Thread measurements for Aerotech 38mm Plugged Threaded Forward Closure

[kjhambrick]

All --

I am building a 38mm min diameter rocket and I will be using a 38mm Plugged Threaded Forward Closure ( part no: 38FCPT ) with a forged eye bolt for an aft shock cord mount,

I've read that the tapped threads are 5/16 - 18.

Is that correct ?

What are the depth of the threads ?

And if anyone has suggestions for locking the eye bolt to the Forward Clusure, I am all ears !

Thanks !

-- kjh

 

[GalantVR41062]

https://www.rocketryforum.com/threads/aerotech-measurement-needed.124403/
Search button works pretty good.

As for retention a few things that come to mind: red loctite, lock washer, drill a cross hole for a pin/cotter key, safty wire, drill and tap a hole for a set screw.

At the end of the day still need to admit the forward closure threads into the case, and besides the threads being larger in diameter what's holding that from unthreading?

 

[user 30299]

All --

I am building a 38mm min diameter rocket and I will be using a 38mm Plugged Threaded Forward Closure ( part no: 38FCPT ) with a forged eye bolt for an aft shock cord mount,

I've read that the tapped threads are 5/16 - 18.

Is that correct ?

What are the depth of the threads ?

And if anyone has suggestions for locking the eye bolt to the Forward Clusure, I am all ears !

Thanks !

-- kjh

Yes, the thread is 5/16" - 18 on the 38mm closure.

It's the same for the 54mm closure - incase you were wondering.

 

[kjhambrick]

Thanks @GalantVR41062 --

I wish there was a "Like it a Lot" emoji -- I would use it here.

I never found the post that gave the depth of the threads until I saw the last post in your link:

The length of the protruding part is about 0.945". Based on ATs external drawing for the 38/720 casing, the dimension you're looking for is about 13.57". The forward hole is 0.67" deep, with a usable thread depth of about 0.45" (UNC 5/16).

Reinhard

But I was wondering also the same thing -- if I lock the 5/16-18 eye-bolt threads, then doesn't that simply move the tendency to unscrew down to the forward closure itself ?

EDIT: UNLESS they are left hand threads ???

Maybe that's why I believe I read somewhere that the plugged forward closures are 'not for anchoring a recovery device' ( or some such some wording ) ???

And I would imagine that set screws and etc would count as a motor case mod ???

That would leave lock washers, jam nuts and ( ick ) Loctite ...

Still pondering my shock cord mount for 38mm motors in a min diameter 38mm rocket ...

Thanks again.

-- kjh

Edit: still looking for ideas to steal

 

[kjhambrick]

Yes, the thread is 5/16" - 18 on the 38mm closure.

It's the same for the 54mm closure - incase you were wondering.

Thanks @QFactor

I found the diameter and thread size ( 5/16-18 ) on the AeroPack Min Diameter Motor Retention Description Pages.

But I was shopping for 5/16-18 Forged Eyebolts with Shoulders and I needed to know how long the threads needed to be still leaving enough length for a Jam Nut ( the best method I've come up with so far that does not involve drilling and taping the plugged forward closure for a set-screw ).

-- kjh

 

[David Schwantz]

Jam nut.

 

[David Schwantz]

I have the AT 38mm forward closure that is drilled and tapped. It is NOT the plugged one. But the threads are .380 deep.

 

[David Schwantz]

Just buy an eye bolt over length and cut to the correct length after you get everything installed.

 

[SolarYellow]

Maybe that's why I believe I read somewhere that the plugged forward closures are 'not for anchoring a recovery device' ( or some such some wording ) ???

I got confused about that and only recently sorted out, too. The Aeropack MD retainer system screws into the phenolic/composite forward closure on CTI 38 & 54mm motors. It basically acts like a wood screw, forming female threads in the part it is screwed into. That's why it's not for anchoring recovery. It's only to hold the motor into the rocket, without even any ejection charge:

https://aeropack.net/products/mc38-cesaroni-pro38-delay-eject-closure-adapter
The AeroTech threaded forward closures have threads machined into the aluminum parts and the web site actually suggests using them as a recovery anchor.

And I would imagine that set screws and etc would count as a motor case mod ???

Any permanent modification of the hardware counts as a mod.

I feel like you're making it harder than it needs to be.

Use a bulkhead positioned to provide clearance for the longest case/closure you'll use. On a composite airframe, you can even use an expandable rubber plug so it's movable. Put the eyebolt through that, so there is the eye portion above the bulkhead and the bolt part sticks through the bottom, providing a stud for the retainer to thread onto. If your bulkhead is fixed and you want to use shorter motors, you can get extensions from AeroPack,

https://aeropack.net/collections/al...e=Retainer+Components&sort_by=title-ascending
or just buy some 5/16-18 threaded rod (you can even get it in aluminum to save weight) and coupling nuts. Set it up so when you install the motor, the thrust ring snugs up against the rear of the MMT, and the friction will keep the motor from unscrewing through the flight. The friction of the motor assembly with the compressed o-rings keeps the motor assembly from unscrewing.

 

[user 30299]

All --

I am building a 38mm min diameter rocket and I will be using a 38mm Plugged Threaded Forward Closure ( part no: 38FCPT ) with a forged eye bolt for an aft shock cord mount,

I've read that the tapped threads are 5/16 - 18.

Is that correct ?

What are the depth of the threads ?

And if anyone has suggestions for locking the eye bolt to the Forward Clusure, I am all ears !

Thanks !

-- kjh

Is this what you're trying to get to ?



That's a 38mm motor case in the pictures.

 

[terryg]

Since nothing is ever standardized, LOKI threaded closures are 1/4 inch. Not sure what kosden and older type cases are threaded for.

 

[kjhambrick]

Is this what you're trying to get to ?

View attachment 606023 View attachment 606024

That's a 38mm motor case in the pictures.

Yes, pretty much !

With a 29/38 and even a 24/38 motor adapter with shock cord mounts.

Then I've got to do something with my 38 mm DMS motors too

-- kjh

 

[kjhambrick]

Is this what you're trying to get to ?

View attachment 606023 View attachment 606024

That's a 38mm motor case in the pictures.

@QFactor --

I've been looking at eyebolts and I don't see anything quite like yours -- they're all large diameter with less marerial around the circumference.

Do you recall where you got the eyebolt in your photo ?

Thanks.

-- kjh

 

[user 30299]

@QFactor --

I've been looking at eyebolts and I don't see anything quite like yours -- they're all large diameter with less marerial around the circumference.

Do you recall where you got the eyebolt in your photo ?

Thanks.

-- kjh

The eyebolt you see in my pictures are actually a Rod End Bolt.

Below is the listing from my order at McMaster-Carr.

Yes, they are expensive. I work in industrial manufacturing so I see these in my work.

McMaster is always expensive. You're paying for the convenience of having everything imaginable on
the shelf and getting it within a day or two. You may be able to find them elsewhere at a better price.

Line		Product	Ordered​	Shipped​	Balance​	Price​	Total​
1	2440K35	High-Strength Fully Threaded Rod End Bolt, 1/4"-20 Shank Thread, 1-1/2" Shank Center Length	2 Each​	2​	0​	9.38 Each​	18.76​
2	2440K22	High-Strength Fully Threaded Rod End Bolt, 5/16"-18 Shank Thread, 1-1/2" Shank Center Length	2 Each​	2​	0​	9.62 Each​	19.24​

The 1/4" bolt is for my Loki cases. The 5/16" bolt is for the 38mm and 54mm AT cases.

The road end bolts are overkill for strength, but you get that nice compact eye.

 

[SolarYellow]

A little cheaper at Zoro, plus free shipping over $50. Sign up for an account. Put stuff in your cart and wait. You'll get a 20% off everything coupon soon enough. They are a good source for a lot of things; many cheaper than anywhere else. Also have Krylon Acryli-Quik if you're into that.

https://www.zoro.com/ken-forging-rod-end-steel-14-20-thrd-sz-6-in-overall-lg-1e-mach/i/G4426667
https://www.zoro.com/ken-forging-ro...-sz-1-12-in-overall-lg-2aa-ssmach/i/G4434857/

 

[kjhambrick]

Thanks @QFactor and @SolarYellow !

"Rod End Bolt" were the magic words that I needed to know !

They have the same at Grainger for just a little more than zoro but a little less than McMaster, and I can order today and then walk in Friday for pickup without shipping charges ( and Grainger is next door to a big Hobby Lobby )

Grainger: Ken Forging - Rod End: Steel, Black Oxide, Right Hand, 5/16"-18 Thread Size, 1 1/2 in Thread Lg

-- kjh

p.s. I still need to figure out those beautiful links everyone but I seems to know how to produce in TRF

 

[SolarYellow]

I'd buy stuff from Grainger, but the nearest branch is $3 of gas and 20-30 minutes round trip, so I'm better off staying at my desk and working. Plus, I never pay freight ordering from Zoro. It probably works out well for them...

 

[kjhambrick]

Yes, I've thought about the gas and time ...

But it is less than 10-miles round-trip and it gets me out of the house

-- kjh

p.s. I didn't know about Zoro so I'll do some browsing there next time I need some goodies ... bookmarked ... thanks for the link !

 

[tsmith1315]

But it is less than 10-miles round-trip and it gets me out of the house

It supports a local paycheck, too.

 

[kjhambrick]

It supports a local paycheck, too.

Good point, @tsmith1315 !

I am a believer of buying from a local shop if I can, even if it costs a little bit more ...

-- kjh

 

[rharshberger]

Thanks @QFactor

I found the diameter and thread size ( 5/16-18 ) on the AeroPack Min Diameter Motor Retention Description Pages.

But I was shopping for 5/16-18 Forged Eyebolts with Shoulders and I needed to know how long the threads needed to be still leaving enough length for a Jam Nut ( the best method I've come up with so far that does not involve drilling and taping the plugged forward closure for a set-screw ).

-- kjh

If the shoulder of the eyebolt is not contacting the surface its being threaded into you are defeating the purpose of have a shouldered eyebolt, even if its just a small gap between the shoulder and the jam nut. You are better off using a non-permanent thread locker and threading the eyebolt all the way in until the shoulder sits securely atop the forward closure....."we never have off linear axis loads...until we do...then things go sideways...."

 

[kjhambrick]

If the shoulder of the eyebolt is not contacting the surface its being threaded into you are defeating the purpose of have a shouldered eyebolt, even if its just a small gap between the shoulder and the jam nut. You are better off using a non-permanent thread locker and threading the eyebolt all the way in until the shoulder sits securely atop the forward closure....."we never have off linear axis loads...until we do...then things go sideways...."

Yes, thanks @rharshberger.

That is a VERY long threaded shank.

I'll was thinking I would trim the shank, leaving space for a Jam Nut and clean the threads by running the trimmed shank thru a 5/16-18 die as @David Schwantz recommended 'up there in this thread'.

There would be a short bit of exposed shank but not too much -- maybe 1/8 inch or so ..between the top of the Jam Nut and the shoulder of the Rod End Bolt ( EDIT: these Rod End Bolts have no shoulders )

Does that sound OK ?

Or would I be better off without the Jam Nut and simply trim the shank so that the shoulder of the Rod End Bolt snugs up against the Threaded Forward Closure ( EDIT: these Rod End Bolts have no shoulders ) ?

-- kjh

EDIT: Is there any reason to not make the Rod End a permanent component of the AT Plugged Forward Closure ?

i.e. does it ever need to be removed ?

EDIT[2]: I didn't notice before but the Rod End Bolts have no shoulders ...

 

[SolarYellow]

A yuuuge benefit to the AT Plugged Forward Closure, for some of us, is to use it to retain the motor in a rocket. In which case, it gets screwed onto and off the rod end bolt or an extension of threaded rod each time the motor is installed and uninstalled.

I swam around in those parts at Zoro a little more.

https://www.zoro.com/b/KEN FORGING/...:Thread Size=5/16"-18&fqv:Thread Size=1/4"-20
Stainless gets expensive, but the difference in cost between 1035 steel and 4140 isn't significant, and on some SKUs, goes the opposite of what you'd think.

I'm reasonably confident that a 5/16-18 rod end bolt forged from 4140 steel will absolutely shred any rocket I'll ever build before it gets close to its yield strength, let alone failing, no matter how far off-axis the loads are applied.

 

[Tractionengines]

Just FYI... Zoro.com is a subsidiary of W.W. Grainger, Inc. Pretty much anything you can get at Grainger, you can get at Zoro.

Grainger, direct to Business with purchase orders, accounts, terms, etc. Zoro.com online order placement with Credit Card payment.

 

[kjhambrick]

A yuuuge benefit to the AT Plugged Forward Closure, for some of us, is to use it to retain the motor in a rocket. In which case, it gets screwed onto and off the rod end bolt or an extension of threaded rod each time the motor is installed and uninstalled.

Dang !

Of course I want the rod ends to be removable from the forward closure !!

Those AeroPac min diameter motor retainers are new since I came back so I didn't think about them

I swam around in those parts at Zoro a little more.

https://www.zoro.com/b/KEN FORGING/...:Thread Size=5/16"-18&fqv:Thread Size=1/4"-20
Stainless gets expensive, but the difference in cost between 1035 steel and 4140 isn't significant, and on some SKUs, goes the opposite of what you'd think.

I'm reasonably confident that a 5/16-18 rod end bolt forged from 4140 steel will absolutely shred any rocket I'll ever build before it gets close to its yield strength, let alone failing, no matter how far off-axis the loads are applied.

Yes, and since this is a 'few of' purchase, the price of the stainless -vs- Black Oxide steel is worth the price.

And like you said, my cardboard and glass cloth rocket or the aliminum forward closure will let go before either of the rod end bolts fail.

-- kjh

 

[kjhambrick]

Just FYI... Zoro.com is a subsidiary of W.W. Grainger, Inc. Pretty much anything you can get at Grainger, you can get at Zoro.

Grainger, direct to Business with purchase orders, accounts, terms, etc. Zoro.com online order placement with Credit Card payment.

Thanks for that info, @Tractionengines

Might be good to know.

-- kjh