【转帖】specifying alignment between two parts on drawing

yang686526

specifying alignment between two parts on drawing
i need to specify that two parts are to be aligned with each other when assembled, in this case welded.  a clevis pin will will be insterted through each of these parts so they must be aligned for the pin to fit without binding.  the two parts consist of two 4 inch lengths of angle and will be assembled with a flat side of each facing each other.  a .500 diameter hole is drilled in each of these facing sides and a clevis pin is then inserted.  these two angles are then welded to a plate and the holes must align for the pin to fit smoothly.  my question is how to specify this clearly on the assembly drawing.  can this be covered in a note? how would this be specified on a drawing not do to gt&t.
thanks
jmarks
ca you drill the hole after assy using a fixture?
chris
systems analyst, i.s.
solidworks/pdmworks 05
autocad 06
jmarks,
   i do not consider weldments to be assemblies.  this is a fabrication drawing on which you specify your requirements.  if you specify your two holes to line up accurately, the fabricator will probably follow ctopher's advise, and drill them after welding.  in this case, you do not care where your two angles go.
   alternately, your two thru-hole parts can be fabricated and attached with screws such that they can be adjusted to fit your clevis pin.  is there any chance of using spherical bearings?
   yet more alternately, you can review your requirements carefully and look for an arrangement that works with sixteenth of an inch tolerances.  this won't affect the layout of your drawing as per my original suggestion, but it may affect the fabricators approach, and the final cost.
   do not tell the fabricator how to do his job.  tell him what kind of parts you will accept.
                           jhg
if you are into gd & t, then a positional tolerance at mmc would do the trick but if you are not, i would suggest stating a rod of the smallest diameter should be able to protrude both holes with the force of 1 finger. that should do it.
hope this helps
dd