Setting Centre to Centre on and escapement

[John T]

Hi Art.
My challenge is to generate an escapement that will perfectly match existing arbour spacing.

I can set the number of teeth and I can set the pallet span and finally I can specify the diameter of the the escape wheel.  Unfortunately the only way I can get an exact arbour to arbour spacing is to adjust over and over the diameter of the escape wheel to "narrow" in on the arbor spacing that I want.

Is there no way I can specify the exact arbour spacing I want and let the math determine the escape wheel size and matching pallets?

John

[ArtF]

John:

  There isnt a built in way, but I can tell you an easy way..

This works once you set the toothcount and spanning angle,

Lets assume you have it set up with a escapement diameter of 100 as a test, but you want an end center distance of
say 195.6mm. (Im assuming metric, inch is the same..).

OK, so I do a regen on 100 diameter. Zoom in on the pallet arbour to find its center, or check the shafting dxf.

Then, heres some simple math..

Lets say you see the center of the pallet is a Y of  70.74. The radius of the escapement is 50 since its diameter is 100. Lets
list them as variables.

R = 50; //escapement radius
Y = 70.74  // center distance currently

  But you want a center distance of say... 123.45

NewEscapementDiamter =  ( 1/ (Y-R)) * DesiredCenter) * 2;

So in this case, NewRadius =    ( 1/ (70.74-50)) * 123.45)) =  .70681 * 123.45 = 87.256 * 2 = 174.512

  So 87.256 is the escape radius that will give you  an arbour distance of 123.45, a diameter of 174.512

Now just enter 174.512 and press regen, your center is now 123.45

This will work for any combination of teeth and span angle..

Art

[John T]

Hi Art,
Thanks for the help.  I tried to follow your arithmetic but was having some trouble.  Upon looking at the formula or equation that you were using I could see that it was a simple linear relation and so I simply did a proportional change and achieve the magic centre to centre distance that I was looking for.

My Jesse now has a "re-engineered" time train using epicycloidal teeth and a new recoil escapement.  The original gear set was cut on a band saw - (don't even be tempted).  Anyway the clock is nicely ticking away.  Thanks again.

John

[ArtF]

cool, good work, looks very strong...

  Yes, in most geared items, even escapements, simple linear transforms will give you the desired centers, modules ..

Art

[John T]

Hi Art
Since I work nearly exclusively in wood I have to make allowances for is weaknesses.
The biggest change I've found is in the tip relief of the escape wheel. If I go less than 1.5 I find that while some of the Baltic birch plies are fine others that are cross grain will chip off making the tips weak overall.
So although it's a bit clunky they are reliable at 1.5 (mostly).

I have another escape wheel project and I'm looking forward to it now.

John

[ArtF]

Hi John:

  Yes, tips are the issue. not too bad in hardwoods, but in plywood it can break then easily. I was thinking of making a glass
escapement ..for that tinkle sound on a tick , but I can imagine thats even worse than plywood. :)

Art

[John T]

Hi Art
I would like to make on of brass but I've never cut brass any tips?  My spindle is very small. (50 watts) - if I go too slow i think heat will be a concern so how fine of a cut could I make?

John

[ArtF]

Hi John:

Being a woodworker, Ive never really cut much brass in my router, but I've always found it amazing how
easy it doesa cut. HEat isnt that much an issue, just cut very small passes, and as quick as you can. Better
to cut .01" at a fair speed that .1 at a very slow one. Try some experiments with shallow passes is my advice..
it really has a lot of variables with your system being the major one, depends on its rigidity, so I suspect
with a 50watt spindle, youd be taking very very shallow cuts, I do with my 750Watt..

Art

[John T]

Hi Art,
I had tried in the past to cut brass but always ended up with a broken bit and no gear to show for it.

So, I took you advice and have cut a 1.5 inch escape wheel that is 1/16 inch thick.  The CNC was set up at 100 inches per minute using a carbide 1/16 inch end mill.

The difference this time was that I set the cut per pass at 0.001 inches and it worked.  Even though it took 62 passed to complete it was worth it.  The photo is as it came off the CNC with no burr removal or anything.

A beautiful gear (in my opinion).

Thanks for your help!!

John

[ArtF]

John:

Excellent!, glad it worked out. Thats the thing about low power machines, you really can do amazing things, you just
have to be patient and take very little at a time. Eventually, you do get through.. 
  :)

Art