need ideas- joining 2 small shafts

Question

need ideas- joining 2 small shafts

subsearobot (Mechanical)

(OP)

2 May 19 21:55

Hello all!
I need a pushrod fabricated at a decent volume, looking for advice on methods to look into.

How to permanently join two pieces, each about 3" long.
It's a pushrod, though it intermittently rotates, so we do not want risk of self-disassembly. it needs to be a permanent joint.

Will need about 100,000/ year.
A: 3/32" hex, 316 stainless or possibly 17-4 hardened
B: ~.100" round stock, aluminum, threads machined at one end
Runout ~.001" (002" or maybe even 003" if there's a large cost demarcation there)
Straightness better than .005" over the entire length if possible
Must withstand autoclaving, so no Loctite

It is not a candidate for Swiss machining from one piece (of stainless)
Consultant wants threads and Loctite (see previous about autoclave and loctite). Their vendor does not want to do an interference fit because of our straightness needs.
Can the joint be crimped or swaged?
Distorted threads and a countersink for alignment? (it's still threads, so I don’t like it.)
How would you make this?

Thanks!

Metalfixer (Mechanical) · Answer 1 · 2019-05-03 11:18:42

RE: need ideas- joining 2 small shafts

Metalfixer (Mechanical) 3 May 19 11:18

Cross drill and rivet?

EdStainless (Materials) · Answer 2 · 2019-05-03 14:31:33

Why can't it be one piece? It would be less expensive and more reliable.
You can friction weld 316 to many Al alloys. The parameters need to be very tightly controlled in order to get good results.

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P.E. Metallurgy, Plymouth Tube

btrueblood (Mechanical) · Answer 3 · 2019-05-03 15:44:47

You might have good luck rotary swaging the 316 down onto the aluminum. But not seeing why you can't just have one piece.

There are loctite formulations that can withstand some fairly high number of steam cycles, you might contact Henkel to find them.

EdStainless (Materials) · Answer 4 · 2019-05-03 17:09:54

Or ScothWeld 2214 for a high temp adhesive.

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P.E. Metallurgy, Plymouth Tube

subsearobot (Mechanical) · Answer 5 · 2019-05-06 15:53:19

Ed,btrueblood, I thought 1 piece too, but perhaps the hex makes it too intensive? I've asked several shops and all declined for 1 piece build. it is a pretty small hex.

I'll look into rotary swaging and friction welding... good call

thanks!

btrueblood (Mechanical) · Answer 6 · 2019-05-06 17:59:39

SSR, see if you can find a shop, likely near a local airport, that supplies control cables for aircraft; they will have the rotary hammers and dies for swaging fittings onto a/c control cables. The shop I know of is called "University Swaging" in Seattle, WA. If you can copy a standard aircraft control cable fitting (my design used a close analog of MS20663), these shops will likely have the dies to fit for their swaging machines.

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need ideas- joining 2 small shafts