Tangent to two curves not arcs

[skyking01x]

Tangents to two arcs are no problem for me. However, I cannot figure out how to draw a tangent to a circle and to a spline curve or a tangent to two ellipses, etc. Any one have a tip for drawing a tangent to two curves that are not arcs? I have looked thru all the X3 help files and can't find anything but the elementary answers about tangents to two arcs.

 

[iowajim62]

You could create a line tangent to one arc/curve and then trim that to the second arc/curve. You could then create an arc snapped to the center of the line you created, This would give you an arc/curve touching both entities.

 

[skyking01x]

Isn't your line perpendicular to the two splines? What am I not understanding? In MCX3 when I draw a line tangent to one circle then bring the cursor close to another circle, it snaps the tangent line to both circles, quickly creating the line. If you try it with an ellipse or other curve (but not an arc) it won't work. I'm thinking I don't have some setting set properly but I sure don't know which one.

[Mike Whitten CAD/CAM Contractors]

For X2:

Create>Spline>Create Blended Spline

My guess is that X3 would be the same.

 

Mike

[skyking01x]

OK, this getting too complicated. How does one draw a straight line tangent to two ellipses?

[Mike Whitten CAD/CAM Contractors]

Hello skyking01x,

 

I am sorry I misunderstood the question. I can't seem to find a direct way to do it in X2 Mastercam. It would seem that there is a way but I can not find it. There are ways to cheat but you most likely know all of them already. Someone may come along and show us how.

 

Thanks,

Mike

[skyking01x]

Right, I can't see how to do it graphically after a lot of "fooling around". I know one could do it mathematically but that's not what I had in mind. I don't want to get into the solution of a differential equation to draw a simple part!

[Mike Whitten CAD/CAM Contractors]

If you get stuck, just break the ellipse into arcs using "Break Many" and draw your line. You could also do it very easily in SolidWorks.

 

Mike

[iowajim62]

Try create,line,create line closest. I used it to get this.

 

[Colin Gilchrist]

skyking,

 

What are you trying to do here? The tangency condition of a spline or an elipse varies along it's entire length. There is no way for the system to figure out what you are trying to do...

 

Michael was on the right path when he suggested several ways you could approach the problem. You could break the spline into arcs with the 'Break many pieces' command, or you can use 'Create | Spline | Blended Spline' to create a curve that is dynamically tangent to two other curves, but you still have to pick the "blend" point (point of tangency along the curve).

 

Solidworks and other design programs may have functions that let you do this easily, but I've yet to find an engineering print that would dimension and callout information in this manner...

 

HTH,

[Piglet Trespassers William]

Arc tangent to two splines with given radius ,using xform-offset contour

[skyking01x]

I wanted to mill around four elliptically shaped bosses. I wanted to connect the bosses with straight lines and create the mill path around the outside of the bosses. I couldn't make X3 construct tangent, straight lines to all the ellipses. If they were circles, no problem. I can draw a tangent from an ellipse to a point but not to another ellipse. The math solution to this is a differential equation. Why does everyone make this more complicated than it has to be? Oh, I forgot, that is what we engineers do!

[skyking01x]

Piglet, I want straight lines to be tangent to splines not arcs.

 

skyking01x

[Matthew Hajicek - Singularity]

I poked at it for a bit but I couldn't find a way. Best I can think of is to break a section of the spline out as an arc and use that as a close approximation.

 

There SHOULD be a way to do it, but I don't think there is. If you need it to be perfect I'd generate the entities in SW.

[gcode]

Have you tried forcing a polar line at A90

or A270 and setting the tangent button??

[Colin Gilchrist]

I guess as a mathematical exercise it is do-able. I understand what you are going for. Is it imperative that you keep the tool down and path tangent when you are traveling from one boss to another?

 

This would be a good enhancement request or chook territory...

 

Are you trying to do super high speed machining (where tangency is important)? I guess I don't understand why you can't just create a contour toolpath and add 4 chains with lead in/out? Is this just a theoretical exercise or are you trying to machine something specific?

[skyking]

Yes, it's a real project and to get it done I just fudged a line that was very close to tangency. I then extruded the profile around the bosses to create a solid from which I created a toolpath. But, of course, as engineers we like to "play" with things, right? So, I got thinking "Why won't that work"? At first, I thought I wasn't doing something properly and finally gave up and asked for help from you guys.

[Colin Gilchrist]

In the real world I would use Create | Spline | Blended Spline to accomplish this. You can use a Blended Spline to create a curve that links two separate curves and it can maintain C1 or C2 continuity depending on your settings. There is an option to trim one curve, both curves, or No trimming, which is what you would probably want here. Setting the "Curve Magnitude" to "0.0" will force a "straight line" curve, but it won't maintain tangency...

 

C1 continuity will force the Blend curve to be tangent at each end to the entities you are blending onto. C2 will force the curve to be tangent at each end, and to share the same initial radius as the curve being blended onto...

 

HTH,

[BernieT]

This method below gets a very quick real close approximation of what you want:

 

 

I Created a Line Tangent thru a Point from one oval to an estimated spot on the second oval. Then Created a 2nd Line tangent thru a Point from the 2nd oval back to the endpoint of the first line on the 1st oval.

Not perfect, but very close. If you did it 2 or 3 more times it would be so close it might as well have been calculated out.

 

 

 

 

.

[skyking01x]

That's a good idea! Mastercam does allow one to create a tangent line from any curve(not only an arc) to a point in space. If you choose that point to be on or near the second curve you have a close approximation. Like you say iterate reversing the process 2 or 3 times and it becomes very accurate. I don't understand why Mastercam didn't take that function and carry it further to include other curves instead of only points. Thanks for your insight.

 

skyking

[Jayson Kramer]

I agree good going Bernie.

[Colin Gilchrist]

Skyking,

 

Features get improved when customers request that functionality. If this is something that would be useful to you please send it in as an enhancement request to [email protected].

 

The other thing that makes Mastercam such great software is the ability to write custom utilities in C++ w/MFC that provide the functionality you desire. If CNC Software doesn't want to devote the time to making this functionality available in the main program, someone might be able to write a chook that will do this.

[Rob @ Target Machine]

If you sketch a line roughly tangent to the two curves,

then create a line closest between the sketched line and each curve,

you now have the tangent points(roughly).

Just create a line between the intersections at the curves.

This is close too and can be corrected as well, by more "iterations".

 

More than one way to do the same thing.

 

[ 12-02-2008, 07:35 PM: Message edited by: mastercamguru ]

[Rob @ Target Machine]

You may have to offset the new line (both curves on same side of line) or rotate (curves on opposite sides of line) between each iteration if a chord has been created by new line. After 2 or 3 iterations the lines created normal to the tangent will be the same length. (normal and tangent)

 

(Line normal to tangent method.)

[skyking01x]

That's a good idea, too. Thank you all for your help and interest.