Need help making noncircular curve for modeling part

[nthomas-2]

Hey guys.  So I'm fairly new to CREO, I'm taking my first class on it this semester.  For a term project we're required to model all parts of a chainsaw.  Right now I'm working on a piece with a noncircular curve and I'm looking for some advice on the best way to do it.  A couple things I've tried so far:

- Datum -> Curve -> Curve through points (I traced my part onto paper, made a coordinate plane to plot points on the curve (did about 25), and then used this curve through points).  The downside on this one is that although I tried my best to be accurate, measuring points to the 64th of an inch, they still didn't line up in a perfect curve.  However, this looks very close to the curve.  The only other thing is I'm not sure what the best way to dimension the part on my drawing would be (dimensioning 25 points would probably look terrible but again I'm new, maybe that's how it's done?)

- Tried plotting the points in the STAT of my calculator and then tried a few different functions for best fit line.  Downside to this is I can't get one that passes through my start and end points, which I believe is critical to the part.  Maybe there's another way to get a best fit line equation that will go through both of those points?  (I was planning on using the curve from equation to plot it this way)

Maybe I'm a little too obsessed with getting this perfect but I just want to learn the program the best I can.  Any ideas on the best way to go about this and the best way to dimension it afterwards as well?

Here's a pic of the part and what my curve looks like with the curve through points method.  The top is the curve I'm trying to get although it would help me in a lot of places to know the best method of doing it.

BTW, using PTC Creo Parametric 3.0

This thread is inactive and closed by the PTC Community Management Team. If you would like to provide a reply and re-open this thread, please notify the moderator and reference the thread. You may also use "Start a topic" button to ask a new question. Please be sure to include what version of the PTC product you are using so another community member knowledgeable about your version may be able to assist.

[mpoling · Accepted solution]

Nick,  You might want to try the Style feature in Creo.  It is still a spline, like the Datum Curve, but you'll have more control of it's shape.  You might also like to try a Curvature Analysis of your curve.

[nthomas-2]

Thanks Mark! I'll give those both a try.

[TomD.inPDX]

What is the basis of the class?  That is a lot of modeling!  Someone really needs to define the level of detail required.

Another thought: Top down design or bottom up design?  It really changes how to deal with the model and the risk level.  I would be very tempted to just do this top down but it may not be the best for a learning curve when errors start creeping in.

[nthomas-2]

The class is called Fundamental Basics of Visual Design for Engineers.  I could definitely get away with a lot less detail as the graders won't actually see the parts we're modeling, only our finished chainsaw model and part drawings.  However, the more accurate I am modeling, the better our assemblies will fit together, and I want to learn as much as I can about the software as well. (btw, the term project is split up into groups of 6 which splits up the work a lot).  That being said, I have a friend who put 50 hours into an engine block on his project (not a chainsaw) and some friends who've taken the class before have put 100-200 hours into it.

When you ask about top down/bottom up are you referring to how we're going about modeling the entire chainsaw?  We each have about 10 parts to model and will then assemble them later.  Of course there will be some error and things won't all fit together 100% perfectly but that's expected.  What would be a way to do it bottom-up?

[TomD.inPDX]

You probably have the advanced assembly suite in the academic package.  This means you can learn to work with skeletons.  You can also work with a master surface that controls certain aspects of the connected elements.  These create the envelopes of your "design".  This also ensures that all the pieces will follow that certain "style".

Just sayin'

[StephenW]

Bottom-up is what you are doing. You are working independently and modeling all the parts and then later assembling them. Top-down is you work within an assembly to build the parts that reference each other or a skeleton (as Antonius mentioned).

From a beginner standpoint, I probably wouldn't take on skeletons or top down design. Build your parts, assemble them and then adjust the parts as necessary to make them fit.