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  • Modified stub acme thread plating allowance help please

    Discussion in 'The main mechanical design forum' started by valleyboy, Mar 31, 2010.

    1. valleyboy

      valleyboy New Member

      Mar 2010
      Likes Received:
      I'm new here so hello everyone.

      I'm working on some aluminium parts that feature a three start modified stub acme thread. The parts are cylindrical electrical connectors, so we will manufacture a mating pair of these threads, this is the thread used to couple the two mating connectors together.

      The problem is that I have a set of dimensions that we are currently working to that are not derived from anything that I can find in any 'standard' stub acme thread data charts (in machinery's handbook for example). The modified dimension set enables us to cut threads with an allowance for a 13um plating thickness. We have been producing parts to this modified set of dimensions for a while. I now need to derive another set of dimensions that will enable us to produce parts that will be subject to a 30um plating thickness.

      Can anyone offer some advice on where to start with this please? I am confused after looking at the simple formulae that can be found in machinery's handbook etc. Results to calculations do not match the dimensions I already have for the 13um data set.

      Hope this makes sense. I'd be very very gratefull for some guidance with this please :oops:

      I think we could potentially produce a working, mated pair of threads, but these could then fail to mate with our competitors parts.


      P.S. I could post the current data that I have if required.
    3. mvalenti

      mvalenti Well-Known Member

      Nov 2009
      Likes Received:
      I may be waaaaay over symplifying this, why does it have to be so tight? In my mind, electrical connectors with twist lock or some derivitives are fairly loose in terms of thread engagement up until the point of max engagement. At that point it comes down to some kind of compression, spring member, or detent.

      In addition, I know that your going to get palting thickness differences just due to the process and the geometry of your acme stub-like thread form. Sometimes you may want to approach this along with your plater, have them run some sampling of test pieces, and find wich recipe works best in your application and develop a specification off of that.

      Hope this helps.

    4. ConnectUTS

      ConnectUTS Active Member

      Sep 2009
      Likes Received:

      I know that you may have these questions answered internally. I am trying to confirm where you are in the process.

      If you are having trouble deriving your thread forms and making them work with the modified dimension, have you validated the original threads?

      Do the threads meet the expected specifications before and after plating?

      Do the final threads of your parts always mate with your competitors parts?

      What class of fit are you looking to obtain? There a number of standard fits for acme threads.

      You should be able simply remove an additional material from all surfaces. Are you doing this for both the female and the male side of the threads?

      Have you confirmed that you are actually plating on 30um additional material on all surfaces?

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