24 Replies Latest reply on Jul 28, 2010 12:23 PM by Lenny Bucholz

    Arcs to Splines

    Travis Godfrey

      Anyone know what I am doing wrong? When I draw a part in SolidWorks then make a drawing of the model then export it to a DWG the arcs are no longer arcs they are splines. I also have a similar problem in SolidWorks as when I draw a sketche (as a radius)  then do a sweep or anything else it changes to a spline so it can not even be dimensioned in solid works is this common? It is giving me all kinds of headaches in the manufacturing end. Thanks in advance to anyone that can help.

       

      Travis,

        • Re: Arcs to Splines
          Jeremy Feist

          I can't help with the DWG splines, but for dimensioning your sweep in SW, try to set it up so that the sketch(es) are dimensioned how you would like the drawing dimensioned (even if you need to use some driven dimensions to do it. that way you can insert the dims into the drawing.

           

          Jeremy

            • Re: Arcs to Splines
              Travis Godfrey

              Thanks Jeremy,

               

              That will work and have not thought about doing that. But still confused why everything is converted to splines in the modeling process....Just seems stupid to me, but then again I have been frustrated with this software lately so maybe it is just me...

               

              Thanks again, Travis

            • Re: Arcs to Splines
              Lenny Bucholz

              of course they will no longer be true arcs or circles, you are createing surfaces (faces) that create the outline of what you have made.

               

              the only items that you can get your arc dims from are from the sketches you used to create the shape. look at your sketch  for the profile and the path, they will be haw you dimensioned them, but how the sweep calulates the shape all edges become splines. welcome to the world of 3D surfaces and how they react.

               

              my question is, how are these part going to be manufactured? If machined, most companies take the SW part file and cut them in a CAM package and the drawing is for calling out hole, tap, tolerencing and important items to be addressed.

               

              think about how would you measure a potato, carrot, apple? the surfaces are not really round, pretty dam close, but no cigar.

                • Re: Arcs to Splines
                  Travis Godfrey

                  yes that is the problem when manufacturing they are going off the model or dwg file and it is converted to splines so when a part is drawn as a model they use it to cam around and now the profile which is supposed to be a radius is showing as a spline and instead of the machine doing one continuous motion around the part is doing 1,000 little tiny line moves which cause bad finishes and not the true radius when checked by cmm.

                   

                  Thanks, Travis

                    • Re: Arcs to Splines
                      Lenny Bucholz

                      Travis,

                      I have been doing this for 25 years and when you are cutting surfaces with the CAM package you will always get little lines!!!! I do not know which CAM package you or your vender is using, but I can crank up the surface tolerence and you whould never know that it's not a true rad. This is the nature of how CAD systems and surface modelers generate surface intersections using NURBS and Rational B-Splines surfaces. I cut injestion molds, prototype models and parts that get CMMed all the time and there are no issues.

                       

                      some CAM packages will use a arc filter to try and mak G2 and G3 move in the GCode, but unless you are making the cutter move in the XZ or YZ planes you will not get a true arc move. I have not found one CAM package that is a true G2 and G3 coge generator.

                  • Re: Arcs to Splines
                    Mark Kaiser

                    If you can upload an example we may be able to help more.

                      • Re: Arcs to Splines
                        Travis Godfrey

                        Ok, Here is the SolidWorks file, drawing and the Dwg. If you look at the SolidWorks file you will see it has 1.625 radius's on the profile in the SolidWorks drawing you can kind of dimension them but for some reason it kicks them up off the part, at least for me, then when converted to a dwg the 1.625 radius's are now splines. Then on the .5 radius being sweep through the middle it is being sweep on a .375 radius across the part witch is a spline right form the word go in SolidWorks so guess I can not complain about that one to bad but I don't understand the 1.625 profile radius........? 

                          • Re: Arcs to Splines
                            Lenny Bucholz

                            the way you are sweeping it is not a arc you are creating an elipse, so it will never be a arc!!!!!!!!!!!!!! to get a true rad the circle needs to be perpendicular to the sweep path!!!!!!!!!!

                             

                            looks like you are trying to drive a 1" ball cutter around the rad?

                             

                            Message was edited by: Lenny Bucholz

                            • Re: Arcs to Splines
                              Lenny Bucholz

                              did the same with a revolve, the 1" dia circle is normal to the sweep path.

                              • Re: Arcs to Splines
                                Anna Wood

                                Travis,

                                 

                                When you Save As to DWG go into the Options and Select "Export All Splines as Polylines"

                                 

                                Cheers,

                                 

                                Anna

                                • Re: Arcs to Splines
                                  Lenny Bucholz

                                  here

                                    • Re: Arcs to Splines
                                      Travis Godfrey

                                      Hey Lenny,

                                       

                                      I think you misunderstood me. It was not that edge I was concerned with, I get why that is a surface. It is the 1.625 Radius around the perimeter of the part that was the biggest issue and also the .375 radius I sweep the .5 Radius around. The outside perimeter in no way should be a surface it was just a sketch that was extruded.

                                       

                                       

                                      some CAM packages will use a arc filter to try and mak G2 and G3 move in the GCode, but unless you are making the cutter move in the XZ or YZ planes you will not get a true arc move. I have not found one CAM package that is a true G2 and G3 coge generator.


                                      And yes unless in 3D machining you go into G18 and G19 you will not get true radius's but when the outside profile of your part (G17) is in a spline and you get 1,000 little lines and not one radius you get very bad surface finishes and not a true radius and close don't usually cut it.

                                       

                                      But thanks for the help Sorry I was not more clear in my original post.

                                       

                                      As frustrated as I get sometimes with SolidWorks(some due to lack of experience, just changed from AutoDesk in Dec.09) I defiantly appreciate its users. Thanks for all the help ladies and gentlemen.

                                       

                                      Travis,

                                        • Re: Arcs to Splines
                                          Lenny Bucholz

                                          So what CAM package are you running?

                                            If I was going to run the part you have the only 3d I would cut is the .5 rad face.

                                          the bottom of the SW model is arcs and lines and i would use the wire frame to cut that portion in the CAM.

                                           

                                          If you would have shown the bottom view in your SW drawing the edges would be lines and arcs like your sketch.

                                           

                                          I run splines all the time and get great surface finish, sometimes it is the CNC with the acceleratin and decceleration that gives the bad finish or the combonation of the 2. Surfcam allows me to set a very high surface and curve tolerance and on the Haas I don't see any facets/flats on the parts and the Haas I run is a VFO 1995.

                                           

                                          What I guess I try to say is you are killing yourself, but then I really don't know what type of work you do. It shouldn't be as hard as your making it.

                                            • Re: Arcs to Splines
                                              Travis Godfrey

                                              I don't understand what I am making hard. I drew it up converted it and got splines and I wanted radius's  there is no need at all for 3d for this part it is a simple 2d part why make this simple part in 3d? What Anna posted is exactly what I wanted. Yes I could of still ran this with splines instead of radius and probably got it fairly good but one with 3000 lines of code instead of 30 and if one of the operators had to make a change he would of sat there scratching his ass for 45 min trying to figure out which of the 3000 lines of code had to be changed to get what he wanted not alone how it reacts with cutter comp. The simplest way to do this part is with arcs bottom line and that is what I wanted to figure out because I knew there had to be a way and yes I could of used the bottom view and got the same results but I would just like to use the same geometry used for the print just less files and more of the features.

                                               

                                              Thanks agian for the help.

                                               

                                              Travis,

                                                • Re: Arcs to Splines
                                                  Lenny Bucholz

                                                  So in the long run you are having the guy program at the machine using it's control and not using a CAM package?

                                                   

                                                  In most of the CAM packages these days they take SW part files and if you make a chang to the SW part it will warn you and ask if you would like to bring in the new geom., then all you have to do is regen the tool path and all is good.

                                                  The thing is every time you make a change to the part file you need to make a new dwg/dxf from the SW drawing, with the SW part file in the CAM you are only dealing with one file and the drawing is just for checking the dims and for info about the part.  are you using a CNC mill to cut this part, the SW model has the lines, arcs on the bottom face for the CAM to use, no little lines and you can use the cutter comp, just have to make the pathes for your CNC guy to use for those cridical areas...........do this every day. Just Trying to save you all the extra work of making the part, the drawing, the dwg/dxf, when a part file and SW drawing is all the machinist needs.

                                                   

                                                  just trying to help save you time.

                                                    • Re: Arcs to Splines
                                                      Travis Godfrey

                                                      No we are using a cam package but it is older and does not take direct SW files, yes the newer packages integrate with SolidWorks fairly well, It will take a parasolid but not the SW file directly. And the fixture is holding multiple parts and it is just way easier to export the geometry as a dwg file array the parts to match the fixture and cam from there and if I can use radius's instead of splines why wouldn't you? For doing this everyday I don't get what is so hard to grasp? I am not doing a one piece mold I am doing production parts. Yes it is on a CNC vs what a manual?

                                                       

                                                      Travis

                                                        • Re: Arcs to Splines
                                                          Lenny Bucholz

                                                          Travis Godfrey wrote:

                                                           

                                                          No we are using a cam package but it is older and does not take direct SW files, yes the newer packages integrate with SolidWorks fairly well, It will take a parasolid but not the SW file directly. And the fixture is holding multiple parts and it is just way easier to export the geometry as a dwg file array the parts to match the fixture and cam from there and if I can use radius's instead of splines why wouldn't you? For doing this everyday I don't get what is so hard to grasp? I am not doing a one piece mold I am doing production parts. Yes it is on a CNC vs what a manual?

                                                           

                                                          Travis

                                                          Travis not hard for me to grasp, I do production and prototyping and use lines,arcs and splines and DNC to the machine and load to the memory/hard drive of the CNC all the time. cutter comp works on it all and you just have to produce the cridical paths that might need to be tweeked at the machine with G43. I really doesn't matter if I get 100 lines of code or 4 lines we get good parts. so to answer your question splines or arc ...who cares.

                                                           

                                                          now another question is why aren't you using iges to get a surface ansd wireframe into your CAM? Parasolids will only give you surfaces and that is probably is why you you only get a crap load of line for cutting your parts in your CAM. Iges will give you both surf and wirefram and the wire will be a combination of of lines arcs and splines. so the part you put up from SW would have the same edges in the wireframe, if its a arc in SW it's a arc in the wireframe.

                                                           

                                                          So the grasping is trying to figure out why you are not getting arcs from the SW file into your CAM...Parasolids is why, no wireframe with arcs.

                                                           

                                                          as for for the CNC vs. Manual....I ment CNC or laser or waterjet or wire edm....most of the lasers and waterjets only take dxf files and since you are making 2d files dwd/dxf that is why i asked if it was a CNC mill.

                                                           

                                                          I have used SW and a CAM package since 97 and have never had the issues of not getting arcs in the CAM, try iges, hell use SW in an a assembly to make the fixture with the parts in it and save out an iges, open in your CAM and you should have surfaes and wire to use to program from.

                                                           

                                                          what is your cam package and what version? that would help me know what your using and what limitations it may have...maybe none, just anorther aproach.

                                                           

                                                          again it seems your cam should produce what you need without have to make dwg's, thats all.

                                                           

                                                          lenny

                                                            • Re: Arcs to Splines
                                                              Travis Godfrey

                                                              tweeked at the machine with G43

                                                               

                                                               

                                                               

                                                              What kind of control do you have that is using a G43(Tool Length Compensation)  for tweaking?  And the problem comes in when one of those lines is broke into let say a .002 segment and you need to make a .0025 offset (with G41 or G42) you will end up with a crc alarm then the program will need altering and I do not let my operators make program changes. As for splines or arcs who cares I will take an arc over a spline any day it is making one smooth move vs multiple moves for the same(ish) result. And my CAM will take iges but I like the parasolid better for my 3D programming and yes I could do it that way but sometimes I choose dwg(2d) because depending on what I am doing to which method I use best/fastest way up and running is the way I go. By the sounds of it I take it you have only used CAM software for programming and never did any free hand programming. I appreciate your opinion but what I needed I have got I really don't need to set and argue with you over this everyone has there own way of doing things and each there own.

                                                               

                                                              Again thanks for the help.

                                                               

                                                              Travis

                                                                • Re: Arcs to Splines
                                                                  Lenny Bucholz

                                                                  yeah haven't hand coded since 91 100% SW to surfcam since 92. yup brain farted on the G41 42. so we agree to disagree. I just have to do alot of parts that people send and when a change comes up you have to get it back it to the cam. so 1 file vs 2 files is better for me...I'm getting old and the memory is fadding or just to many side jobs going on.make alot of parts for the bike builders here in AZ. have fun lenny