Deep hole position tolerance
Deep hole position tolerance
(OP)
I need to make a hinge support for a heavy hatch. The part has to be machined from a single piece of metal. The hinges on the hatch are about 24" apart and will hang/attach to my support with two .50 dia pins, each about 4" long. So my support needs to have two clevises machined into it, one for the upper pin and one for the lower. I would like the pin holes to be .501 - .502 diameter. My question: How "in-line" can I get the final four holes? In GD&T what true position tolerance would I need to specify to make this practical to manufacture.
Initial piece of stock is 4 x 4 x 28. Alum 7075 or Titanium 6-4 depending on how much strength is needed (not final on that yet)
Initial piece of stock is 4 x 4 x 28. Alum 7075 or Titanium 6-4 depending on how much strength is needed (not final on that yet)





RE: Deep hole position tolerance
specify hole(s) must be machined & inspected inline.
HTH
Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.
RE: Deep hole position tolerance
The old school way would be to insist that say a .500" gage pin of 4.5" length slide through both holes in a clevis while neither hole can be larger than .502" dia. GD&T can say that concisely.
Doing the same thing for all four holes may not be realistic, or desirable.
One, a .500" dia x 28" long gage pin is going to be a little flexible, so gravity can affect the measurement. If the nominal diameter were say 2.500", gravity would be less of an issue in inspection.
Two, it's possible to 'line bore' both holes of a given clevis with a single tool in a single XY location, only feeding the spindle in Z direction, so the stated requirement is achievable. But it's not possible to line bore both clevises without moving and reorienting the spindle or the workpiece, so the desired tolerance may not be achievable. Again, easier for a larger bore, where a secondary line bore operation is slow, but possible.
I think the alignment of the two clevises relative to each other can be looser, because the pins are not all that stiff, and probably the clevis ears are somewhat flexible too, so the assembly is to some extent compliant or self-aligning. How much misalignment you can tolerate depends on the geometry of the door and the jamb, the size of the pins, and operational requirements not yet revealed.
You might consider making one of the clevises flexible enough in non-radial directions to align itself, or bolted in place instead of integral, to allow a little adjustment.
Mike Halloran
Pembroke Pines, FL, USA
RE: Deep hole position tolerance
RE: Deep hole position tolerance
RE: Deep hole position tolerance
A big lump of air in the middle doesn't help.
Mike Halloran
Pembroke Pines, FL, USA
RE: Deep hole position tolerance
I am old school, & I prefere to verify the holes are inline with a minimum size diameter pin in both holes.
it is done consistantly this way. This way it is assured it is in line.
a CMM can also verify if the positioning is good, I prefer the pins because I know it will assemble. like a go gage. yeppers.
but for you just specify that it must be inline let the mfg worry how it's done.
but only if you have to have it this way.
Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.