Re: Re: Rubber test figure

From: Bill Gowen <b.gowen_at_comcast.net>
Date: Sun, 8 Mar 2009 15:30:04 -0400

Tony Mathews tests catapult rubber to loads that make me shudder. He has a knot that works for this.

  ----- Original Message -----
  From: Tapio Linkosalo
  To: Indoor_Construction_at_yahoogroups.com
  Sent: Sunday, March 08, 2009 3:26 PM
  Subject: Re: [Indoor_Construction] Re: Rubber test figure


  RLBailey_at_care4free.net wrote:
>
> I tried stretch testing motors of F1D size to assess quality but found
> that the knots, which work OK when winding, repeatedly fail on stretch
> testing. I found it easier to test via winding since I could get much
> nearer to maximum and therefore abandoned the stetch method.
>

  Yup, the knot is a problem. Also when testing and breaking in F1B
  motors. For several years every one or two motors out of 10 failed
  during the process, many of these from the knot, that cut trought the
  ruber and then broke away. When one strand of a fully stretched motor
  fails, the motor starts to unwind, and the strands cut trough each
  other, making the whole motor unrepairable. Eventually I found a knot
  used by Bror Eimar, "norsk strykknute", that can stand the pull of the
  test. This knot needs to be tied into lubed motor, in unlubed rubber the
  knot will cut and damage the strand. However, I have found that when
  using proper thick silicone for lubing is too slippery and the knot will
  slip, instead I need to use thinner (1000 cts) silicone for lubing the
  know, this stuff lets the knot slip when tightened, but then lets the
  knot "stick" when tight enough.

  -Tapio-

  


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Received on Sun Mar 08 2009 - 12:30:09 CET