Matilda Bow Saw.

Discussion in 'Saw Makers Forum' started by planemaker, Nov 18, 2009.

  1. planemaker

    planemaker Active Member

    Messages:
    39
    The traditional wooden framed bow saw has some natural design design flaws when it comes to transferring all the inward pressure (applied by the upper tightening cord) to create outer pressure too tension the lower blade.

    You will not come across too many frame breakages that occur below the stretcher!

    At a point during this upper tightening,compression at both ends of the stretcher joints prevent further free outward movement within the lower half of the arms.

    At what point this compression stops the free movement at the stretcher is most likely a reflection on the type of timber used within the wooden frame. The harder the timber is resistant to being compressed,the further the lower arms will free move.

    Using a hardwood timber versus a softwood timber when designing the bow saw frame comes at cost. That cost is additional weighting.

    (These are my own personal views).


    I have designed a new wooden framed bow saw that overcomes most of these primary issues.I named it the Matilda Bow Saw.(Australian designed). Will keep you informed on my progress.

    Regards Planemaker.
     
  2. planemaker

    planemaker Active Member

    Messages:
    39
    Hi all. This is the 12\" Matilda Bow Saw.


    [​IMG]

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    The saw steel tensioner generates effective outward pressure to the lower half of the frame,creating tightening of the bow saw blade, while not over stressing the upper frame. The main role of the twisted cord is to provide rigidity within the frame.

    Regards:planemaker
     
  3. ray

    ray Administrator Staff Member

    Messages:
    671
    Hi Planemaker,

    Interesting concept, if I understand it correctly, the blade tension comes primarily from the spring steel strap rather than from the twisted cord.

    I imagine the amount of tension would depend on the stiffness (thickness) of the spring. On that basis I can\'t see that you would get sufficient tension using 20 thou plate. You might be better off with 40 or 50 thou?

    Regards
    Ray
     
  4. planemaker

    planemaker Active Member

    Messages:
    39
    Hi Ray. The 0.040\" gives adequate tension to the bow saw blade. From what I understand,0.042\" is available as new stock,and is close enough.

    The role of the cord is to keep the upper arms tight against the horizontal spreader.

    If you can provide me with the 0.042\" saw plate at some later
    order, it would be much appreciated.

    Regards Planemaker.
     
  5. ray

    ray Administrator Staff Member

    Messages:
    671
    Hi Planemaker,

    The success of the idea, really depends on getting enough tension in the blade. Which in turn depends on the spring steel strap.

    Haven\'t really thought it through but what about trying some old used bandsaw blades? 3/4 or greater?

    The other thought that comes to mind is to put more than one point of attachment to the stretcher.

    Regards
    Ray
     
  6. planemaker

    planemaker Active Member

    Messages:
    39
    Hi Ray. Thanks for the reply. Bandsaw blade is typically 0.025 gauge from what I understand so it would not be an ideal benefit in this design. As for more attachments to the stretcher, the steel band already makes contact with a 4\" area of the stretcher.This is probably at a maximum area if a natural arc is to be maintained that focuses most of the expansion force at both ends, nearer to the bow saw blade.

    The feedback and advise is always welcome Ray.

    Regards Planemaker.