mcdanlj

mcdanlj, 23 hours ago

@smellsofbikes Ok, when I'm back at the computer I'll model the lid dovetail separately instead of subtracting the base from the lid, and add a clearance parameter.

For fudging the visible edge, I'd consider getting a 40° internal angle, 20° per side cutter, to reduce the visible curve at the edge.

Another idea would be SLM or SLS now that it's relatively cheap. But... not in 316 stainless!

mcdanlj, 23 hours ago

@smellsofbikes They have made excellent progress on the new integrated Assembly Workbench. It's fairly streamlined, and they have kept it to a small number of flexible constraints ("joints"). It's not finished yet, but they paid attention to UX while building it. They are clearly intending it to be generally usable in a few months, since it was one of the defining features for "1.0" and they are currently hoping to get there by August, last I read. 🤞

Unfortunately, the author of Assembly4 took umbrage at some of what Ondsel wrote in their rationale for building a new workbench with a C++ solver, and he became so abusive that he was permanently banned from the FreeCAD forum. 😭

mcdanlj, 22 hours ago

@smellsofbikes The eye probably wants the clearance to be normal to the surfaces, but actually what we want is horizontal and vertical clearance, so despite the illusion, the vertical and horizontal clearances here are the same 0.1mm, which is a parameter so people can adjust for their printers.

I have pushed the new files. I suspect that stable FreeCAD can read the Parts file. A current weekly build should be able to read the Assembly file that puts them together properly. The lid should be able to rotate in the assembly because I use a Revolute joint, but I haven't figured out how to do that.

mcdanlj, 21 hours ago

@done If you want to become more comfortable with #FreeCAD, @concretedog has a freely-downloadable introduction.

https://blog.freecad.org/2022/10/05/new-book-freecad-for-makers/

I find that written tutorial material for FreeCAD is somewhat limited. MangoJelly and Joko Engineering are two helpful YouTube channels.

The current development versions of FreeCAD have a lot of usability improvements. ❤️

mcdanlj, 21 hours ago

@smellsofbikes The problem with the lid not revolving was that I was using Gesture navigation. Switching (temporarily) to Touchpad and making sure the assembly itself is the active object allows me to rotate the lid around by dragging it.

(I tried to post a screencast showing this success, but Mastodon rejected it for being 1000fps (it's not) and I'm not going to debug that right now... ☺)

mcdanlj, 18 hours ago

@kbob @smellsofbikes I don't think they have the same shape; they are curved to create different conic sections as far as I can tell intuitively. I haven't tried to math it or model it though, so feel free to show why I'm wrong.

To model it, I would create the four dovetail surfaces, and then find the intersections with the plane defined by the axis of rotation and the opposite corner.

To math it, I would ask someone else better than me at that sort of thing to do it for me. 💃

mcdanlj, 4 hours ago

@chrishuck @smellsofbikes Approximating the cuts with a straight dovetail cutter and accepting curved lines on the side, or making a set of custom dovetail cutters?

If you have a CNC lathe handy, I think you have a better chance than me of making all the custom dovetail cutters. I think with Realthunder's fork, the ability to use imported geometry as defining geometry in a sketch could make the cutters easier to define.

The fact that any set of eight cutters would be specific to a single size of box (ignoring height) makes this feel like a lot of work to me.

mcdanlj, 3 hours ago

@kbob @smellsofbikes @chrishuck I used a sketch to look at what the cutters would have to look like. For my example 4mm high dovetails 15mm max width, 30° angle, and a 60mm outside box with rotation point 4mm inset in both X and Y in from the corner, it looks like if one used straight cutters instead of curved cutters, the max deviation from the defined curve would be about .016 mm, which in reality would be half of that if you split the difference top to bottom. In imperial, that's about 3 tenths (ten thousandths of an inch) which is beyond the skills of most home gamers like me.

Also, good luck finding a set of 10.736°, 17.541°, 30.399°, and 30.965° dovetail cutters off the shelf! 🤣

Realistically, I do wonder how close the most extreme angle would have to be to deceive the eye on casual inspection. Especially after some creative deburring work. It doesn't have to be straight, it only has to look straight.

Extreme close-up view of dimension showing max deviation of chord from conic section

mcdanlj, 2 hours ago

@chrishuck @smellsofbikes I just pushed a fix to my model. I had somehow gotten a sketch attachment not parameterized. Now the box resizes when the parameters are changed.

My model with 200mm square plan

mcdanlj, 1 hour ago

@kbob @smellsofbikes @chrishuck Never having taken analytic geometry, I am not equipped to find the chord mathematically, even though I can model it concretely.

I haven't figured out how to model it in a robust parametric way. An analytical solution would let me use expressions to determine cutter angles for each surface parametrically, so if anyone wants to contribute those expressions I'm all (virtual) ears. Besides an analytical solution, it's possible that the TNP mitigations could make a model sufficiently robust in practice to allow configuration.

For recording iterative solutions, I could reasonably set up multiple configuration tables, including one just for the combinations of parameters that impact dovetail edge shape, and keep that separate from other configuration.