Full Version: Polygonal Converter.

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Hello chrisd,

The engraving and texturing maps can be created from various bitmap and vector formats, they don't need to be NURBs. I believe you can also use scan data as well. I'd investigate having the items modeled to within a manageable tolerance, have the molds milled conventionally, then have the NURBs data, maps and/or scan data sent along with the molds so the detail can be mapped accurately to your molds. The molds are then engraved by subtracting a relatively small amount of material for the finish and detail you desire. I know you can accomplish this chemically, through EDM and laser ablation.

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Hi Chris,
"""""""""""" I fail to see in many situations where the nurbs is actually going to better to machine from where there is a lot of surface variation.""""""""""""

The NURBS will be preferred by your CAM system. With a NURBS model, you are allowing your toolpath generator to perform the path calcs and decisions with regard to the settings within the CAM system.

With a poly model, you will be forcing the toolpath calcs, tolerances, moves etc, in conjunction with the CAM settings, which is less desirable and can be problematic when you are doing precision work (especially molds)

Frenchy mentioned reducing the poly count, which I do a lot. The programs today are getting really good at this, but there are some considerations (mostly with molds)

Is DOES morph the intent (but so does the NURBS conversion), so if you are doing 2 part work, you will want to re-create the second/split half from the morphed result. The "decimation" can be done to allow for tolerances specked on the part.

I use 3dcoat for poly retopo's or "decimation".....

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While I understand the relation of surface finish and precision to the nurbs surface, I have explained to numerous vendors that I am not interested in high polish or extremely high precision surfaces.

The fact is most cam systems even now compute a toolpath based on a tesselated model derived from a nurbs model. Therefore, even though I may give a vendor a nurbs model, their machine is cutting it as G1 or straight line moves. So when they complain that they can't machine from from a triangulated model, that points out me they actually don't understand their own machining process very well.

Its quite funny actually when I asked to see sample G-code from one shop, to clarify this, they refused.

What I believe is happening is that most machine shops assume high precision work, and they won't stop and switch gears for projects that might be a little different from what they usually do.

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"""""""""The fact is most cam systems even now compute a toolpath based on a tesselated model derived from a nurbs model. Therefore, even though I may give a vendor a nurbs model, their machine is cutting it as G1 or straight line moves. So when they complain that they can't machine from from a triangulated model, that points out me they actually don't understand their own machining process very well.""""""""""

Well, yes to what you said, but:

Forcing the CAM program to generate it's path based off of the given little flat lines and patches and hundreds of thousands of edges (each requiring the calc to start and stop THERE as opposed to where IT DECIDES) is problematic for CAM programs and post processing into a proper toolpath. Some of your vendors may have just decided that the cost of problems that can arise because of that is not something they want to keep dealing with.

It's far better for the CAM program to be allowed to generate it's own little sliced up model based on the tolerances supplied within the system. Mixing those tolerances with the "forced dice" of a polygon model is hard at best.

Many CAM programs handle toolpath differently. Some will calc off of the "display mesh" created (way junk). These are the apps that will put a toolpath on a multi million poly model "really fast"... Some will just give you a set, hard coded tolerance which can burn past any of the really hard calcs. Most of the higher end stuff, will be looking at the surfaces supplied.....

CAM'ing a multi million poly model out when the specs are a little looser like you mention, is not super difficult, but it requires an understanding of the nature of the model. Not a lot of CAM shops are very versed in the underlying structure of the models they are working with. They are Machinists....

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Hello,

Trying to calculate an optimized toolpath through even 100000 points seems to be some insane traveling salesman problem, let alone millions of points. Perhaps the reason nobody wants to touch the job is because they realize that computationally it is not practical, and there are already well established alternative procedures that will provide an acceptable result.

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"Perhaps the reason nobody wants to touch the job is because they realize that computationally it is not practical"

That statement is simply not true.

If I had a mediocre CNC mill with a $2000 -$3000 CADCAM program like DeskProto or VisualMill (MasterCAM, SurfCAM, or Delcam not needed), I could cut this in steel myself. So the problem is not the file. And its not computation power.

I CNC milled files with more than a million triangles 15 years ago using DeskProto. Its ludicrous for a machine shop to say it cannot be done now.

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You have to read the entire sentence:

"""""""""Perhaps the reason nobody wants to touch the job is because they realize that computationally it is not practical, and there are already well established alternative procedures that will provide an acceptable result.""""""""""""


And then:

""""""""""Its ludicrous for a machine shop to say it cannot be done now.""""""""""

Remember to note the difference between "can not" and "will not"....

Could probably find a thousand hobbiests to cut stl's.... However, it will be different for guy's running mastercam on $100,000 machines, with employee's doing the machine work (and even the CAM work)....

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Hello chrisd,

Apparently you misunderstood my first statement which made my following statement unclear, I'm talking about calculating the optimal tool path from each point on each line of each triangle in relation to its neighbors. I'm not sure how you could say that my computationally impractical statement was not true. I didn't say it was impossible, but it is highly inefficient, and unnecessary given the other options that are available. Did the CNC mill each one of those million plus triangles poly by poly fifteen years ago? Of course not, tool paths were created from an input surface. But I guess that's the point, start with a lightweight surface set and add detail where needed through further secondary finishing processes that are appropriate for the desired output.

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A polygon surface meets my needs in terms of producing a finished product. I do not need aerospace finish or accuracy, which I have made abundantly clear in my dicussions about getting the work produced.

If I could machine a million plus poly surface 15 years ago, it can certainly be done now. Its as computationally intensive now as it was 15 years ago.

CNC machines can cut from polys or nurbs. They don't care. What matters is the CAM software that creates the toolpaths, and whether the CNC machine does spline interpolation from G1 moves on the fly.

If was concerned about finish and accuracy I AGREE that nurbs would be preferable for the reasons that have been stated, which I am previously aware of.

I talked to a shop that even had a license of VisualMill. The problem is not machines or software. Unfortunately its ignorance.

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Hello chrisd,

You milled an object based upon tool paths created from a million plus point mesh. That is another thing entirely than using the exact points of the mesh itself for the tool path and trying to optimize that route. I'm not sure it's ignorance on the machinists part, they probably know your requested process is not optimal, so rather than have an unhappy customer they'd rather pass on the work, it's a reasonable expectation.

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OSTexo, I appreciate your input on this as well as everyone else.

What I would have expected from the services I have talked to is "We can't do it because ..." with some specifics instead of leaving me to speculate about what the problem is. If they can't qualify the problem to the customer, is that not ignorance?

I'm not overly concerned with a high surface finish or accuracy, and I have clarified this to the services I have communicated with. So despite not needing these things, it appears that most services don't have an easy way to dumb down the process. The optimization and spline interpolation that is maintaining a higher accuracy and surface finish also makes for less wear & tear on the machine.

I am aware that the Jewelry industry, who I would not consider hobbyists, produce work from STL files by milling. In many cases they mill wax although, that has largely gone the way of 3d printing. They also machine small molds for non-investment casting.

There are some "micro" milling machines with a work volume of less than 3", and perhaps part of the difficulty in finding someone to do the work is relevant to the size I require.

I need a minimum of 3" XY, up to perhaps 12" -18" max XY and 2" in Z. I only need 3 axis machine (no undercuts).

Once I get some software to convert polys to nurbs, I'll have another go at this.

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Hello chrisd,

You're not a customer, you're a prospect (big difference). You're asking them to do something they are not willing to do, perhaps due to your insistence of having them follow a flawed procedure which they know will produce an unsatisfactory result. A company is under no obligation to educate you on why they aren't willing to do something, but I gather by the content of some of your posts that you aren't making any friends by minimizing the operators experience and abilities to properly assess your project, and that certainly doesn't make them ignorant. Even with my very limited knowledge of mold production and injection molding, my limited experience tells me you're barking up the wrong tree when it comes to the software, process and type of equipment you think can be used to create those sort of parts.

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"You're asking them to do something they are not willing to do, perhaps due to your insistence of having them follow a flawed procedure which they know will produce an unsatisfactory result. "

No, they need to tell me why they can't do it. It is the responsibility of the service provider to explain what service they can provide (or not). I can't tell them why they can't do it because I don't know.

Logically, only they can tell me why they can't do it.

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"Even with my very limited knowledge of mold production and injection molding, my limited experience tells me you're barking up the wrong tree when it comes to the software, process and type of equipment you think can be used to create those sort of parts."

If you don't have any experience with what is being used in the Jewelry industry, then you would not understand that there is a big difference in what is an acceptable 3d file format.

I suspect this comes down to the fact that they are using much smaller CNC machines, and are not pushing around as much mass of the machine to do the milling.

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Hello chrisd,

Again, the shop is under no obligation to educate you why they are unwilling to provide a product or service. I suspect that it has something to do with your insistence that they are too ignorant of their own shops capabilities. My knowledge is limited relative to others I know that view these boards that make a living in the mold design industry. That's not to say that I don't have mold or CNC experience, I just don't pretend to know more than others on the subject, and I've found that operators are happy to provide alternatives if you give them room to move. It sounds like you haven't done a thorough evaluation of the available technology to provide you with a proper part to acceptable tolerance using an efficient and relatively affordable workflow. You can bang in a nail with just about any tool given enough time and effort, but hammers do a better job than most for that task.

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"Again, the shop is under no obligation to educate you why they are unwilling to provide a product or service."

If the service provider cannot or will not explain their service, that is simply poor customer service, and IS ignorant if the service provider believes that will improve the experience.

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"It sounds like you haven't done a thorough evaluation of the available technology to provide you with a proper part to acceptable tolerance using an efficient and relatively affordable workflow."

Again, not true. A machine shop tells me they cannot machine without a nurbs based file. Another machine shop tells me they can machine from an STL, but the size I need is too large for their equipment. I did not fabricate this information, it is true.

If you can draw an intelligent conclusion from this info, then you are smarter than I am. That is why I say I need more information.

At this point it makes sense to deal with the service that can handle the size, and give them the file format they require to do the work.

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And I have been polite with them. What you are hearing is the frustration at this point.

I am doing my job as an informed customer, seeking knowledge about a products or services. If a customer does not get that information directly from the service provider, then it indicates ignorance on the part of the service provider either about their service, or about good customer relations. If they do not want to educate the customer about their product, what then should the customer do?

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Hello chrisd,

Honestly, you really don't need to convince me of anything. If you're being treated the same way by multiple shops you have to at some point step back and reevaluate your questions and requests especially if you're getting similar responses. I'll admit that it takes patience to deal with the challenges associated with fabrication markets, but that time can also afford you some benefit by exploring your manufacturing options.

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