[roc-chat] Re: Using Aluminum Hardware: Lighter but strong enough?
- From: "jim" <jim@xxxxxxxxxxxxxxx>
- To: <roc-chat@xxxxxxxxxxxxx>
- Date: Sun, 19 Aug 2012 21:58:16 -0700
Adjustable tap? or do you mean an adjustable threading die (taps make
internal threads, dies make external ones.)
Unless there's something I haven't understood yet, I haven't bought a
threading die yet that didn't need to be opened up wider to
make the correct pitch diameter on a stud.
Jim G
_____
From: roc-chat-bounce@xxxxxxxxxxxxx [mailto:roc-chat-bounce@xxxxxxxxxxxxx]
On Behalf Of Kurt Gugisberg
Sent: Saturday, August 18, 2012 3:07 PM
To: roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Re: Using Aluminum Hardware: Lighter but strong enough?
Hey Richard. Great work on the testing. It confirms my thoughts on fin
attachment. I am interested in seeing how nylon nuts hold up under high
shock loads. After pulling steel eye bolts straight and seeing fender
washers pulled through 1/2 plywood bulkheads, I have my doubts about
aluminum and nylon holding up.
Also, what is an adjustable 10/24 tap?
Kurt
-----Original Message-----
From: Richard Dierking
Sent: Aug 18, 2012 10:20 AM
To: roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Using Aluminum Hardware: Lighter but strong enough?
Since I've had the opportunity to go through some of my old projects lately
(cleaning out the garage), I've been taking some rocket airframes apart
including some destructive testing. It's interesting to see what holds and
where weakness occurs. For example, for through the wall fins, the surface
fillet doesn't seem to do much. The most important thing is that the fin
slot is tight. So the lesson here is to create tight slots and don't expect
for epoxy to fill the gap and hold strong.
For attaching the fin, creating many small slots (1/8" deep) in the root
edge for attachment to the motor mount works well and doesn't require much
epoxy. Bryan showed me how to do this. If the surface is roughed-up with
80 grit sand paper a fillet doesn't seem to be required. The failure I'm
seeing is the motor mount tube material. The surface of paper tubes peels
and phenolic fractures and peels. And, as expected, fiberglassing the root
to the motor mount tube works best, and it doesn't require much resin. In
fact, the lay-up can be pretty dry and it seems to do fine. The extra
amount of resin I commonly use for a good finish is not necessary. I guess
drilling small holes in the motor mount tube where the fins are attached
might help hold the epoxy bond between the fin and the tube. I haven't
tried this yet.
Another thing I've been experimenting with is the altimeter bay. This is
the important part of this message, and sorry it took so long to get around
to it. Recently, I've done a few deployment tests using 3/16" aluminum rods
that are tapped to 10-24 tread and nylon hardware (nuts and wing nuts) to
hold the bay together. Also, I reduced the size of the U bolts
significantly. I replaced the 1/4"-20 U bolts (1" wide) with U bolts from
Home Depot that are in packs for cable clamps (5/8" wide). Even though the
cable clamps say they are 1/4" size, the nuts are actually 6 mm metric.
Just to give an idea of the weight savings; Replacing the steel hardware
and reducing the size of the U-bolts on a 4" diameter altimeter bay reduced
the weight from 495 grams to 325 grams (34% less). Also, instead of using
metal fender washers, I've been fiberglassing both sides of the bulkheads,
and switched from 1/4" thick plywood to 1/8" thick. So, no more fender
washers. I'm wondering if I could make aluminum U-bolts without causing too
much stress on the aluminum rod during the bend?
The deployment tests have gone so well, that I just ordered some 3/16"
high-strength aluminum (alloy 7075) rod, aluminum nuts, and other
light-weight hardware from McMaster-Carr. I also ordered an adjustable
10-24 tap. I would appreciate any advice on threading this new aluminum
rod.
So, do you think this will hold? Are there problems with using aluminum
hardware I need to consider.
If you're interested in using light-weight materials and techniques for your
project, I would like to discuss at the September launch. I'm planning on
launching a two-stage rocket with the 'new' hardware.
Richard
-- ROC-Chat mailing list roc-chat@xxxxxxxxxxxxx
//www.freelists.org/list/roc-chat
Other related posts:
