The FreeCAD corner....

Recently MagPi suggested there be a thread focused on FreeCAD.  So as an initial offering I though to go through the steps I used to create a multi-motor mount drawing on the ideas in a STL file that I printed for MagPi....

Below is a photo of the original motor mount (lower part of the model) and two versions I created.  On the left is a simple extrusion of bolt holes that fits three sizes of motor mount plus corner holes for mounting it to something, on the right is that initial design but with the addition of hex retainers.

 

First things first - got out the callipers and measured up several of my motors. The motor mounts were cross shaped. One was 31.5mm c-to-c, one was 34mm c-to-c and one was 20mm c-to-c.  The smallest would fit inside the largest but the other needed to be at a 45 degree rotation. Some motors have a shaft that extends out the back so there needed to be a centre hole and it is always nice to have one or two places one can pass the motor cables through.

Opened up a new project in FreeCAD, switched to the part workbench and asked for a new sketch in the X-Y axis.  I started with a 'centred rectangle' and gave it dimensions.  Next I created a series of circles in Roughly the locations needed. And then one at a time I constrained the horizontal and vertical distances (either from the centre or from one of the edges).  

To get the 45 degree rotation, there are probably many ways to do this but I chose to create 'construction lines' (dashed) from the centres of the relevant holes to the centre.  I then constrained the angles of those construction lines.  I also constrained their lengths.  Gradually lines turn green.  The dimensions in the sketch are seen below - tidying up dimension locations helps!

 

I exited from the sketch and then extruded it 5mm thick.  This minimally could be a workable motor mount if you don't mind the risk of nuts loosening....  But it would be better to add take away a few of the rough edges at the corners and for the wiring passthrough.

 

 

I decided to make a variant of that CAD model (simple expedient of save the model to a slightly different file name and carry on working in that new file).  I already knew where the centre of the holes were from the sketch.  In the part workbench there is a button for 'primitive shapes' and one of those is a 'regular polygon'.  It asks how many sides and what the circumpolar radius is. It creates this at the origin.I then took that new regular polygon and extruded is 2mm as seen in the image below:

 

I named the new extrusion hex_extrusion_a and edited its origin to match the centre of one of the existing holes.

 

I want 8 of these beasties. They are all the same so I go to the draft workbench and in the draft pull-down menu is an option to 'clone' and item.  I make 7 clones.  I grouped them together in the tree under 'hex_to_cut' Then one at a time I set their origins to match the centre of the holes.

 

Then the task is to highlight the main body "fillet" and control click on 'hex_to_cut' and do a boolean cut.  This gives me:

 

I can go back to the intial CAD file and work with that.  Or I can go back into the main sketch of the revised model and tweak the constraints of the hole sizes or their placement and then locate the relevant hex body and shift its origin to match. if I want a larger nut then I go to the original regular polygon and alter its circumference and all of the clones should pick up on that change.

And there may be ever quicker ways to do this - e.g. to more easily rotate the 4 holes than the way I did it.

So..... I yield the floor to the next FreeCAD practitioner who wants to share some tip....


 

I may be wrong but if my understanding of Free Cad is correct hexagons done that way would be ignored by CURA during printing. The same would apply to the radii added to the cable feed out holes.
Other print systems may handle them OK.
I love to be proved wrong if you are using CURA. 

I have not used Cura for a while. I could give it a try.  I know it is a hassle to switch slicers and sometimes having an alternative tool to use for edge cases is a good investment.  

In the interium.... the Prusa slicer is free and has downloadable profiles for the following mfgs:
AnkerMake, Anycubic, Artillery, BIBO, BIQU, Caribou, Creality, E2D, Elegoo, FLSun Geeetech, INAT, Infinity3D, Jubilee, LNL3D, LulzBot, MakerGear, Print4Taste, QIDITechnology, RatRig, Rigid3D, Snapmaker, Sovol, TriLAB, Trimaker, Ultimaker, Voron and Zoestar.

I don't think that MagPi's printer maker is in that list.  But if yours is (I need the model name) I could try and generate a g-code file
and you can see if it will print.  That would prove or disprove one route...

CURA was/is developed by Ultimaker whose machines are on that list. On this basis it would appear that the PRUSA slicer should create a g-code file that would be acceptable to my Ultimaker compatible ANET A8 printer.

I discovered very early on that CURA did not like some of the FreeCad characteristics. CURA has been upgraded many times since but so far it has made no difference using FreeCad.
To be fair much of CURA development is done by expert FreeCAD users who are unlikely to give an issue in FreeCad much priority.      

Ah - Ultimaker - more than a decade ago I and a bunch of other folk at a Maker collective in Glasgow bought their first plywood model and over several weeks put it together!
And eventually Ultimaker went seriously expensive....

I will have a go at generating some g-code for an A8.

A follow-up question on the A8 - you say it is Ultimaker compatible - is there an Ultimaker model which it is 'equivalent' to if I get a choice? 

After a bit of a hunt through the internet it appears Anet  make printers A8, A6, AT4  & ET5 with further sub options. They specialise in budget printers. The A8 was the first released.
The A8 is apparently a modified version of the Prusa Mk2.
When I got my A8 a version of CURA was included and the printer type was set to Ultimaker.
That's about all I can find.

I have recently installed the latest version of CURA (5.10.2) and the A8 still works with the printer type set Ultimaker so I assume it is compatible.
  
 

Agreed as far as the screws into the back of the motor but if you mount the motor using the supplied ally plate it has its holes centered in a 33mm square.
 

jon
The mounting plate you sent me certainly appears to work in CURA.
 
Both the hexagons and radii are shown.
I have LW-PLA in the printer at the moment so an actual print will have to wait until I reload it with PLA.

Is there a reason why one of the hexagons is slightly deeper by a single layer (0.15mm) than all the rest?
 
That particular hexagon first layer starts one layer earlier than all the rest.
I am sure it will make no difference when it is printed.
Just curious.

The X-plate for the motors I got were;

LE 2212 33mm PCD

T 2830 34mm PCD

The difference in depth - the method I used was to create one extruded hex and then use the Draft workbench to clone it.  I took each of the clones and edited their origins to match the sketch and probably one I just missed out on.I also just downloaded Cura 5.10.2 and gave it the STL file and it previews fine (I flipped it over so the hex on top) and then I set it up for a Prusa MK3 and generated g-code.

And then I took the g-code into the Prusa slicer which has a g-code preview function and it looks ok - just somewhat offset to one side of the print bed.So perhaps either Cura has improved or the entities and order I assembled them in FreeCAD managed not to trip up the hex inserts.

One thing about the Cura with a generic PETG - the default bed and extruder temperatures are about 20C cooler than I normally use on the Prusa. 

Loading the STL into Cura:

 

What Cura previews after slicing

 

What the Prusa g-code preview thinks of the Cura generated g-code