What version?
I'm trying to learn Altium since we have a license for it through school.
I wanted to do a PCB that had a really specific shape as it will be soldered on top of an existing product. For this I took a photo and drew the board shape I wanted in Illustrator, saved that as a DXF-file and imported that into Altium to use as board shape.
That worked well enough and was easy to figure out. However, late in the design process I realized that I had to tweak the board layout a little. For example I had a U-shaped notch that I wanted to replace with a hole. I was able to highlight the U-shape on the mechanical layer and delete it, but that left me with a gaping hole in the outline, and I haven't been able to reconnect that again (see photo). How do I do that? If I press and drag any of the line's anchor-points it will just move the entire outline.
You should be able to edit the lines via the grips as you expect. If the entire outline is moving when you grab one line, it sounds like the lines were imported as a union. If you right click on one of the lines, and select the 'Unions' submenu, do you see a 'Break objects from Union' option? If so, you can click that, and then uncheck click the 'All Off' button, then 'OK' to remove everything from the union and then delete it. Alternatively, in the 'PCB' Panel, select 'Unions' from the dropdown at the top, then select '<All Union Types>' in the box below that, then in the box below
that you should your union listed somewhere. If you right click on it, you can select 'Delete Selected Unions' which will do the same thing. If you see multiple unions listed, make sure that the 'Normal/Mask/Dim' dropdown at the top of the PCB panel is set to 'Mask' or 'Dim' and 'Clear Existing' is checked. Then you can click on each union in the list and see it highlighted to find out what each union is.
Once you have everything broken from the union it should be possible to edit via the grips.
Unfortunately they detected an error in the mechanical 1 layer, and contacted me about it. They suggested that we used "ko" layer as board outline instead. That looked alright to me, so hopefully that works, but I would like to know how to edit the mechanical layer properly, so that my next pcb will be error-free
I wouldn't use the keepout layer, because that gets special 'keepout' handling in design rules, it's not just another mechanical layer. The fabricator only sees the gerber, so they have no way to know or care what layer it was in the PcbDoc, and it doesn't really matter as long as the geometry in the gerber is correct. I would stick with M1 and just make sure your gerber file names match one of the conventions or are otherwise clear as to what they contain. Also if your Altium version is new enough to have layer types (AD22+?), make sure those are set correctly. Not just for the board outline, but especially for your component layer pairs, otherwise things can get messy when you import footprints that have those set.
But there is no way to shrink or expand a shape on the mechanical layer then? As you can see in my image the board shape (the black area) has been slimmed a bit and made a bit taller too. I would like the mechanical layer to match. Am I correct that the best way to do this is to change the X/Y coordinates of the lines so they match?
Generally it's easier to have your board outline drawn on M1 (or whatever) and set the board shape from that, rather than try to match the the drawn outline to the board shape.
Another question. Do the Mechanical layer 1 represent everything that is being cut? I ask because I created a logo, also in DXF that I wanted to show up in copper on the top layer. In the gerber viewer this does look correct but the outline is present on both the Mechanical 1 and the top solder mask layer, and the engineer at JLCPCB was unsure if I wanted the logo cut out.
Generally, yes, M1 is used for the board outline and should include all edges of the board, including edges of internal cutouts. I believe JLCPCB recommends that you place 'CUTOUT' text inside of any of those internal cutouts for clarity. For your logo, the objects that you want to appear in copper should only be on the copper layer (or on the silkscreen layer for silkscreen objects, same for soldermask).
If I delete the outline from Mechanical 1 the logo still shows fine in the gerber viewer, so am I correct that I should just do that?
If you *regenerated* the gerbers and they came out okay, then it sounds like you'll be fine, and likely had multiple copies of the logo objects on different layers. For future reference, you should be able to select which layers from a DXF end up imported onto which layers in the PCB.