How to draw Cam lobe

[JD Mather]

I ran a Dynamic Simulation assuming the cam follower was Ø10. No offset (follower translates up/down in same plane as axis of rotation).

Acceleration curve is dependant on direction of rotation.

 

Sharp changes in acceleration are generally not good (especially the higher the RPMs).

 

CW Rotation Acceleration Curve

 

 

 

Displacement curve is smooth (because the curves are tangent). CCW rotation)

 

Edited May 15, 2013 by JD Mather

[Guest AARi]

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Edited June 20, 2013 by AARi

[JD Mather]

so then we need re restriction to get the center points of the circles

 

So by your calculations - what are the coordinates of the centers of the arcs (don't get them from my geometric solution)?

[Guest AARi]

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Edited June 20, 2013 by AARi

[JD Mather]

That doesn't answer my question, "What is the centerpoints (x,y) for your arcs?" (assuming those lines converge at (0,0))

[Guest AARi]

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Edited June 20, 2013 by AARi

[JD Mather]

The problem is a geometry problem - so of course the solution will be the same in any CAD program.

Here is the SolidWorks solution (identical to the AutoCAD and Inventor solution).

 

[JD Mather]

Tomorrow I will post the Creo (Pro/E) solution (I don't have Creo on my home machine).

[henrynguyen]

Thanks everyone for the input. Sorry I have been busy' just got bumped to third shift, so it's really mess up my time.

 

For the drawing, it's was just an exercise from a book call "Engineering with Autocad 2009" by Bethune. I was just got stuck at this exercise.

 

@ AARi. I'm here and still alive, hehe

 

Thanks JD for the drawing. I knew that all arcs don't share the same center point. I just didn't know how to connect the arcs together. What method do you use to connect them together? I drew circle using TTR between the lines of an angle, after trimming that would just give an arc facing the other way and not connect to the 90deg arc.

btw what do you mean when you say constraint?

[welldriller]

MY CAM DRAWING.dwg

 

Mr Mather here is the redrawing of the cam i could not get the 90 & 59 degree circles to meet up but the degrees are correct. i know that it is not near as good as the rest of you are doing but i think the drawing is close. i know that you all are busy but would appreciate some feed back when you have time

 

another mistake -- i removed the center points of the circles to clean up the drawing sorry

Edited May 16, 2013 by welldriller
add information

[JD Mather]

...btw what do you mean when you say constraint?

 

Constraints were added to a later release, I think r2011 or 2012.

They are different than Osnaps in that they are persistant.

For example if you add a Tangent constraint between two circles - no matter where you move the circles they remain tangent.

 

[JD Mather]

... but the degrees are correct. ...

 

The degrees (angles) are not correct in your drawing.

The arcs are not tangent.

Centerpoints of arcs cannot be removed - they are still there.

 

As I indicated a couple of times - none of the arc centerpoints are on any of the lines. (except for the hole of course)

You put the R45 arc on ALL FOUR lines? (the vertex)

 

[welldriller]

The degrees (angles) are not correct in your drawing.

The arcs are not tangent.

Centerpoints of arcs cannot be removed - they are still there.

 

As I indicated a couple of times - none of the arc centerpoints are on any of the lines. (except for the hole of course)

You put the R45 arc on ALL FOUR lines? (the vertex)

 

[ATTACH=CONFIG]41922[/ATTACH]

 

 

Wow what a mess i thought that i at least had the cam correct guess that is what i get for trying to think

 

i can not for the life of me figure out how you are doing your degree arrows with out a circle or ark or can i not do that in Autocad LT 2000 i notice that every one else on here can an it sure is neat and yes i know you can not remove the centermarks of a circle or ark i meant the lines pointing from the degree text to the center of the circle not very good at explanations

 

THANK YOU very much for checking the drawing and letting me know what was wrong

[JD Mather]

You should have dimension tools for linear, aligned, diameter, radius and angle.

I have never used AutoCAD LT, but I am quite sure it has an angle dimension tool.

[Lee Mac]

I'm no draftsman, but this looked interesting, so here is my solution:

 

Construct first arc, radius 45.0 spanning 0 to 90 centered at the centre of the cam and construct a vertical line of length 80.6 and horizontal line of length 61.0 through this centre as shown:

 

 

Create a construction line at an angle of 59 degrees from the vertical passing through the centre as shown below, and construct an arc centered at the end point of the vertical line, with start point at 90 degrees and end point meeting the construction line:

 

 

Create another construction line at an angle of 228 (= 90+59+79) from the X-axis; construct an arc centered at the end point of the horizontal line of length 61.0 with start point at the construction line and end point at 0 degrees:

 

 

Construct final arc using Start/End/Radius:

 

[neophoible]

I'm no draftsman, but this looked interesting, so here is my solution: ...

Lee, this problem is actually a lot more interesting than what you did. Are your arcs cotangent at the endpoints? That should be one of your criteria. Take a look at JD's solutions, all with identical results. It looks like the solution is unique, as JD points out. I would have thought your preferred approach would be more like AARi's where he is deriving equations to solve simultaneously. Perhaps a worthy challenge for the mighty Mac?

[henrynguyen]

It's work! I finally got it Thanks Mac and everybody

[neophoible]

i can not for the life of me figure out how you are doing your degree arrows with out a circle or ark or can i not do that in Autocad LT 2000

Hi, welldriller. It looks like you substituted diametral dimensions for angular. Have you tried invoking DIMAngular and picking a couple of lines? That should help you get where you want to be in showing angular dimensions.

[Lee Mac]

Are your arcs cotangent at the endpoints? That should be one of your criteria.

 

The first two arcs are constructed tangent to the end points of the 90 degree arc by virtue of how the center is defined, however, the remainder of the construction was based only on the given dimensions and hence the end points of the final arc are not cotangent (but not far off).

 

I would have thought your preferred approach would be more like AARi's where he is deriving equations to solve simultaneously. Perhaps a worthy challenge for the mighty Mac?

 

If I've got some time I might try that route, though my post was predominantly aimed at showing how I would go about constructing the cam in AutoCAD (via geometric construction) using the dimensional information provided.

[Lee Mac]

It's work! I finally got it Thanks Mac and everybody

 

You're welcome Henry.