The part is not centered in the stock. The reason is that I did a first test in a piece of wood, that happened to be slightly smaller than my aluminum stock. Resizing the stock is a lot of work (lots of dependencies), so I just skipped that part. The idea with wood is that it is a whole lot cheaper to scrap and start over again, should Path or I do something wrong. I am an electrical engineer, so do not have proper machinist schooling. This is just for my hobby projects.
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One first, very positive, finding so far, is that what you see, is indeed what you get. The difficulty is in interpreting and scrutinizing every detail in the generated path, such as tool engagement and direction of cut. On top of that, you also have to consider part and cutting tool holding, such as vises, clamps, collets and chucks. All of these can interfere.
The part is milled with the bottom first, then turned over and a new origin is probed.
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The bottom (step 1) is milled with a 50mm face mill of this kind:
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Generating a toolpath for a mill bigger than the part does not work reliably. I laborated with stepover, boundary shape and pattern. At 90% stepover and line, it was possible to get two passes with approximately 50% tool engagement, which is what I was after, but the path is not symmetrical. Very strange.
The line pattern does not make lines, which I was expecting. One line across, reposition, and make another line with the proper stepover and respecting the cut mode (climb/conventional), is what I expected. In this example, the first facing operation is made to full depth in just one pass, but if it is done in two or more passes, the tool will find its new depth at the end of the previous pass and follow the path backwards, disrespecting the cut mode. With a large face mill of this kind, this is a problem.
The lower shelf (MillFace lower) was done with the help of a helper object. I see that there is now a dressup that does essentially the same thing. I was unable to use line here, so tried other strategies and ended up with spiral. Of course, with spiral, it is only possible to respect the cut mode if you are going around a part. Ideally, I would have used line here, doing the outer part climb milling at 50% tool engagement, lift, go back and do the inner part of the shelf the same way.
For the top side, I gave up the large face mill. It did not provide a nice surface finish that I was hoping for anyway. Instead I used a 12mm end mill.
It was easy to select the three horizontal surfaces as region, although they are at different depths. Nice!
With "face region" and "offset" pattern, the cut mode was respected on the entire surface. Nice!
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On MillFace003, the line pattern creates a zigzag pattern that does not respect the cut mode. I found no way around that. It also does not quite reach all the way to the "wall" of the part.
Disastrously, on the next cut depth, it starts the processing from the wrong end, creating a slot with 100% tool engagment, leaving a very ugly finish as result. I did not observe this in the path. The chips in the picture are welded to the part. This is often the result of "conventional" cutting, as each cut starts with the cutting edge rubbing against the wall before the pressure is enough to break through and start the cutting action.
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I ran out of picture space here. Pls see next post!
100% tool engagement can be ok, if it is planned for and the cutting depth and feed rates set accordingly, but not as a surprise when 50% has been set... But again, this information was there in the path. I failed to see it.
Profile
With lead in, it is a perfect tool - no issues, but I wish that we will get a tool that allows us to do multiple horizontal passes. If my stock had been thicker, one pass would not have been enough to reach the target shape. But I think that is for another tool. Profile is designed to cut things out of a slab, board or sheet metal - one cut only.
Pocket with spiral pattern
What a charm! It generates very efficient tool paths that allows you to cut holes better than drilled and slots without breaking the tools or overheating. One little issue, though. By default start depth, the pattern starts a millimeter or two inside the part. You have to trick it to start above the part to get it right.
I can't add more pictures here. They will be in the next post.
OS: Linux Mint 20.1 (X-Cinnamon/cinnamon2d)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.
Build type: Release
Branch: unknown
Hash: e8566f22bbeb0b7204e3c45519d0963e8881100b
Python version: 3.8.5
Qt version: 5.12.8
Coin version: 4.0.0
OCC version: 7.5.1
Locale: Swedish/Sweden (sv_SE)
