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09-09-2017, 03:12 PM
Almost a year has gone by since I started on my Treadwell, and I thought it was high time I actually made something. Other than CAD models, that is. Something tangible.
Where have I been, you ask?
I've mentioned here and there that my printer has been sick. Specifically, it has been printing parts with a consistent lean toward the negative Y axis, rather than the random layer shifts you'd get with a slipping belt. This was a problem for any sort of functional prints (i.e. Treadwell and Artie Deco's drivetrain). Wheels ended up with a pronounced wobble, screw holes were distorted enough to cause the screws to bind up, etc. I've been puzzling over the problem off and on for months. It completely blocked Treadwell, because I can't print my eyeboxes if they are going to be bent all out of whack. I spent a long time where I just didn't print anything at all.
A few weeks before Dragon Con, I finally started printing again; a mostly aesthetic project -- my teapot racer for the alternate history track -- so I didn't have to worry about the distortion. But as a result, it was fresh in mind during the convention. After Dragon Con ended, I took advantage of the fact that we were in Atlanta to drop by the Micro Center there (since we don't have one locally) to replace filament I used for my racer and get another Pi Zero. I mentioned the problem to the guy staffing the 3d printer area. He was as puzzled by it as I was, and didn't really have any suggestions.
As it happens this was the beginning of the end, because it started really annoying me and forced me to think about it rather than randomly trying things, especially once I started discussing the issue with my friend during the trip back home. I realized it couldn't be an issue with any one axis, and the two that are affected (Y and Z) are mechanically unrelated. Once I got home, I was absently staring at the printer when the solution suddenly smacked me. Or possibly my palm connected with my face.
Remember back in march when I was building the enclosure, I said that I took advantage of the downtime to remove and trim down my Z braces? The Z braces are there to hold the Z gantry rigid, and do a very good job of it, so I basically never have to think about that part of the printer as a source of problems. And so I didn't. When I put the braces back on, I squared the gantry as usual and then promptly forgot it was even a thing.
It was blindingly obvious... the gantry was not actually square to the rest of the printer. It leaned forward. And therefore, so did every single part printed since then. But since I had (seemingly) squared it, that possibility literally never occurred to me.
Massive fail. I'll be turning in my 3d printer operator's license soon.
In the meantime, I said at the start of this post that I would actually be making something tangible. I commented elsewhere that I've been considering resin-casting my Treadwell lenses, and one of the first prints I did after the printer was working was a test of that part. I just did another print today with a lens retainer to test how well they fit together (perfectly, as it turns out).
So here it is, the first official part for my Treadwell (the blue retainer)...
Someday I might move up to printing something I've actually designed from scratch...
As I mentioned in the other thread, the lens was sliced with Prusa's Smooth Variable Layer Height feature. Basically the entire upper surface of the lens uses 0.06 mm layers for smoothness. I could potentially go thinner than this, but I'm not sure what the lower bound is on this printer, and I know that this value works. If I sand the concave surface a bit, and possibly wax coat it, I should get something that might actually be a reasonable master for resin casting. I just have to be careful about dimensional accuracy. Much of rest of the lens was printed with 0.3 mm layers for speed, aside from the area where it shifts gradually from thick layers to thin.
Regarding the rest of the droid, it has occurred to me that I might want to employ the trick used by the red carpet BB-8: control Treadwell's head tilt with bowden-style bicycle cables. That would let me move some stuff to the base, which might help avoid some of the wobble-producing weight at the end of Treadwell's stick body. It would require moving the slip ring and probably the head rotation mechanisms to the base as well, as the tilt servo has to feed through the slip ring in order to allow the servo (and the cables attached to it) to rotate with the head. If not, the bicycle cables would get twisted up and quickly prevent full head rotation.
Where have I been, you ask?
I've mentioned here and there that my printer has been sick. Specifically, it has been printing parts with a consistent lean toward the negative Y axis, rather than the random layer shifts you'd get with a slipping belt. This was a problem for any sort of functional prints (i.e. Treadwell and Artie Deco's drivetrain). Wheels ended up with a pronounced wobble, screw holes were distorted enough to cause the screws to bind up, etc. I've been puzzling over the problem off and on for months. It completely blocked Treadwell, because I can't print my eyeboxes if they are going to be bent all out of whack. I spent a long time where I just didn't print anything at all.
A few weeks before Dragon Con, I finally started printing again; a mostly aesthetic project -- my teapot racer for the alternate history track -- so I didn't have to worry about the distortion. But as a result, it was fresh in mind during the convention. After Dragon Con ended, I took advantage of the fact that we were in Atlanta to drop by the Micro Center there (since we don't have one locally) to replace filament I used for my racer and get another Pi Zero. I mentioned the problem to the guy staffing the 3d printer area. He was as puzzled by it as I was, and didn't really have any suggestions.
As it happens this was the beginning of the end, because it started really annoying me and forced me to think about it rather than randomly trying things, especially once I started discussing the issue with my friend during the trip back home. I realized it couldn't be an issue with any one axis, and the two that are affected (Y and Z) are mechanically unrelated. Once I got home, I was absently staring at the printer when the solution suddenly smacked me. Or possibly my palm connected with my face.
Remember back in march when I was building the enclosure, I said that I took advantage of the downtime to remove and trim down my Z braces? The Z braces are there to hold the Z gantry rigid, and do a very good job of it, so I basically never have to think about that part of the printer as a source of problems. And so I didn't. When I put the braces back on, I squared the gantry as usual and then promptly forgot it was even a thing.
It was blindingly obvious... the gantry was not actually square to the rest of the printer. It leaned forward. And therefore, so did every single part printed since then. But since I had (seemingly) squared it, that possibility literally never occurred to me.
Massive fail. I'll be turning in my 3d printer operator's license soon.
In the meantime, I said at the start of this post that I would actually be making something tangible. I commented elsewhere that I've been considering resin-casting my Treadwell lenses, and one of the first prints I did after the printer was working was a test of that part. I just did another print today with a lens retainer to test how well they fit together (perfectly, as it turns out).
So here it is, the first official part for my Treadwell (the blue retainer)...
![[Image: normal_20170909_173956-small.jpg]](http://www.rebeldroids.net/gallery/albums/userpics/10380/normal_20170909_173956-small.jpg)
Someday I might move up to printing something I've actually designed from scratch...
As I mentioned in the other thread, the lens was sliced with Prusa's Smooth Variable Layer Height feature. Basically the entire upper surface of the lens uses 0.06 mm layers for smoothness. I could potentially go thinner than this, but I'm not sure what the lower bound is on this printer, and I know that this value works. If I sand the concave surface a bit, and possibly wax coat it, I should get something that might actually be a reasonable master for resin casting. I just have to be careful about dimensional accuracy. Much of rest of the lens was printed with 0.3 mm layers for speed, aside from the area where it shifts gradually from thick layers to thin.
Regarding the rest of the droid, it has occurred to me that I might want to employ the trick used by the red carpet BB-8: control Treadwell's head tilt with bowden-style bicycle cables. That would let me move some stuff to the base, which might help avoid some of the wobble-producing weight at the end of Treadwell's stick body. It would require moving the slip ring and probably the head rotation mechanisms to the base as well, as the tilt servo has to feed through the slip ring in order to allow the servo (and the cables attached to it) to rotate with the head. If not, the bicycle cables would get twisted up and quickly prevent full head rotation.