Last night, after
a little encouragement from Bart, I looked again at the laser tube support brackets. My recollection was that they were way too big for the four inch printer at my makerspace. I had tried laying them out diagonally, because some other long parts fit in that orientation, but the tube support brackets do not. They
almost fit, though, in the regular orientation. We installed a new glass bed on the printer last Friday night, and it measures 110mm in the long (Y) dimension. The tube support bracket is nominally 120mm wide.
My first idea was to chamfer away the bottom corner so that the bottom surface is only 108mm. That looked like this in OpenSCAD.
After taking away material right where the post holes go, I thought I'd better add some material and move the post holes away from the chamferred corner. So I came up with this. There's no reason why the holes have to be on the part's center line.
This morning I printed it. The print was pretty bad. The print shifted over as the printer reached the tops of the chamfers. That means, I think, that the printer has a full 120mm range of movement, but it is not centered over the table.
Then I tried to drill out the post holes. The printed material split. Apparently, it's sort of like plywood. If you drill through the plies, the alternating grain direction of successive layers holds it together pretty well. But if you drill parallel to the plies, it's just pulp. Er, it's strings of plastic that aren't stuck together very well.
That piece was ruined, but I decided to drill out the holes for the alignment bolts anyway. I found that the dimples in the model aren't big enough to attract the drill bit on the rough surface of the plastic. Also, 8.5mm thickness with a 7/32 hole leaves very thin sides, especially in pulpy plastic. So I decided to go thicker near the alignment bolts and to print the holes instead of drilling them. I could have just made the whole piece thicker, but I was in a plastic saving mood.
It is conventional wisdom that you can't print a horizontal hole. But I've been printing horizontal holes with no problem on this printer. I don't know why it works, but it does. Anyway, those changes led to this model. Note that I also cropped 3.5mm off each end, leaving a fairly thin wall between the post hole and the end.
I made two, and I made them mirror images of each other. That way, the "legs" will protrude to the outside on each piece. Tiny thing, but it would bug me if I hadn't. (-:
The nuts were a tight press fit — I had to push them into place with needle nose pliers. The bolts slipped right through their holes, no cleanup required.
Here they are holding up an old fluorescent tube I found in the junk pile.