What is the stopover you have set from the endmill? From my experience you should be able to achieve an acceptable finish with 4-6% step over on the endmill. If the preview is still showing scalloping, reduce the step over until you achieve the desired look.
If you want to clean up the sides of the letters, take a look at Vectrics tutorials on Rest Machining, this is a method to create vector boundaries to work on specific areas and clean up tool marks.
You can also increase the feed rate on the tapered ball nose end mills, they are not as fragile as a smaller standard endmill.
I get that, for sure.
I was just throwing out some ideas.
When I was using Artcam, I could machine the same model more than once, and each time, I would use a different Finishing tool, and no roughing, running the simulation after each tool.
Iāve spent a good chunk of two days trying to get this model into a millable state in Fusion 360. My problem was that the STL file produced too many triangles and it became almost impossible to work with the model with my computer. I proceeded to model the easy parts and got as far as the letters. I tried different methods and got nowhere in an efficient way. I decided, for the sake of getting a milling quality and time estimate to model the words myself using another serif font that would give me an idea of what I had to do. My conclusion is that I donāt have the tools/experience necessary to mill this properly. I think I agree that a hi quality 3d printing machine might be better. Sharp inside corners are a limitation of CNC bits. Maybe with the right v-carve bit?. My estimate is about 2hrs (not bad) but the quality is not ideal.
I am getting good at milling but my confidence is not that solid to know I can get this done in a timely fashion. I am interested in learning so this process of figuring out how to make this work has been good and productive.
Either machine is capable of what you desire.
It depends on the CAM, and the persons skill level with that CAM.
I can give some pointers to help you choose.
I donāt have the Nomad, but Iāve built a lot of machines in my life, so I can give an estimated guess.
Unless you live with your machine, and keep a good eye on calibration, then I would say the Nomad will be the most accurate, and sturdy for itās size, and the most maintenance free.
What I donāt like is the slow spindle speed.
A machine that small, doing that small of work should be able to go 3 to even10X faster. Itās the reason, I believe, people brake small bits on it so bad, and have such long machining times.
If you can get the Shapeoko dialed in good enough for you, you will have a lot more room for experimenting with the right feeds and speeds.
The finest finishes (in metal) have a fast rpm, shallow cut, and slower feed.
Being as you are doing plastic, Iām not sure the RPM speed will benefit you at all.
In that case it would be the Nomad for sure.
You might even consider a fast, low res, 3D printer (cheap), then do finishing work with the Nomad. Similar to machining castings. I donāt know how many you plan to make in the future.
Thanks Jerry. I make a living working with 3d printers so that is an area I know pretty well. However CNC mills are totally unknown to me. I get what you are saying. The issue IĀ“m having is that with 3d printing (because of print area on my SLA machine) I can only print the individual chocolate bars which I then paste to a wooden board using molding paste, let dry and then I pour the silicone over that. However, I do get silicone coming underneath the individual bars, even when I use hot glue (which I hate because it is messy and doesnĀ“t give a professional look). So I traying to CNC instead because that way I can cnc an entire slab of acrylic including the chocolate bars and wonĀ“t have the issue of the silicone coming underneath the individual 3d printed bars.
If only you had a Shapeoko. You could mill shallow, tight pockets in the wood, making āshut offsā, so it doesnāt go underneath, like an inlay.
A trick I used to use with plastic mold shut offs (Kiss offs).
Now Iām not sure that would work for you, either. The wood having to be at least a little wider than the bars.
I dont have an image, and I dont work there any more, but basically if you make your bars a little taller (+ the depth of the pocket), put them in the pocket (a snug fit), then the silicone wont flow in, and if any does, itās just a little flash to clean up, but it probably wont.
Heck, I guess you could print a tray too.
Thats a fantastic idea. I can laser cut a whole grid and then fit the bars into this grid of shut offs. That way I also make sure the bars are aligned correctly to fit on my clientĀ“s production line.
There is a Vectric how-to here that explains this technique. Of course, you donāt need the Vectric how-to to do it on a 3D printer, but it does at least demonstrate the principles involved.
The step-over was set to 20%. I re-ran the simulation at 4% to see what would happen (in VCarve).
Youāre right that the scalloping is dramatically reduced (see image below). The bridges between letters remain though (likely because the taper bit cannot reach into those areas without cutting into the tops of the letters) and there are strange artifacts along the edges of the lettering (likely due to the pixel-based processing that VCarve employs).
The job time went up to about 5.5 hours with a feed rate of 40 IPM. I didnāt check G-Wizard to see if that is at all realistic, so reality could be longer or shorter.
This was a fun exercise to figure out how to best carve this part in theory, but I still believe 3D printing would be easier, and Iām glad @jdg3 had a good suggestion to solve the 3D printing problem @Luismchiri was facingā¦
is there a dxf file of this some where? My older version of v carve wont bring in an stl. file.
I just cant believe this little 2d cut would take 5 hours.
You may already know this, but you have to open a blank job first, before you can open a 3D model, like an .STL
Then you can go to file-import component.
A lot of people donāt know that, because it opens those differently than a normal file.
There are two things that made it 5+ hours to cut (the way I did it, anyway):
First, the edges of the letters are not orthogonal to the surface, they have some slope to them, so you canāt cut them with a square end mill and a deep DOC, you have to use a ball mill and a tiny DOC on the watermark tool path.
Second, since it is going to be a mold, there needs to be extremely high quality.
Combine these two, and you end up with a very small step-over and DOC for the finishing path. Since there are lots of tiny pockets that need to be milled out in the letters, and VCarve doesnāt support real rest toolpathing, you have a trade-off between using a large-ish area clearance tool (0.25) and not being able to mill out the letters at all, and then taking forever on the finishing pass with a tiny end mill, or using a much smaller area clearance tool (0.125 or 0.063) and spending much more time on roughing.
I think VCarve Pro and Aspire have a much better way to do true rest machining, so you could do multiple roughing paths with progressively smaller bits, but my version doesnāt support that.
If anyone else has suggestions for overcoming these challenges, Iād love to learn them!
Yup, a mold will most definitely have to have some (a few degrees or more) draft to it or whatever youāre molding canāt be removed unless youāre molding something rubbery I guess. And molds need to be ultra smooth, both for the finished product and also for the same reason as above. High end molds are sometimes machined at one place, then another shop will do a separate operation to polish them afterwards. Itās almost like how the guy who makes the Samurai swords sends it off to another professional polisher/sharpener, theyāre two separate professions. I donāt think you will get a high quality mold straight off any CNC, thereās going to be a secondary operation to make it āfinishedā. Just my $0.02
