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Old Dec 29, 2012, 11:06 PM
Entropy is happening!
Jim.Thompson's Avatar
Australia, NSW, Bellingen
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Quote:
Originally Posted by wyowindworks View Post
Oh, sorry, Jim. I see that you are parting the fuse the other way....which is just fine. You would just layup the mold halves around the drill guides.
That is all clear now Adam. Very nice.

It brings up an option that I had not thought of. At least for a mid wing plane. I just had another look at my plug and it would not work for a low wing model like my Wompoo. Pity.
That would avoid all the anxiety about the wing fillet draft angle.

However, I'm fairly confident the fuse plug will pull ok out of the mould. I'll be using wax and PVA on top of 2 pack finish on the plug.

Comments?

Jim.
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Last edited by Jim.Thompson; Dec 30, 2012 at 04:45 AM.
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Old Dec 31, 2012, 03:49 PM
Entropy is happening!
Jim.Thompson's Avatar
Australia, NSW, Bellingen
Joined Aug 2008
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Air assisted plug and part release.

I'm toying with the idea of incorporating a vent in the mould to provide compressed air entry port. The air can be then used to assist the pulling of the mould off the plug.
It's easy enough to later drill a hole in the mould to allow compressed air to assist pulling parts from the mould I know. In my case with this fuselage, I will do it and place the port on the wing root. This is, I am guessing, the most likely part of the fuse to be resistive to pulling without assistance, due to the small draft angle above and below the wing roots.

However, it is the first step, making a vent in the mould to assist removing the plug, that is the challenge. I'm thinking that I could start with a small diameter brass tube and first of all, flare one end. Then place a small ball of plasticene in the flared end. This end could be sat vertically on the wing root of the release system prepared plug, then carefully retained in place with some gel coat around the tube flared end. When tacked off, the remaining gel coat could be applied and the usual procedure followed taking care not to disturb the brass tube.

The theory is (maybe obvious), that when it comes time to split the mould off the plug, compressed air at 5 - 10 psi or so, is applied to the ports on each side.
Then the usual methods to split the mould can be used.

Brain wave!
As I was writing this I had the following epiphany!
I could use the drill guide method of locating the joiner holes as desribed by Adam above. Thes could then be used (I think) for air entry ports. I just have to work out the details a bit more......
Maybe one could be blocked and the other fitted with an inner tube valve stem. I just need to sort out some sort of insurance that the air will find it's way to between the plug and mould.

Jim.
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Old Dec 31, 2012, 07:46 PM
Life begins at transition
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This guy uses millions of them...
http://www.rcgroups.com/forums/showp...&postcount=233
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Old Dec 31, 2012, 09:05 PM
Entropy is happening!
Jim.Thompson's Avatar
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Thanks Odysis.

I just need to study the detail in the thread to work out how he makes sure the air will find a passage between the mould faces.
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Old Dec 31, 2012, 09:41 PM
Life begins at transition
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Most don't, they're for seperating mould halves.
There are a few in the wing saddle area where he puts one between the mould and part, but only in areas where it won't be seen on the final model.
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Old Dec 31, 2012, 10:16 PM
Entropy is happening!
Jim.Thompson's Avatar
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Quote:
Originally Posted by Odysis View Post
Most don't, they're for seperating mould halves.
..........................
That's what I meant in the post above. In my case, I want the air to go between the plug and mould actually.
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Old Jan 01, 2013, 01:22 AM
Life begins at transition
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I guess the issue then is avoiding 'print-through' of the air hole... Hence Slow & Low has only done a few part/plug and mould vents.
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Old Jan 01, 2013, 01:38 AM
Entropy is happening!
Jim.Thompson's Avatar
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I'm planning on doing only one on each wing root. The mark can be later leveled with splooge or just plasticene.
The idea going through my mind is to use the drilling guides (which I will machine up) to serve as both guides for drilling the joiner holes in the part and air injection ports.
I"m planning to slide the joiner mandrel (bright mild steel rod) into the plug and slide the drill guide over it and sit it on the wing root. Then simply rely on wax/PVA to make a sufficient seal to prevent the epoxy seeping into the joiner mandrel.

I just realised this will not work as the hole has to be drilled into the part for the joiner before any attempts at pulling it happen! After that, air injected here will only inflate the part!

Ssooo, it looks like I make a separate air injection port between the wing joiner position and the rear incidence pin.

No problem really. I just have to choose the right fittings which I probably already have in the shed.

edit: I found some off the shelf brass fittings that will serve the function well! Pics later.
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Old Jan 01, 2013, 05:54 PM
Arrarrar!
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Australia, NSW, Wagga Wagga
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Hey Jim I was just gonna say that! I like your plan of one fitting for a drill guide and then another for a pressure valve. You can still drill out the joiner hole while in the mould and then the other hole will still aid release. Are you going to put in smaller drill guides for the incidence pins?
Cheers mate
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Old Jan 01, 2013, 11:40 PM
Entropy is happening!
Jim.Thompson's Avatar
Australia, NSW, Bellingen
Joined Aug 2008
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Quote:
Originally Posted by josh18 View Post
Hey Jim I was just gonna say that! I like your plan of one fitting for a drill guide and then another for a pressure valve. You can still drill out the joiner hole while in the mould and then the other hole will still aid release. Are you going to put in smaller drill guides for the incidence pins?
Cheers mate
Josh,

Yes to all the above. I'm feeling pretty confident about it now I have this sorted out. Thanks to Adam, you and others!
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Old Jan 02, 2013, 04:41 PM
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Hi Jim & Josh,
The Graphite Turned up today and so I shall mix up a little tooling coat tommorow and let you know how it fairs.
Chris
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Old Jan 02, 2013, 05:46 PM
Entropy is happening!
Jim.Thompson's Avatar
Australia, NSW, Bellingen
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Quote:
Originally Posted by Fubar 123 View Post
Hi Jim & Josh,
The Graphite Turned up today and so I shall mix up a little tooling coat tommorow and let you know how it fairs.
Chris
Chris,
I should have mentioned before this that Graphite can be bought at engineering supplies stores. It is used as a general purpose dry lubricant.
Anyway, you have some now, all's well.
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Old Jan 02, 2013, 05:50 PM
Entropy is happening!
Jim.Thompson's Avatar
Australia, NSW, Bellingen
Joined Aug 2008
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Parting board preparation.

I've been finishing the parting board preparation. I've sealed the routed alignment trenches with thinned epoxy and sanded. Just about ready for primer.

I just remembered, I have forgotten to rout out the tail parting boards with alignment trenches!
I'll have to do them now.
In the meantime, I'm getting ready to build another moulded plank or two.

Jim.

who is a bit forgetfull at times...........
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Old Jan 02, 2013, 06:48 PM
Arrarrar!
josh18's Avatar
Australia, NSW, Wagga Wagga
Joined Jan 2010
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Good to hear about the moulded plank Jim!
Hey, about the epoxy/ graphite tooling coat, I know Adam recomends it but I though I'd heard him say in the past that he doesn't like epoxy based tooling coats because they are hard to polish. Does the graphite make it polishable? also, does the graphite make for a more durable/ harder/ more scratch proof surface or is it just a colouring agent? (I did read it adds to surface lubricity). Ive also read about people adding aluminium oxide but never really knew what it was for. Confusinger and confusinger!!
Cheers mate
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Old Jan 02, 2013, 07:10 PM
Just fly it!
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Cody, WY
Joined Nov 2007
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I prefer epoxy surface coats. I never polish my molds though. Perfect plug = perfect mold.....at least with Frekote.
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