Our team has started on CAD on onshape and we don’t have any experience with screw joints but we want to learn how to do them. We gave it our best shot and ended up with this.
Can anyone give any insights on how we do screw joints and if we are doing them right? (By the way, there are spacers between the wheel and gears, the order of parts used on the screw left to right are: 2" screw, keps nut, bearing flat, keps nut, 1/8" nylon spacer, 48T HS gear, .5" Standoff, bearing flat, keps nut, 3/4" screw)
That way your screw can’t vibrate loose. The only thing you have currently holding it together is your standoff. The reason I put c-channel and bearing flat together is because it doesn’t really matter whether the bearing flat is on the inside or outside of the c-channel, just whatever works for your spacing.
Overall, it looks pretty good and I’m sure it will work as it is right now. There are multiple ways of doing things and I think the CAD you have is a valid way of doing it.
This isn’t related to screw joints, but I noticed that your drive shafts are on the top row of the c-channel, but a motor won’t fit there. I would recommend moving the drive shafts down to the middle row of the c-channel so that the motors will fit and moving the screw joints down to the bottom row.
Also, if you’re using bearings, I would definitely recommend having the bearings on the inside of the c-channel in addition to the rest of what NO1 said. Although there isn’t really a fundamental difference between having it on the inside or the outside, having it on the inside saves a lot of space by making your drive thinner. However, in my opinion, it’s better to completely get rid of the bearings entirely, especially if you have shoulder screws. This would save even more space and weight.
You don’t need to use shoulder screws, but they will help make sure your drivetrain is aligned, and they’re good parts to have in general. But you can still use bearings without shoulder screws to make sure it’s still aligned and it will function the same.
Generally, in situations where the mechanism is going to be experiencing a lot of vibration or when you are using the screw as a joint, I recommend using nylock nuts.
I don’t remember the legality for HS/MS, but I know in Vex U we are allowed to use low profile lock nuts and those are about the same weight as a keps nuts, so we tend to use those almost everywhere since it tends to hold up better over time.
The main advantage to using a keps nut here is that it’s not nearly as much of a pain in the but to screw all the way down to the end of a 2" screw as a nylock is. Using keps nuts on screw joints just makes them much easier to assemble and maintain, and they aren’t that much more likely to come loose than a nylock if properly tightened.
