Ragged edges to finished parts

[Mike F]

I am a teacher of Design Technology and recently got involved with CNC work, both at school and as part of my hobby of competition aero modelling. A lot of what I do with my students is a spin-off from my work at home and whilst most of it has been 2.5D, I have started machining 3D patterns for making wing and fuselage moulds.

The problem I am encountering is that the finished, 3D parts are coming out with ragged edges, when those edges are not quite parallel to the X axis. This is despite my machine's capability of 0.01mm resolution. I am supposing this is to do with the software's interpretation of the model which was created using Pro/Desktop, exported as a .stl file and the toolpath created from that file. Is this a limitation of .stl files? If so, which is the best format for faithful reproduction of 3D models and can anyone recommend good, cheap software for creating toolpaths from said files?

The problem of affordable software for educational use is a serious one and one that ought to be addressed by manufacturers as we ought to be using industry standard software, albeit cuy-down versions, to educate the engineers of the future.

As a relative newbie to CNC machining and a definite one to this group, I hope this is posted in the right place.

Thanks in anticipation.

Mike

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[HuFlungDung]

Hi Mike F,

I have been told that stl files are not good for machining from. Isn't that based on a mesh of some sort?

Anyways, for your other question "cheap software", what is cheap to you? Maybe we can recommend what would be the best you can get, for your needs and budget.

I have not had time or money to try out many varieties of CADCAM, but for 3d machining, I don't think you would be disappointed if you look at OneCNC XP Mill professional for starters. It is not cheap in the home hobbyist sense, but I think it has as good, or better, ratio of features for your dollar...er.... pound......, compared to anything else. I still rave about it whenever I can

OneCNC has an educational licence program, but I have never been made aware of the cost of it that way. Give Michael a call at Onecnc as see what he has to say.

Check out www.onecnc.net for contact info.

There is also a support contact closer to you in the UK. His name is Peter.

[cadman]

I've also been told by a shop down the street from me that STL files are not very accurate files to machine from. They work with them all the time. The surfaces are composed of polygons

[timf]

i work with edgecam for my programming and i do alot of 3-d machining.
it is made by pathtrace industries and is based in england i believe.
they are starting to push a educational version of edgecam.
more info can be found at www.edgecam.com check products for education link.

[timf]

oh, i only use .stl files for a stock reference when programming.
i usually get .iges files from customers.
you may be able to tweak some of the ragged edges by tightening system tolerances (if possible) but that also creates larger code.

[CAMmando]

STL consists of polygons (triangles) that approximate surfaces.

Iges is prolly' the safest route. Depending on the softwares involved and the part geometry, you may want to request that you get bothsurfaces and wireframe geometry in your .iges file. Even if they need to give you 2 separate files. Having the wireframe geometry is handy for toolpathing profiles and pockets etc. the surfaces obviously are required for machining complex surfaces.

Talk to whoever is creating the STL's to see what there IGES capabilities are.

[HomeCNC]

Mike,

You are over there where DelCam is. We use STL files ONLY. Delcam PowerMill is the best we have seen for STL work. My company is trying to make a standard to accept only STL files.

You should contact DelCam and ask them about a Student license. I have heard that they are very willing to help the schools because the more students that become good with a program, the more they will influence purchase decisions when they get with a company.

[Mike F]

Thanks to all who have posted replies. I shall certainly be following up some of the suggestions.

I am aware that stl files represent the surfaces as a series of triangles but what I was surprised at was the inaccuracy of the edges where a vertical surface met a horizontal surface at anything but square or parallel to the X axis, and this despite setting the highest possible resolution in ProDesktop. If I recall, chordal tolerance was set to 0.01mm and angular tolerance to 0.5 degrees.

The toolpath software supplied with the machine is called Mayka and will only import stl files so I am looking for the best value for very little money that will import iges or other, more suitable formats for 3D work.

Thanks again.

Mike F

[dcd121]

check this link, http://www.picasoft.com/index3.html , with pictures of work done with Mayka.