(I had saved about 80% of the lost message in the clipboard, so I pasted it into Word and retyped what had been lost, more or less (mostly less)).
I have a hole in a circular case, into which I will insert a USB-C cable when I need access to the microcontroller inside. The rest of the time, I want to plug it with a "soft" cover than can be easily pulled out, probably printed in Ninjaflex, which I happen to have a spool of.
So I did the following:
I created a circular case using a sketch with a circle 60mm in diameter (I later enlarged it to 66mm so that all the parts would fit inside). I extruded it, then Shelled it with a 2mm wall thickness. So now I had a circular case.
I created a plane tangent to the side of the circle where I wanted to put the hole for the USB cable.
On this plane I drew a (filleted) rectangle of a size large enough to accommodate the USB-C cable connector.
I extruded, with a cut extrusion, the hole I wanted in the side. I got a nice hole in the side.
I created a plane 2mm further away, parallel to the plane I used to create the hole.
I created a sketch on it, of a filleted rectangle, that was 2.54mm (which is a random number, but .1in felt right) larger than the edges of the hole, which I had projected onto the sketch.
I created another sketch on the same plane, projected the hole dimensions onto it, and created a filleted rectangle 0.25mm smaller ("hole_clearance") than the hole. I may adjust hole_clearance once I have printed a couple drafts and see how well the Ninjaflex and PLA shrinkages play together.
I extruded the first profile from the plane defining the outline of the cover TO the surface of the cylinder. So I now had a part that was flat on top and curved to fit the case at the bottom. I created this as a new body, since I wanted to print it as a different material.
Next, I created, on the side of the new body, a new sketch parallel to the end of the cylinder, which contained a circle concentric with the case, but tangent to the top of the extrusion I just created. This meant that I had a sketch with a circle 2mm larger than the case.
Next, I put a rectangle on this sketch, which had its "top" side .5mm "above" the flat top of my extrusion. With a bit of Trim and Close Loop, I got a sketch that contained the material I wanted to cut away.
I extruded, with a cut extrusion, this shape. Now I had a 2mm thick object that fit the curve of the case.
I was now happy.
So next, I went to the profile on the other sketch, the profile that was just ever-so-slightly smaller than the hole.
I created another sketch parallel with the end of the cylinder, and drew a circle .5mm smaller than the circular case.
I tried to extrude the "plug" part to that line. No happiness; TO expects a surface.
I created am extrusion from the circular inner sketch, which filled up all of the inside except for the .5mm gap.
I created this as a separate body.
I now could extrude the "plug" part to that cylinder, so I had a plug whose “cover” was 2.54mm larger than the hole, and the smaller “plug” part protruded .5mm into the case.
I changed the name of the new body to include the phrase "never visible" and when I clicked off its “visibility” it disappeared, leaving me with what I needed: a plug with a cover.
I was happy, mostly.
But I noticed that the top of the plug remained flat, and had not been cut by the cut extrusion. A few minutes of starting at this revealed in the Explorer view that I had
- Extruded outside of cover
- Extruded a cut to make it cylinder-shaped
- Created the plug part
- Extruded it.
you can see what went wrong here: the cut extrusion only cut the first extrusion; the second extrusion came after the cut.
That seemed easy enough to fix: just drag the cut extrusion to the end of the part, so it is the last thing done.
Except when I tried to do this, it would not let me drag the cut extrusion below the plug extrusion. It would not let me drag the plug extrusion above the cut extrusion. As far as I could tell, there was nothing in that sketch that required that the cut extrusion precede the plug extension. After some groveling over the documentation (always a futile effort, I tend to find), I decided to delete the drawing and extrusion, and re-create them as new items after the two extrusions. Note that I did the plug extrusion as a separate body, because I couldn't find (no surprise that I couldn't find it) how to make an extrusion be part of an existing body. Strictly speaking, the cover and plug should be one body. But good enough to make them two, as long as I remember to make both visible when I print it. So now I have two bodies. On the outside "front" surface of the outer body (the "cover" part of the plug) I placed another sketch. I repeated the make-a-concentric-circle, trim, close path that I had done earlier. Now the cut was later than both the positive extrusions. I did the cut extrusion, and expected to be happy.
I was not. The central plug still extends above the surface.
I was told that I should use projects, because I could then easily package up my example so you could read it. I tried this, and got a 272MB file. It apparently packaged up my entire “my parts” subdirectory, even though only about five parts were used. This is silly and unwieldy.
I looked into doing a screencast, but I was asked a number of unintelligible questions whose answers were not at all apparent, so I gave up.
I am attaching three screenshots that may help explain what is going on up above.
The first one is Case V3 First Extrusion.png. This shows the two planes; one tangent to the case, and one 2mm above it. The sketch for the extrusion profile was drawn on the upper plane, as was extruded as a New Body, using the TO option, where the TO was the outer surface of the cylinder. Other than having that ugly flat shape, it is fine. This extrusion is known in the Explorer pane as Extrusion 15. It is the third-to-last element in the Explorer pane.
The one which is Case V3 Cover and Plug.png shows the complete extrusion of the cover part (on the outside) and the plug part (which you can see protruding into the cavity, because I extruded it TO the invisible body that was .5mm smaller than the ID of the cylinder. The extrusion of the plug was a separate new body than the extrusion of the cover. Note that at this point, the top of both extrusions is on the upper pane, and flat. The plug extrusion is labeled as Extrusion 17. It is the second-to-last element in the Explorer pane.
The one labeled Case V3 Cut Failure.png shows the outcome of the entire effort. Note the profile (which I made visible) which is on a sketch placed on the front side of the cover extrusion. It started out as a concentric circle 2mm larger than the OD of the cylinder, and I added the rectangular form (which actually sticks up about .5mm above the top surface of the two extrusions), then applied Trim and Close Path to get a valid profile.
I then did an extrusion, which is Extrusion 19 and the last element in the Explorer pane. Note that it cut Extrusion 15 but not Extrusion 17. I do not understand why, and I have made a couple conjectures that I would not know how to fix.
One conjecture is that because the profile is on the body of Extrusion 15 that it will only cut Extrusion 15. One way to fix this would be to make Extrusion 15 and Extrusion 17 be a single body, but I do not know how to do this.
Another would be to put the profile someplace else, not directly on the body. But if I were to put a sketch on the front of the case (we are looking at it from the front, and this hole is in the bottom of the case), but if my previous conjecture is correct, I would now have no cutting of anything, since the case is yet another body (the bodies are: Case, Front Cover, USB-C Cover, USB-C plug (as in hole plug, not electrical plug) and Inner Cylinder (the TO target of the USB-C hole plug). The cover is the piece that is constant thickness, and the plug is the part that sticks down into the hole in the case. After I get to print a few exemplars and understand the fit & finish issues of how PLA and Ninjaflex shrinkages Play (Well?) With Each Other, some of these dimensions may change, and I may add a “bead” at the part that protrudes into the case so it seals well.
This case may be used outdoors, although it will not be anywhere that it can be rained on. But I do want to seal the holes, lest it become a hotel for six-to-eight-legged travelers. This is the only hole that has a removable connection; all other holes are very precise fits with no space around them. The holes that you see Cover and Plug are (and the image is upside down) South, the reprogramming cable; Southwest, the 5V power supply (2.5mm power connector), West, the sensor cable (which fits exactly), and North, the readout display (which also is a very precise fit).
If you can point me at something intelligible on using Screencasts or Pack And Go, I will be able to do a better presentation of the problem.
These are all being done in Inventor Pro 2018, because the makerspace I inhabit only has that version, and I want the things I am working on to be editable from home and the makerspace.
