Laying Out and Making Cutouts in Parts

Is there a standard method, tools that help, plugins that help… for laying out relief cuts in parts (like the triangles in the top part and the 4 and 5 sided cutouts in the bottom one)?

It seems like I spend more time making something like that look decent then I do designing the part.

Generally I would draw the shapes of the openings while the piece is flat and delete the faces inside before extruding it to make it 3D. In some cases it makes more sense to draw a volume to act as a cutter and either use Trim and Keep (for Pro users) or Intersect Faces to cut openings.

From your screen shot, though, I’d go for my first method with those.

The key thing with anything you’re drawing, especially for 3D printing is don’t let it get messy. Check frequently to make sure it’s clean so you wind up with a solid.

Here’s a start to give you an idea.

ETA: If the holes for the screws need to be accurately located, I would be inclined to omit them from the model for printing . Drill and countersink them after the part is finished so you don’t have to worry about dimensional changes as the part cools.

And if you want mould relief as you said in an earlier post, highlight top or bottom edges of each hole, and use the Scale tool, with the modifier key (Ctrl on Windows, or Option on Mac) held down to ‘scale about centre’. That will give you a taper on the hole.

The thing is that right now I’m very much designing on the fly- I don’t have a finished part in my head when I start, I have some dimensions and what I want it to do, and I start with 1- trying to make something that fits those dimensions, 2- will work for what I want, then I try to make it look “pleasing” (otherwise step 1 and step 2 can result in something that looks like a gift wrapped elephant) and then finally I’ll make the cutouts because it really doesn’t need to be solid and it gives the part some additional character.

If I knew what it would look like before I started it would be pretty simple to just lay out the holes on a flat plane and go like you said.

What I’ve been trying to make work is something like ending up with the shape that I wan and then choosing the flat areas and using the offset tool to make a boarder and then push/pulling it through to make the cutout. That ends up getting surprisingly tedious, especially in the case of something like the part that you played with since the offset doesn’t play nice with the screw holes (the geometry gets really complicated so you end up trying to draw some boarders in to avoid the screw holes…) and then rounding the corners adds to how tedious it is- if you use the arc tool before you push it through the shape it seems easiest to draw in a bunch of guides first, and if you push it through and then use the RoundCorner extension you often get shapes that don’t work or break your model (maybe there’s an easier way to do this?).

The screw holes do need to be accurate, but I haven’t had any issues with locations yet (the couple of times I’ve been worried I printed the first few layers and stopped it, took it and measured it/compared it to where it was supposed to fit and adjusted if it needed it).

Drilling afterwards would be the answer with more traditional machining processes but not for 3D printing because you rarely print a part solid, typically it’s something like 15-30% infill in some sort of pattern so if you drilled and chamfered a hole like that you’d end up with a weak spot that would never hold a screw.

It would be cool if you could do something like “I want 100% infill in these areas,” but I don’t know of a slicer that can do that and I don’t know how to design something that a slicer would interpret that way.

[quote=“DaveR, post:2, topic:50826, full:true”]
The key thing with anything you’re drawing, especially for 3D printing is don’t let it get messy. Check frequently to make sure it’s clean so you wind up with a solid.[/quote]

In the few weeks since I built my 3d printer “Check with solid inspector EVERY time you make a change to the model because you never know…” has become my mantra. A little tiny crack in the surface that you can’t see can do really crazy things to your prints. I had one that had a pinhole in a lip of an open end that I didn’t see, it didn’t show in the slicer and it somehow ended up printing a perfect flat sealed end on the part with no support, something that I would have never pulled off if I tried it on purpose (this is supposed to be a push plug with an open end):

I’m not sure what else to call it besides a relief. It’s not like relieving a detail to get it out of a mold.

In automotive racing we call them “speed holes”- holes that are added to parts to make them lighter, in 3D printing you do it not to uses as much filament and in both cases there are people that think they just look cool.

DaveR, this is why in a previous thread when you linked and suggested I use the “Dave Method” I said it didn’t work right for me- I found that if I used the scale tool to modify the scaled part I ended up with the wrong results in the end. Instead I ended up scaling the group of parts by 100, and then scaling them back down by .01 before printing to get around it, but that has caused a problem- I have a model that Sketchup crashes with EVERY time I try this with It’s driving me crazy and I’ve even lost track of which autorecover is the best one now >:-(

That “mould relief” is called “draft” and not needed for 3D printing as you say.

If scaling up and scaling back down work, there’s no reason the Dave Method won’t work. You’re only scaling up by say 100. The original is still there at the correct size. But since you can’t make it work for you, do what does work.

To give you guys a better idea of what I’m doing, this part needs a “floor” in it (well the walls still need to be modified, some openings added and moved for wiring…):

This one is a little different in that it doesn’t have a floor in it at this point and the space is relatively open, but I’m just looking for a way to lay out something like the previous 2 parts have quickly and that looks good. For example, there are other parts out there on Thingiaverse that have a hex pattern on the flat parts (personally I hate a hex pattern on parts like this, not sure why) and I have no idea how to lay something like that out quickly and even if I did I could see issues with running into the needed parts of the shape or ending up with weird looking blank areas.

Something like this (this is the part that I’m taking dimensions off of, it doesn’t fit right to start, but it gave me a baseline where things need to be or be moved, and again, I wouldn’t do the hex pattern but right now I don’t know how to do the hex pattern either, at least not quickly, and that bothers me):

Scaling up and scaling back down does work on some, on others it’s causing sketchup to crash (I have a file called AutoSave_AutoSave_AutoSave_AutoSave_{filename}.skp at this point). On the example that we were talking about before that I said it didn’t work I made the copy, scaled it and then made changes, some of the changes involved scaling parts of that. Everything worked on the small copy but the scaling part.

As a side note, DaveR, I’m very curious what your background is/what you do for a living. You seem to have fairly broad knowledge (not just about sketchup) and you also seem to have more time to answer questions (which is greatly appreciated, you’ve always turned up when I was stuck) than I seem to have to do anything, much less things that I want/like to do. I’ve wondered if you work for Trimble or something…

No. I don’t work for Trimble. I’m just an underpaid volunteer who enjoys helping others use SketchUp. In my day job I’m what is known as a Biomed. I keep medical equipment running. My area of specialization is critical life support equipment; anesthesia machines, patient ventilators and the like. I’m also an Instructor in the Mayo College of Medicine.

As for knowing what draft is in relation to casting, I thought everyone knew that term. :smiley: Actually, my father was in quality assurance and worked for many years in a die casting plant so I picked up a fair amount of knowledge about casting from him. I have a wide variety of other interests, too and I can get lost reading encyclopediae and technical books.

Enough about me. What about you?

An IT Contractor running Security Operation’s Centers in the defense/intelligence field… Though I’ve “dropped out” a number of times for years at a time to do custom fabricaton, machining and building prototypes (at one point or another I’ve contracted work to a speed shop, machine shop, military (army and marines)… I’ve been itching to combine the 2 with CNC stuff and building the 3D printer was my first step (I may convert my Bridgeport Mill next).

My CAD history goes back to being 12 and fixing drawings at my dad’s engineering consulting firm on weekends on one of the original versions of Autocad, but I’ve only had the opportunity to touch the stuff on and off for the last few years. You should know when I’ve touched Sketchup, the first time years ago for like a week when I needed some drawings for a prototype at work, the second time for a few weeks a few months ago drawing up some stuff I was making for my kids, and the last few weeks after building the printer. Each time it was almost like starting over and each time I asked questions here that you answered :slightly_smiling_face:

Any more thoughts on my making cutouts problem? :wink:

There are essentially two ways of cutting holes in SU.

1 If the hole is to go between two plane parallel surfaces, use PushPull. And if there are many holes, draw just one plane first, draw round all the holes (circular, or irregular shapes) first. Delete the inside faces of the holes.

THEN pushpull the face to extrude all the holes at once.

2 The second way. when you want a hole or holes where the opposite faces are NOT parallel, nor even planar, is to create an extruded version of the hole (draw the hole shape, then pushpull it into a solid), move it into position if necessary then in Make use Edit/Intersect Faces with selection, model, or context, and trim off the excess, or in Pro, use the Solid Tools - usually to Intersect.

Better than the native Solid Tools, try Jim Foltz’s Trim and Keep plugin - it keeps the original components rather than make them into groups named Difference.

If you are working on a small scale, use the Dave Method. Work on a scaled up copy of your component, and delete the scaled up copy when done.

I find it easiest, when working in metric units, to work in metres, and pretend they are mm.

:+1: :+1: :+1:

Huh, since I’m just multiplying everything by 100 I guess I’m doing that but dealing with seeing everything in mm… that would make sense, now I need to figure out how to change the units in everything…

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