Bolt Clearance holes
Bolt Clearance holes
(OP)
In most books I can find, e.g. Machinery's, the recommended clearance holes for bolts increase disproportionally with the diameter of the bolt. I.e. the bigger the bolt, the more diametral clearance it will need.
Can anyone think of a reason why this maybe so.
Why is it not just a constant factor added to the diameter.
E.g. 0.5mm (which would allow for positional tolerances of dia0.35mm on the tapped hole and dia0.15mm on the clearance hole).
The same rule also applies to limits and fits for close tolerance holes.
Can anyone think of a reason why this maybe so.
Why is it not just a constant factor added to the diameter.
E.g. 0.5mm (which would allow for positional tolerances of dia0.35mm on the tapped hole and dia0.15mm on the clearance hole).
The same rule also applies to limits and fits for close tolerance holes.





RE: Bolt Clearance holes
I would imagine it has something to do with the disproportionate increase in the thread pitch with the diameter of the screw/bolt.
For tightly toleranced holes the hole clearance will increase (to a point) with the diameter of the pin/locating feature for ease of assembly.
RE: Bolt Clearance holes
Think about the perpendicularity issues....
Then you should see why.
Remember...
"If you don't use your head,
your going to have to use your feet."
RE: Bolt Clearance holes
Collinsda:
Thread pitch has nothing to do with the diameter of the
clearance hole.
Meintsi:
Perpendicularity is only an issue when the length of the
clearance hole is taken into account. When I said bigger
bolt, I didn't mean length, I meant bigger diameter.
Machinery's Quote (pp.1536: 26 Edition):
M5 - 5,5 (0.5mm Clearance)
M6 - 6,6 (0.6mm Clearance)
M8 - 9,0 (1.0mm Clearance)
M12 - 13.5 (1.5mm Clearance)
RE: Bolt Clearance holes
RE: Bolt Clearance holes
This difference multiplies exponetially as factor of the radius from pitchline center. The resultant requirement is a larger allowable tolerance zone for the bolt to be able to be started. (The bigger the bolt, the more room you need to get it started,)
You are not going to put a 8mm bolt thru a 2mm plate, so there is always a thickness to worry about.
Hush is also right with his statement which limits the maximum size of the clearance hole to achieve the desired clamping force.
Remember...
"If you don't use your head,
your going to have to use your feet."
RE: Bolt Clearance holes
Large assemblies are often heavy and unwieldy, making it harder to put them together. A little more slop in the clearance holes often goes a long way toward making it easier to put such things together.
RE: Bolt Clearance holes
the recommended sizes to prevent
excessive bearing loads at the
surface under the washers for these
bolts. Normally the larger
diameter bolts are used on larger
diameter bolt circles and heavier
cross sections. The 5 to one ratio
is kind of a guide for length to
diameter that should be generally
used for dynamic applications.
RE: Bolt Clearance holes
The real question is "why are you concerned about it?" I have always found that if there is a standard, don't deviate from it without rock solid justification. If you deviate, and if you have a failure (too big) or the assembly personnel can't readily assemble it (too small), you're going to be hosed!
RE: Bolt Clearance holes
Steven van Els
SAvanEls@cq-link.sr