(Yet Another) Ruler Stop Block

TLDR: Just my take on a simple stop block for my Neilsen steel rule. 

Before we start, I can't claim credit for the knob you see in the pictures. I found it in my spares tin and just cut it to length with a hacksaw. I have absolutely no clue as to its origin. Since you're unlikely to have the same one available, I've chucked in a simple design for a knob to fit a standard M6 bolt. If you don't like it, have a search on this site. You'll find plenty of other designs to choose from! 

I've been meaning to do one of these ruler stops for ages, and I'm sure everyone does their own version at one time or another. For my purposes, great precision wasn't a necessity. So I didn't have to worry about anti-slew designs or crazy close tolerances. Just a simple slider and clamp was good enough.

My first design was literally a block with a slot, and a threaded hole for the bolt. Meh, it worked fine, but it was lacking any style or finesse. So I did another with a little more pizzazz, and that also worked perfectly. But I wasn't keen on the bolt clamping directly to the face of the ruler since it was almost certain to scratch it over time.

So I revised it a final time by adding a small plate as a buffer between the bolt and the ruler. This plate just slides in through the front slot (with its ridge uppermost), and inserting the ruler retains it in place.

As mentioned above, I already had the knob bolt. So I simply designed an M6 thread into the slide body. How long the threads will last is anybody's guess. But it's not like it's securing an ocean liner in place or anything!

I designed the slider with a 0.2mm tolerance either side of the ruler. But this revealed that my cheap Neilsen branded rule actually has quite a lot of width variation over its length. It slides beautifully at each end, but gets a little tighter in the middle. Rather than increase the 0.2mm tolerance (adding to the risk of skewing), I used a little squirt of household furniture polish to improve slideability on the tighter part. Works for me!

Just for completeness, the ruler has a nominal width of 23.5mm (0.925") and a thickness of 0.75mm (0.0295") - but note the variance mentioned in the paragraph above!

I printed the slider with the small flat face on the print bed, and designed in enough tolerance (hopefully!) for the bridging of the upper slot so that supports weren't needed. This worked out just fine on my Bambu X1-C, but I can't speak for other printers, obviously.

I chose to use PETG at a 0.16 layer size, but took advantage of Bambu Studio's variable layer size tool to ensure the threaded part printed at 0.08 to avoid issues. Probably overkill on my part, but it made sure that the threads printed beautifully; the bolt went straight into the threads without difficulty.

As usual, I've included my FreeCAD file, the .stl, and .step files, and also I chucked in the .3mf files that I used on my Bambu Labs X1-C printer to actually print the parts.

So there ya go. That's my take on this useful gadget. I gauge that, with measured usage, it'll come in pretty handy as a rule!

Happy printing!