Tolerance on centre distance between two dowels

[Emo01]

Hi

I am looking a two dowels separated by a distance D which must match up with two holes on a corresponding part.

The fit between the dowel/hole is to be a H7/g6 close sliding fit.

The max shaft diameter under this spec is 9.995, the min hole diameter is 10.000 under this spec.

Surely in order for these two parts to go together under all circumstances then the tolerance on the centre distance must be +/-0.005, please see attached pic. Or perhaps even less than this as if the distance between the dowels was D+0.005 and the distance between the holes was D-0.005 then the overall difference would be 0.01.

How easy are the tolerances to achieve they seem crazy!?

 

[3DDave]

How much for perpendicularity and how much for the parts being different materials/temperatures?

 

[drawoh]

Emo01,

Your tolerance is way too accurate. One of your clearance holes should be a slot. Problem solved.

--
JHG

 

[greg2835]

I second what drawoh said above. This is common practice and typically other features are dimensioned from the non-slotted hole.

Greg

 

[juergenwt]

One pin should be a diamond pin.

 

[powerhound]

The only time your idea will work is when the mating part is always perfect. We all know that will not be the case so if your hole pattern is +.005 and your dowel pins are -.005, they will not fit. Then add to that the holes being at the bottom of the tolerance and that makes it worse. This is where using GD&T and calling things out at MMC really shines.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[drawoh]

Emo01,

The other option is to drill the dowel holes after assembly, making your assembly repeatable, rather than accurate. Any time I have seen two dowels in accurate clearance holes, this is how it has been done.

--
JHG