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Three inch CTI M2245 minimum diameter build
#11
Fillets ... figured I try something new.   I decided to use Aeropoxy  6209 for the fillets.  I was thinking of using JB Weld hi-temp epoxy for its 500deg F capability, but in all the post flight pictures of mach 2.5+ flights I've seen, fin fillets seem to be pretty much unscathed.  The top of the fillet at the tip of the fin root usually gets blasted though, so I plan to go back and fill in the 0.5 inch or so at the top of the fin root with JB weld.  The Aeropoxy tensile strength is about twice that of JB Weld. 

I used a 38 mm G339 warp nine grain to mark the tube for taping, and to pull the fillets. Now I've got an inert Warp 9 grain, but a good 38mm fillet tool.  If I hadn't launched it in seven years I probably wasn't going to burn this load anytime soon.

couple more pics.  (5 pic limit per post)


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#12
Not the easiest epoxy to work with for fillets, and I will probably never try this again, but they are good enough.  I've definitely made prettier fillets.  The only redeeming quality to JB Weld for fillets is that it sands easily.  I still need to fill in some low spots here and there, but they are nearly done.


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#13
Try Proline 4500 for your fillets. It has adequate heat resistance as well, although not as high as JB Weld.
Greg Young - L3
TRA 00234
NAR 42065
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#14
Wow Mark, 6209 for fillets, I did that once, and I feel your pain. On the up-side it is a strong epoxy. On my 54mm MD I followed your "Plan A" and used 6209 on the root to bond it to the airframe, then switched to ProLine 4500 for the fillets. 4500 in contrast to 6209 for fillets has to be the easiest epoxy work with.

Looks great so far. What are you doing for a retainer?
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#15
Greg, I ran out of Proline 4500, and have probably used it on my last 5 rockets or so. It does make great looking fillets and is easy to use, but I don't think I'll be buying it again, because there are no published specs. on Proline 4500 that I've seen. I'm sure it has a higher TG than Aeropoxy ES 6209, but for all I know it is no better than Rocketpoxy in terms of TG.



Pitter, retention will be by eyebolt to motor forward closure through a forward bulkhead.

... I used Aeropoxy to lay down the initial fillets, which was pretty easy, and then covered them with JB Weld. Next is a laminating the fins with some uni directional carbon fiber.
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#16
Cut out 4 layers of 4 oz uni carbon x 4.

Covered 2 sides and put it in the bag.



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#17
8 hours later.  It doesn't look too bad.  I put a 2 oz layer of satin fiberglass on top.  Will sand off the FG layer  later to smoothe out the ridges from the backing lines on the carbon fiber.  Still need to cover the other 2 sides.   The Cotronics epoxy I'm using has a 30 minute pot life, and it took me 2 hours from mixing the first batch tilll I had it in the bag, mixing a separate batch of epoxy for each of the 2 sides.  The epoxy is still relatively thin even after 2 hours


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#18
Great work so far.  I am unclear as to what caused the ridges in the fiber glass, did you use peel-ply?  Also I see you are using a refrigeration pump to pull your vacuum, how are you regulating the vacuum and do you have an accumulator in-line?  I ended up building a vacuum press as per the following link, looking forward to seeing more as it progresses.  I really like the look of a 4 fin rocket!

Joe woodworker project EVS
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#19
(07-13-2015, 10:22 PM)Pitter Wrote: Great work so far.  I am unclear as to what caused the ridges in the fiber glass, did you use peel-ply?  Also I see you are using a refrigeration pump to pull your vacuum, how are you regulating the vacuum and do you have an accumulator in-line?  I ended up building a vacuum press as per the following link, looking forward to seeing more as it progresses.  I really like the look of a 4 fin rocket!

Joe woodworker project EVS

The lines are from the glue on the back of  the uni-directional carbon fiber.  The carbon fiber is not woven so there are glue lines that run perpendicular to the fibers to keep it together. You can see these white lines in the picture of the cut out carbon fiber pieces.  The surface of the finished layup is actually a lot smoother than it looks in the photos. 

The vacuum pump runs continuously so there is no need to regulate vacuum.  It pulls nearly a full vacuum, 29 to 30 inches Hg,  as long as there are no noticeable leaks.  I let it run for about 4 - 5 hours until the epoxy I had left in the mixing cup started to get hard.

The peel ply is the beige material in the last picture above, after I removed the fin can from the bag.
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#20
Not much progress but here is round two of the fin can reinforcement with a little more detail.


...Hose runs straight from air valve on bag to the pump with quick disconnects on both ends. Bag material is Home Depot lawn and leaf bag, shown in post 16.

The pump vents off a small amount of oil so I run the hose outside with the door cracked. The pump gets a little hot running for a several hours straight, so the fan blowing on pump adds a little more cooling.


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