My little Chinese BALLS 2012 Project

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Will this project meet its stated goals? [See slide 2]

Yes
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Not a snowballs chance in hell
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Maybe
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Total votes: 0

Passaretti
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Re: My BALLS 2012 Project

Postby Passaretti » Mon Apr 30, 2012 2:26 am

What I think will help will be to switch to a thicker wall for welding. This is a very easy thing to do right now. I can get the same OD tube in 0.25" or 0.5" wall thickness. I'm going to bring the assembly into work to have the machinist take a look at it tomorrow. Pretty sure our shop can't handle the boring, but I have a few other shops in mind. Ideally, the same shop can do the welding and post machining.

Thanks for the input guys.

Mike
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Re: My BALLS 2012 Project

Postby PK » Mon Apr 30, 2012 10:06 am

Agree.
If you went to a 0.5" wall tube, you could address another potential problem.
Unless you have two welders, working on both sides of the fin, then the guy doing the job has to alternate from one side to the other as he stiches.
This will warp the fin. Starting with a milled slot in the tube that the fin is a tight fit into will help this.
PK

Passaretti
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Re: My BALLS 2012 Project

Postby Passaretti » Mon Apr 30, 2012 11:16 am

The fin-can (w/ the fins welded on) ... ya' think the machinist would have any trouble holding it in the lathe to open up the ID?
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FinCan_Assy.jpg
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Re: My BALLS 2012 Project

Postby PK » Mon Apr 30, 2012 11:37 am

Passaretti wrote:ya' think the machinist would have any trouble holding it in the lathe to open up the ID?

He needs to make a plug (actually he needs two) for the end that goes into the chuck. Otherwise you'll end up with a tri-lobed profile..
PK

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Re: My BALLS 2012 Project

Postby Passaretti » Mon Apr 30, 2012 11:57 am

Ok, I watched some videos earlier and saw this (support thingy w/ radial rollers):

Image

Wasn't sure if it was needed for what I'm doing...

What's the second plug for? Are they spaced apart?
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Re: My BALLS 2012 Project

Postby OverTheTop » Mon Apr 30, 2012 1:18 pm

It would definitely fit in my lathe.
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Re: My BALLS 2012 Project

Postby strud » Mon Apr 30, 2012 1:53 pm

I've made one of these previously and started with thick walled tube, welded then bored out on the lathe.

ID was about 80mm from memory. Will post some pics.

Important to make up an accurate and rigid jig for welding of course.

CS

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Re: My BALLS 2012 Project

Postby PK » Mon Apr 30, 2012 10:02 pm

Passaretti wrote:Ok, I watched some videos earlier and saw this (support thingy w/ radial rollers):

Image

That's called a fixed steady. Your job isn't long enough to need one. There isn't anywhere for it run on the aft end of the can anyway.

What's the second plug for? Are they spaced apart?[/quote]
He makes one plug to suit the ID of the unmachined tube.
He inserts this plug and clamps one end in the three jaw chuck.
He machines most of the ID to the correct dimension.
He then machines a second plug to suit the new, larger, ID.
Flips the tube around, new plug in the machined end.
Back in the three jaw and machine out the last bit.
PK

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Re: My BALLS 2012 Project

Postby cryoscum » Mon Apr 30, 2012 10:11 pm

Hi Mike

Are you going to have the completed fin can heat treated again? The welding would lead to localised loss of the T6 temper, so the whole thing may need to be normalised and tempered again. Not sure if you've run some numbers to see if its necessary, but if you are planning to heat treat, it may be worth starting with Al6061-T0 and then, when complete, heat treat the lot to T6.

Cheers
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Passaretti
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Re: My BALLS 2012 Project

Postby Passaretti » Tue May 01, 2012 5:38 am

Short answer - I sure as f*ck hope not! I'm inclined to avoid this at all costs, even if it means scrapping the welded approach all together. I say this mainly because I don't want to even think about what would happen to this relatively thin material after quenching/cooling. Assuming the pre-machining wall thickness is pretty heavy, I would still anticipate the fins to do a little dancing once quenched. Personally, I think I'd be in over my head at this point ... Then again a stack of fire-brick, a box of matches, a propane tank and plenty of ice water sounds like it could be a real hoot ...??

I need to do a little more thinking and page flipping to make sure I understand the potential problem here. However, my gut feel is that one approach to mitigate the undesirable loss of strength is to use more material (thicker fins, thicker wall). As for right now, my fins are 0.198ish at the root edge - call me crazy but I feel this is beefy as is. Increasing the wall thickness of the tube stands to help out on a few different fronts - the obvious one is post weld machining. There will of course be a hit in drag due to the increased cross sectional area but ... so be it.

Additionally, I need to understand the ranges of loads/forces that are expected during flight. This is also necessary to call-out the correct welds to begin with. Again - need to hit the books. I'm operating way outside the realm of my feeble EE degree.... Having looked through some welding resources yesterday, it's not as complicated as I once thought to calculate forces for a given weld/weldment....

Good question though - I hope to put this one to bed soon.

Mike

PS - Is this a good resource for me to follow? http://www.mitcalc.com/doc/welding/help ... ingtxt.htm
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Re: My BALLS 2012 Project

Postby Bourney » Wed May 02, 2012 6:48 pm

I'll probably show my ignorance of all matters metalwork here, and perhaps this would be out of the question budget wise or time wise, but....

What about a one piece unit machined from a solid billet. No welding.
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Re: My BALLS 2012 Project

Postby Scoop1261 » Wed May 02, 2012 7:23 pm

Bourney wrote:
What about a one piece unit machined from a solid billet. No welding.


Ouch! ........ There goes the budget! :oops:

The cost of the billet, whilst not the GDP of a third world nation, is going to be significant to start with.
The difficulty in machining will also have its own complexities and associated costs. I guess if you had a 3 axis CNC lathe/mill laying around the cost would come down, but probably not to where the average hobbyist is going be able to afford it.

Having said all of the above, someone with the right tooling and know how could turn out something without much issue.
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Re: My BALLS 2012 Project

Postby PK » Wed May 02, 2012 7:26 pm

Scoop1261 wrote:Having said all of the above, someone with the right tooling and know how could turn out something without much issue.

Not a snowballs chance in hell!
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Re: My BALLS 2012 Project

Postby Scoop1261 » Wed May 02, 2012 7:38 pm

PK wrote:Not a snowballs chance in hell!
PK



I dunno about that snowball ....... I mean if you had one of these.....

http://www.cncmachine.com.au/mtc_PMX2100ST.php
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Re: My BALLS 2012 Project

Postby cryoscum » Wed May 02, 2012 7:40 pm

Passaretti wrote:PS - Is this a good resource for me to follow? http://www.mitcalc.com/doc/welding/help ... ingtxt.htm


Looks pretty good to me!
As for the tempers, good old wikipedia shows some expected strengths for the different tempers:
http://en.wikipedia.org/wiki/6061_aluminium_alloy
and more here, including effects of welding:
http://www.alcoa.com/adip/catalog/pdf/C ... y_6061.pdf
http://www2.galcit.caltech.edu/~tongc/h ... y_6061.pdf

In short, the temper is locally effected, but hard to say by how much. Knowing that is fine, but using the correct alloy then becomes critical e.g. 7075-O (or TO as I incorrectly called it earlier in the thread) has about the same tensile strength as 6061-T6 (pre-welding), hence a welded 7075 fin can will, inspite of being welded, still be better than a 6061. And doing the heat treatment is also a bad idea, because the results may be unpredictable and you'd have to machine again at the very least. This from http://www.aluminum.org/AM/Template.cfm ... 5e71a88258
1.JPG


When all is said and done, 6061 is probably not ideal, but I'm going to use it for my Balls attempt too. Just use more of it I guess...
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