Author Topic: Using CAD to design and layout the cuts for a flywheel  (Read 7045 times)

Offline Alan Haisley

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Using CAD to design and layout the cuts for a flywheel
« on: March 01, 2013, 10:00:41 PM »
 While you can lay out a flywheel and calculate the various cuts using trig and analytic geometry , its easier to just use a 2D CAD program to do the work. I have used DesignCAD for several years and will demonstrate with it, but any other reasonable program of the type will do the job. To start with, I laid out the basic shape:

This will be a 3 flywheel with a .25 axle. The hub and rim are both .25 thick.
Once I had this decided, I needed to decide on the basic spoke layout. If the spoke is .25 at the rim and .375 at the hub it might look nice, so, I added verticals of those lengths at those points:

Notice that because of the taper, the actual dimensions where the spoke meets the hub and rim will be slightly different.
Next, I connected the ends of these lines and extended the connections to meet the rim and hub. My CAD program allows for extending a line and also for trimming a line where it crosses another. As you can see, the dimensions for the spoke width have changed slightly:

The next thing that I needed was to round off both ends of the spokes. I chose .25 diameter for this because it looked good. Here is a place where CAD really helped; my program allows me to draw a circle tangent to two lines of a specified radius. Using it saves a ton of math at this point and gave me this:

Im making progress. Now for some cleanup. Youll notice along the way that Im ignoring the rim and hub lines where the spoke intersects. That part of the work is not relevant to the actual work of laying out the cuts to open out for the spokes. In a finished, machined piece part of the rim and hub may be left thicker than the web, but that need not be shown on these drawings.
This next drawing is a clean-up. My CAD program, along with allowing me to trim a line intersection, allows trimming between where one line crosses two others. In this case, Im doing it to keep the drawings clean:

Note that that even though I have deleted parts of the four circles, their center points are still known to the program. This will become very important shortly. This next drawing is not strictly necessary since I know that the finished spokes will be 120 degrees apart. Still, it helps in visualizing the finished product:

Now, at last, comes the exciting part. My program has two features critical here: First, I can dimension the angle between two lines without having their intersection point; and second I can dimension a coordinate relative to a point.
In my case, for the coordinate dimensions I specified everything relative to the center of the hub, which will of course also be the center of my rotary table.

Now I can tell where to drill starting holes for each spoke. When it is time to drill, I will move my (x,y) to .391 x and .3117 y (or as close as I can get.) There, I can drill the first three holes, rotating the table 120 degrees between each. For the other holes around the spoke Ill follow the same practice, moving to 1.0942 x and .2614 y, drilling three holes, and so forth.
Then, I can go back to the first hole, drop an undersized mill through, and rotate until I meet the opposing hole for the next spoke. Continuing this process will cut out all of the arcs. I can then repeat with a full sized mill, being careful at each end.
The challenge now is to cut the straight sides of the spokes. I need to start at one hole and cut straight to another. This is where CAD really replaces a lot of math. For each side of the spoke it is a two step process.
First, I used a CAD feature to rotate the drawing around its center by the spoke angle:

This makes one side of the spoke parallel in x and so I can cut it easily. At the same time, the CAD program recalculated all of the coordinate dimensions and so I know where to start and end each cut. In this position I can easily cut one side of each spoke. The challenge here is that the rotary table is no longer starting at zero and so I need to carefully calculate the 120 degree rotations for the other two spokes.
Going back to my unrotated drawing, I then rotated it in the opposite direction by the spoke angle. Once again the coordinate dimensions changed to reflect this rotation. This will give me the numbers I need to do the straight cuts on the opposite sides of the spokes.

The main features of the program that makes this all happen are the ability to rotate a drawing around a specified point and the ability to specify coordinate dimensions. If the program hadnt automatically recalculated the coordinates I could of course manually respecified them.
Fewer or more spokes would not be a problem, just a different amount of work. Ill leave it as an exercise for the reader to see how this would all work if different fillet radii were used at the hub and rim.
Near Raleigh, NC, USA

Offline vcutajar

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Re: Using CAD to design and layout the cuts for a flywheel
« Reply #1 on: March 01, 2013, 10:17:10 PM »
An interesting and timely (for me) post Alan.  I have never made flywheels before and you are showing me another method of doing it.

Thanks

Vince

Offline Don1966

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Re: Using CAD to design and layout the cuts for a flywheel
« Reply #2 on: March 01, 2013, 10:21:35 PM »
That's the way I was doing my flywheels, but now use a spreadsheet a lot quicker. Don't you just love how easy cad makes it though and you have the drawing with the dimenisions?

Don

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Re: Using CAD to design and layout the cuts for a flywheel
« Reply #3 on: March 01, 2013, 10:25:30 PM »
Alan,

You should have a look on Marv's website, he has a great little Flywheel.zip program that does everything for you for very little input.

http://www.myvirtualnetwork.com/mklotz/

John

Offline ozzie46

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Re: Using CAD to design and layout the cuts for a flywheel
« Reply #4 on: March 01, 2013, 11:07:12 PM »
I used that same technique to lay out and machine the drivers and coupled loco wheels for my 5" gauge Simplex Loco.  Did not use castings. Made out of 6061T6 with Steel tires shrink fitted on.


 Good tip.


   Ron

Offline Alan Haisley

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Re: Using CAD to design and layout the cuts for a flywheel
« Reply #5 on: March 01, 2013, 11:13:56 PM »
Alan,

You should have a look on Marv's website, he has a great little Flywheel.zip program that does everything for you for very little input.

http://www.myvirtualnetwork.com/mklotz/

John
Unfortunately, John, I bought a new computer with a 64 bit CPU and when I tried to use Marv's program It wouldn't run. So, I thought I'd go back to my college math and work up formulas. When I realized how messy it was getting, I slapped myself up the side of the head and remembered that my CAD program had more trig and analytic geometry built in than I ever learned and so I decided to walk my way through the above. As I tried various things I realized that CAD gave me flexibility that other methods didn't - at least without a great deal of work. For instance, I can lay out either straight or tapered spokes, spokes with the open hub shown above, spokes with a triangular cutout like Marv's program, or anything else. The real trick to it is what I describe in the last couple of drawings: rotating to line up the straight sides of the hub and recalculating the end points.
Alan
Near Raleigh, NC, USA

Offline mklotz

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Re: Using CAD to design and layout the cuts for a flywheel
« Reply #6 on: March 01, 2013, 11:21:02 PM »
Instructions for running my programs on 64 bit computers are on my site.  Read the section labeled "Introduction".
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Regards, Marv


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http://www.myvirtualnetwork.com/mklotz

Offline Gary Brooke

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Re: Using CAD to design and layout the cuts for a flywheel
« Reply #7 on: March 01, 2013, 11:34:53 PM »
Alan
I have used design cad 2000 since it was released. Just done the same thing laying out bogie wheels for my locomotive. Did you draw one spoke then use circular array lets  the computer do all the work.
rdgs Gary

Offline b.lindsey

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Re: Using CAD to design and layout the cuts for a flywheel
« Reply #8 on: March 02, 2013, 12:53:12 AM »
Nice write up Alan. CAD can indeed save a lot of calculating and save time.

Bill

Offline Alan Haisley

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Re: Using CAD to design and layout the cuts for a flywheel
« Reply #9 on: March 02, 2013, 03:42:42 AM »
Marv, I'll check your Introduction. Even if this is more flexible for me for this task, there are a lot of useful programs in your body of work that I can use.
Gary, I did use the circular array function. I always need to remember with it to set the control point for the selected entities - I've made some really odd circular arrays before I remembered.  :Lol:
Near Raleigh, NC, USA