SW drawing saved as DWG, then open in Autocad geometry has gaps

[TomMalinski]

Much of our cnc toolpath geometry is created direct from our SW models, but we often save a SW drawing as a dwg file and then bring it in to Autocad for non SolidWorks designers to use as ref, and quite often geometry is used for cnc toolpaths.

Here is my issue. In Autocad prior to sending geometry to our cnc machines we are in the habit of converting connected geometry to a continuous polyline to insure its integrity of being properly constructed and trimmed with no gaps from endpoint to endpoint. For some reason after saving a SW drawing to Dwg I always have very small gaps that prevent a continuous polyline from being created. In other words our integrity test fails!! When I measure a simple rectangle way out to 7 or 8 dec places endpoint to endpoint should be .00000000 but I'm finding .00000020 gaps. Is there a technical method or process to resolve this? We work in a multi CAD software environment and doing everything in SW is not an option per my Boss!!

Thanks for your help
Tom Mlainski

 

[ArtL]

Tom My cnc machine has a gap allowance of .00005. This can be set to just about any value, depending on what the tolerence of the parts you are making are. So the varience you are seeing, should not make a difference in the final output.Making a polyline is old school and I feel isn't necessary with todays machines.Going back to the "bad old days" when I did all my designing in AutoCad,Isn't there some way to tie lines togather to make continous polylines? I know you can use the fillet command with the R=.000 and join corners so there is no gap. I have also saved SW as a DXF, and imported the DXF into AutoCad, then saved as a DWG, but I did not check for small gaps.But the DWG's imported into my CAD software and made good parts.

 

[ctopher]

Anytime there is a conversion, it's not 100% accurate.
Not much to do about it.

I don't like to mix CAD software in one company.
Let arch/facilities use ACAD, engineers/designers use SW.

Chris
SolidWorks 11
ctopher's home
SolidWorks Legion

 

[mflayler]

Since the DWG file that SW uses is not a trusted DWG file, there will always be problems. The same doesn't happen near as much with Inventor for obvious reasons. I have seen these anomolies for years and it will probably never be perfect, the best bet as mentioned is to have your machine take care of it, but I have also seen larger arcs not appear as well, so a visual inspection is always required when translated.

 

[TomMalinski]

Thanks everyone!
We generaly dont have nay issues with cnc toolpaths even with the gaps. It is just piece of mind by ACAD users that all is good even though they can't polyline it. Back in the day we had many CAD meetings talking about good construction methodology to avoid gaps and lines on top of lines. It is Ironic that with technology as good as it is today we seem to have no choice but to settle for accepting gaps in our geometry due to conversions from CAD systems. We know we could go and fix all of the gaps but then that is a waste of time if cnc doesn't care if the gaps exists.
I agree 1 CAD system is best.

 

[progdie]

I do this all the time, create a model in SW and save out as .dwg from .slddrw. Most of the time, it's sheet metal. I also create polylines and regions from that geometry requiring contiguous lines and arcs. Seldom do I have a problem, perhaps one in hundreds. Would it be possible to share a troublesome file and let me see the results I get. One of the reasons I like SW is just for the reason that its easy to share between the two platforms.

 

[rfus]

Tom, are you using the DWG Export Options?

You can select -> Export all splines as polylines
You can also select -> Enable End Point Merging

You can specify the tolerance within which gaps between line endpoints are eliminated. Select High Quality as well.

The DWG version is also important.

You could also try bringing your DWGs into the free DraftSight or SW DWG editor as an intermediate step and see if the files come in with gaps and these two 2D editor packages may create better DWGs for auotcad.

I don't really agree with your mixing CAD software comment ctopher. There are good reasons we use autocad at my company in addition to SW. We have non Solidworks drafters who really only do simple drawings that only require autocad. Putting them on SW would be overkill, but the MEs do provide dxf and dwg items for them to use in Autocad. We use ECAD software too and dxf/dwg is really the format to go between ECAD and MCAD.

Most of all, we send files all the time to vendors, 3d and 2d. Should we only use vendors who use SolidWorks? Lots of these guys use DWG/DXF for machining and we are required to get them good dxfs and dwgs that they can work from/with.

There is a lot you can do to get good conversions versus saying it will never be accurate and you should only use SolidWorks.

 

[ewh]

It can save many headaches running only one system. Much of this of course depends on the industry, and who is in the drivers seat (engineering or manufacturing).
As for sending files out to vendors (or other down-stream processes), I don't know of any reputable CAD packages that can't export neutral formats.

We have non Solidworks drafters who really only do simple drawings that only require autocad. Putting them on SW would be overkill

The same thing was said about CAD itself when boards dominated, and it depends on how you look at it... do you ever need to reconstruct models to solve issues discovered on the floor? Is AC just a substitute for a drawing board? Does your company invest in it's employees? It may seem overkill, but having a workforce able to use more than one tool is a great benefit.
If you aren't concerned with any type of regulatory agencies and don't really care about data retention, this hybrid system can (and does) work fine. If you do have to answer to regulatory agencies and have to keep all (company and customer) data under control, run!!!
We use Autodesk products for larger scope drawings as well as high-end CAD for the actual engineering definition, and unfortunately it seems that duplicate part files get created... imagine that. With a good data control procedure in place, the problems may be relatively minor but without, remodeling something every time you need it (creating duplicate parts) is often easier short term than locating the one correct, approved existing model. That path is the often the one of least resistance and is the opposite direction of good configuration control. It will bite you in the a$$ one of these days.
If I could invent a good a$$guard, I'd be rich!

My apologies for the trip into the weeds!

Technically, the glass is always full.

 

[rfus]

ewh,

Tom needed to create DWGs for his CAM / CNC machining operations, and ctophers answer saying you can't do much about conversion accuracy to DWG (or as you call it, a neutral format) and the best thing to do is not to mix CAD in the company does not really get Tom anywhere and it is also not true. His fundamental problem was that he had problems exporting to this neutral dwg format (within his company and not to a Vendor), so if I follow your point, your saying that SW is not reputable because Tom has problems correctly exporting to dwg? Should Tom go buy new CAM software that runs as an add in to SW?

My company is a vertically integrated, engineering centered, contract manufacturer and design house. We do system and circuit board design and engineering, program management, Protos and NPI, System assembly, test, direct fufillment, etc.. all under a very complete QMS outlining our SOPs. We focus on Medical (510k), Military, and High End regulated industries, and do a lot of hand holding for our customers. We will do back of the napkin to out the back door manufacturing or do a build to print. We are not the least expensive, but we always get it right. We are very successful, have an extremely talented workforce, and work with some very high profile customers. We have some of the highest tech in our state.

We invest in the latest technology, and have so many software tools at our disposal, and the company will pick up whatever we need as long as there is justification for it. The ERP and manufacturing software systems are running hybrids of 3rd part software with our own databases and coding. We have requirements management, verification and validation, and FMEA tools. Our PDM system was created from the ground up and handles all of our documentation, ECRs, Parts Lists, Item Masters, Customers data, and Job Exceptions. It is linked to our DHF. Our prints also contain references to sources on the DHF/PDM. It has been audited many times by regulatory agencies and customers. Data retention and being audited is a big thing to us.

People always want to talk about the tools and end up putting way to much focus on the tool itself. We have 100s of thousands in MCAD, ECAD, FEA, Optics and Software development tools. I use SW for mostly everything to do with mechanical design, engineering, and analysis, but the fact of the matter is the Autocad is the right tool for some jobs. Have you ever made routing diagrams in SW or cable drawings? Certain schematics, not done in our ECAD caputre, and blocks are way better in autocad. Driving 2d machining is done with native Autocad formats. Circuit board prints and panel drawings, not gerbers, are done in AutoCad. Clerical updates to legacy data and information is done in AC. Simple drawing that don't need to be done by the high paid engineering team can be done in AC.

So we should run next time our customers, potential customers, ISO, and the FDA audit us becuase we use Autocad and Solidworks under the same roof? We continually improve our QMS and SOPs, but we also do not put too much weight or focus on the tools we use to get the job done.

 

[ewh]

I apologize for coming across as I did... my rant was intended to be of a more general nature, related to experiences I have encountered using multiple CAD systems. I have had to address data control issues with various aerospace composite part customers, and let's just say that their standards are very strict, and the components, when broken down to basic constituent "pieces", were quite complicated. It is required that every, every dataset used in the creation of that part be recorded and controlled so that database integrity was ensured to be accurate, and any part produced could have it's entire fabrication history documented.

On the opposite side of the spectrum, I have worked at companies that use multiple CAD systems, and the logistical log-jam can be a nightmare. 3 different systems, disciplines overlapping, and innumerable duplicate files, both within and outside of the systems in which they were originally created. It is very easy to understand why at this company it was easier to just keep remodeling, but they will never be selling airplanes. Those are the ones I was referring to run from.

Regarding the "reputable" remark, I was referring to the format choices offered by CAD systems today as being sufficient for most tasks of this sort. Problems do occasionally occur, but almost always can be worked out. Research will still be required as to which "solution" is best for your application, but solutions are out there.

I admire your setup and have no problem with using multiple software, just with using different ones to document the same actual part, doubling the effort of controlling that data. I do understand the necessity in the examples you cite.

As for valuing employees, SW is very effective at anything AC can do and I just thought it would be better for the company to have a more adaptable workforce by having more employees who could be utilized more fully if needed, provided of course that the company could afford the extra licenses.

I was in no way trying to disparage your company... from what you have told us of it, I am impressed.

Again, I apologize if I offended you.

Technically, the glass is always full.