First escapement :(

[Ian]

Trying to build my first escapement and it didn't work
Laser cutting birch ply

Went for a recoil type. ratchet 60mm diameter and 24 teeth. the pallet had a tooth span of 5.5

I am not using a crutch. Pendulum is directly connected to the pallet !!

first attempt
when I hand rocked the pendulum ratchet turned but backwards  (sort of did this consistently)
but when I added a small weight it just ran away :(

Measured items and they were all wrong by 1mm or so thought this might be the problem( maybe kerf of the laser)
so resized and recut a bit bigger. The items now measure up correctly
Now works even less. Jams eaisly, although rocking pendulum by hand slowly turns ratchet right way but for a few swings only


Anyone any suggestions
Or size of mechanism I should use for full proof operation

http://www.youtube.com/watch?v=vqYfDkmutHo
Many thanks in advance

[John T]

In general the bigger the escape mechanism the better and that's because the amount of error from your machine is fixed so that if you change the size of what you are cutting the relative error to the mechanism gets less and less.  In general escapements are the most sensitive part of any clock was respect to clearances. 

I would suggest that you double the size of your ratchet to about 150 mm and increase to span to 7.5

I would hope that you're using your CNC machine to also cut the arbor holes as the distance between these is very critical.

One last point is that a recoil mechanism actually will work in reverse although will not as well in the correct rotation

[ArtF]

If you can , post a picture of the mechanism, its sometimes easy for us to spot a weak spot in the build..

Art

[Ian]

Thanks John

I am using cnc (laser) to cut arbour holes.
Will try larger ratchet  ASAP.
Was trying to make it small so there would be less inertia.


Interested that the recoil escapement can work in reverse !


ART. Will post picture of larger ratchet when made

[ArtF]

I agree, always build big the first time, so much easier to figure out mistakes...

Art

[Ian]

In the video below is my second attempt 150mm ratchet as suggested by John.

Some success !!
First 39 seconds is pendulum swinging on its own with the pawl

then I lined ratchet up with pawl with small weight attached. Gave pendulum a small push it works sort of for a few swings.

Any advice about what I should do/look at to improve things would be appreciated


video not great as made with phone held in one hand
http://www.youtube.com/watch?v=vqYfDkmutHo

No sniggering please

[ArtF]

Ian:

  No sniggering required :), your almost there. The first escapement can drive you nuts because you havent the feel for it as yet, but after you get this one going youll find its all downhill and future ones take much less time and are
much easier.
  Lets get this one running. A recoil escapement should recoil..but your is recoiling too much. When you watch that
upper tooth hit note how far its pushing back the ratchet..too much. This means one of two things ( which is why I say its all a balance..), either the pendulum is too heavy and thus too hard to stop, OR the weight driving the ratchet is too light making it too easy to push backwards. Youll know you have it just right when the recoil is minimized. In theory the perfect point is where no recoil occurs, this means the pendulum is just right as is the drive weight.
    Heres my advice.. remove some weight from the pendulum, but make sure it still has enough that it will swing back and forth a few times when you release it unhooked from the pallets. Doesnt have to be much 5-6 swings gradually reducing to zero motion is fine I think. Then give it a try, note how much recoil occurs. It shouldnt go so far as to hit the curved portions of the tooth as it does now, that indicates not enough weight driving the ratchet.

  You are very close to getting that running, a bit less weight on the pendulum and a biot more on the ratchet I think will make it run. The ratchet is supposed to just add the amount of energy lost to friction as the pendulum swings, by the time the pallet hits the pendulums tooth it shoudl be just about out of steam , the ratchet will stop it fast because its about out of steam so it shouldnt recoil too much, if it does then less pendulum eight or more ratchet weight is required.
  Dont despair, youll get the hang of it fairly quickly when you hit the next spot. Your soon going to get 30-40 seconds of motion, then 5 minutes,..then forever. It just seems to work that way. Did for me anyway.. Im thinking just removing pendulum weight will do it now..but its possible you cant remove enough and will need some more ratchet drive weight..

Art


Art

[Ian]

Thanks Art


will try your suggestions as soon as possible

[John T]

Hi Ian,
I think you're a lot closer than you think you are.  By watching your video, as Art noted the upper pallet is going through a lot of recoil, if you tilt the vertical member of your frame a little to the left "clockwise" you'll notice a change.  You're looking for an even tick tock.  I'm pretty sure if you adjusted the vertical orientation to achieve a really even tick tock sound your mechanism will do its job.


John