Non MC specific drafting help- splines

[MattW]

Being a newbie to the use of splines, I have never seen one on a drawing. I have a part that I need to send out, and although I know they will just cut to the solid, I would like (need) to document this a bit better than 'cut per solid file'. I can dream up ways to do this, but it would be better to use some sort of standard method. If someone could send me a sample drawing, or throw some quick details on my part (currently in Solidworks), I would greatly appreciate it.

 

MattW

[MattW]

Am I to gather from the chorus of responses that splines do not get documented beyond a table of points that lay on the spline?

[Matt Berube at Ferron Mold]

Our detail prints for injection mold components usually just have basic 2-D views and simple dimensions along with a note that says "SEE CAD FILE FOR 3-D GEOMETRY" (or something like that)

[John Summers]

MattW, you're right -- splines are defined by a number of points that lie on the spline. Actually, it's the other way around -- the spline is made to lie on the given points by a complex mathematical process. Therefore, the process should be included, defilning the spline as a parametric cubic spline, a Bspline, or whatever. For most curves, though, it doesn't matter much. Any of the common methods will produce a reasonable spline. Most, but not all Mastercam spline are Nurbs.

[MattW]

I suppose my question would be better put- How do you dimension a spline on a drawing? Edges and radii are straightforward, but the mathematics of splines are complicated enough to not be of practical use. So, I was wondering if a simplified method has been developed to accurately convey the shape. What did y'all do before CAD/CAM systems? Argue and point fingers with designers?

 

 

MattW

Vertex Pharmaceuticals

[?Mark]

quote:

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How do you dimension a spline on a drawing?

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The most popular way that I've seen is a table of points.

For ex, if there is 20 points you mark 1st and 20th point of a spline on a drawing and build a separate table with each point's coordinates.

Works well.

Just recently got a drawing (no cad file) with a table of 30 points and it's a pain in the ... typing it in... not to mention checking and double checking myself took a minute or two

 

hth

[John Summers]

Better yet, reference an ASCII file of points. In the old days, prints DID have a list of points which had to be transferred by typing. We have better tools now.

[88Matt]

We still have more than our share of THOSE prints in our shop. We cut a lot of splines with tight all around tolerances. As stated above, machine to the solid and use the the table of points for inspection only. If your tolerance is loose enough, convert to lines and arcs is possible, but not recommended.

[88Matt]

We still have more than our share of THOSE prints in our shop. We cut a lot of splines with tight all around tolerances. As stated above, machine to the solid and use the the table of points for inspection only. If your tolerance is loose enough, convert to lines and arcs is possible, but not recommended.

[Mike Mattera - TFM]

All you can really do is specify that at a specific angle/point the radis should be "X". Much like you'd do with a table.

 

Mike Mattera

[MattW]

Thanks all. I kinda suspected the clumsy-but-effective method (a table of points) was about the only reasonable method. Since my current issue is only for aesthetics, "cut per CAD file" is going to do it- I think.

 

MattW

Vertex Pharmaceuticals