Rule of Thumb for Chamfer Dimention in Drilled Holes

[WillCole]

Hey folks,

We are dealing with a cylinder (rod) with a few full-depth holes drilled cross-wise.

I am wondering if anyone has a rule of thumb for chamfer / fillet sizes for the edges of drilled holes.

Basically, I am trying to figure out if there is a easy way to rough guess at the optimal chamfer / fillet sizes as either a function of the diameter of the hole versus the diameter of the bar or as a function of the diameter of the hole.

I am not looking for any sort of perfect number, but more a conceptual model as to what 'reasonable' looks like...

Cheers!

 

[MintJulep]

Optimal for what?

 

[WillCole]

The primary purpose of the chamfer / fillet is to reduce stress risers that result from non-axial loads.

I recognize that this will vary depending on the angle of the load, but I am not looking for a ideal number. I am more looking for a rule of reasonableness. If you any any such rule you tend to go by even if not perfectly applicable I would be quite interested.

 

[looslib]

With cross-drilled holes, take into account the curvature of the rod, then a chamfer that is visible all around the hole would be good. Hard numbers would be hard to calculate.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[flash3780]

For tight tolerances in space-limited applications, I sometimes use a .047±.005 chamfer with a .032±.010 radius so that the features never bump. I wouldn't consider holding either tolerance any tighter than that.

 

[WillCole]

In the interests of full disclosure I should say that an old machinist told me told me that his experience was that on curved materials that are thicker than the hole diameter (like rods) a good approximation is chamfer so that the narrowest part of the chamfer is about 10% the diameter of the hole. I was just trying to get a feel if that was a reasonable starting point.

 

[racookpe1978]

If the chamfer is to fit a screw head so the head is flush with the surface, then you have to start with the available screw sizes (Nbr 6, nbr 8, nbr 10, nbr 12, 14, 1/4 inch, 5/16, etc.), decide what size suits the forces you need, plot the screw against the diameter of your work so the head is recessed, then get the chanfer from what's left over.

 

[WillCole]

I am sorry I should have been more clear. This is just chamfering to avoid undo stress risers. Obviously, it will vary with material etc. Thanks for all the feedback!