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EX motor casings?

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Gunkie

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I was reading a thread and wanted to ask a question that was not in-line with the ongoing thread.

To paraphrase AlexNUMB, his 5-grain, 75mm, M-motor casing developed a bubble after a test firing and that it would cost $15 to replace.

I'm so new to EX motor development that can't imagine a $15 M-motor case. I guess my questions are:

1. Do I need to develop skills and a small metal shop to produce $15 75mm motor casings?
2. If not, who sells reusable motor casing of this caliber for $15.

I'd hate to do a static test using a 76mm Loki Research case and have it bubble. Costs range from $70-$200.

Thanks! I'm still very low on the EX learning curve.
 

AlexNUMB

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Hey Scott--

Here's the thing. I have a good friend of mine who is doing the machining of casings for me.

We picked up a 24' stick of .125" x 3" OD aluminum for $140. 30" of that works out to be about $14.59 or so (which is what the 6K case is... 30").

If I had to pay for machining time, I am sure that figure would run much higher.

I have seen the Loki hardware and it is top notch, although, imho, the larger hardware is over priced... by the time you are ready to fly a P motor, you can source the casing and the closures for far less. ($150 for a 6' chunk of 6" OD .25" wall tubing, locally)

If you know any machinists in your area, buddy up with them. It will save you lots of money on hardware (casings, closures, nozzles) in the long run.

Alternatley, when it comes time to procure a set of snap ring style hardware, it is often cheaper to do a group run of it. i.e. buy the material locally, find a machinist local to you, and have him run off 20 or 30 cases. Amortize this cost accross your local flying group and your per unit cost drops well below Loki, Mostly Missiles, or any of the other hardware suppliers out there.

Let me go on record as saying that the amount of time involved with taking all of these routes is sometimes more of a PITA than it's worth. I'm seriously thinking of picking up a set of 54mm stuff from Loki in the near future, because the time involved with machining, etc, will take awhile until delivery.

--Alex
 

Gunkie

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Thank you! That is a great way to distribute the costs and develop a resonable way to build larger caliber motors. I have a brother in-law who is a machininst that may be able to help me out in the future.

I've purchased a set of the Loki 38mm HW which I plan to play around with during my initial foray into EX motor making. I think this will keep me busy for a while.

Thanks again for the explaination!
 

Loki

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Originally posted by AlexNUMB
Hey Scott--

Here's the thing. I have a good friend of mine who is doing the machining of casings for me.

We picked up a 24' stick of .125" x 3" OD aluminum for $140. 30" of that works out to be about $14.59 or so (which is what the 6K case is... 30").

If I had to pay for machining time, I am sure that figure would run much higher.

I have seen the Loki hardware and it is top notch, although, imho, the larger hardware is over priced... by the time you are ready to fly a P motor, you can source the casing and the closures for far less. ($150 for a 6' chunk of 6" OD .25" wall tubing, locally)

If you know any machinists in your area, buddy up with them. It will save you lots of money on hardware (casings, closures, nozzles) in the long run.

Alternatley, when it comes time to procure a set of snap ring style hardware, it is often cheaper to do a group run of it. i.e. buy the material locally, find a machinist local to you, and have him run off 20 or 30 cases. Amortize this cost accross your local flying group and your per unit cost drops well below Loki, Mostly Missiles, or any of the other hardware suppliers out there.

Let me go on record as saying that the amount of time involved with taking all of these routes is sometimes more of a PITA than it's worth. I'm seriously thinking of picking up a set of 54mm stuff from Loki in the near future, because the time involved with machining, etc, will take awhile until delivery.

--Alex
Replacing your case cost you more than $14.59. First you had to lay out $140 for the material, sure you had some left over, but it's still money out of pocket. Then you had to impose on your "good friend" to do the machine work. He's gonna hit you back for a favor some day, nothing is free. At the end of this you have a case that may work, but isn't anodized and won't hold up as well over many firings. You didn't mention whether the tube was draw or extruded. Some people won't know or care what the differences are, but it's details like this that make Loki hardware worth every penny.

EXers may be able to "buddy up" to a machinist, but making good motor parts takes time and why should you expect a professional to work for less than they are worth? Maybe the free machine work that you got is worth just what you paid for it. Gonna bet your rocket on that?

Getting together for a group buy from your local machinist is exactly how my business got started, and I will guaranty that the only way my prices can be beat is by either getting someone to donate their labor or by building an inferior motor. I do this every day. My hardware is either better or less expensive (and usually both) than anything else on the market. Want to buy 20 casings for your club? Look no further than Loki as I'll be happy to make deals on bulk purchases.

Finally, the prices on my 152mm motors only seem high until you factor in the cost of building your own and having it blow up. My 6" motors are the best and that always commands a premium price. Purchase one and you'll know that you have the best available hardware and the assistance of someone who has successfully fired motors of this size. You can buy experience here. Was that $150 piece of 6" tube you saw any good? Will it hold the pressure? Loki 6" motors are hydrostatic tested to 1.5X operating pressure. There were four 6" motors fired at BALLS last year. One was professional (Kosdon) and of the other three one worked and two catoed. Not a very good track record.

In short, you can spend less but you won't save.
 

AlexNUMB

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Hi Jeff!

Originally posted by Loki
Replacing your case cost you more than $14.59. First you had to lay out $140 for the material, sure you had some left over, but it's still money out of pocket.
You are absolutely right! It did take more out of pocket. Buying a cut piece would definatley run you more through places like www.onlinemetals.com etc.

On the flip side, we made 2 full sets of hardware out of that tube and still have a little bit left.

Then you had to impose on your "good friend" to do the machine work. He's gonna hit you back for a favor some day, nothing is free.
You met Dave at BALLS! He's a wacky rocket guy too... The only favors he hits me up for is not hitting him up for gas money when we go to launches... and borrowing my lawn mower. Oh and drinking all my beer... :D

Of course not everyone is lucky enough to have a machinist/auto mechanic for a best friend. :)

At the end of this you have a case that may work, but isn't anodized and won't hold up as well over many firings.
Anodizing is cheap. There's a place down the street from us in Portland (Electro-Chem Metal Finishing, Inc) that does small runs in their stock colors (i.e. red, black, gold or light blue) for $45 in type I or type II anodizing.

You can also do anodizing at home your self: http://www.focuser.com/atm/anodize/anodize.html


You didn't mention whether the tube was draw or extruded. Some people won't know or care what the differences are, but it's details like this that make Loki hardware worth every penny.
I should have mentioned that... we use drawn tubing. We've been getting our supplies from Tube Services. Same place Purple Woody gets his stuff. They have dealers on the West Coast, but I don't think they have any on the East Coast. (http://www.tubeservice.com/)

Of course Aluminum prices keep going up... :(

EXers may be able to "buddy up" to a machinist, but making good motor parts takes time and why should you expect a professional to work for less than they are worth? Maybe the free machine work that you got is worth just what you paid for it. Gonna bet your rocket on that?

Getting together for a group buy from your local machinist is exactly how my business got started, and I will guaranty that the only way my prices can be beat is by either getting someone to donate their labor or by building an inferior motor. I do this every day. My hardware is either better or less expensive (and usually both) than anything else on the market. Want to buy 20 casings for your club? Look no further than Loki as I'll be happy to make deals on bulk purchases.
Which is exactly why I recommend your products to folks who ask! :)

The truth is, alot of EX'ers are of the "do-it-yourself" mentality, myself included. However there are those who aren't. I wholeheartedly recommend your company to folks who don't want the hassle of doing it themselves.

I also get asked about altimiters quite a bit. I often find myself recommending the ARTS as a superior product than the RDAS.

Finally, the prices on my 152mm motors only seem high until you factor in the cost of building your own and having it blow up.
Ooooh.... Cheap shot! Heh LOL... :D

As you know, our P motor cato'd last year. How embarrassing that was. You even have pictures of it on your website. An immortal testament to your superior products. :)

Last year we tried it with a 1/8" wall threaded casing. This year I'm going with a .25" dual snap ring design.

My 6" motors are the best and that always commands a premium price. Purchase one and you'll know that you have the best available hardware and the assistance of someone who has successfully fired motors of this size. You can buy experience here.
No doubt you have the best 152mm EX hardware on the market right now. As I said before, all of your products are top notch.

For me, part of the fun of all of this is trying new designs and (again) doing it yourself. I surely hope I didn't sound like I was disrespecting you or your products with my previous post.

Was that $150 piece of 6" tube you saw any good?
Haven't actually seen it yet. I just called up the supplier and said, "I'd like a quote on some 6" OD x .25" wall drawn 6061 aluminum tubing, please."

He said, "Well, there's a minumum 12' order. We can cut it into 6' sections for you for free. The tag on that looks to be $25 a foot. If you get 2 lengths, I'll discount you 20%"

So, spec wise, it's what I'm looking for. I'll let you know when I pick it up next week... :)

Will it hold the pressure?
Dunno... This year, we intend to static test. :)

Loki 6" motors are hydrostatic tested to 1.5X operating pressure.
Each motor is tested before leaving the shop? Wow... I guess that would play into the price a bit. That's a good tip... I just googled and found a place in Portland that can do it... looks like it will cost about a hundred bucks or so. I'm definatley going to do that on these casings. :)

There were four 6" motors fired at BALLS last year. One was professional (Kosdon) and of the other three one worked and two catoed. Not a very good track record.
One could argue that the motor Mark made was professional, considering what he does for a living. :)

In short, you can spend less but you won't save.
Buy LOKI!!! It's great hardware... Didn't mean to imply otherwise!!!

--Alex
 

Loki

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I knew that you weren't dis'n me Alex :)

EXers do like to do things themselves, but there's only so many hours in a week and everyone has to decide where to put their efforts. To the newcomer motor hardware looks easy and a good place to save some money. But it's a false economy in most cases. (pun intended :D )

The double snap ring idea is something that I've seen done, but it makes no sense to me. I haven't done the tests, but it's my gut feeling that two snap rings will be weaker than one snap ring, due to the wider groove. What possible good could it do?

Ok, if you count Mark's motor as professional, then the score was pros 2 and amateurs 0.
 

jerryb

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Originally posted by Loki
Will it hold the pressure? Loki 6" motors are hydrostatic tested to 1.5X operating pressure.
new to the HP sport of rocketry.... but OLD to the machining/testing business... 18 year design/production manager for an oilfield tool machine shop.

we hydro tested all of our pressure equimpement to 2x working pressure w/ 15min at pressure with no visible loss of pressure passing... unless the working pressure got over 15k psi then we went to 1.5x.

we had a saying... the trick is not getting the genie IN the bottle... its KEEPING it there!!

just how much pressure are we talking about when you say your 6" motors are tested to 1.5X op pressure?? yield of 6061t6 heat treated alum is around 35K... but i've seen it fail at 1/2 that many times...

also have seen voids in alum stock before as well that could lead to catestrophic failure under a shock force of ignition.. where the gradual buildup of pressure from hydro testing would hold just fine..

not being nosey or anything... just wondering?? I have a few pumps and hoses left over from those days...

later
Jerryb
 

Loki

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Originally posted by jerryb
new to the HP sport of rocketry.... but OLD to the machining/testing business... 18 year design/production manager for an oilfield tool machine shop.

we hydro tested all of our pressure equimpement to 2x working pressure w/ 15min at pressure with no visible loss of pressure passing... unless the working pressure got over 15k psi then we went to 1.5x.

we had a saying... the trick is not getting the genie IN the bottle... its KEEPING it there!!
Here! Here!


just how much pressure are we talking about when you say your 6" motors are tested to 1.5X op pressure?? yield of 6061t6 heat treated alum is around 35K... but i've seen it fail at 1/2 that many times...
Typical design pressure is 1000psi, so 1.5X is 1500psi.


also have seen voids in alum stock before as well that could lead to catestrophic failure under a shock force of ignition.. where the gradual buildup of pressure from hydro testing would hold just fine..
Yes, voids, cracks, etc. are type of things I'm hoping to discover during testing. The gradual pressure build up typical of hydro testing isn't ideal but it is still a useful test and inexpensive when compared to other methods (like X-ray).
 

jerryb

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Originally posted by Loki
Here! Here!

Typical design pressure is 1000psi, so 1.5X is 1500psi.

Yes, voids, cracks, etc. are type of things I'm hoping to discover during testing. The gradual pressure build up typical of hydro testing isn't ideal but it is still a useful test and inexpensive when compared to other methods (like X-ray).

ahh.. in relation to what i'm used to testing..thats relatively low pressure for a 6" vessel.. although when you multiply the 5.5" id X 1500 psi.. theres still a heck of alot of force pushing on those end caps... i think i'd be more concerned about thread choice on the caps failing/shearing... than the stock failing... <g>

nothing more sickening than the "SCHREECH" of a galling thread in aluminum...eh?

these motors definately sound like a project for a cnc turning center...
 

AlexNUMB

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Originally posted by Loki
Here! Here!
Typical design pressure is 1000psi, so 1.5X is 1500psi.
You are a madman, Jeff... :)

I still don't have the confidence. I tend to run my motors at a lower pressure. say 500psi on pressure, 700 peak or so? I stay toward the "just-above-chuffing" KN range at this point.

Oh yeah and your dual snap rings question... I'm not sure the scientific reason for dual snap rings. Honestly, I'm copying someone else on this one (i.e. Lyngdal's 138mm O casings).

When our Motor cato'd at BALLS last year, the steel retaining snap ring was a little bent out of shape. I would think that the thicker amount of steel would be less likely to blow out due to bending/bulging.

--Alex
 

Loki

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Originally posted by AlexNUMB

When our Motor cato'd at BALLS last year, the steel retaining snap ring was a little bent out of shape. I would think that the thicker amount of steel would be less likely to blow out due to bending/bulging.
Just put a steel washer before the snap ring and get the same result. I'll ask John about it, but I'm fairly sure that doubling up the snap rings is rocket voodoo, rather than rocket science.

-Jeff
 

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