The future is weird. This morning, I used my timeshare supercomputer subscription to (somehow) guess how write a plugin for a piece of modeling software I don’t own (you are welcome, autodesk). This little piece of code solves a problem that people have been aware of since the beginning of design, but that is hard to put your finger on. To put it less literally, I vibe coded a g3 curvature-continuous sketch fillet tool for fusion. You can get it here. If you care to know more about the problem, or if this table edge bothers you and you don’t know why, read on:

Curve Continuity

The edge of the table above is (supposed to be) made of two lines coming into an ellipse. Even though the lines are tangent to the ellipse (at east to the best of my ability), they look kind of strange. That is because an ellipse (or more commonly a circular arc) has curvature, and a line does not. So even for a tangent line going into a circular radius, there is a discontinuity.

Here is an image of what’s going on – the transition is from the line (no curvature) to the ellipse, which does have curvature. That jump is something that you can see and feel. The little lines are called a curvature comb, and the length is related to the curvature where it touches down, and they comb lives on the “outside” of the curve.

The fix is to use a G2 or G3 continuous curve. Note that both combs now start at zero curvature and ramp up. The difference is that a G2 will have a constant initial “velocity” (first derivative) of the curvature, while a G3 curve accelerates that change over time. So a G3 is smoother.

How this helps my 3D prints, and other things

The curve on the left is a radius, and on the right is a G3 curve. You can see the very tiny shadow on the radiused side, while the G3 curve is smooth. I think this is both a print artifact from deceleration and a result of my careful lighting, but based on the geometry I also expect a little discontinuity there. I can also feel a slight “hitch” in the smoothness as I slide my finger around the curve.

This is a different corner, where the radius is on top and the G3 curve is on the bottom. You can see where the deceleration happens in green, as the print head cannot move smoothly around the corner at high speed.

Unsurprisingly, these smooth curves have tons of more important uses in the real world, particularly in transportation, where smooth curve transitions are used to prevent trains from derailing, cars from flying off of roads, and (least importantly) they are famous for being the non-radius shape for corners that apple uses. They are also used by industrial designers to terrorize mechanical engineers everywhere. There is nothing quite like getting a model with no flat surfaces and no radii that explodes when you sneeze at it, and these curves seem to be amazing for building that kind of geometry.

In my own life, I might start using them to replace radii in my 3d prints, at least when they are in the xy plane of the printer, so they come out extra nice, and ever so slightly faster. I also intend to use them on future woodworking projects to avoid the odd looking corner that I shared above, which is the real reason I made this plugin.

Lately I have gotten access to an xtool F1 Ultra. One of the advantages of this laser is its ability to ablate (I wont say cut) metal. I’ve seen videos of people making pcb solder paster stencils, or cutting really thin metal on similar fiber lasers, and I wanted to try too. All of this is applicable to making small “positive” parts with the xtool as well. Here are my notes.

Settings and Cut Ordering

When working with thin material, its important not to heat the metal up too much in one spot. This means making many light passes is better than a single, really aggressive pass. This is especially true for cutting out tiny windows, or cutting out a thin “web” between two windows. Too much heat too fast will distort the final geometry.

The settings I used were 100% power, 8000 mm/s speed, and a variable number of passes. For a single large cut/window (like a ~3mm square or above) you can just go ahead and set it to 500 passes and let it rip. The cut is long enough that by the time the laser comes around again, the heat has had time to conduct away.

Below about that size of window, I had better results from repeated cuts – e.g. cut 50x times, wait 10 seconds, then repeat 10x for a total of 500 cuts.

In addition to taking many passes, I needed to semi-randomize the ordering of the cuts. The Xtool sofware optimizes for time, by cutting from the top left to bottom right. This means that cut profiles that are next to each other together are done at the same time. This leads to overheating local overheating, and warping. The left stencil was randomized, the right one was not.

Sadly, there is not feature to do this in the xtool studio. The best you can do is select->ungroup your stencil, then go through and assign each cut in your stencil to a different layer. Then, using the “…” menu near the process button, choose processing path-> user defining and choose “by layer”. There are about 10 default layers, so the laser will go “somwhere else” for about 9 cuts before returning to where it was cutting before. This greatly reduces local heating.

Workholding to Prevent Warping

Warping happens when some part of the aluminum gets so hot that it expands, and causes plastic (permeant) deformation in the rest of the sheet of aluminum. To avoid this, I constrained the sheet with tape. This prevents deformation in exchange for stress in the aluminum. By minimizing heating, we minimize this stress.

This fixturing also holds the aluminum material so it doesn’t move due to the exhaust fan.

The best way to achieve this fixturing seems to be an aluminum block (safe to laser), then a layer of removable double sided tape, then another layer of painters tape, then the aluminum stock. Without the layer of painters tape, the aluminum card is hard to remove without bending. The painters tape releases from the doublestick pretty cleanly, so a single doublestick tape bed can last many laserings.

Focus Focus Focus

One issue I have run into repeatedly with this laser is that the autofocus does not work, at all. I guess its better than nothing, but I find that its off by about -3mm-4mm. So every time I create a new fixture, turn the machine on, or jog anything, it needs refocusing. I just start by taking the autofocus distance, subtracting 3, then I focus by .5mm increments until I go through a “sweet spot”. It seems like for metal ablation, the beam is tight enough to be focused over about 1.5mm

Surprisingly, the laser cutting makes a distinct snapping/humming sound when its cutting well. I assume this has to do with the metal rapidly expanding/contracting as the laser heats it up and deforms it.

Stencil Performance

My hope is that this can make stencils for everyday use, and for emergency use, like pcb rework. PCB stencils usually cost a couple bucks and cause a few cost related problems for ordering PCBS – specifically in the US, the stencils are relatively expensive (if coming from somewhere like sunstone), or you have to get them at a separate website with separate shipping (osh park/osh stencils), or if you are ordering small boards from overseas, stencils make shipping really expensive as dimensional weight goes up (the box is bigger).

This stencil was quite usable, but it seemed thick (around .18). In the future, I’ll try a slightly thinner material to reduce paste application, especially for “middle”/large pads. The good thing is that its easy to delete or reshape the windows for components if they cause trouble!

I’m back at trying to propagate a lingonberry plant from a cell culture gathered from the wild! This time, I seem to be having a lot more success in terms of growing something that at least resembles a callus culture. Encouragingly, I have had similar growths from various parts of plants that I plated. I tried to excise buds from the meristem, without magnification, so its hard to say exactly what tissue the cells came from, because they were very small (generally, they are from in the buds).

In the future it might be worth looking at callus induction from leaves, a technique I did not know about.

These cultures are growing relatively slowly (months between re-plating), possibly due to the totally uncontrolled and unoptimized conditions they are in, aka an funky basement. Surprisingly, contamination has not been a huge issue (transfers have been done in a pcr hood).

The next step will be to take some larger cell masses and try to get them to grow a bud, shoot, root or leaf- to start turning back into a plant. My plan is to grow them on a deeper media in a different container, undera lighting, without 2ip on something like WPM with zeatin (although zeatin is expensive, so maybe just WPM!).