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# 123D Design tutorial for technical parts with accurate dimensions? Answered

I'm an engineer with ~7 years of experience using Solidworks (professional CAD software). After hearing about Autodesk 123D Design here on Instructables, I tried to start using it to design and print things with my home 3D printer. However, I'm initially finding it very frustrating to use (more detail on that in a minute) - and I'm not sure if this is just because I'm stuck in my ways with the software I'm used to, or if I'm just trying to use 123D for something it wasn't really intended for.

To try and give some concrete examples - I understand that you can create 3D shape primitives (rectangular prisms, cylinders etc) and assign them dimensions when you create them. I also understand that you can create 2D sketch objects and define their dimensions. What I don't find intuitive at all is how you can assign the dimensions of objects relative to each other. For example, say I want to make a 10x10x1mm bracket, with two 2mm diameter circular holes that have their positions on the face defined by the distance from their centers to the edge of the bracket. In a parametric CAD program, that is very easy to do in a 2D sketch and then extrude to a 3D solid. In 123D, I understand that I can create a rectangle primitive and then put holes in it using cylinder primitives - but it seems impossible to define the exact location of those cylinders relative to the edges of the rectangle; also impossible to create a sketch with two circles in it and a dimension defining the distance between their centers.

To give another concrete example: at the 4:20 mark in this video (from this Instructable), he draws a circle on top of an existing rectangular part, and then "centers" it by just dragging it around freehand and eyeballing it. Would it be possible to define the center of that circle relative to an edge, corner, or center of that existing rectangle? Or can 123D just not do that?

What I'd like to see, if anyone is up for it, is a step-by-step tutorial (preferably in video format) for making some sort of "technical" part where the dimensions matter and it isn't sufficient to just eyeball it and drag things around. e.g. a bracket like this (exact dimensions don't have to be what I drew here, but you get the idea). All of the tutorials I've seen so far - including the official Autodesk ones - seem to just focus on eyeballing it/free-handing dragging parts around.

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## Discussions

would be quicker if you copy & paste the first part and align it straight up... :)

Googling for answers to the same question, I keep coming to this Instructable!

It prompted me to sort out a technique which can be used. AutoDesk 123D may have evolved since the question was posed; but here is a link to a video which shows my attempt. It could be done in well under the 10 minutes of the video!

I bet there are better ways to do it! Hope this helps somebody.

Thing is that 123 is not really any good for this knd of work.
It is meant for people with quite simple designs where accuracy is not a vital requirement.

You might be right, but lots of 3D printed projects have to be made to quite tight tolerances. For example, separate parts need to fit together, and components have to mesh together, etc.

The models created by 123D are very precise - dimensions are entered to three decimal places - that's to one thousandth of a mm! (I was surprised to learn that Sketchup has an absolute limit on its resolution to 1/64th inch - about 0.4mm - which is interesting for 3D printing).

The attached photos show a shower door runner designed in 123D. The hole is a sliding fit on a 5mm rod - it is drawn at 5.1mm diameter. In measuring the one I had to copy, I used a digital caliper and measured to 0.05mm (which is easily achieved), so some precision is needed, even for every-day objects.

Many thanks for your interest. Best wishes.

Ok I thought I could do this by drawing some 2x2 squares and aligning them on the corners of the base, then I would put a circle on each corner and extrude it down. But no, a square will not snap to a cuboid. So I had another great idea, make up the base square with 4x4 squares and some cuboids between. then each hole can go at the centre of one of the squares, it snaps to centres. So why won't my cuboids stick together? In the instruction video the solids cruise across each others faces, but mine go through each other!! And If I use snap to stick a to b then b to c, b comes off a!!! Eventually I did a 4x4, a 2x4 and another 4x4 and go them to stick together as a group to make the front part of the bracket base. Great, how on earth can I duplicate it!!! The next piece would be a 2x10 but when I try to snap the long side to my assembly (group) they ungroup! For heaven's sake, this is not a drawing package it is a puzzle and a very frustrating one.

You can do this with the R command. Lets say you have the main rectangle down on the grid. you place the cylinder that will become one of the holes on your plate near where you want it. press R for the ruler. Move the mouse over the cylinder. The ruler will snap to the center of the cylinder and left click. Then select the nearest edge of the plate. You will see the distance from the center of the cylinder to each edge of the rectangle. You will see two arrows extending out. You can left click on one of the arrows and a widget will appear where you can type in a value you want to change to. Voila! your parth has moved to an exact distance. Now you can do a subtract operation to make your hole where you want it.

No, you can't. If you use this method the rectangle shape will move relative to the circle's position, and not the other way around.

I think this is what you are trying to do:

http://www.youtube.com/watch?v=wHO8CBTj_6c Starting around 5:30 Yes it is frustrating and I have been pulling my hair out.

Agree with this completely. I've had the same problem with Sketchup. Is there CAD software besides Solidworks that lets you easily define accurate relative dimensions?

Autodesk has professional software similar to Solidworks called Inventor, but just like Solidworks, it's expensive. I have done some googling around for free or open-source CAD software, and a bunch of things pop up but I haven't had time to try any of them out yet.

This is the top Google result: