Rack Hook Landing on the Point of a Tooth

Discussion in 'Hints & How-to's' started by bangster, Aug 16, 2018.

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  1. bangster

    bangster Moderator
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    #1 bangster, Aug 16, 2018
    Last edited: Aug 16, 2018
    Fixing A Rack Tooth Problem
    Thanks to :
    Shimmystep, for the article and the picture
    TeaClocks, for suggesting that it ought to be in this forum
    novicetimekeeper, for telling me that Shimmy was the author
    bangster, for trying to make the description clearer
    and for adding it to this forum
    Shutterbug, for being in on the original dialog
    If I missed somebody, let me know.
    --bangster


    If the rack hook is consistently landing on the tip of a rack tooth, instead of between the teeth, then the rack tail is out of adjustment. A slight adjustment of the angle of the rack tail and the rack will likely give good results. If the tolerance increases or decreases over the length of the rack then it is the wrong length.




    rack til pic.jpg

    To find the correct tail length:



    1) Measure the distance that the rack teeth must fall for 12 to drop, i.e 12 teeth from tooth 1 ”C" to tooth 12 “B”. Call that Length C-B. Draw that line on a piece of paper.

    2) Draw another line that represents the distance between the centre of the racks pivot point and the 12th tooth, A to B. It has Length A-B

    3) Then draw another line from the centre of the rack pivot point to the 1st tooth C. It has Length A-C. Lines A-B-C form a triangle

    4) Then measure distance F, i.e the length of the drop from the 1 o clock plateau to the 12 o clock plateau. Call it Length F

    5) draw a line of Length F between lines A-C and A-B. It will only fit in one place. Call the points where it touches the two lines D, and E.

    6) The lengths A-D and A-E will be equal. That is the correct length for your rack tail, i.e distance between centre of the racks pivot point and the centre of the chamfered pin that is fitted at the end of the rack tail
     

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