I’m not familiar with the term ‘king pin’ I think I would call it a draw pin or something such. It is a hitch of some sort I would guess.
A king pin is the pin used in an 18 wheeler rig to secure the trailer to the tractor. Unlike this toy, though, the king pin from a semi is located on the trailer, not the tractor.
50 years ago when I worked for a couple of years at Weston’s bakery in Saskatchewan I used to back up semis to the loading docks so that we could load the trucks but I really know nothing about their hitches. Other hitches more or less but not those.
The part that goes on the tractor is called a 5th wheel which is more or less a circle with a hole & locking mechanism in the center and a V on the back end with the point of the hole going to the center hole. The same setup is used in some travel trailers on a smaller scale.
I have always known king pins being used on large trailers and 5th wheels on smaller ones, typically on pickup trucks. Maybe they’re called different things in different regions?
BTW, a test print of my remix of the axle and wheel is printing right now. If that works as expected, that should be pretty much it.
OK, axle and wheel done:
[ATTACH=JSON]{“data-align”:“none”,“data-size”:“medium”,“data-attachmentid”:12261}[/ATTACH]
The axle is a “press fit” into a groove inside the wheel.
[ATTACH=JSON]{“data-align”:“none”,“data-size”:“medium”,“data-attachmentid”:12262}[/ATTACH]
Maybe a little hard to visualize, but this shows the 2 bumps on the axle where they engage with a groove inside the wheel.
[ATTACH=JSON]{“data-align”:“none”,“data-size”:“medium”,“data-attachmentid”:12259}[/ATTACH]
The 2 bumps engage with a groove inside the wheel. The rectangular hole provides the flexibility needed to permit the bumps to squeeze into the hole in the wheel.
[ATTACH=JSON]{“data-align”:“none”,“data-size”:“medium”,“data-attachmentid”:12260}[/ATTACH]
Closeup of the axle in the wheel. The fit is loose, which I think is just fine for a kids toy.
It’s done. I’ve uploaded STL files of the 5 parts: [LIST=1]
A couple of notes: [LIST=1]
image_1760.stl (127 KB)
image_1761.stl (200 KB)
image_1762.stl (763 KB)
image_1763.stl (916 KB)
image_1764.stl (1.78 MB)
I must be loosing my mind I don’t see any files or links to files 
hmmm, this is what I see:
[ATTACH=JSON]{“data-align”:“none”,“data-size”:“custom”,“height”:“403”,“width”:“583”,“data-attachmentid”:12282}[/ATTACH]
OK, so I’ve zipped the 5 files. SemiCrayonHolder.zip
I think I figured out what’s going on. Apparently, it’s necessary to Insert a non-picture file in order for it to show up for everyone.
SemiCrayonHolder.zip (1020 KB)
Very nice work!
When clicking on the zip file it opens a page saying URL not found. The separate files download but not with the file name shown it downloads as image_xxxx.stl I checked and they are the stl files I could open them in Prusa Slicer
Not sure what’s going on with the zip file. I downloaded it to my local downloads folder, opened it, and the files were there as expected, right down to the names. Perhaps you only downloaded a link to the file??
The individual STL files thing is weird. I can only assume it’s something the forum software is doing. Maybe it only likes to think it’s working with image files. In any case, the files appear to be correct and intact, so they should be sliceable and printable. I would download each 1 and rename it after it’s done.
Received an email from my S-i-L this morning. The semi crayon holder is a hit with the grandchildren, who came over to visit today. Apparently the 15-month old granddaughter surprised them all by putting crayons into the silos.
@Gramps, I just updated the axle to include a taper from the retention knobs to the center of the axle. This should give the axle a little tighter fit. Beware, I haven’t printed this 1. I would be grateful, if you print it, to post back how well it works. Thx.
[ATTACH]n12343[/ATTACH]
Thanks I’ll print it and let you know how it fits.
@Ender5r I printed the new axles they went together pretty easy. I put a pair through the hole in the trailer. Put a wheel on each side and pressed, they popped together with a little pressure. Can’t compare them to the originals but these are okay. Don’t spin real easy but I think that it my printer setting, I’m printing another set at 1.2mm instead of 2.0mm to see if there’s a difference. The trailer has a couple of hiccups but I think it’s my printer not your design.
[ATTACH=JSON]{“data-align”:“none”,“data-size”:“medium”,“data-attachmentid”:12419}[/ATTACH]
Looks pretty good @Gramps. The main thing with the wheels, for me at least, is that they fit tight enough on the axles that kids are unlikely to be able to pull them off. Of course, it’s also important that crayons and colored pencils fit into the holes well and the trailer fits on the king pin nicely.