GearHeads Corner

Well, I have made a start  ;D

I tried laser cutting but the dimensional accuracy is just not there so resorted to milling. Once I get a few parts machined and assembled I will take a few more pics.

Tweakie.

Tweaky:

  Dimension wise I was of the opinion one should enter a pin diameter slightly larger than that they intend
to use. The drawings are done with zero allowance. I expect a backlash is required to allow for at least
some tolerance.  Other than that they should ( math wise anyway ) work out well.

Love to see your end product.. :)

Art

How did you make the back plate and eccentric inserts?

Kirk

Hi Kirk,

The stator had the OD added in Vectric with the pin positions from the Vexx DXF.
The cam was produced in Vectric using the offset displayed in Vexx.

Hi Art,

I am not yet sure of the best way to achieve the running clearances - a system I used from a previous project was to lie about the tool diameter when creating the path but it needs a few practice runs (trial and error) - I think I have plenty of engraving laminate in stock so that is what I am trying  ;D

Tweakie.

Hi Tweaky:

  When designing it, say you want to use 5mm outside pins, declare them as 5.25mm pins. Then
cut to profile for the toolpath. You should get a .25 clearance. Though thats basically  the same
as you just defined only from the tool side.
  I use about that much for my laser..

Art

Hi Art,

Many thanks for the info.

I have yet to make the drive disc but I am making progress albeit very slowly.

Tweakie.

Tweaky:

  Looks pretty good. Ill be interested in how you find it works.
I have a few lazy susan bearings that will be used as my
axis drive. They have a large enough hole in the middle to
contain the center bearing and should ease that rotational friction
you may hit with the small offset circular parts.

  Keep posting your experience.. Ill post my first stage when
its cut.

  You know I have a conjecture on the number of pins needed to
be used on the outside ring. If, for example, you use 21 outside pins,
you get a 20:1 reduction, but my thought is that you need use
only the number of pins in construction as determined by torque
requirement. The number of pins used must be  (n > 2) for any
ratio above 2.

  So a 20:1 reduction could in construction use as few as 3 pins
if the torque requirement is low. I intend to use 3 pins on each
of 4 stages to reduce a clubfoot to  the hour hand.

  Dunno how that will work out, but simulations seems to show
a min of 3 should do the job.

Art

Hi Art,

It?s early days yet (for me) but I had planned for ball bearing the cam (shaft and outer) but (from my model) observation shows that although the cam will roll on a pin the exact opposite side of the cam slides on a pin and there is quite a lot of friction there especially as I plan on dual cams / rotors. Looks like my pins will be ball bearings as well and while I am at it ball bearings for the final drive dogs.
It could turn out to be a neat little reducer but it is going to be heavy  :)


Tweakie.

If I'm well, the hypocycloid reduction was (amongst others ?) invented by the famous clockmaker Aaron Dodd Crane:

https://www.google.nl/search?q=aaron+do ... 20&bih=894

A well known appliance is the "daisy wheel": a small number of pins (e.g. 3 or 4 or ..) on the outside and (flower..) lobes/"teeth" (e.g. 11) on the inside.
A nice clock with the mechanism as 12:1 reductor (here 3 pins and 11 lobes) here:

http://woodenclockspot.blogspot.com/p/g ... lator.html

Animation here:

https://www.youtube.com/watch?v=RVWd-QedUTY

Hessel

Excellent information Hessel - that is all going to take some reading.  :)

Tweakie.

That's a pretty cool clock!

I've got a stack of russian birch and thin hardwoods (including some nice in the picture quarter saw white oak)  sitting in my Ocooch Hardwoods shopping cart.  Maybe it's time to click the buy button and quit screwing around with goopy plastic stuff.

Ocooch HW is just down the road (if you call 6 hours driving "just") from the Mooselake Manor, but quite a bit further to the snow free winter cottage.  They get good reviews but never bought from before.  Anybody dealt with them?  I have a few bucks left before the flat rate shipping jump, any suggestions on a nice clock/ticker hardwood before I pull the trigger?  Who knows, maybe I'll actually complete something this time

Kirk

Kirk:

Im a fan of almost any african hardwood. Im trying to make it so my rotors are only a few inches across
to preserve wood.

Art

Hessel:

Thx, good information. Proves my thought that 3 pins are enough as well.
I like it.

Art

A few seconds of poor quality video, just to prove that it works  ;D

https://youtu.be/u3Mh1E4GgHE

Tweakie.

Great Paul/Tweakie !

If I remember well NYC CNC (on YouTube) once made a hypocycloid reductor of a normal speed electric motor to 1 rotation in 30 years !!!
They did put several reducer layers behind each other, so it's clear now that Paul is --not-- fully ready at this moment .... ;)

https://www.youtube.com/watch?v=Eds48L4cJjM

Some nice explanations also here:

http://www.zincland.com/hypocycloid/

and

http://www.meccanotec.com/gearlesshands.htm

Hessel

p.s.

My interest in this subject is caused by the fact that I'm trying to build the Woodward gearless clock
(which has in the John Wilding drawings, also a daisy wheel for the 12:1 reduction for the dials).

https://www.dropbox.com/sh/jjwli7femazj ... YszSa?dl=0