# What did you do rocket wise today?

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#### Doug Holverson

##### Well-Known Member
Trying to solve a weird problem with the Crealty. Building that Quest Mini Space Clipper. It's in sort of a lull as the first salvo of glue dries.

#### Doug Holverson

##### Well-Known Member
I'm wondering how many here brain fart and say "drying" when talking about resin, epoxy, bondo, or even solder? Or saying warming up when your computer is booting up because you use to come home from school and had to wait a few minutes for the family console TV to warn up before you could watch Bugs Bunny?

##### Lonewolf.... No Club
TRF Supporter
String tested my scratch build F-79 Lonewolf.

#### Wally Ferrer

##### SRE
TRF Supporter
I'm wondering how many here brain fart and say "drying" when talking about resin, epoxy, bondo, or even solder? Or saying warming up when your computer is booting up because you use to come home from school and had to wait a few minutes for the family console TV to warn up before you could watch Bugs Bunny?
I was waiting for other folks to chime in as I certainly remember waiting for the TV to warm up... Now I just feel old...

#### o1d_dude

##### 'I battle gravity'
I was waiting for other folks to chime in as I certainly remember waiting for the TV to warm up... Now I just feel old...
I remember drawing on the TV screen with a special Winky Dink crayon and plastic sheet. Missing bridges, doors to escape from, ladders, and such.

Wonder how much radiation I absorbed from the TV using that nationally advertised product.

I really wasn’t just making this up.

Fifty cents for the Winky Dink TV kit.

Seriously.

#### DRAGON64

##### Well-Known Member
TRF Supporter
Sent specifications to a machinist for 18mm, 29mm and 54mm custom motors.

#### jqavins

##### Joseph Avins
TRF Supporter
I'm wondering how many here brain fart and say "drying" when talking about
resin: overly general term; may refer to epoxy, acrylic, or other things. But yeah, I'd probably say "dry".
epoxy: yes
bondo: haven't use it, but probably would say "dry"
solder: no
Or saying warming up when your computer is booting up: got over that one. I can't say when. I used to do it and now I don't anymore.[/QUOTE]

#### RocketTree

##### Active Member
Found out the shear strength of threads on a 1/4" aluminum rod is not enough for electronics bay. Will have to use steel rod I suppose...

##### Well-Known Member
Found out the shear strength of threads on a 1/4" aluminum rod is not enough for electronics bay. Will have to use steel rod I suppose...
I was curious so I looked it up...

AL - 40k psi tensile strength, $3.70/ft TI - 50k psi,$36.21/ft
316 Stainless - 70k psi, $2.54/ft Normal grade steel (B7) - 120k psi,$3.57/ft
High-strength Steel (Grade 8) - 150k psi, $5.72/ft I'm kinda surprised. Unless you have to worry about EM interference, then I don't really see a reason to use anything besides steel. #### mbeels ##### Yes balsa TRF Supporter Found out the shear strength of threads on a 1/4" aluminum rod is not enough for electronics bay. Will have to use steel rod I suppose... I'm curious, was that determined by testing, or by calculation? For how heavy a rocket, and what deployment acceleration? #### RocketTree ##### Active Member I'm curious, was that determined by testing, or by calculation? For how heavy a rocket, and what deployment acceleration? Just a mechanical pull test on it. The steel nut sheared the aluminum threads off the rod like it was nothing. Just noticed another post on the forum mentioning nylon rod 1/4-20 (same size). Can't seem to source that anywhere in Canada, but would like to try it. This is for a 4" rocket up to I power motor. #### RocketTree ##### Active Member I was curious so I looked it up... AL - 40k psi tensile strength,$3.70/ft
TI - 50k psi, $36.21/ft 316 Stainless - 70k psi,$2.54/ft
Normal grade steel (B7) - 120k psi, $3.57/ft High-strength Steel (Grade 8) - 150k psi,$5.72/ft

I'm kinda surprised. Unless you have to worry about EM interference, then I don't really see a reason to use anything besides steel.
Thats the tensile strength of the rod itself, which is more than enough for this application. My test failed at the threads. It is likely that a different thread type, or fasteners with more inside surface area would correct some of that. I also noticed the threads would probably not last through repeated assembly/disassembly of the bay, since the aluminum threads are quite easy to mangle.

##### Well-Known Member
Just a mechanical pull test on it. The steel nut sheared the aluminum threads off the rod like it was nothing. Just noticed another post on the forum mentioning nylon rod 1/4-20 (same size). Can't seem to source that anywhere in Canada, but would like to try it. This is for a 4" rocket up to I power motor.

Not in Canada but you should have a company that does similar.

##### Well-Known Member
Thats the tensile strength of the rod itself, which is more than enough for this application. My test failed at the threads. It is likely that a different thread type, or fasteners with more inside surface area would correct some of that. I also noticed the threads would probably not last through repeated assembly/disassembly of the bay, since the aluminum threads are quite easy to mangle.
You probably want an ACME or square thread for that.

I've used 1/4"-20 mild steel on a 20lbs 5.5" rocket on a K motor without issue. 4" rocket on an I, you should be fine.

#### RocketTree

##### Active Member
You probably want an ACME or square thread for that.

I've used 1/4"-20 mild steel on a 20lbs 5.5" rocket on a K motor without issue. 4" rocket on an I, you should be fine.
Thanks for the suggestions. Might give it another try since I still have a few more rods cut for it. Dont think I have square thread dies here but its possible that a coarse thread might increase the bite on the fastener to rod. This rocket is already heavy, so was trying to keep the added weight down, although might be over-complicating things as a result.

##### Well-Known Member
Thanks for the suggestions. Might give it another try since I still have a few more rods cut for it. Dont think I have square thread dies here but its possible that a coarse thread might increase the bite on the fastener to rod. This rocket is already heavy, so was trying to keep the added weight down, although might be over-complicating things as a result.
Understand the desire to keep weight down but the recovery connections isn't the place I'd look to cut.

ACME threads are much stronger than typical threads but it's way overkill for the application.

and

McMaster-Carr will ship to Canada but only to business addresses. I'm sure any local machine shop can tell you a local supplier of similar items.

#### mbeels

##### Yes balsa
TRF Supporter
Just a mechanical pull test on it. The steel nut sheared the aluminum threads off the rod like it was nothing. Just noticed another post on the forum mentioning nylon rod 1/4-20 (same size). Can't seem to source that anywhere in Canada, but would like to try it. This is for a 4" rocket up to I power motor.
How much force resulted in the failure?

#### Wally Ferrer

##### SRE
TRF Supporter
I remember drawing on the TV screen with a special Winky Dink crayon and plastic sheet. Missing bridges, doors to escape from, ladders, and such.

Wonder how much radiation I absorbed from the TV using that nationally advertised product.

View attachment 418954View attachment 418955

I really wasn’t just making this up.

Fifty cents for the Winky Dink TV kit.

Seriously.
Never had Winky Dink, but well aware of it...

#### Greg Furtman

##### Well-Known Member
TRF Supporter

Not in Canada but you should have a company that does similar.
Gotta love McMaster-Carr. Lots of everything, decent pricing, and fast delivery. Been buying from them for many years.

#### jqavins

##### Joseph Avins
TRF Supporter
If I understood this right, you were using a steel nut on aluminium threaded rod, is that right? You mentioned mangling the thread with assembly and disassembly, and I think it's the difference in materials that most likely to cause that, and also the difference in hardness not strength. It takes hardened steel to make a tap or die for steel parts, but you could cut threads in aluminium with unhardened tools. By accident.

As for the strength: sure acme or square threads would give you better holding strength; I bet they'd also be a lot harder to find and more expensive if you want acme or square threaded aluminum. All to save a few grams. I think you're exactly right to just keep it simple and use steel.
McMaster-Carr will ship to Canada but only to business addresses. I'm sure any local machine shop can tell you a local supplier of similar items.

#### rharshberger

##### Well-Known Member
Thanks for the suggestions. Might give it another try since I still have a few more rods cut for it. Don`t think I have square thread dies here but its possible that a coarse thread might increase the bite on the fastener to rod. This rocket is already heavy, so was trying to keep the added weight down, although might be over-complicating things as a result.
Use double nuts to increase the area holding threads, I have several 3" HPR rockets using 1/4" aluminum rods that I threaded in the Altimeter bays, rockets weight between 6-10lbs never had an issue an no signs of damage.

#### tOD

##### Sinking in the quicksand of HPR
TRF Supporter
The BT60 Speed Demon is starting to look like a rocket. Some nosecone work, and some AV bay loose ends to tie up.

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#### RocketTree

##### Active Member
How much force resulted in the failure?
I did not have a gauge on it to measure that, since it was unexpected to happen.

#### RocketTree

##### Active Member
Your test seems to contradict the experience of most machinists, e.g., this discussion where the pull out force for aluminum 1/4-20 thread is more like 6000 to 8000 lbs. https://www.practicalmachinist.com/vb/general/how-calculate-thread-pull-out-6061-aluminum-331438/
You are completely correct. It has to be in the thousands.

But without indicating the fine details of it, there was no test or comparison. As an update, just tried a M7x1 and was not able to pull it apart. The 1/4" hardware seems to have a ton of clearance.

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#### NateB

##### Well-Known Member
More sanding and painting on 4 different kits. I'm still taking a break from my Punisher and working on smaller rockers that I can fly this Summer.

#### rharshberger

##### Well-Known Member
You are completely correct. It has to be in the thousands.

But without indicating the fine details of it, there was no test or comparison. As an update, just tried a M7x1 and was not able to pull it apart. The 1/4" hardware seems to have a ton of clearance.
And that may be your problem, sloppy clearances only engage part of the thread thereby lessening the amount of tension required to strip the nut off the threads. My 1/4-20 die and 1/4-28 dies are the "adjustable" type but they seem to cut a minimum clearance thread so I dont mess with them, I have a Hanson brand non-adjustable die that cuts almost a sloppy loose thread, I bought the Hanson, the other two were inherited from my wifes grandfather when he passed, he was a millwright for over 40 years and probably paid a good penny or three for high quality taps and dies.

#### prfesser

Nice! What did you form the conical sections with for that one?
Thanks! My L3 project transition and nozzle cones were made in much the same way, five or six layers of heavy kraft paper, stacked and saturated with epoxy, topped with a layer of fiberglass cloth and filled with expanding foam. The cones were so big that it wasn't convenient to use Rocksim or other electronic means of printing them. Instead they were laid out by hand on a very large piece of kraft paper (I have a 900' roll bought about 20 years ago, it's found all sorts of rocketry uses), with a homemade beam compass.

I'll try to dig out the photos of the rocket, they're somewhere on my computer.

Best -- Terry

#### Charles_McG

##### Ciderwright
Busy day with decals.

#### rklapp

##### NAR# 291223
Finally shot my Falcon 9. Had 3 out of 5 parachute failures. (Fixed link)

Finished up the decals on the Interceptor. Mostly pleased with the many decals with a few blemishes. Wasn’t happy with the pods and ended up painting them several times.

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