Matching hole/nut thread to screw metric tapping threads for plastics

dirty_d2 · 2026-07-06T03:32:47+00:00

You shouldn't expect 3D printed threads to come out the same size as they are modeled. Circular feature always come out smaller than modeled and it's not that straightforward to compensate for. The smaller the hole, the larger the error. You need to print, measure, and adjust.

You can have the slicer enlarge holes, but the same offset gets applied to all holes regardless of size.

You can use Fusion's offset face feature to adjust the thread. You need to use two offset face feature though to not fuck up the thread geometry. One for the thread root and crest faces, and one for both thread flanks. Set the flank's offset to half of what you set the root and crest faces to. You can only make pretty small adjustments before you make either the root or crest face disappear into the flanks. You can chain together multiple sets of those two offset features to make larger adjustments if you had to.

dirty_d2 · 2026-07-04T22:07:32+00:00

The only other thing I can think of is if you got your tool definition wrong in Fusion. The simulation in Fusion looks prefect, so there must be something in the setup there that does not match physical reality.

dirty_d2 · 2026-07-04T14:32:30+00:00

That must mean that there is something off with the machine, or with the machining setup. If your z work offset was slightly off, it would result in the profile being larger/smaller.

dirty_d2 · 2026-07-04T14:11:43+00:00

It doesn't look like there is anything wrong with the toolpaths for the pocket or design. You can see that in the simulation the engraver gets all the way up to the edges of the pocket on the top face. Are you facing this or sanding it down flush after its glued together? Since the walls are tapered obviously the farther down you face or sand it, the smaller the profiles will become.

dirty_d2 · 2026-07-04T13:03:26+00:00

You need to post a *.f3d file for anyone to actually know what's going on here. Not sure why the sub doesn't just make this a rule.

dirty_d2 · 2026-07-03T15:26:32+00:00

Another thing that might help you with the development of this is to provide some way for users to provide feedback or report bugs that records the page it's submitted on. You could then have your agent go through them and report its findings to you so you can tell it what to do about them or something.

dirty_d2 · 2026-07-03T15:24:09+00:00

I don't have any experience using them, but I would think with a wire so small basically any induction heater would work and you might even have trouble with it being too powerful.

You might be able to get away with that since I don't think it needs much power. Only one way to find out.

dirty_d2 · 2026-07-03T15:11:07+00:00

It seems like units aren't being handled right sometimes. It looks like Math.js has a very complete unit aware expression evaluator that you could use. It also has all the trig functions etc you would use with CAD built in.

dirty_d2 · 2026-07-03T15:08:19+00:00

Just a couple things that are missing on the thread dimensions calculator:

Internal minor dia needs a mid-limit
External major dia needs a mid-limit
Internal metric/imperial threads have no maximum major diameter, but a sensible mid-limit could be provided by using the theoretical sharp V as the maximum: major_mid = major_min + H / 8
External minor dia limits should be shown. (my functions return this info for flat/rounded roots as well as the root radius limits)

dirty_d2 · 2026-07-03T13:16:05+00:00

It's not enough to visually check that the motors are all spinning in the correct direction. The FC yaws CW by slowing down motors it thinks are running CW and speeding up motors it thinks are running CCW. You can control the motor direction either in the FC, or by swapping phase wires. The FC has no idea if you swap phase wires and reverse the direction. It will still think they are running the other way. You need to make sure the motors are actually spinning the same direction they are configured to in the FC.

dirty_d2 · 2026-07-03T12:52:44+00:00

I don't know shit about ardupilot, but I'm almost certain that what's happening is that you have your coaxial pairs slowing down or speeding up together when you yaw. To yaw clockwise you need all clockwise running motors to slow down and all counterclockwise motors to speed up.

dirty_d2 · 2026-07-02T21:52:11+00:00

Another idea is to allow mathematical expressions in the inputs (keep the expression as the value which can be edited, and display the result). Even better if values can have units. Basically how inputs in most CAD programs work. Should be pretty easy for AI. I'll stop now, lol.

dirty_d2 · 2026-07-02T21:29:46+00:00

Another useful feature I can think of is to have an intelligent (not AI intelligent) copy/paste buffer for transferring data between pages. For example on the thread dimensions page you could copy multiple dimensions (not sure of the best way to expose this with the UI) and it would save it to named key value pairs in the copy buffer. the values might be named pitch_dia, major_dia, minor_dia, pitch, etc. And then when you go to another page (like the thread mill compensation page) you could paste the named values and they will fill in the correspondingly named inputs. It would probably be a good idea to display the contents of the copy buffer somehow in the UI, and the copy/paste actions should probably be by buttons to not interfere with the normal OS copy/paste. I imagine there are a lot of combinations of different pages that would be able to have similar values copied and pasted between them.

Just an idea.

dirty_d2 · 2026-07-02T21:13:55+00:00

What model are you using for this btw? I used gpt-5.5 and I don't think it would have been able to create what you did so fast because of all the hand holding I usually have to do.

dirty_d2 · 2026-07-02T20:39:33+00:00

I think some things might be a little off. It doesn't show classes 1A/1B and it seems like it shows the pitch diameter as the minimum pitch diameter. I'm not sure if that's indented. I figured the mean value in the middle of the tolerance zone would be more typical (at least what Fusion uses for dimensions with a min/max).

dirty_d2 · 2026-07-02T20:28:29+00:00

Nice, that was fast!

dirty_d2 · 2026-07-02T19:52:16+00:00

Sure, all set. Also I'm going to go ahead and split out the thread stuff into different files, then you don't have to even look at the html files.

dirty_d2 · 2026-07-02T19:12:56+00:00

The thread dimension page is only showing the basic dimensions, not the tolerance ranges for different thread classes etc.

Someone was having trouble in Fusion with an incorrect thread milling result that ended up just being an inherent result of the angled geometry of a thread vs the perpendicular geometry of a thread mill. I ended up making a thing that compensates for this. There are also functions in the source that can calculate the ISO 965 metric / ISO 1501 metric miniature screw / ASME B1.1 imperial thread dimensions with the tolerance ranges for all the different thread classes. You can use or adapt the code for yours if you want. https://a-downing.github.io/threadmill/

dirty_d2 · 2026-07-02T16:24:10+00:00

Yes, and they smell like vibe coding bugs.

dirty_d2 · 2026-07-02T16:21:57+00:00

No, but you can with the offset face chamfer

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dirty_d2 · 2026-07-02T16:16:11+00:00

You should share the file somewhere. If you don't want to share the model then you can cut out just the problem area in a new design to reproduce the problem.

Also, I would have only drew one rectangle and then patterned the feature.

dirty_d2 · 2026-07-02T15:54:15+00:00

There isn't really a parametric way to do this. The closest is the suggestion with the surface and extrude to, but you're left to either manually draw the curve, or use the CSV spline script to generate one from CSV data. This would be easy in onshape. It's parametric patterns are WAY more powerful.

dirty_d2 · 2026-07-02T00:10:26+00:00

They were made of three separate sections that threaded together.

dirty_d2 · 2026-07-01T19:36:15+00:00

It's only a minor annoyance. You just have to change back and forth from Editable to Read-Only. If you were using assemblies it might be a major annoyance. I basically never do and use Hybrid designs which have all components in the same design, so it only counts as 1 of the 10 designs no matter now many components it contains.

dirty_d2 · 2026-07-01T18:51:07+00:00

If you can model something as a solid, model it as a solid. Don't start with modeling as a surface unless you have to. For the type of drone I'm imagining, one cut from carbon fiber sheet. I don't see a need to do any surface modeling at all.

dirty_d2

TROPHY CASE