【转帖】iming 2 sprockets on a shaf

yang686526

timing 2 sprockets on a shaft
how would one show using gd&t the timing of (2) indentical sprockets on a shaft? there will be a conveyor chain with slats that will run on the sprockets and need to be timed pretty close or there is a good chance that the conveyor slats will skew and possibly become jammed.
scorch
don't worry about people stealing your ideas. if your ideas are any good, you'll have to ram them down people's throats.
--howard aiken, ibm engineer

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it would be better to have permanent markings on the pieces or have them arranged so that they can't be timed wrong (keyway or similar).  at some point someone will be rebuilding this and won't have your drawing.
is this something that you plan to "adjust at assembly", or do you want to control the individual components so that any assembly will be good?

scorch,
   is there a clocking feature on your sprocket that can be mechanically contacted and inspected?  
   can you design one in?
               jhg
there are no features on the sprockets that can be referenced. we do have a keyway on one end of the shaft that the sprockets are welded to, i am not sure how to reference that. these sprockets will be welded to the shaft with no adjustment at the assembly level. we are just not sure how to index the sprockets to one another. in the past we controlled the indexing with a note on the drawing that stated: "sprockets must be timed". we want to move away from using a note and give manufacturing specific dimensions and tolerances to achieve this.
don't worry about people stealing your ideas. if your ideas are any good, you'll have to ram them down people's throats.
--howard aiken, ibm engineer

i would set up the timing requirements as follows:
i would make datum a the portion of the diameter on the side of the shaft with the keyway used for the bearing on that side. datum b would be the portion of the shaft used for the bearing on that side. (i am assuming that the shaft fits on bearings on each side.) datum c would be the keyway and datum d would be the keyway end of the shaft.
i would relate the teeth one of the sprockets to the shaft with a true position tolerance to [a-b][c][d]. call this set of teeth datum e. then create a true position tolerance of the 2nd set of teeth to [a-b][e][d].
to make this easier to make, i would cut a long keyway on the side of the shaft using a tight tolerance for size and straightness. then cut a keyway on the id of each of the sprockets with a tight tolerance for size and position to the teeth. if the timing of the teeth to the existing shaft keyway is not important, fixture them together with the teeth timed and cut both keyways at the same time. fit the sprockets and shaft together using keys to keep the alignment while you weld everything together.
  
peter stockhausen
senior design analyst (checker)
infotech aerospace services
how is the "timing" currently accomplished?  does whatever is being done now work?
rather than changing the process, why not simply quantify and document what you are doing now?