[AR] Re: machining aluminum pipe
- From: Norman Yarvin <yarvin@xxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Thu, 6 Dec 2018 00:29:28 -0500
On Wed, Dec 05, 2018 at 07:59:03PM -0800, Paul Breed wrote:
Carl the way I would do this is to get some 8" OD steel pipe.
Weld Plates on the ends so I can be turned between centers on a lathe....
Turn it down to your Id.
Cold soak the steel with LN2....
Heat the aluminum pipe.....
Shrink the aluminum over the pipe....
(This will true up the pipe )
Now turn down the outside, leaving some beefy end on the aluminum pipe....
Now set up to pull the aluminum off the steel, IE Press or cable pull....
Put LN2 inside the steel and heat the Al, till it comes off...
If one had to do many many of these, I'd set the steel up with a slot that
had a machined piece go in....
IE Set up steel pipe in mill and machine opposing Tee slots on both sides
of length wise slot....
Machine piece for slot, drive into pipe....
Machine round, drive piece out of slot install aluminum reinstall piece in
slot... when time to remove aluminum drive piece out of slots...
Might also need parts inside pipe to pull both sides together to collapse
slot....
The phrase for the latter sort of setup is "expanding mandrel", though
usually they have more than two slots. See, for instance:
https://www.xpandrel.com/5000series.html
(Not a brand recommendation, just one of the first few links to pop up
in a quick search. And of course an expanding mandrel 7+ inches in
diameter and 24 inches long isn't going to be cheap.)
It doesn't solve everything, though. If your tube is banana-shaped to
begin with, for instance, installing it on the mandrel will bend it
straight for the moment, but it'll spring back once the mandrel is
removed. (Assuming there's only a slight banana-shape aspect to it,
of course; no starting material worth working with here will have a
visible banana shape.)
It also doesn't address the challenge of machining the ID. The answer
there might be to not machine the ID but to take it as given and
design the rest of the rocket around it. But the request was for
machining both ID and OD. (It of course was also for a shop to do the
work, not a DIY recipe; but even when hiring a job out it's usually
best to know how it's done.)
Anyway, a 0.300 wall might be thick enough that one could do without
the mandrel, perhaps using a traveling steady rest.
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