This 3d printed 3 Jaw chuck might work well. Did a couple of test prints this morning & modifying the design for my needs. I changed the trapezoidal to have arcs, so the 3 jaws can be printed on their side. Will have to do some filing on the parts for a nice smooth motion. Seems like this might come loose during burning, so probably need to put a rubber band around the jaws to keep them in place.

 

I am almost finished with the modification of this 3 Jaw chuck design. The guy that designed this did a really nice job & made it easy to modify since he included the fusion 360 file. He used a coil for the spiral. My printer does not seem have quite as good of tolerances as his, so I tapered the tops of the spirals & jaws for less filing. I looked at a couple of sections of it to see how well the mating parts met & rotated the scroll plate to match the jaws. I cut a slot on one side of inner scroll plate to miss the M5 motor mount bump out (about 40degrees of the circle).

 

I am still unable to get this scroll plate design to work for me, so I am going to modify it further to use the Cam & follower idea from my previous self-centering turntable design. I uploaded what I had changed for the scroll plate design as 3_JawChuck_v13.zip if someone wants to take a look at it & try it. I have the STL files oriented for printing & included the fusion 360 file.

 

Here is an interesting link for Celtic Knots that someone on the V1engineering site mentioned. Celtic Knot Generator in HTML5 / Canvas (w-shadow.com)

I used these settings on the web page & then imported the PNG file into Lightburn to burn a bamboo pen.
Randomize, Close border, 24 width x12 Height, 30 cell px, 7 string size, 4 stroke width, string color of black #000000 & other 2 colors of white #FFFFFF. I imported Png directly into Lightburn, scaled it to fit pen, right clicked on image & did a trace image. I would have liked to have another option of more gap where lines crossed, but still came out well. Might be able to play with numbers more to get more gap another way. Here is image of it. It is about 5mm shy of wrapping all the way around the pen. I will also added Celtic_Knot_Randomize_CloseBorder_24x12_30_7_4_00_FF_FF.zip with a .lbrn2 file in it.

[Edit] This file was replaced with CelticKnots.zip that has more patterns and information in it.



[Edit 8/8/2022] Further testing, 30 cell px, 7 string size & 4 stroke width gives me a better gap where lines cross & also a little less burn time.

 

I deleted the previous Celtic knot file I uploaded & uploaded CelticKnots.zip which has 30 .png files with the parameters I used along with a text file with some explanation & a generic .lbrn file that should load into any version of Lightburn. I added generic John Doe text to the Lightburn file so anyone can just substitute a name.

 

I decided to revisit this 3-jaw chuck design for a vertical pen mount. I couldn’t figure out the spiral path a couple of years ago, but after watching a YouTube video on it, it was quite easy. After reproducing this design Nano Chuck by PRIma by PRIma - Thingiverse with better tolerances for me, I realized something interesting. All the chuck designs I had seen used a rectangle profile along the spiral path. Why not use a gear tooth profile sweep along the spiral path. I was using a spiral with a 6mm pitch, so I wanted to match the gear tooth spacing to that. In fusion 360, I used the spur gear python script to create the gear. I used a 24-tooth gear with all the other defaults. I changed the module size until I got an arc length between teeth to be about 6mm. A module size of 1.91 came out to an arc length 6.0004 between teeth which was closer than I expected. 2020 hindsight, I should have used a backlash of 0.2mm instead of dropping the tooth down 0.2mm from the opposite tooth. I still have to tweak the design a little, but my first test of this works better than I expected. This is designed to fit on top of a Nema 17 motor & I added the threaded nut to keep the scroll plate in place rather than clip. Now that this works, I might try to make it smaller as I mostly just using this to engrave bamboo pens. Here is a section image showing the teeth.

Here are a couple photos of the 1st test print assembly.

 

Since Fusion 360 displays the Pitch diameter as you change the module size, I used a spreadsheet to work backwards from the Pitch Diameter needed to get the spiral pitch I wanted to use to see how small a pitch I could use. I used the formula (Pitch * Teeth) / pi = Pitch Diameter
After knowing the Pitch Diameter, I went back to fusion 360 spur gear script & changed the Module size until I got as close to that pitch diameter as I could. I am sure there is a math formula to get this exact, but only takes 30 seconds or less with trial & error to get a reasonable number. Actually with plastic, this number is far more accurate than it needs to be. With a Module of 1.114085, it gives me a spiral pitch of 3.500001251mm. Using this method for the 6.0mm Pitch, the number came out to1.90986 for the Module. I used spiral pitches 3.0, 3.5, 4.0, 5.0 & 6.0. After creating a spur gear for each pitch, I measured the smallest width of the tooth. The tooth width for the 3mm Pitch was 1.63mm which might work but seemed a little small. I printed a little spur gear with this size to visually see what the tooth size would look like. The width of the 3.5mm pitch at 1.92mm seemed big enough, so I redrew this design with this criteria & printing it today. I was able to get the chuck down to 62mm diameter from the 74mm diameter used with the 6mm pitch. I was hoping to get a smaller diameter than that, but I would have to use less than 3 spirals and I can't change the center hole size because of the size of the mount to the Nema 17 stepper motor. I use this formula to calculate Spiral pitch. (Pitch Diameter * pi) / 24

 

This is a little sloppy fit which I kind of expected, but more so than I thought. I added some more support for that inner gripper as that bent a little too much without that 45-chamfer added. I have a 0.2mm clearance on the jaw sliders horizontal movement & a 0.2mm backlash for the spiral gearing. I think the backlash is ok. The jaw sliders I am making 3mm thicker & adding 4mm to the height of the base of the chuck. I also changed the clearance of the jaw sliders to 0.15mm. I will have to file and sand these down some to fit smoothly. I had to file them down before but will have to do more this time. One of these days I will get a printer that can print with tighter tolerances. I kept the 3.5m pitch for the spirals as that looks ok when I print to spur gears with the numbers I used. I am printing the new version today.

 

I had to do some tuning to my printer this week as my prints were not coming out as well as I liked. I tightened the belts, eccentric nuts, changed the y-axis wheels to the Xtreme Solid V Wheels & changed my y-axis limit switch that was starting to misbehave. I also calibrated the x, y & z axis closer than I have before. It is amazing how much better the prints look now. I finally uploaded this design to thingiverse if anyone wants to try it. It is still a little sloppy fit but might be useful. I have a new Atezr L2 24W engraver, so will probably switch to using their rotary attachment soon.
Three Jaw Chuck with Spiral Gearing by GeoDave

 

Since using Fusion 360, screw thread limitations have always bugged me. I was used to how flexible you could change all the variables of a thread, but mostly the diameter & thread angle using OpenSCAD. After a few weeks of frustration in learning the syntax of the python API for fusion, I have an Add-In that works quite well for me. There are a few things I would still like to do but haven't figured them out yet.

I started a topic here: Drawing more Flexible Screw Threads in Fusion 360 - Random or Off Topic - V1 Engineering Forum to show my thoughts as I worked through this idea.

These are drawn using a thread profile & a helix drawn with spline points. The profile then uses the sweep command with the helix as the path & either a centerline or another outer diameter helix as the guide rail. It is not a true helix & if you use too many spline points, it will really bog down your computer. 18-36 points per revolution is about the most I use. Maybe one day Autodesk will add a helix primitive and make this a more accurate helix. It is probably close enough for 3D printing though.

I am working on adding a Bolt & Nut option to it now, so you input the tolerance between the Male & Female threads the way that works best for your 3D printer.

Here is the link to the Add-In.
GitHub - geodave810/ThreadTune: Fine-Tune your Screw Thread Designs in Autodesk Fusion 360

Here is what the Input Dialog options currently give you.

Here are some examples of the types of custom threads you can create. Someone sent me a link to a YouTube video of someone using the inverted threads on 4 corners of at 3D printer with only a quarter cylinder of the female threads. Seems like you would need supports to print that style.

 

Think I am done with adding all the features I wanted to this thread program. A week or so after initially creating the GitHub repository for this program, I found another repository by the same exact name. I was surprised that GitHub allowed that. I have been thinking about renaming this for a while. In order to keep the name similar, I just changed it to **P_ThreadTune** with P standing for Python. I will keep the other repository for now with a link to the newer one but will probably eventually delete it. I might sometime in the future rewrite this in C++ and use the prefix C_ for that. It is fast enough for me, so not sure whether writing it in C++ would be beneficial other than teaching me how to use this API in C++
Release v1.4.0 Real Offsets Added · geodave810/P_ThreadTune
The dialog box changed considerably since the previous version.