Re: Ugghhh cross threaded CW shaft into CW shaft adapter with metal threaded sleeve


Cheng-Yang Tan
 

OK, I got a hold one of the mech. eng. that I work with. He works with SS all the time and here's what he said about preventing galling by changing materials used for the sleeve:

(1) Brass. Soft and will still have the cross threading problem like Aluminium.
(2) Silicon Bronze. It is as strong as SS. But it's a lot more expensive than SS.
(3) Zinc coated Steel. Cheap, but zinc will wear down over time and so will need to be replaced.
(4) Black oxide steel. Cheap, but has the same problem as zinc coated SS.


I also asked him about whether having a very clean surface will help prevent galling. Surprisingly, the answer is "No". The problem is that SS surfaces don't get oxidized to form a lube layer. So, in fact, dirt actually helps lube the surface to prevent galling. (The tech I worked with actually said the same thing).

As usual, since I'm clearly not a mechanical engineer, and all round klutz, YMMV :)

cytan








On Tuesday, August 17, 2021, 03:53:26 PM CDT, Don Anderson via groups.io <jockey_ca@...> wrote:


Good articles on galling Cytan. Thread galling is a potential problem with any metal threaded joint but is particularly problematic with SS due the the properties of this SS.
If I had to guess, it is likely you had some contamination in the threads possibly a metal shaving which caused damage to the threads. Once you tried to back it out, the threads became galled. Another possibility is when you last 
installed the shaft that the flat faced surfaces were not fully mated; if they weren't, and there was a gap, it is possible the counter weights pulling down on the pin of the shaft damaged the threads on the the shaft or adapter or both.

I thing the take away on all of this is to insure that the threads (shaft and adapter) are scrupulously clean. I would apply a little anti seize compound and only make up the joint hand tight. Make sure the two flat faced surfaces on
the shaft and adapter are fully mated with a fibre washer in between. 
Just some ideas.
  

Don Anderson


On Tuesday, August 17, 2021, 01:28:35 p.m. MDT, Cheng-Yang Tan via groups.io <cytan299@...> wrote:


The techs I work with use a lot of SS here (vacuum compatibility) and those threaded SS parts easily seize up and gall. That's why they use anti-seize.

Here's a few links that talk about SS on SS:




The mech. eng. whom are nowhere to be found today. I'll get back to you after I talk to them.


cytan



On Tuesday, August 17, 2021, 02:19:51 PM CDT, Roland Christen via groups.io <chris1011@...> wrote:



I thought I had heard it about because SS on SS is always prone to galling
I have never experienced that. SS is quite hard and does not gall in my experience.

Rolando


-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Tue, Aug 17, 2021 2:01 pm
Subject: Re: [ap-gto] Ugghhh cross threaded CW shaft into CW shaft adapter with metal threaded sleeve

Hi Rolando,

This thing about using brass could be an old wive's tale that I thought I had heard it about because SS on SS is always prone to galling. Let me talk to the mech. eng. that I work with to see what they think.

It's definitely possible that it is dirt that caused the seizure, but it could easily be the SS on SS galling problem.

Just out of curiosity, do you use any type of grease or anti-seize on the threads of the CW shaft? 

cytan


On Tuesday, August 17, 2021, 12:22:52 PM CDT, Roland Christen via groups.io <chris1011@...> wrote:



 Do you think that a brass insert might actually be better rather than SS?
In talking with our machinists here, they don't think that using different materials will prevent this. It appears some contaminant was present on the threads which then locked up the shaft inside the adapter. Putting graphite on the threads may have attracted or held a bit of metal or other contaminant.

Rolando


-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Tue, Aug 17, 2021 11:43 am
Subject: Re: [ap-gto] Ugghhh cross threaded CW shaft into CW shaft adapter with metal threaded sleeve

Hi Rolando,
   Believe me, I stopped once I felt it got stuck. I know enough to know when to stop :) But I guess, I wasn't fast enough ..,

   Do you think that a brass insert might actually be better rather than SS? The brass insert will just be a perishable that needs to be replaced once every few years.

cytan



On Tuesday, August 17, 2021, 11:39:42 AM CDT, Roland Christen via groups.io <chris1011@...> wrote:



The more important question, is how to not do this again.
If it doesn't thread in easily, don't force it. Unscrew it before it galls the metal and clean out whatever is causing it to not thread in.

Rolando


-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Tue, Aug 17, 2021 11:32 am
Subject: Re: [ap-gto] Ugghhh cross threaded CW shaft into CW shaft adapter with metal threaded sleeve

I owe the guys doughnuts :)

I'll have to ask a real machinist to do this and that'll cost me lunch :) 

I have to get a new CW adapter anyways, so it's more cost effective to buy both directly from AP.

The more important question, is how to not do this again.

Suggestions?

cytan

On Tuesday, August 17, 2021, 11:29:09 AM CDT, Geert <geert.vandenbulcke@...> wrote:




You still have a perfectly good counterweight shaft if the machineshop cuts new thread on it, it will only be some inches shorter.

Geert

--------

cytan

P.S. I'll be ordering a new CW shaft + adapter today ...


--
Roland Christen
Astro-Physics

--
Roland Christen
Astro-Physics

--
Roland Christen
Astro-Physics

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