Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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  #1   Report Post  
Airy R.Bean
 
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Default Watts' Parallel Motion

Having finished my Stuart Turner 10V, SWMBO complained
that she what really had wanted was a beam engine. I now feel
confident to make one out of the scrap box (not sure how to use
the lock or the hinges :-) ), especially as my best mate has gone and
bought the Brunell Models one, just to put his nose out
of joint.

I've conceived of a way of producing the beam by milling from
a bar and then screwing in the bushes, but what I don't know
are the intricacies of the Watt's Parallel Motion.

(Apart from ensuring that the distance from the ground anchor
of the swinging pivot to the parallelogram when it is rectangular
is the same as the distance from the beam's pivot to the same
point vertically above)

Also, I assume/guess that when the parallelogram is rectangular,
that the piston should be half way along its travel through the
cylinder?

-----ooooo-----

Also, in order to get a large enough flywheel, are scrap flywheels
from motor cars of a suitable cast iron to be easily machined - I envisage
doing the crossing out (a la clock wheels) to make the spokes?


  #2   Report Post  
Brian Drummond
 
Posts: n/a
Default

On Thu, 10 Feb 2005 11:32:36 -0000, "Airy R.Bean"
wrote:

I've conceived of a way of producing the beam by milling from
a bar and then screwing in the bushes, but what I don't know
are the intricacies of the Watt's Parallel Motion.


It provides a 5th order approximation to a straight line.

Discussed on the Yahoo groups "MLProjects2" group around 5-12 January
2004, refer to their archive for more info.

Here's a spreadsheet and diagram which should help design an accurate
link motion to any scale you want, and plot the error (deviation from
straight line) on a chart. For a given stroke, the spreadsheet lets you
find the beam length (and exact geometry) to meet any given error
criterion you want.

http://www.shapes.demon.co.uk/files/Beamer-5.xls
http://www.shapes.demon.co.uk/files/wattlink4.dxf

How it works...

All the input settings are in column B3-B11 of spreadsheet Beamer-5.xls.
Points A, B etc are illustrated in the CAD sketch wattlink4.dxf.
Outputs C(x,y) and CD tell you the remaining dimensions for minimul
error, and Chart 1 plots the error itself.

(excerpt from above discussion)

Start by setting the beam length (radius), and desired stroke of the
engine (currently 1000 and 720mm) in B3 and B4. If you are happy with
the bridle and link rods (half the beam and stroke respectively), leave
them, though you can enter different numbers and it SHOULD design you a
consistent and accurate linkage.

Then note that the beam angle A'Stroke is output in H4. Using it, decide
where you want to put the four zeroes in B8-B11. For example, choose 21
and 10.5 degrees for B8,9, and -10.5 and -21 will appear in B10,B11.

It will calculate 4 positions for D corresponding to zero error at these
4 angles, and use these (which lie on a circle) to calculate the centre
and radius of the circle, which gives the position of C, and the length
of CD. NOTE that if the bridle is shorter than half the beam length, CD
will be longer - and vice-versa - and the error can still be very low.

(If B10,11 are not mirror images of B8,B9 then the four positions of D
may not lie on the same circle, and the calculated positions of C (in
columns N8-O11) will not be the same. This is a good check that the
model is working...)

The resulting error is calculated in O16 to O42, involving the Cosine
Law (thanks to Robert Smith for that one!) roughly as per his
spreadsheet, and plotted in Chart 1. (You can modify the range to
display using Chart/Source Data when the chart is displayed)


Try 21 and 13 degrees, for slightly lower error.

Or 21 and 0 degrees, it should re-create the motion according to Jeynes.
(oops! try 21 and 0.001 degrees :-)

Or set the stroke to 600mm, note the beam angle is now only 17.45
degrees, and choose 17 and 10 degrees for B8 and B9. The error is under
0.1 mm!

Enjoy...

- Brian
  #3   Report Post  
Dave August
 
Posts: n/a
Default

Brian,

COOL Stuff!
Since you seem to be up on this, do you have a source as nice as this for
building fly ball governors? My highschool physics is really rusty and I
don't want to work the math from Watts original formula, and certainly don't
want to work from Maxwells' dissertation on why Watt was wrong ... LOL..

FWIW if you are into valve motion you have seen Charlie Docksteadrs work
haven't you?
http://www.tcsn.net/charlied/

Dave August


"Brian Drummond" wrote in message
...
On Thu, 10 Feb 2005 11:32:36 -0000, "Airy R.Bean"
wrote:

I've conceived of a way of producing the beam by milling from
a bar and then screwing in the bushes, but what I don't know
are the intricacies of the Watt's Parallel Motion.


It provides a 5th order approximation to a straight line.

Discussed on the Yahoo groups "MLProjects2" group around 5-12 January
2004, refer to their archive for more info.

Here's a spreadsheet and diagram which should help design an accurate
link motion to any scale you want, and plot the error (deviation from
straight line) on a chart. For a given stroke, the spreadsheet lets you
find the beam length (and exact geometry) to meet any given error
criterion you want.

http://www.shapes.demon.co.uk/files/Beamer-5.xls
http://www.shapes.demon.co.uk/files/wattlink4.dxf

How it works...

All the input settings are in column B3-B11 of spreadsheet Beamer-5.xls.
Points A, B etc are illustrated in the CAD sketch wattlink4.dxf.
Outputs C(x,y) and CD tell you the remaining dimensions for minimul
error, and Chart 1 plots the error itself.

(excerpt from above discussion)

Start by setting the beam length (radius), and desired stroke of the
engine (currently 1000 and 720mm) in B3 and B4. If you are happy with
the bridle and link rods (half the beam and stroke respectively), leave
them, though you can enter different numbers and it SHOULD design you a
consistent and accurate linkage.

Then note that the beam angle A'Stroke is output in H4. Using it, decide
where you want to put the four zeroes in B8-B11. For example, choose 21
and 10.5 degrees for B8,9, and -10.5 and -21 will appear in B10,B11.

It will calculate 4 positions for D corresponding to zero error at these
4 angles, and use these (which lie on a circle) to calculate the centre
and radius of the circle, which gives the position of C, and the length
of CD. NOTE that if the bridle is shorter than half the beam length, CD
will be longer - and vice-versa - and the error can still be very low.

(If B10,11 are not mirror images of B8,B9 then the four positions of D
may not lie on the same circle, and the calculated positions of C (in
columns N8-O11) will not be the same. This is a good check that the
model is working...)

The resulting error is calculated in O16 to O42, involving the Cosine
Law (thanks to Robert Smith for that one!) roughly as per his
spreadsheet, and plotted in Chart 1. (You can modify the range to
display using Chart/Source Data when the chart is displayed)


Try 21 and 13 degrees, for slightly lower error.

Or 21 and 0 degrees, it should re-create the motion according to Jeynes.
(oops! try 21 and 0.001 degrees :-)

Or set the stroke to 600mm, note the beam angle is now only 17.45
degrees, and choose 17 and 10 degrees for B8 and B9. The error is under
0.1 mm!

Enjoy...

- Brian



  #4   Report Post  
Chris Holford
 
Posts: n/a
Default

In article , Airy R.Bean
writes
snip
but what I don't know
are the intricacies of the Watt's Parallel Motion.

-or you could be really flash and use 'Peaucelier's Inverser'
(google for animations of the same)
--
Chris Holford
  #5   Report Post  
Airy R.Bean
 
Posts: n/a
Default

ISTR seeing that in ME somewhere.

Par la Web, il y'a beacoup des references
a Peaucelier, mais rien en Angleterre-speak.

"Chris Holford" wrote in message
...
In article , Airy R.Bean
writes
snip
but what I don't know
are the intricacies of the Watt's Parallel Motion.

-or you could be really flash and use 'Peaucelier's Inverser'
(google for animations of the same)





  #6   Report Post  
Chris Holford
 
Posts: n/a
Default

In article , Airy R.Bean
writes
ISTR seeing that in ME somewhere.

Par la Web, il y'a beacoup des references
a Peaucelier, mais rien en Angleterre-speak.

"Chris Holford" wrote in message
...
In article , Airy R.Bean
writes
snip
but what I don't know
are the intricacies of the Watt's Parallel Motion.

-or you could be really flash and use 'Peaucelier's Inverser'
(google for animations of the same)



TRY;
http://poncelet.math.nthu.edu.tw/dis...java/peau.html
http://www.museo.unimo.it/labmat/invrseng.htm (not animated)
http://www.apm.pt/atractor/mecanismo.../peaujava.html (in
Italian, but the animation is self explanatory)
http://www.math.toronto.edu/~drorbn/...s/homepage.htm

--
Chris Holford
  #7   Report Post  
Airy R.Bean
 
Posts: n/a
Default

Sorry, Brian, I've just realised that your print-out has been
sitting on my desk submerged for a week, and that I hadn't
acknowledged your help. I don't have a means of displaying
DXF files (I did try to install one of the monthly-magazine disks release
of TurboCAD v4, but it trashed the computer)

I'll reply once I've had the chance to decode the calculations in
the spread sheet.
TA!

"Brian Drummond" wrote in message
...
On Thu, 10 Feb 2005 11:32:36 -0000, "Airy R.Bean"
wrote:

I've conceived of a way of producing the beam by milling from
a bar and then screwing in the bushes, but what I don't know
are the intricacies of the Watt's Parallel Motion.


It provides a 5th order approximation to a straight line.

Discussed on the Yahoo groups "MLProjects2" group around 5-12 January
2004, refer to their archive for more info.

Here's a spreadsheet and diagram which should help design an accurate
link motion to any scale you want, and plot the error (deviation from
straight line) on a chart. For a given stroke, the spreadsheet lets you
find the beam length (and exact geometry) to meet any given error
criterion you want.

http://www.shapes.demon.co.uk/files/Beamer-5.xls
http://www.shapes.demon.co.uk/files/wattlink4.dxf

How it works...

All the input settings are in column B3-B11 of spreadsheet Beamer-5.xls.
Points A, B etc are illustrated in the CAD sketch wattlink4.dxf.
Outputs C(x,y) and CD tell you the remaining dimensions for minimul
error, and Chart 1 plots the error itself.

(excerpt from above discussion)

Start by setting the beam length (radius), and desired stroke of the
engine (currently 1000 and 720mm) in B3 and B4. If you are happy with
the bridle and link rods (half the beam and stroke respectively), leave
them, though you can enter different numbers and it SHOULD design you a
consistent and accurate linkage.

Then note that the beam angle A'Stroke is output in H4. Using it, decide
where you want to put the four zeroes in B8-B11. For example, choose 21
and 10.5 degrees for B8,9, and -10.5 and -21 will appear in B10,B11.

It will calculate 4 positions for D corresponding to zero error at these
4 angles, and use these (which lie on a circle) to calculate the centre
and radius of the circle, which gives the position of C, and the length
of CD. NOTE that if the bridle is shorter than half the beam length, CD
will be longer - and vice-versa - and the error can still be very low.

(If B10,11 are not mirror images of B8,B9 then the four positions of D
may not lie on the same circle, and the calculated positions of C (in
columns N8-O11) will not be the same. This is a good check that the
model is working...)

The resulting error is calculated in O16 to O42, involving the Cosine
Law (thanks to Robert Smith for that one!) roughly as per his
spreadsheet, and plotted in Chart 1. (You can modify the range to
display using Chart/Source Data when the chart is displayed)


Try 21 and 13 degrees, for slightly lower error.

Or 21 and 0 degrees, it should re-create the motion according to Jeynes.
(oops! try 21 and 0.001 degrees :-)

Or set the stroke to 600mm, note the beam angle is now only 17.45
degrees, and choose 17 and 10 degrees for B8 and B9. The error is under
0.1 mm!

Enjoy...

- Brian



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