Text-to-CAD for mechanical parts: brackets, mounts, and fixtures

I keep a cardboard box under my desk full of 3D-printed brackets that didn't work. Some came from bad sketches. Some from wrong dimensions I typed while tired. And a growing number, over the last year or so, came from text-to-CAD tools. The brackets in that box all look roughly correct. They have flanges, holes, stiffening ribs, the usual. But "roughly correct" is a generous description when the bolt holes are 0.6mm off and the thing won't actually mount to the DIN rail it was supposed to fit.

That said, brackets, mounts, and fixtures are genuinely the sweet spot for text-to-CAD. Not the only use case that works, but the one that works most often with the least cleanup. And I've been doing this long enough to appreciate a tool that saves me even twenty minutes on a part I was going to iterate anyway. So here's what actually works, what breaks, and where the line is.

Why simple mechanical parts are the right test#

The dirty secret of text-to-CAD is that the training data is mostly simple mechanical parts. Brackets. Plates. Standoffs. Flanges. The kind of geometry you'd find in a first-year engineering project or a McMaster-Carr catalog page. That's not an insult. It means the AI has seen thousands of these shapes and has a decent statistical model of what they look like.

A basic L-bracket is a sketch-extrude-cut operation. Two legs, some holes, maybe a fillet at the bend. There's nothing parametrically complex about it. The geometry is prismatic, the features are standard, and the dimensions are all related in ways that aren't hard to infer from a text description. Compare that to a turbine blade, a multi-body mold insert, or a swept lofted handle, and you can see why the AI does better here.

I tested Zoo.dev, AdamCAD, and a couple of prompt-based generators on a set of ten common mechanical parts: mounting plates, L-brackets, cable clips, standoffs, DIN rail adapters, sensor mounts, PCB standoffs, a motor mounting bracket, a U-channel, and a flat plate with a bolt pattern. Not glamorous. Just the kind of parts that show up three dozen times in any hardware project.

What the AI got right#

The surprise, if you can call it that, is how much was close enough to use. On six of the ten parts, the AI produced geometry I could import into Fusion 360 and start modifying without wanting to delete everything and start from scratch. The overall dimensions were within a millimeter. The shapes were recognizable. The feature count was approximately correct.

The standoffs were perfect. A cylinder with a bore and a counterbore is about the simplest thing you can ask for, and the AI nailed it every time. Outer diameter, inner bore, height, counterbore depth. All within 0.2mm of the prompt. I could've sent those STEP files directly to a print job.

The L-brackets were close. Leg lengths were right. Thickness was right. The bend radius was usually present, which is more than I expected. The hole positions were the weak spot, usually within a millimeter of where I asked for them but not exactly on the mark. On a clearance hole bracket for M4 screws, a millimeter of drift is something you can live with. On anything tighter, you can't.

The mounting plates were solid. Flat geometry is easy for the AI. A rectangle with counterbored holes is basically the AI's comfort food. I got usable output on all three plate variants I tested.

What the AI got wrong#

The cable clips were a mess. A cable clip is a simple part, but it has a snap-fit feature, an undercut, and geometry that depends on the cable diameter in a way that the AI couldn't infer from the prompt alone. I asked for a clip sized for a 10mm cable. The slot opening was 8mm. The retention lips didn't have enough return to actually hold anything. It looked like a clip in the viewport, but it was structurally a channel with aesthetic bumps.

The DIN rail adapter was the most interesting failure. The AI generated something clearly inspired by a DIN rail adapter, with the right general profile. But the retention clip was solid geometry, not a sprung feature. The rail slot width was off. And the mounting hole pattern was symmetrical when it should have been offset to account for the rail's asymmetric cross-section.

The motor mount bracket was also wrong in a specific, educational way. It had the right overall shape: a flat base with a raised portion and holes for motor bolts. But the bolt circle diameter was generic, not matched to any standard motor frame size. In real life, a NEMA 23 motor mount has a 47.14mm bolt circle. The AI gave me 45mm. Close enough to look right. Far enough to not work. I've had this exact argument with a 3D printer at 11 PM, trying to force M3 bolts through holes that were juuust slightly too close together.

The fixup time is the real metric#

The question everyone asks is whether text-to-CAD saves time. On simple mechanical parts, the answer is yes, but less than you think, because the fixup time eats into the savings.

For the standoffs, fixup time was zero. Straight to print.

For the L-brackets and mounting plates, I spent five to fifteen minutes in Fusion 360 adjusting hole positions, tweaking a fillet radius, and verifying wall thickness. Modeling these from scratch would've taken maybe twenty to thirty minutes each. So the net savings were ten to fifteen minutes per part. Real, but not dramatic.

For the cable clip and the DIN rail adapter, I spent more time trying to fix the AI output than it would have taken to model the part from scratch. The cable clip needed a complete redesign of the retention feature. The DIN rail adapter needed the rail interface geometry rebuilt. At that point, the AI's contribution was a rough shape I could've sketched freehand in Fusion 360 in about ninety seconds.

The pattern is clear. If the part is prismatic, symmetric, and doesn't depend on interface dimensions with other components, text-to-CAD saves time. If the part has functional features that interact with specific mating geometry, the AI's output is a starting suggestion at best and a misleading distraction at worst.

What makes a good prompt for mechanical parts#

After running through dozens of prompts, a few things consistently improve results. Specify material thickness explicitly: "3mm thick aluminum L-bracket" beats "L-bracket" every time. The AI treats thickness as a free parameter if you don't pin it, and it picks weird numbers like 4.7mm that don't match any standard stock.

Give bolt patterns in absolute terms. "Four M4 clearance holes, 4.5mm diameter, on a 40mm by 30mm rectangular pattern centered on the face" is better than "mounting holes for M4 bolts." Include standard interface dimensions if the part mounts to something specific: "31mm bolt circle, 22mm central bore" for a NEMA 17 plate. And keep it to one part. The moment you describe two parts that fit together, you're asking for an assembly, and text-to-CAD can't do assemblies.

Where this fits in a real workflow#

My workflow for simple mechanical parts starts with a text-to-CAD prompt about half the time now. Not because the output is perfect, but because it's faster than setting up a new sketch, picking a plane, and drawing the first rectangle. Then I import into Fusion 360, measure everything, fix what's off, add proper constraints, and save it as a real parametric model. The AI's version stays in the import bodies folder as a reference. The actual model is mine.

For fixtures and jigs, the tolerance on "good enough" is wide. A 3D-printed fixture that'll be used for a few weeks and thrown away doesn't need to hit every dimension. Text-to-CAD is genuinely useful here.

For anything going to CNC machining or injection molding, the AI output is a starting conversation, not a finished part. The AI doesn't know what a cutter is, doesn't know what a mold is, and doesn't care about your tolerances.

The honest take#

Brackets, mounts, and fixtures are where text-to-CAD earns its keep, and even here, the earn is modest. The text-to-CAD guide I wrote earlier covers the general workflow, but for mechanical parts specifically, the real value is in skipping the first five minutes of modeling setup on parts you've built a hundred times before. It's not going to replace your engineering judgment. It's not going to give you manufacturing-ready output. And it's not going to know that your NEMA 23 bolt circle is 47.14mm, not 45mm.

But if you're honest about what it can do, treat the output as a draft, and keep your calipers within reach, it's a useful addition to the boring part of mechanical design. I just wish the boring parts were the only parts that mattered.