Clearance/movement between internal external threads
Clearance/movement between internal external threads
(OP)
Hi
I have a design where I have one dowel and one threaded hole.
I want to work out what the tolerance on the centre distance needs to be so I need to work out how much the screw can move in the hole, as the part is being wound up and down (adjusted) on the screw.
I know this is different for different classes of fit for the screw but I can't seem to find a clear answer. Essentially the more free play there is between the screw and threaded hole the less tight the tolerance on the centre distance needs to be. However I don't want specify a loose class of fit if I can avoid it.
This is the same as knowing the movement of a shaft in a clearance hole except for a screw in a threaded hole.
Cheers
I have a design where I have one dowel and one threaded hole.
I want to work out what the tolerance on the centre distance needs to be so I need to work out how much the screw can move in the hole, as the part is being wound up and down (adjusted) on the screw.
I know this is different for different classes of fit for the screw but I can't seem to find a clear answer. Essentially the more free play there is between the screw and threaded hole the less tight the tolerance on the centre distance needs to be. However I don't want specify a loose class of fit if I can avoid it.
This is the same as knowing the movement of a shaft in a clearance hole except for a screw in a threaded hole.
Cheers





RE: Clearance/movement between internal external threads
I.e., it's basically a sophomore kinematics problem, like the monkey/clown that jumps and grabs a stick, with the further complication that the driving force is offset by the center distance.
Mike Halloran
Pembroke Pines, FL, USA
RE: Clearance/movement between internal external threads
RE: Clearance/movement between internal external threads
Not so much under cantilever/moment load.
Mike Halloran
Pembroke Pines, FL, USA
RE: Clearance/movement between internal external threads
RE: Clearance/movement between internal external threads
You might want to provide a sketch of your assembly, or at least the relevant portion.
What type of screw thread are you using?
pylfrm
RE: Clearance/movement between internal external threads
You are on the right track that the class of fit will dictate the maximum movement of a screw shaft relative to a hole. It all has to do with pitch diameter and how much that is allowed to vary (which is defined by fit class i.e. 2A/2B).
For example, from ASME B1.1 a 4-40 2A screw has a pitch diameter .0950/.0925 and a 4-40 2B hole has a pitch diameter .0991/.0958. The most that screw can shift from hole center is (.0991 - .0925)/2 = .0033.
RE: Clearance/movement between internal external threads
Here's an article on the topic: Threads - Long Engagement Problems (pdf)
RE: Clearance/movement between internal external threads