle) which gives an even application and perhaps also limits buildup in the rivet holes.

 

[IBob]

Roller for the black stuff: Paint Buddy Roller

[Marty_d]

That looks like the goods. I needed one of those for primer on rivet lines  - too late now! 

Edited January 18, 2021 by Marty_d

[IBob]

Yep, Marty. I tried a brush, then a little speed brush, and of course they push the black stuff through the rivet holes. Then I switched to a sprayed primer, but if I was building again, I would definitely reconsider the black stuff (that comes with the Sav kit) and one of those rollers.
I don't think they're available at this end of the globe now, but they still seem to be available in the UK, and would definitely be worth getting.

 

Having said that, the black stuff is a water based primer, and so not fast drying on brushes or rollers. It seems to me a roller setup would probably go hard pretty quick with spirit based primers...

[rmorton]

Bit late for me too but a very good idea. I did some parts with primer sprayed on but I am dependant on the temperature in the garage for that so this lot will be black stuff and paintbrush on the kitchen table. The black isn't very resilient so sliding surfaces with a close fit aren't the best. 

 

[eightyknots]

I am using Cortec VpCI-373, a corrosion inhibitor that is recommended by Zenith.  VpCI-373 is frequently used by North American aluminium aircraft builders. So far, I have found it easy to apply with a brush.

 

This Cortec product is supposed to prevent any vapour (and airborne corrosive salts) entering into the small gaps between the riveted parts which may eventually cause corrosion.