Author Topic: Spin 1:48 Ansaldo SVA 5  (Read 4911 times)

Offline smperry

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Re: Spin 1:48 Ansaldo SVA 5
« Reply #45 on: April 02, 2020, 06:05:41 AM »
I could do with a bit of resin advice here.
I managed to get struts glued in place that hold the wings parallel, (if you don't count the lower wing dihedral), viewed head on. The problem arises when the model is looked at from above. The top wing is about 10 or 12 deg out of line with the lower wing (comparing straight leading edges)

View head on with added struts


I was able to use magnetic jig fixtures to push and hold the upper wing in place. Then I glued in the inboard pair of struts. I know this isn;t going to counteract the twist of the upper wing when the fixtures are removed.

view of Jig fixtures holding wing in correct orientation to lower wing



Plan view showing how jig holds wing leading edges parallel. Note how twist is countered by one fixture pushing on top wing tip and the other fixture is holding opposite lower wing in place counter to the twist.



Are there any tricks to use with resin so the wings will hold their correct positions. All struts are resin and quite flexible. Would sitting in the jig under warm conditions for a while get the struts to solidify into the new and correct normal? Dunking it in hot water is out, is a hair dryer or Monokote gun too hot? I'm thinking a 40 or 60 watt bulb 8 or 10 inches away might be close. Do the resident resin experts have any thoughts on this?
Thx
sp
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Online RAGIII

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Re: Spin 1:48 Ansaldo SVA 5
« Reply #46 on: April 02, 2020, 06:27:34 AM »
You are making progress in spite of strut issues! I don't have your answer but am sure someone will!
RAGIII
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"Don't slop it on" Lynda Geisler

Offline smperry

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Re: Spin 1:48 Ansaldo SVA 5
« Reply #47 on: April 02, 2020, 08:04:45 AM »
I think this model is getting it's revenge for sitting half done in a box for a decade. I no more than wrote asking for advice on how to get resin to hold a new shape when I figured I could get the rear row of struts attached if I turned the model around, I was hoping that would help make it more rigid. I take the model out of the jig and the twist I was complaining about was just about gone. From over 10 deg off to 1 deg or less.  I wouldn't have believed it if I hadn't seen it. I then reversed the jig pieces and set it all up again facing the other way.

If sitting for a little over an hour nearly cured the problem, I will let it sit another 24 and then glue in the back row of struts. That should fix it. (Oops, maybe I shouldn't have said that :-) I had images of sagging, heat softened resin ricocheting around in my head and was not at all sure that top wing twist could be fixed. It seemingly fixed it self. Here's hoping the resin gods were satisfied with my penance or will they extract more revenge for a decade on the Shelf of Doom?
sp
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Offline Alexis

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Re: Spin 1:48 Ansaldo SVA 5
« Reply #48 on: April 02, 2020, 10:25:25 AM »
Sounds like you work it all out in the end , good for you SP . Resin kits can be tricky . Not all resin is the same , some softer while others are harder . Softer resin struts I will not use . In warm or cold climate will cause warpage over time . So I make new ones either brass tubing with a stell wire core and flatten this in a vice and do any sanding a clean up . One very strong strut . Or I use contrail strut ( plastic  or brass ) which is very hard to find . Went under many many years ago . Wish someone would start this up again .

Looks like you got the many area which aids and that is getting the cab struts and wing center . (A) plus . There really isn't much difference between plastic and resin kits . except for one thing . Plastic is easy to replace from over sanding , resin not so much and can be more challenging . Looking forward on how this turns out , keep up the good work !


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Offline lawqbarr

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Re: Spin 1:48 Ansaldo SVA 5
« Reply #49 on: April 04, 2020, 04:16:51 PM »
Hi Steve
Long time no see (from your WW1 Modelling page days)
Wing alignment and struts

Struts
Try bamboo - might be grass but looks like wood, it is rigid, stays straight, shapes well takes a really convincing wooden colour and look and it's as cheap as chips - Just use tooth picks or decent quality skewers that are straight !

Do you remember Robert Karr and his Gotha ? - Bob used bamboo for the struts with a wire core
Works really well and offers much greater strength than plastic or resin material

Method -
We will worry about getting an aerofoil shape later -
First - Use oversized material - It's much easier to sand down to shape than it is to begin with really small material that is close to the finished dimensions !
Next - Split the bamboo in half (or you can plane or sand down your round material to half way - a cabinet/ card scraper works well too )
You will need to create enough length to do a right and left hand side for each strut,
Using a "V" jig to hold the material ( see below) straight and true, razor saw a slot for the wire core length-ways into each half ( this slot should be placed toward the leading edge ! - A line cut into the material with a razor blade helps start the cut and keeps the saw true ) 
lay in your steel or brass wire and CA/ super glue the two halves back together leaving a bit of wire protruding at both ends to mount into the wings.
 
Now you can shape the strut,
use the protruding wires at each end as a guide . You want to keep the wire in the middle of the material and close to the leading edge. Don't overdo the sanding the back/ trailing edge or you can expose the wire

It's a bit of a fiddle - you need an opti-visor and a simple V jig to hold the strut so you can razor saw the slot, but it works pretty well and the resulting strut is really strong !

Method 2 - still uses bamboo but instead of a full wire core you just drill wire posts into each end of the strut.

Method 3 - Bamboo again but with a hole drilled length-ways through the strut - I have never attempted this one - If you could pull it off it would be the easiest and strongest way to go, but keeping a fine drill bit steady and true over just 1 - 1.2 " is quite an achievement, even if you do drill into the middle of the strut from both ends ... 

The V jig is just a small block of wood around the same size of 12" wooden school kids ruler with a shallow V cut or sanded into it length-ways. This will allow you to hold your material straight and steady while you plane or sand it down and cut the slot.
To cut the V rule a line down the middle of this jig
With a steel ruler and razor blade cut along the centre line at 90 degrees to a depth of around 1 mm
Next move the steel ruler left or right to centre about 1.3 mm and cut again, but this time at 45 degrees back into the centre cut -
do the same on the other side of the centre line cutting back into the centre line
Now remove the waste material you have just freed up to create a very shallow V shaped groove
Use a block of wood with sand paper wrapped around the edge to refine the shape of the groove - Don't over do it  The groove should not need to be deep
Bon chance mon brave !
David

Offline smperry

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Re: Spin 1:48 Ansaldo SVA 5
« Reply #50 on: April 04, 2020, 05:45:03 PM »
Hi Dave
The struts on the SVA 5 have little PE fittings that have a pair of ears folded up for each strut in the Vee. So wire inserts wouldn't do here, but plain bamboo planed thin and cut to shape would be much stronger, OTOH the darn thing is so out of square I'm thinking the flexibility of the resin struts is what pulled my bacon out of the fire on this one :-)
Thanks for the recipe on making wire core struts. I am saving it as I am planning to build a Revell 1:28 Spad and the struts you describe sound like just the ticket for that old hunk of plastic.
sp
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Offline IanB

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Re: Spin 1:48 Ansaldo SVA 5
« Reply #51 on: April 04, 2020, 06:16:07 PM »
Hi Steve,
It may just be the angles of the pics, but it looks as though the right wing (left as we look at it) is mounted slightly further forward than the left wing and then pushed backwards by the jig to line it up. Looks to me as though the problem is the lower wing mounting points!

I hope that helps.

Ian

Offline smperry

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Re: Spin 1:48 Ansaldo SVA 5
« Reply #52 on: April 04, 2020, 06:33:32 PM »
Ian
That is the likely culprit. the resin stubs were equal, but the brass pin in one of them may have slipped out of the fuselage. Past my ability or desire to fix at this point. You have a keen eye sir :-)
sp
There is something fundamentally amiss with a society which forces it's modelers to work for a living.