Learning Freecad / problem with a specific design aspect.

[remco]

I am considering getting a 3D printer but I promised myself (and my wife) that I would first get to grips with the basics of CAD design so I don't end up with either an expensive paperweight or 3000 benchies...

I am following the Freecad tutorial that Irv made and I can follow the steps he takes and I understand them as well so far so good.
Besides the tutorial I am trying to design some things myself, one of them is a dustcover for our e-bikes to cover the contacts when not in use and the battery is removed. There is a ready to go model in Thingiverse but that defeats the purpose of me wanting to learn to design it myself.
One aspect that I am not getting on how to design is what you can see in the attached pictures, on the mounting bracket on the bike there are three 'mushroom' shaped pins and on the bottom side of the battery there are the three corresponding keyhole shaped recesses.
I can design the shape of the recess but I don't know how to create the 'overhang' that encloses the pin when you twist the battery on the mounting plate.

The ready made one on thingiverse is this one: https://www.thingiverse.com/thing:2732426

It seems so simple but I can't seem to figure it out. Can anyone give me some guidance on how to design that feature?

[irvshapiro]

The key to a more complex model is to layer sketches on top of solids. Take a look at my video when I build a cable storage bracket for my desk. Here is a link to the video:

https://youtu.be/A817EnC3wnk

[Zardozer]

I did a version of this for some practice. Obviously the dimensions are made up, but I did it with dynamic data, so you can plug in your measurements if you want. The keyholes are going the opposite direction, but you can easily tweak the design to change them.

I did the keyholes one-by-one, and then their corresponding holes on the other part with a polar pattern, just to change it up. However, the polar pattern is limited in that the holes must be equidistant around the circle. So if you want to adapt what I've done, you'll probably have to do each hole separately (or copy them as separate sketches). I notice in your device that the keyholes are NOT equidistant around the hole. You can make each part separate to print (maybe add screw holes or just glue it together), or actually it might print as one whole part with supports added in the holes.

[Geit]

The easiest way is to create a datum plane and create a surface, where the bottom of the hole should be. Now you create two sketches on top of that.

The first sketch is the external size of the hole. You create a pocket though all.

The second sketch is placed on top of the same datum plane. But you make the "key hole" a little bigger this time and instead of creating a pocket through all, you subtract the wall size off from the depth and use that as pocket size.

Of course it does not matter which pocket you do first. This is a good example of how handy it is to define measurements. You simply define a radius for the key, a radius for the "flat" side of the keyhole and a distance between them. The first sketch is also a good place to create a dummy key depth line, a wall size for the overlapping plate and the side difference between inner and outer holes.

In the second sketch just need so reference the values. e.g. for the radius you use "keysketch1.bigradius+keysketch.overlap" and so on. The pocket depth, gets calculated too. "keysketch.depth-keysketch.wallsize". So the inner hole will always be bigger sideways, but less deep and you just need to edit one measurement and everything will calculate itself in place.

If you want a more fancy slot, where the pocket holes on the inside are not vertical, the method above of course does not work. In this case you need at least three sketches and they need to be vertical. You basically draw the outer shape of the hole you want. Kind of like you would create a vase, but here you rotate the vase shape out of your block. There is probably a more elegant way, but I would do it this way.

[remco]

Thank you so very much for the help and tips. I am going to try to design it myself since I want to learn it but this really helps!

[Geit]

I am considering getting a 3D printer but I promised myself (and my wife) that I would first get to grips with the basics of CAD design so I don't end up with either an expensive paperweight or 3000 benchies...

This is the really smart move of yours. I know a few people who just ran out of "ideas" what to print from thingiverse and sold their printers.

A 3D printer is just a toy, until you combine it with CAD and make it a tool!

[Ender5r]

This is the really smart move of yours. I know a few people who just ran out of "ideas" what to print from thingiverse and sold their printers.

A 3D printer is just a toy, until you combine it with CAD and make it a tool!

I generally agree. It is possible that someone could find everything they want/need already designed for them, so they only have to download an STL file, but it's not really very likely.

[Country_Bubba]

I generally agree. It is possible that someone could find everything they want/need already designed for them, so they only have to download an STL file, but it's not really very likely.

And to further this in most cases when I find something to download, it must be modified for some reason to suit my desires. To this end, because most do not include an importable solids file (such as a .stp) I find FreeCad is about the best choice to convert the STL file to a solid. May take a while, but it has done anything I have thrown at it whereas Fusion360 won't even try on many of them!

Good luck with your learning curve and keep at it. It will all make sense with practice.

[remco]

I did a version of this for some practice. Obviously the dimensions are made up, but I did it with dynamic data, so you can plug in your measurements if you want. The keyholes are going the opposite direction, but you can easily tweak the design to change them.

I did the keyholes one-by-one, and then their corresponding holes on the other part with a polar pattern, just to change it up. However, the polar pattern is limited in that the holes must be equidistant around the circle. So if you want to adapt what I've done, you'll probably have to do each hole separately (or copy them as separate sketches). I notice in your device that the keyholes are NOT equidistant around the hole. You can make each part separate to print (maybe add screw holes or just glue it together), or actually it might print as one whole part with supports added in the holes.

I have been working on it the past few days and you example has really helped me more in understanding the design process. The Dynamic Data workbench is awesome to, it really makes changing basic parameters a lot. Dissecting an example like this makes learning easier for me.
So thanks again for this.

[remco]

Took the basic design idea from the generously provided example and started from scratch.
The first part is ready and after one earlier testprint with one keyhole to determine the spacing and sizing the second testprint was spot on.
It fits the mounting plate on the bike perfectly (it will become a dustcover for the battery connector on our e-bikes).
The two additional holes are for the detent balls that are in the mountingplate on the bike.
As a complete beginner in desiging with CAD software I am quite content with myself up to this point.
It is so nice to able to design something and print it out and try it out in a very short time span.

[mochalatte]

As a complete beginner in desiging with CAD software I am quite content with myself up to this point.
It is so nice to able to design something and print it out and try it out in a very short time span.

Indeed! Creating is satisfying. Congrats.

[remco]

Quite content with the results

[Ender5r]

If it meets the need(s), it's a success