#10 threaded rod for EBay - 5lb rocket

[MikeyDSlagle]

I'll just get right to the question for those who don't care to read the entire post.

Will two pieces of #10 threaded rod be sufficient in a 5lb rocket? (4"Madcow Tembo) Electronic deploy at apogee and JLCR for the main. 54mm motors up to maybe the AT/1280.

I've been working on my 4" Tembo and Tyrannosaur concurrently and designed me a new bay for the nose cone of the Tembo, and it should work in the Tyrannosaur as well to add a tracker if I need to later on. I have a tried and true nose cone bay in my Cowabunga, but I like trying new things. But for now I am talking about the Tembo.

So basically, I got a ring in the Nose above the shoulder, that I call the permanent plate. It has two 1/4" holes in it for threaded rod (all thread). The lid of course has the same two 1/4" holes. After fiddling around with it I realized it will be much easier to use #10 weld nuts in the 1/4" holes in the permanent plate, epoxied to the backside. It will allow me to use wing nuts on the lid. There is not enough clearance to use 1/4" wing nuts. I will just have to use more washers on the 1/4" hole if I go with #10. It has a 5/16" U bolt in the lid to attach the harness. I ordered 5/16" for a specific hole spacing and I just never went back to anything smaller.

I'm not too worried about weight in the nose cone because I will have to add some anyway, maybe as much as 8 oz. So I am not trying to cut down on weight.

Will #10 all thread be sufficient? The rocket will come in around close to 5 pounds with the biggest 54mm case I have. I'm building it with the intent to fly on the 54mm "Soda Can" motors, but may stick a 1280 in there. Electronic deployment at apogee and a JLCR to open the main. I can always go with 1/4" and grab some knurled nuts to keep from using tools to open the bay.

I am somewhat familiar with tensile strength and shear strength and what not. I would think tensile strength comes more into play here, but I am no engineer.I would like to hear what a honest to god engineer has to say about it too.

Thanks,
Mikey D

 

[Steve Shannon]

I think you should be fine. The threads work in shear; the rod works in tension. If the apogee charge doesn't work the rocket will fall fast, but the JLCR won't open the main at high speed. If the apogee charge works, the rocket will fall more slowly and the main won't cause a high stress deceleration.

Some things to consider:
What's the thicknesses of the permanent plate and lid? What material are they?
What grade steel is the allthread (assuming it's steel)?
What about the weld nuts? How much material is there preventing them from pulling through the permanent plate?
Can the permanent plate pull out of the nosecone?
What hardware do you have in the lid for the shock cord to attach? A closed eyebolt? A u-bolt? An open eyebolt?


Steve Shannon

 

[Buckeye]

Yes, #10 is plenty for a 5lb rocket. 1/4"-20 is not much bigger, and people use this in every rocket imaginable. My ~8lb MAC rockets comes with aluminum 1/4-20 rods.

Give yourself plenty of shock cord, and then you can easily use basic hardware found at any big box home store.

 

[DAllen]

I know some folks are going to think I am nuts but I've used two 6/32 rods on a 8# rocket no problem. The amount of tensional force those rods can sustain is rather amazing.

 

[NateLowrie]

I know some folks are going to think I am nuts but I've used two 6/32 rods on a 8# rocket no problem. The amount of tensional force those rods can sustain is rather amazing.

Let's put some numbers to this instead of guessing.

The SAE J429 spec lists the stress area of #10-32 threads as 0.0200 in^2. Grade 8 steel has a 150,000 PSI minimum tensile stress. So, the minimum tensile load is 0.0200 * 150,000 = 3000lbs. The rod must meet this load when taken to a total break. The proof load stress is 120,000 PSI for Grade 8, which gives us a proof load of 2,400 lbs. This load is slightly below the yield point which means it will not enter elastic deformation and will return to it's original length. You want to keep your loads under the 2,400 lbs at all costs.

If we assume a safety factor of 2, that's 1,200 lbs per rod force those rods can take. So, if you use 2 rods, you are at 2,400 lbs max load with the safety factor of 2. From here it's a simple matter of find the maximum normal recovery force on the rocket. However, I suspect you won't even have to do that because you eyebolts/U-Bolts now become the weaker link.

The tensile area of #6-32 threaded rod is 0.009 in^2. That gives us a proof load of 1,080 lbs per rod. Still rightly sized for the application.

Note that these numbers are for Grade 8 low carbon steel. Aluminum rods will be a lot lower. Stainless Steel 304 or 18-8 will be slightly lower.

 

[MikeyDSlagle]

I think you should be fine. The threads work in shear; the rod works in tension. If the apogee charge doesn't work the rocket will fall fast, but the JLCR won't open the main at high speed. If the apogee charge works, the rocket will fall more slowly and the main won't cause a high stress deceleration.

Some things to consider:
What's the thicknesses of the permanent plate and lid? What material are they?
What grade steel is the allthread (assuming it's steel)?
What about the weld nuts? How much material is there preventing them from pulling through the permanent plate?
Can the permanent plate pull out of the nosecone?
What hardware do you have in the lid for the shock cord to attach? A closed eyebolt? A u-bolt? An open eyebolt?


Steve Shannon

So threads work in shear, good to know. Thanks.

Yeah, high speed deployment is unlikely. Nose cone pops, all is good. If not...then I'll be looking for a shovel.

All you mentioned to consider were considered.. Except for the area of the weld nut.

Permanent plate and lid are both 3/8" plywood, cut by UpScaleCNC.
Thread is the stuff from local hardware store, grade 2 I would imagine.
The weld nuts are 3/4" across the base, from McMaster.
The permanent plate has larger OD than the shoulder ID, it won't slide straight out, has to be turned and squeeze nose cone to get it in. Then it will be epoxied and possibly pinned.
5/16" U bolt in the lid for attaching harness via quicklink. Went back and edited original post, it said all thread.

Shock cord will be what came with the kit, which I think is 15' of TN, plus 2' of kevlar on each end.

Gonna check local sources to see what I can round up as for knurled nuts or wing nuts.

6-32 huh? If it works it works.

Thanks folks,
Mikey D

 

[DAllen]

Let's put some numbers to this instead of guessing.

The SAE J429 spec lists the stress area of #10-32 threads as 0.0200 in^2. Grade 8 steel has a 150,000 PSI minimum tensile stress. So, the minimum tensile load is 0.0200 * 150,000 = 3000lbs. The rod must meet this load when taken to a total break. The proof load stress is 120,000 PSI for Grade 8, which gives us a proof load of 2,400 lbs. This load is slightly below the yield point which means it will not enter elastic deformation and will return to it's original length. You want to keep your loads under the 2,400 lbs at all costs.

If we assume a safety factor of 2, that's 1,200 lbs per rod force those rods can take. So, if you use 2 rods, you are at 2,400 lbs max load with the safety factor of 2. From here it's a simple matter of find the maximum normal recovery force on the rocket. However, I suspect you won't even have to do that because you eyebolts/U-Bolts now become the weaker link.

The tensile area of #6-32 threaded rod is 0.009 in^2. That gives us a proof load of 1,080 lbs per rod. Still rightly sized for the application.

Note that these numbers are for Grade 8 low carbon steel. Aluminum rods will be a lot lower. Stainless Steel 304 or 18-8 will be significantly higher.

Thanks for that. A long time ago in another lifetime (TRF 1.0 perhaps?) I recall a thread or comment to that effect and that's when I just started using 6/32 for everything...plenty strong but still big enough to be manageable.

-Dave

 

[FredA]

Let's put some numbers to this instead of guessing.

Oh the sanity!
The bulk of this hobby is about physics and mechanical engineering....not guessing or "I heard" or "Saw" or "Did" and it survived statements.
This is a "Thinking man's (and women's) hobby"

All the anecdotal "evidence" that shows up in this forum drives me nuts.....
Thank you NateLowrie

 

[BuiltFromTrash]

Lol, I know right. Get some logic in here.

 

[MikeyDSlagle]

Let's put some numbers to this instead of guessing.

The SAE J429 spec lists the stress area of #10-32 threads as 0.0200 in^2. Grade 8 steel has a 150,000 PSI minimum tensile stress. So, the minimum tensile load is 0.0200 * 150,000 = 3000lbs. The rod must meet this load when taken to a total break. The proof load stress is 120,000 PSI for Grade 8, which gives us a proof load of 2,400 lbs. This load is slightly below the yield point which means it will not enter elastic deformation and will return to it's original length. You want to keep your loads under the 2,400 lbs at all costs.

If we assume a safety factor of 2, that's 1,200 lbs per rod force those rods can take. So, if you use 2 rods, you are at 2,400 lbs max load with the safety factor of 2. From here it's a simple matter of find the maximum normal recovery force on the rocket. However, I suspect you won't even have to do that because you eyebolts/U-Bolts now become the weaker link.

The tensile area of #6-32 threaded rod is 0.009 in^2. That gives us a proof load of 1,080 lbs per rod. Still rightly sized for the application.

Note that these numbers are for Grade 8 low carbon steel. Aluminum rods will be a lot lower. Stainless Steel 304 or 18-8 will be significantly higher.

Awesome. This helps quite a bit. Thanks. I'll have to save a copy of this.
Curious though, where did you find that info?

 

[Steve Shannon]

Awesome. This helps quite a bit. Thanks. I'll have to save a copy of this.

That's what happens in engineering. We don't calculate those limits for allthread every time. We build a body of knowledge that we reuse over and over. Then, lazily, we simply say "That should be fine," instead of calculating it like Nate did.
Nate did the right thing. His post not only addressed your question but also helps others understand how they can do the same. Kudos to Nate!

 

[NateLowrie]

Let's put some numbers to this instead of guessing.

Oh the sanity!
The bulk of this hobby is about physics and mechanical engineering....not guessing or "I heard" or "Saw" or "Did" and it survived statements.
This is a "Thinking man's (and women's) hobby"

All the anecdotal "evidence" that shows up in this forum drives me nuts.....
Thank you NateLowrie

No problem. Drives me nuts too. While we're at it, a few more things.

Regarding the numbers, please note that the quoted numbers are spec'd for grade 8. If you use grade 5 or heaven help you Grade 2 you need to calculate using the appropriate tensile strength.

Also, you do have to watch your nut configuration otherwise shear failure on the threads comes into play. You can do the math, but I recommend:

• Make sure you are using at least one full height hex nut and not a jam nut. You need to engage enough threads to spread the load and a jam nut just doesn't do it.
• I also maintain that you should not use a wing nut. While it's convenient, there are some risks with over/under torquing and loosening during flight.
• Always torque down to proper tolerances. For 10-32 it's 68 in-lbs for Grade 8 and for 1/4-20 it's 12 ft-lbs for grade 8.
• Always use a retention method like a spring washer, nylon locknut, or threadlocker to keep the nut from vibrating loose.

 

[NateLowrie]

Awesome. This helps quite a bit. Thanks. I'll have to save a copy of this.
Curious though, where did you find that info?

I could have opened up my engineers handbook. However, a quick google search was sufficient.

https://www.google.com/webhp?source...&espv=2&ie=UTF-8#q=tensile+strength+grade+8&*


https://www.google.com/webhp?source...espv=2&ie=UTF-8#q=tensile+stress+area+10-32&*

See first result in each google search.

 

[FredA]

Nate - check that torque spec on the 1/4-20 in your post

 

[Steve Shannon]

Nate - check that torque spec on the 1/4-20 in your post

My strength of materials professor, Conrad Hilpert, said always check at least three different sources. Too many times one source will have at least one error somewhere.

 

[NateLowrie]

Nate - check that torque spec on the 1/4-20 in your post

Fred,

Sorry about that. My sources I normally use quote values for both plain and plated. I checked a few other sources and both values matched. For 1/4-20, plain is 12 ft-lb and plated is 9 ft-lb. Most every screw I use in Grade 8 is zinc plated so I am not sure how I goofed and selected the wrong column.

Regards,

Nate

 

[DAllen]

Let's put some numbers to this instead of guessing.

Oh the sanity!
The bulk of this hobby is about physics and mechanical engineering....not guessing or "I heard" or "Saw" or "Did" and it survived statements.
This is a "Thinking man's (and women's) hobby"

All the anecdotal "evidence" that shows up in this forum drives me nuts.....
Thank you NateLowrie

Fred, how about instead of complaining about the anecdotal posts you show the rest of us non engineer types how you derive such information. That would be far more beneficial than complaining. Sometimes coming up with that info for us stupid non-thinking people is kinda hard. :bangpan:

-Dave

 

[jd2cylman]

Let's put some numbers to this instead of guessing.

The SAE J429 spec lists the stress area of #10-32 threads as 0.0200 in^2. Grade 8 steel has a 150,000 PSI minimum tensile stress. So, the minimum tensile load is 0.0200 * 150,000 = 3000lbs. The rod must meet this load when taken to a total break. The proof load stress is 120,000 PSI for Grade 8, which gives us a proof load of 2,400 lbs. This load is slightly below the yield point which means it will not enter elastic deformation and will return to it's original length. You want to keep your loads under the 2,400 lbs at all costs.

If we assume a safety factor of 2, that's 1,200 lbs per rod force those rods can take. So, if you use 2 rods, you are at 2,400 lbs max load with the safety factor of 2. From here it's a simple matter of find the maximum normal recovery force on the rocket. However, I suspect you won't even have to do that because you eyebolts/U-Bolts now become the weaker link.

The tensile area of #6-32 threaded rod is 0.009 in^2. That gives us a proof load of 1,080 lbs per rod. Still rightly sized for the application.

Note that these numbers are for Grade 8 low carbon steel. Aluminum rods will be a lot lower. Stainless Steel 304 or 18-8 will be significantly higher.

I'm not really a rocket scientist by trade, but I'm not sure about this. The numbers I come up with show gr8 to have 150,000 psi tensile strength. OK. However, the numbers I see for stainless show 70,000 for 18-8 and 316. Ultra corrosion Alloy 20 stainless lists as 80,000. And Hardened 316 lists as 100,000 per the McMaster Carr site where I buy all my rod. I mostly use 316 as it is plenty strong for my usage. And I want the resistance to corrosion from BP. Edit: I never looked at 410 stainless but, it still is listed at 110,000. And magnetic, which I try to avoid.

 

[NateLowrie]

I'm not really a rocket scientist by trade, but I'm not sure about this. The numbers I come up with show gr8 to have 150,000 psi tensile strength. OK. However, the numbers I see for stainless show 70,000 for 18-8 and 316. Ultra corrosion Alloy 20 stainless lists as 80,000. And Hardened 316 lists as 100,000 per the McMaster Carr site where I buy all my rod. I mostly use 316 as it is plenty strong for my usage. And I want the resistance to corrosion from BP.

You are correct. I need to go back and edit that.

 

[jd2cylman]

You are correct. I need to go back and edit that.

Wahoo! I'm not in trouble... :wink:

Seriously, this is interesting stuff. Good discussion. I also didn't know until today that the smaller #10 rods came in anything longer than 6" until I poked around a bit.

 

[MikeyDSlagle]

I could have opened up my engineers handbook. However, a quick google search was sufficient.

https://www.google.com/webhp?source...&espv=2&ie=UTF-8#q=tensile+strength+grade+8&*


https://www.google.com/webhp?source...espv=2&ie=UTF-8#q=tensile+stress+area+10-32&*


See first result in each google search.

I did a google search but was on my phone running around outside. Thanks again, that helps too.
Both are bookmarked.
On this one I will probably go with 1/4" because it was designed and cut for 1/4".

 

[FredA]

Dave - I try as often as possible. This forum is filled with examples.
In this case, Nate had already done the work and I was thanking him.
:bangpan:

:bangpan:

:bangpan:

:bangpan:

:bangpan:

 

[dixontj93060]

I have a glass-half-full guy on my team at work. Compliments are not his forte. Sometimes when he tries, he's misinterpreted. As he has people reporting to him, I have to coach him on this all the time, but you know, he is invaluable in other ways. We all have pluses and minuses.

 

[Handeman]

The only thing I would add to this, based on the design description, is the force applied to the all-thread should be calculated using the weight of the nose cone only since the all-thread is holding the nose cone parts together and all forces felt by them will involve those parts only.

If this all-thread was holding the caps on a standard center positioned av-bay, then yes, the total weight of the rocket, minus av-bay weight, should be used.