Subject: Re: Rack and Pinions

From: Larry Phillips <[email-masked]>
Date: 15 Jan 1995 06:10:37 GMT

[email-masked] (James Kirkpatrick) writes:

  > I'm considering building a very strange clock called an
  > inclined-plane clock.

Neat project. I have always been fascinated by some of the more strange
ways of supplying power to a clock (my favourite, locally, in Vancouver,
BC, is the steam clock, which not only uses steam to power the mechanism,
but uses it to 'toot' the Big Ben chimes).

The only illustration I have of an inclined plane clock shows that it has
no apparent rack or pinion. It seems to be running only on the edge of its
circular case, in a slightly ornate wooden 'channel', similar to a 
'Hot Wheels track' in cross section. It was a late 17th century piece,
and appears to have only a single hour hand. The position as illustrated
is with the hand slightly clockwise from vertical (say about 12:30),
but pointing at the '3'. This would seem to indicate that the hand stayed
somewhat vertical, but that the face rotates with the rolling case.

It is, of course, easy to visualize a scheme whereby the face would stay
straight up, as you mentioned.

As for using a rack/pinion sort of arrangement, I think you'll find that
it would, indeed work, but that the actual shape of the teeth might be
different from those that operate at a fixed spacing that does not cause
the teeth to fully mesh. Your prime consideration in this project will
be to minimize friction, so the teeth will have to have full clearance
all the way into and out of mesh.

Good luck! Please feel free to keep us posted on your progress.

Oh, and this same book has another fascinating one... a 'falling ball'
clock, that looks like a ball, with the hand moving around the middle,
and gets its power from its own weight, while descending a cord.

-larry

-- 
"Mind you, not as bad as the night Archie Pettigrew ate some       
sheep's testicles for a bet...God, that bloody sheep kicked him..."
            -= Ripping Yarns =-

---

From: [email-masked] (Mark Fraser)
Date: 15 Jan 1995 07:13:50 GMT

There's quite a lot of discussion in a recent issue of Model
Engineer; Bill Smith's current article on building a skeleton
clock in Home Shop Machinist, and his books, also tell a tale
or 2.  Basically, there are sets of cutters [8] for each gear
pitch [in typical use for clocks etc] including the "top" one
which is suitable for rack/pinion use.  The choice of 8 seems
to derive from an accuracy [friction / backlash] requirement
over a range from avery small diameter gear to a very large
[infinite, as in rack] one. 

Lantern pinions use different profiles [epicycloidal] that
might be harder to grind a cutter for.  As you will have 
noted, there are also several different angle of mesh 
"standards" for pinion gears; different cutters again,
charlie....

/Mark

Larry Phillips ([email-masked]) wrote:
: [email-masked] (James Kirkpatrick) writes:

:   > I'm considering building a very strange clock called an
:   > inclined-plane clock.

: Neat project. I have always been fascinated by some of the more strange
: ways of supplying power to a clock (my favourite, locally, in Vancouver,
: BC, is the steam clock, which not only uses steam to power the mechanism,
: but uses it to 'toot' the Big Ben chimes).

: The only illustration I have of an inclined plane clock shows that it has
: no apparent rack or pinion. It seems to be running only on the edge of its
: circular case, in a slightly ornate wooden 'channel', similar to a 
: 'Hot Wheels track' in cross section. It was a late 17th century piece,
: and appears to have only a single hour hand. The position as illustrated
: is with the hand slightly clockwise from vertical (say about 12:30),
: but pointing at the '3'. This would seem to indicate that the hand stayed
: somewhat vertical, but that the face rotates with the rolling case.

: It is, of course, easy to visualize a scheme whereby the face would stay
: straight up, as you mentioned.

: As for using a rack/pinion sort of arrangement, I think you'll find that
: it would, indeed work, but that the actual shape of the teeth might be
: different from those that operate at a fixed spacing that does not cause
: the teeth to fully mesh. Your prime consideration in this project will
: be to minimize friction, so the teeth will have to have full clearance
: all the way into and out of mesh.

: Good luck! Please feel free to keep us posted on your progress.

: Oh, and this same book has another fascinating one... a 'falling ball'
: clock, that looks like a ball, with the hand moving around the middle,
: and gets its power from its own weight, while descending a cord.

: -larry

: -- 
: "Mind you, not as bad as the night Archie Pettigrew ate some       
: sheep's testicles for a bet...God, that bloody sheep kicked him..."
:             -= Ripping Yarns =-