[DsKnees]

Here is a photo of a project I just finished machining. I cut it with VCarve Pro, since the program came with my machine. For reference, the rectangle is .75"x .75"

There are 2 issues I am concerned about. The first is there is a strange divot/ indentation by the corner of the rectangle, and the second is the way my smooth curves got turned into polygons. They aren't supposed to be like that.

The divot is not present in the original drawing. And it is only on 1 side, even though both sides were created by mirroring. The file includes 2 of these parts, and both have the same defect in the same spot.

I made it with an *.skp file (sketchup). I tried all the file types VCarve Pro says it supports, but only the *.skp and *.stl files actually opened. The other file types opened, but none of the content was present when I opened them.

Comparing the *.skp file to the *.stl, the *.skp had the most detail by far. The *.stl has such large polygons that it isn't usable.

The piece in the photo is good enough for my immediate needs. I can fix it. I coated it with epoxy, and I will sand it smooth. But I want to do better in the future.

I'd like to know what you think. Is there a way to get a better result in VCarve Pro? Or do I need different software? If I need different software, which one will have the best chance of success? (I would prefer something that runs on MacOS, since my main computer is a Macbook. And if it works, I am willing to pay for it.)

 

[John Smith_]

I'm not a machinist, but, I would like to see more photos of the project itself
and a little info on what it will be used for. (epoxy is what piqued my interest).

 

[DsKnees]

I'm not a machinist, but, I would like to see more photos of the project itself
and a little info on what it will be used for. (epoxy is what piqued my interest).

The epoxy is to seal the MDF, that is all.

This is a "plug" used to create a fiberglass mold. It is for a product I am designing. I will show it eventually, but I'm intentionally not showing the whole thing right now.

 

[John Smith_]

yes, I see the "divot" now around the corner.
maybe on your second prototype, it will be better.

 

[PhilBa]

Take a look at the GCode in a simulator. See if the divot is there in the gcode. STL will be a problem because of the polygons - that's how STL works.

I would try modeling it in F360. Solids modeling is better than STL meshes. But F360 mainly for the gcode generation options. Best out there.

 

[DsKnees]

Take a look at the GCode in a simulator. See if the divot is there in the gcode. STL will be a problem because of the polygons - that's how STL works.

I would try modeling it in F360. Solids modeling is better than STL meshes. But F360 mainly for the gcode generation options. Best out there.

Thanks. I will try to export my Rhino3D file to F360 and see if F360 can do the CAM part.

But I can't model it in F360. I made an attempt. The problem is the "free form" compound curves in my part, which is the entire part. The part has the type of curves you would see in a boat hull. So I drew it like a boat hull--creating cross sections and lofting a surface over those sections. I don't know how else it could be done. (I can convert the surface into a solid model, and F360 will open the files. I know that much.)

Rhino 3D is the only program I have found that is within my grasp and can do this kind of modeling. (There is a CAM add-on for Rhino, but it only runs on the Windows version....and I've been actively avoiding Windows since Windows 8.)

 

[BalloonEngineer]

Nothing from SketchUp will ever have true curves, it approximates with straight lined. STL files are faceted triangles Meshes. Will need a higher end program that can actually smooth surfaces (numbs). But since there is no gcode for Bézier curves, any surface will be approximated by straight line segments.

 

[DsKnees]

Nothing from SketchUp will ever have true curves, it approximates with straight lined. STL files are faceted triangles Meshes. Will need a higher end program that can actually smooth surfaces (numbs). But since there is no gcode for Bézier curves, any surface will be approximated by straight line segments.

Thanks. At this point I really just want finer resolution than the *.skp file, and I want a program that opens standard file types. If I could control the resolution, that would be great. Getting it "perfect" doesn't really matter, since I have to do a lot of sanding and finishing regardless.


I'm have been going through my options for other software. I'm looking at the other Vetric products. The VCarve pro is actually pretty handy. It does have a "kludgy" interface (that might be partly due to the >1080 resolution monitor that came with the router), but at the same time I was instantly able to make complicated parts with zero experience. They have "3D cut" and the full "Aspire" product.

I tried F360 yesterday. First time I opened it since they "updated", and I gotta say, I so don't want the google maps of CAM software! I had to pay for the month just to open my file, and then their server was offline for maintenance....so dead in the water. Plus I'm not to keen on the idea of everything I draw being stored across the internet.

But enough of that. I gotta get back to sanding! I told myself I was just coming inside to get something to drink....

 

[Oscar36]

There are many programs that can manipulate STL's. Two free ones are MeshLabs and Blender3d. I personally use Blender3d and you can make patterns as high geometry as your system or CNC software can handle. Zbrush is another software package I use and its pretty awesome for 3d sculpting but the interface is a little on the high cliff side and its a bit pricey but Zremesher is a great tool for retopologizing the mesh for cleaner geometry.

 

[gwilki]

Are the divots visible in the 3D preview in VCarvePro? What other files types did you try that didn't work?

 

[DsKnees]

Are the divots visible in the 3D preview in VCarvePro? What other files types did you try that didn't work?

Starting in Rhinoceros, I exported my model in all the file types that Rhino can export to, that VCarve lists as valid file types.

I don't remember the complete list. There was .3dm, .dxg, .dwg, .skp, .stl, mtl, .obj.

These files all opened, technically, but the .skp and .stl were the only ones that had my model in them when they opened. The others opened as a blank file.

My drawing in Rhino is a surface. I should probably convert it to a solid and then re-try. That could be the issue...I just thought of that.

(I didnt look for the divots in the preview, because that's too tedious and I know it is in the program. The defect shows up in the finishing pass, and the mold is 18x20" w/ .012 step over, rastering. The divot is atleast 10 passes wide. The thing I did that my have fixed it is I changed from the default 2013 version .skp to the 2019 version skp. I haven't seen the divot since.)

 

[maddog]

Go into VCarve Modeling Tab, and create a Vector around your model (Looks like arrow pointing right), then go to Node editing mode. There you'll see a lot of little squares (Nodes) that you can then edit individually or you can drag a selection box around all of the nodes and then hit the "S" key. This will sometimes eliminate all the jaggies by turning everything to Curves. Hope this helps.

 

[DsKnees]

Thanks! I will try it out.

I did find and experiment with the "smoothing" feature, but it caused more problems than it fixed. While it did smooth hard edges (including edges that were supposed to be square), it also created crazy spikes at some filleted corners.

 

[maddog]

Yeah, that happens sometimes, but for the most part it does smooth out the edges instead of millions of little stairsteps. Good luck on your project.

 

[DsKnees]

Updating on my progress, I did some experiments to improve the surface finish.

I've heard from a variety of sources that when making a mold from MDF, you need to seal it with epoxy. And in the original post, the photo was just that--I machined it, and then I brushed on some epoxy resin and wiped off the excess that didn't soak in.

That approach worked ok, but the surface wasn't great. It was super fuzzy. And there was some tear out as well.

Then I remembered what a forum member said several months ago. He said to machine the part down to within ~0.010" of the final size, coat it with "thin" epoxy, and then run the final finish pass once the epoxy has cured.

This approach yielded by far the best results! There is zero fuzz, just a flat, smooth surface. And no tear out. It's much easier to finish, because no filling is required. Just a light sand and it's ready to seal. The nice thing about this approach is, you do not have to be careful with applying the resin. Any puddles or drips will be removed when you make the final pass. So put it on thick to ensure maximum penetration.


(What is "thin" epoxy? I used a laminating epoxy with a visconsity of 1,100 cps. And I also used a much thicker "general use" thick epoxy. Both worked, but the thinner one did penetrate further, which gave a more consistent final finish. With the thicker epoxy, there were areas where the router cut through the resin layer, leaving a few fuzzy spots.

Not that hardware store epoxy intended for gluing is not just thick, but very thick!

You can also thin your epoxy with denatured alcohol (or acetone?).

Cure time matters too. Most thin resins are slow to very slow setting. Beware of casting resin (including bar top resin) and wood preservation resin. Both can take days to cure. And the casting resin may not cure correctly if at all. Of the two, the wood preservation type would be the better bet, but you gotta make sure you can re-zero your machine and locate your part a few days after the initial machining. I'm not excited about that!

Anyway, I would recommend buying resin from a composites supplier. And avoid hardware store epoxy for this application.)

 

[maddog]

Try the MAS Penetrating Epoxy Sealer. It's use to pre-seal woods to help eliminate off gassing and helps prevent bubbles. MAS Penetrating Epoxy Sealer

 

[DsKnees]

Try the MAS Penetrating Epoxy Sealer. It's use to pre-seal woods to help eliminate off gassing and helps prevent bubbles. MAS Penetrating Epoxy Sealer

I built several canoes with MAS epoxy. I like their products, even though I'm not using their stuff at the moment.

But I wouldn't use this product for this particular application. To me it's all about cure time. This product is "tack free" in 10-12hrs @ 75F. Compare that to the epoxy I am using is mostly cured in 2 hrs @ 75F. I can wait 2hrs, but waiting 12hrs is too much for me!

 

[DsKnees]

Update/ Solved!

It turns out my problem was inexperience with the *.stl file type.

What I didn't realize is that Rhino has a hidden/ expandable menu of detailed adjustments that allow the resolution of exported *.stl files to be adjusted with a high level of precision. I didn't realize this menu existed, and the default settings yielded such a poor result that I wrote off the file type completely.

But now I found the menu, and I created a much more detailed file. All that is left to do is glue up another block of MDF and machine it. I believe the resolution of the model I made exceeds the resolution of the finish pass settings I plan to use, so the result should approximate a perfect copy of the CAD model.

All that's left to do now is go out to the garage and glue up another block of material. Oh, that and waiting for 10-12hrs of machining to be completed.....

 

[DsKnees]

Alright, another update. As I said previously, I learned a little about setting up a *.stl file export to get a higher detail file.

The settings I used in the photo was minimum line length of 0.0001", and maximum line length of 0.100". On flat or gently curving areas, this breaks it up into a grid of .100x .100". This grid is a lot more visible in the final result than I was expecting.

I realize that my results would be a bit better if I used a tooling board product, and I will in time. But I'm trying to learn as much as I can with MDF, since it is cheap and available.

The dark lines seen in the photo are from the epoxy coat applied before the finish pass. Those lines show the center of the "rough" finish passes.

I started by roughed it with a 1/2" ball nose. Then I did a second "rough" pass, using the 1/8 ballnose and with fairly large step over, which cut down to 0.015" from the final surface. Then I coated it with epoxy. When the epoxy hardened, I made a third and final finish pass using a 0.005" step over (4%), 300ipm feed, and 18,000 rpm. It took 8 hrs.

The rough surface will sand out pretty easily with 320 grip paper, but I am trying for as good as reasonably possible. I feel like there is still room for improvement.

Unfortunately, at this point I think I'm at the limit of the VCarve program?

It doesn't seem to have the ability to create tool paths that follow features of the model. But what I really need is a program that can create a tool path that machines the flat areas flat...with a large diameter bit. And then a separate tool path with a small diameter cutter for just the more detailed areas. And a tool path that traces the edges of the details, that would ensure the filleted edges come out smooth.

I guess I'm saying I'm chasing pro results, so I probably need pro software?

 

[ger21]

Unfortunately, at this point I think I'm at the limit of the VCarve program?

Also a limitation of the .stl format, which is just a list of triangles, and has no "features".

But what I really need is a program that can create a tool path that machines the flat areas flat...with a large diameter bit. And then a separate tool path with a small diameter cutter for just the more detailed areas.

Not sure if it's feasible with your particular model, but if you can draw a vector around the flat areas, you can use the vector as a boundary, and do a finishing toolpath with a flat tool within that boundary. Then use those same vectors to exclude the flat areas from your normal finishing passes.

And a tool path that traces the edges of the details, that would ensure the filleted edges come out smooth.

This is usally called a pencil toolpath, and is usually restricted to higher end packages. Again, an .stl file does not really contain the information required to calculate these types of toolpaths.
I think that MeshCAM does have some feature detection with .stl files, and can do "some" pencil toolpaths, but most likely not as well as you'd like.