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Help with repairing PML QT

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lalligood

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This past weekend I flew my PML Phobos on a G35-4W. I'd be surprised though if the delay made it to 3 seconds. It was *short* :( And the Phobos suffered as a result.

I am guessing that the quicklink that attaches to the payload section is what caused the damage to the main airframe, which is made of PML's Quantum tubing. The dent is serious enough that I can no longer insert the payload coupler into the tube. Anyone have any ideas on what would be the best way to repair this?

I've included a picture of the dent.

Thanks.
 

rstaff3

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You mean that small little ding? I've never fixed QT but off the cuff, I think I''d carefully grind the inside so the coupler fits. It appears to me that it would be flyable at that point. I might then try to fill the gap with bondo putty (the spot filler, I'm sure someone else can provide the exact name).

I need to look back at my library of HPR mags. There was an series of articles by Ed mIller. I'll check to see what he said.
 

rstaff3

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I checked and the article I remembered showed how to fix phenolic. I have used a similar technique on paper and phenolic, but never QT. I used an epoxy filler called SuperFil, but am not sure that it would be the best for QT.
 
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Austin

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I have worked with and used Quantum tube for many years...great stuff. Your problem can only be solved by cutting off that 1/8-1/4" of damaged tube. The shortening will not effect model performance and it is the only way to repair it. Trying to add epoxy, glass or cutting it flush will leave the area weak. This can and has caused cracks, which in turn caused seperation in mid launch...a bad thing! Cutting as instructed below, your paint job should maintain it's finish without needing touched up.

Take a piece of paper and cut it about 2-3" wide, then wrap it around the tube and tape it together. slide this "tube" of paper toward the bad spot, stopping just short of the damaged area. Tape the opposite end to the tube so the paper sleeve won't slide down on you, then use a Zona/Razor saw and cut evenly around the tube using the edge of the paper as a guide and just barely scoring it all the way around. Go around again, cutting a bit deeper. Continue until it cuts through, then remove the damaged end piece. Follow up by lightly sanding the edge, still leaving the paper on so you can keep the edge even all the way around.

Hope this helps...I have had a to fix a few Quantum tubes in my time and it is not that bad. Show us an "after" pic! :)

Carl
 

rstaff3

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OOH hadn't thought about the possibility of a crack spreading. Of course, that's why TRF pay's you that exorbitant consulting fee :D
 
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Austin

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Dick, yea, that tip comes from experience... haven't seen my fee yet though! ;)

The paper trick works really well. I use more of a thicker card stock than sheet paper as the blade can "side rest" against it easier without going over the top of the paper guide. It also prevents you from slipping and screwing up your paint job underneath since it is coated by paper.

Carl
 

havoc821

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Can't you have a couple of wraps of paper towels around the rocket (to protect paint) and cut that portion off with a table saw, or whatever that thing is that has a big saw blade on the handle and you pull down and it cuts right through? I used that saw to cut QT and it cut it very easily. I don't know if this will work. Just a thoght.
 

Frodo2801

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I use dry wall tape for this purpose it is pretty stiff and straight. Its cheep too.
 
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Austin

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Havoc...you sure could, pretty much wrapping it with anything be it paper towels, cloth, paper, card stock, wallboard tape or what ever else you can think of to protect the finish. The paper or plaster tape gives you a straight line in case you don't have the band saw you mentioned.

Carl
 

lalligood

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Update:

As much as I was hoping to find someone with a compound mitre saw, it just didn't pan out & attempted an alternate solution...

I carefully put several wraps of masking tape around the tube about 1/2" down from the dent gave me a great line to follow. However to make sure that I wasn't going to have any issues cutting, I made a starter cut with a standard hacksaw & a 22 tooth blade. Frankly, it cut like a warm knife through softened butter :) I went for it at my taped mark & it made a beautiful cut! To clean up the burred edges, a sanding block with 150 grit paper confirmed my straight cut & left a smooth edge. For what few burred edges that were left, I massaged them with 220 grit paper. You'd never know if I didn't tell you :D

Twas all really much ado 'bout nothing, you see... Thanks for everyone's input!
 
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Austin

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Excellent job lalligood...glad it worked out for ya!!!

I also noticed you did a light sand on the edges...that's something I always do automatically and take for granted. Ever so lightly rounding all your edges "breaks" the cut mark and relieves stress, thus preventing cracks. A sharp edge is more prone to cracking then one that has been "rounded/edged". You probably knew this, but it's a good tip for the others.

Have a great one and pics...we want to see pics!!! :)

Carl
 
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