lakeroadster
When in doubt... build hell-for-stout!
String tested my scratch build F-79 Lonewolf.
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'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 remember drawing on the TV screen with a special Winky Dink crayon and plastic sheet. Missing bridges, doors to escape from, ladders, and such.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...
resin: overly general term; may refer to epoxy, acrylic, or other things. But yeah, I'd probably say "dry".I'm wondering how many here brain fart and say "drying" when talking about
I was curious so I looked it up...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...
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?
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.
https://www.mcmaster.com/98831A360Just 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.
You probably want an ACME or square thread for that.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.
Understand the desire to keep weight down but the recovery connections isn't the place I'd look to cut.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.
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.
Never had Winky Dink, but well aware of it...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.
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I really wasn’t just making this up.
Fifty cents for the Winky Dink TV kit.
Seriously.
Gotta love McMaster-Carr. Lots of everything, decent pricing, and fast delivery. Been buying from them for many years.https://www.mcmaster.com/98831A360
Not in Canada but you should have a company that does similar.
Or, perhaps you could get things shipped to your workplace address; that's a business, whatever business it happens to be.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.
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.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.
How much force resulted in the failure?
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/I did not have a gauge on it to measure that, since it was unexpected to happen.
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/
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.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.
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.Nice! What did you form the conical sections with for that one?
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.
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