[Motor Purchased] 5 inch diameter rocket and a CTI O3400.

[Chrisn]

Rather than explaining/describing in my own words check out this site which will end this argument about thread length vs strength

"It has been established that,for carbon steel, there is no increase in thread shear strength by having a thread engagement length in excess of the screw diameter."

https://www.roymech.co.uk/Useful_Tables/Screws/Thread_Calcs.html

That is a pretty common rule in the engineering trade

 

[bobkrech]

That's correct as long as both the male and female threads are made from the same material and have the same heat treatment.

To answer John's earlier, the material heat treatment, cold working or annealing is more important than the actual alloy for determining the yield and tensile strength. https://matweb.com/search/QuickText.aspx?SearchText=316 list these properties for 316 stainless steel.

Bob

 

[Zephhyr]

On topic;

Build looks great!

Off topic;

When it comes to hardware, especially cheap stamped hardware, percentage of thread interface has a greater affect on assembly strength than the ultimate material strength of the nuts and bolts. The thread tolerances on the cheap T-nuts leave MUCH to be desired.

 

[ColumbiaNX01]

I am going to do some self promoting. "Hey my build is going great."

 

[Blastcap Rocketry]

There are 3 mounting holes in the thrust plate. I attched 3 t-nuts and then glued over them. I am using the same technique GaryT used. Once I am ready to attach the retainer I will glue in all 4 center rings and then glue thrust plate on (I have no reason to remove it). With everything glued in place with the t-nuts its not going anywhere.

The 3 holes in the thrust plate are to attach it to the bottom CR, the holes are countersunk so the screws lay flush under the retainer. Once thats attached I used all 12 of the Aeropack retainer screws to attach the retainer to the thrust plate.

 

[ColumbiaNX01]

GaryT said it perfectly to what I am doing!!

 

[Rrwjr]

I am going to do some self promoting. "Hey my build is going great."

I just started following this thread. A 5 inch rocket with a 4 inch motor- there's a bunch of excitement waiting to be unleashed. Your external fillets are beautiful. Mine are getting better but not quite at your level. You mentioned you were going to use 2 part foam in earlier post for fins. How did you decide on what density of foam to use? Is there any prep you did/do to fins for foaming? I ask because I'm looking at an application where I'm thinking of using 2 part foam, however I thought if I drilled holes thru the fins and inserted dowels thru them, then put my internal fillets on with epoxy and chopped carbon and then added the foam it would make the fins hold better to the Motor Mount and make everything more rigid. Does this make any sense or am I adding needless weight to rocket?

 

[ColumbiaNX01]

Yea I see what you are talking about. I did drill holes through the fin tabs every few inches along the tab. When I do the interior fillets the epoxy will spill through the holes onto the other side. It creates a epoxy rivet!!!! Once I am ready to foam I will mix the foam and pour it in and then let the excess escape out the back end of the rocket. I am using the foam from rocketry warehouse. It is the 4lb density stuff.

 

[ColumbiaNX01]

pics coming soon of internal fillets

 

[dixontj93060]

Yea I see what you are talking about. I did drill holes through the fin tabs every few inches along the tab. When I do the interior fillets the epoxy will spill through the holes onto the other side. It creates a epoxy rivet!!!! Once I am ready to foam I will mix the foam and pour it in and then let the excess escape out the back end of the rocket. I am using the foam from rocketry warehouse. It is the 4lb density stuff.

If you seal your fin root right you shouldn't get any "spill through."

 

[ColumbiaNX01]

I have all 12 internal fillets done. Now I have some sanding on the aft end to clean up so epoxy that is in the way for the aft CR. Pics coming soon!!! Once I clean it up and foam the fin can (foam from Rocketry Warehouse) I then will install aft CR's and thrust plate. Anyone use the foam from RW? I plan to coat the entire aft end of the rocket with epoxy before I install CR. Is the foam once cured pretty solid meaning no little holes that epoxy can run into? Should I use Proling 4500 Epoxy to intstall aft CR's or use Aeropoxy structural epoxy? They are both quality epoxies. The only noticable differences are the one is high temp, black, and thick and the other is not. I have both, Just what do you guys think?

 

[CarVac]

I have all 12 internal fillets done. Now I have some sanding on the aft end to clean up so epoxy that is in the way for the aft CR. Pics coming soon!!! Once I clean it up and foam the fin can (foam from Rocketry Warehouse) I then will install aft CR's and thrust plate. Anyone use the foam from RW? I plan to coat the entire aft end of the rocket with epoxy before I install CR. Is the foam once cured pretty solid meaning no little holes that epoxy can run into? Should I use Proling 4500 Epoxy to intstall aft CR's or use Aeropoxy structural epoxy? They are both quality epoxies. The only noticable differences are the one is high temp, black, and thick and the other is not. I have both, Just what do you guys think?

It shouldn't matter in the slightest. Use whichever you feel is easier to use.

 

[CCotner]

I have all 12 internal fillets done. Now I have some sanding on the aft end to clean up so epoxy that is in the way for the aft CR. Pics coming soon!!! Once I clean it up and foam the fin can (foam from Rocketry Warehouse) I then will install aft CR's and thrust plate. Anyone use the foam from RW? I plan to coat the entire aft end of the rocket with epoxy before I install CR. Is the foam once cured pretty solid meaning no little holes that epoxy can run into? Should I use Proling 4500 Epoxy to intstall aft CR's or use Aeropoxy structural epoxy? They are both quality epoxies. The only noticable differences are the one is high temp, black, and thick and the other is not. I have both, Just what do you guys think?

If you want to be safe against possible heat damage from long burning loads (though probably only EX loads will be long-enough burning to matter), use the proline. Otherwise, save it, it's more expensive. But like CarVac said, I don't know how much it matters.

 

[ColumbiaNX01]

When mixing up foam and pouring it into the fin can is there a way to measure how much you need to fill the void? For example is there a forumula that you can plug in how deep and wide the void is and it will tell you how much space there is and so this is X amount of 2 part foam you need? I assume I could just eye ball it and pour it in and just cut off any over flow. I rather not do that but if I have no other choice I will. I just want to be accurate and not wastefull.

 

[BLKKROW]

When mixing up foam and pouring it into the fin can is there a way to measure how much you need to fill the void? For example is there a forumula that you can plug in how deep and wide the void is and it will tell you how much space there is and so this is X amount of 2 part foam you need? I assume I could just eye ball it and pour it in and just cut off any over flow. I rather not do that but if I have no other choice I will. I just want to be accurate and not wastefull.

https://en.wikipedia.org/wiki/Annulus_(mathematics)

The easiest way would to calculate the area is taking the aread of the outside diameter and subtract the area of the inside diameter. Then take that area and multiple by the height of the space you want to fill.

 

[CarVac]

https://en.wikipedia.org/wiki/Annulus_(mathematics)

The easiest way would to calculate the area is taking the aread of the outside diameter and subtract the area of the inside diameter. Then take that area and multiple by the height of the space you want to fill.

Also, divide by the number of compartments (number of fins). Don't try to do all of them at once or else you will get inconsistent results.

 

[BLKKROW]

Also, divide by the number of compartments (number of fins). Don't try to do all of them at once or else you will get inconsistent results.

The only thing that comes to my mind is if the compartments are not sealed from one another you may attempt to fill one and it will leak to another.

 

[CarVac]

The only thing that comes to my mind is if the compartments are not sealed from one another you may attempt to fill one and it will leak to another.

When you want foam to leak from one to another, it won't happen.

When you don't want foam to leak from one to another, it will happen.

 

[BLKKROW]

When you want foam to leak from one to another, it won't happen.

When you don't want foam to leak from one to another, it will happen.

One solution is to fill 3 cups with the proper amount for each compartment and pour one right after the other this would fill the compartment to the exact capacity for each and prevent leaks from one to the other.

 

[CarVac]

One solution is to fill 3 cups with the proper amount for each compartment and pour one right after the other this would fill the compartment to the exact capacity for each and prevent leaks from one to the other.

That would best be done with 6 hands. You don't want to be rushing when dealing with expanding foam.

In any case, unless you are incredibly lucky, you won't get 3 cups of expanding foam to reach the exact same volume, because the resultant volume has to do with how it's poured as well. A puddle of the mixture against the forward bulkhead won't expand as much as a smear that drips down the length of the motor mount tube.

 

[CCotner]

personally, I suggest just going with wasteful. I like to mix up foam into a syringe and inject the liquid into an otherwise sealed volume, then blue tape over the hole. That forces the foam to pressurize the compartment, but once the pressure gets great enough it forces the blue tape off-it tends to reliably fill the entire target volume that way.

 

[ColumbiaNX01]

View attachment 158939View attachment 158940View attachment 158941

You will see that there are fillets from where the fin touches the motor tube on both sides. There are also fillets where there fin just enters the airframe.

 

[bill2654]

Get that rocket off the CARPET!:kill:

 

[ColumbiaNX01]

View attachment 158991View attachment 158992View attachment 158993View attachment 158994

This is the first time the whole rocket is put together. The things that are left is to foam the fin can. Attach rear center ring(s) and thrust plate with aeropack. Put together E-Bay. Configure an E-bay for tracker(s) using nose cone coupler. One last thing Carbon fiber T2T!!!

 

[ColumbiaNX01]

Just wanted to let the followers of my thread to know that I took 400 grit sandpaper and sanded the 4500 fillet using the wet sanding technique and the fillets came out fantastic. They turned a pretty silver color. If I was not going to do tip to tip then I would be very happy happy happy with the look of it as is. Pictures this evening!!!!

 

[ColumbiaNX01]

View attachment 159276
got 3 sections foamed
View attachment 159277
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over the top
View attachment 159279
Proline foam from rocketry warehouse, very easy to use!!!!

 

[CCotner]

That's a fairly familiar sight! Though I'd be impressed by the scale in person I'm sure =)

 

[ColumbiaNX01]

View attachment 159462
trimmed foam
View attachment 159463
close up
View attachment 159464
foamed between CR

 

[ColumbiaNX01]

View attachment 159465
sanded 4500 epoxy
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sanded using 400 grit paper wet sanding

 

[CCotner]

Looks really neat! I really dig the colored fiberglass body tube, I'll have to try that sometime.