Designing basic deadbeat escapement

Discussion in 'Clock Construction' started by Knas, Feb 7, 2017.

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  1. Knas

    Knas New Member

    Feb 7, 2017
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    Hello

    I'm new to this forum. I'm trying to design a basic 30 tooth deadbeat escapement but i'm having some issues finding consistent and complete information. I'm trying to make a basic cad drawing and was going to follow up making a brass prototype to verify my design. This is coincidentally *not* for a clock or watch but i am using the escapement in a mechanical design intended to advance a perforated tape 4mm per pallet cycle and it needs to have zero (or near zero) cumulative error. I figured a escapement design would be the easiest way of achieving this with near-perfect accuracy. Any information highly appreciated!

    Thanks

    Knas
     
  2. Tinker Dwight

    Tinker Dwight Registered User

    Oct 11, 2010
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    I don't think you'll be to happy using a deadbeat escapement.
    Your advancing requires an exact diameter wheel to advance
    the tape.
    It is better to us pawls that are linear in motion.
    The advance of tape over a wheel depends on the thickness
    of the tape. Tape laying flat and push with a ratcheting
    action is more accurate.
    The deadbeat as you've suggested is simple. The pallets follow
    a circular path for the locking surfaces.
    The pallets need to be a little less than 1/2 the spacing between the
    teeth. In a clock, we usually set them to 40-45%.
    The teeth on the escapement wheel need to have a backwards rake
    to clear both the exit pallet and entrance pallet.
    A ratchet wheel and a pawl to push it is more consistent. In order to
    get a deadbeat to work it has to have a drop for clearance.
    The pawl and ratchet has 0 drop and can be driven from a crank.
    What problem are you having.
    Tinker Dwight
     
  3. Knas

    Knas New Member

    Feb 7, 2017
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    So what i'm trying to do can be seen here; https://vimeo.com/144454867

    It seems to me that this works really well, the main issue i'm having is that the pallets are not designed right so there's an in-between position where the wheel can spin freely which can cause major problems some times. It took me quite some time just to make it work as well as it does thus i was hoping to find a thorough description of how to properly design the escapement bottoms-up.

    The parts are machine cut so the size should be more or less dead on (cut with a cnc-router right now, i might go for plasma or water jet in the future) - but i guess you're right that there could be cumulative errors after a few hundred turns or so? I thought i'd use this design since clocks are generally very exact devices (my dad was a clockmaker). How would the ratchet be more beneficial? Also, as can be seen in the video i'm using the downwards motion of the machine in question in order to advance the tape - this is something i'd like to keep doing, not sure how i would do this with the ratchet?

    Many Thanks!

    Knas
     
  4. Tinker Dwight

    Tinker Dwight Registered User

    Oct 11, 2010
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    You need to make the pallets longer. Not much just enough to make it stop on each
    rock of the anchor.
    You may have issues with the straight escape wheel teeth.
    They need to have a bout a 15-20 degree rake opposite
    the direction of rotation. The amount depends on the amount of over travel.
    I wasn't able to view the video because of the machine I'm on right now.
    I'll look at it later when I have a different machine.
    Tinker Dwight
     
  5. Tinker Dwight

    Tinker Dwight Registered User

    Oct 11, 2010
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    I just looked at the video. The pallets are tapered, unlike a clock that has
    impulse faces. I see no reason that it shouldn't otherwise work.
    The locking surfaces need to follow an exact circle of the arbor.
    The exit needs to be 1/2 of a tooth radius larger than the entrance
    for the LOCK surface.
    You may need to make them both slightly smaller radius arc to compensate for
    the width of the teeth tips ( maybe 2-5% smaller ). The anchors arbor needs
    to be mounted such that the average radius of the two lock surfaces
    forms a circle that passes mid way between two of the teeth on the wheel.
    They need to be long enough that as one drops off the other, it lands on a
    lock surface and not missing the end. It only needs to be a small amount
    ( maybe 1/16 inch longer ).
    Tinker Dwight
     
  6. LaBounty

    LaBounty Registered User
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    Aug 29, 2002
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    Hi Knas-

    Click Here for an article which includes laying out a deadbeat escapement.

    Good luck with it!
     
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