Altering STL files in Rhino

[PcS]

Nice work !!! If I ever encounter that issue I will grab your .stl !!!

[pyronaught]

I've got another mod that turned out pretty good I'll have to post soon. I've always been annoyed with how the Z knob wobbles as it spins due to the set screw being driven between the threads of the ACME screw and pushing the thing off center. No matter how I try and adjust the thing it just would never mount perfectly centered on the screw. I've tried redesigning the knob with a longer neck that fits down inside the recess to try and get more of the screw to be in contact with the knob to fight the cockeyed forces being applied by the set screw, but no luck. It helped a little, but still wobbled as it spins. It just doesn't look right to have this machine that is built from all these precision parts and then there's that damn knob making it look like the shaft is bent.

So what I finally did was ditch the collar and set screw altogether and just make an ACME thread inside the knob that exactly fits the screw. Since you only ever need to turn the knob clockwise, it doesn't matter that turning it counter clockwise would remove it. I just had to get the threads tight enough, otherwise the knob builds up enough angular momentum during the platform drop at the end of a print that it can spin itself off and dance around the M2 like a top. So after printing about a half dozen thread plugs I got one that fits just right. I'll post a .3dm file with the thread plug so anyone wanting to make their own knob can Boolean it in, and also the knob I made along with the stop key.

I had no idea ACME threads are actually four separate threads offset by 90 degrees each. I spent a few hours trying to get normal threads to match that thing before I finally noticed the multiple threads terminating on the end of the shaft. I guess that's the secret to how they get such steep pitch on a screw like that, I never really gave it any thought before.

z_knob.jpg (188.35 KiB) Viewed 9824 times

[jimc]

haha and i thought i was the only one. it drives me nuts. takes me 20min of messing with it to get it just right so it doesnt wobble or atleast to a minimum where i dont notice it.

[Jules]

Fantastic! Definitely something to play with! Think a little spinning ballerina would be over the top?
.....
(Just kidding fellas......try not to freak out!)

[pyronaught]

haha and i thought i was the only one. it drives me nuts. takes me 20min of messing with it to get it just right so it doesnt wobble or atleast to a minimum where i dont notice it.

Cool, OK now I don't feel like I'm being anal about the knob wobble. This threaded one does not wobble at all, and you don't have to keep a special hex key around for that one odd-ball 10-24 set screw. I lowered the height of the knob a little so that I could increase it's diameter, which I think has a better feel when making tiny adjustments like when setting the z stop. The lock key is printed with the layers running vertical so that it can't snap under twisting forces, it's just a U shapped thing that plugs into the top of the knob (and then gets lost when you need it).

[PcS]

Nice work I will take one when you get it up .

[pyronaught]

I posted the files in the modifications forum. I guess I should have put that other mod over there too.

[PcS]

Thanks !