Countersink with head relief

Dean_Gardner

I cannot see that the hole tool for countersink has head relief.  I.e. ability to add a small pre-counterbore same size as the c'sink OD that drops the screw in slightly.  Is this the case, that this is not in the tool?

S1mon

 I was just looking for this recently and it seems to be missing. Make an improvement request…

Dean_Gardner

Posted, thanks: https://forum.onshape.com/discussion/20294/countersink-head-relief/p1?new=1

PeteYodis

Yes, this is a known need for sure.  But to explain further... you need to be able to pick which particular fastener type you want to add a relief for.  There could be several different valid options that would all require differing amounts of relief based on head geometry.   It's possible an improvement like this will really start to pair holes with content.  

nick_papageorge073

Just curious, how is this done in manufacturing? Is there a specialized countersinking tool per fastener, so it does the c-sink and the extra straight wall in one shot?

nick_papageorge073

I think I found them? https://www.mcmaster.com/28145A61/

I thought only 60 deg lathe center drills came in this form factor, and that the c-sinks for screws were all the one-size fits all oversized variety. Good to know if I have a need for this:)

S1mon

In the case where I wanted to do this, it's in an aluminum die casting. The cavity pins are likely ground steel and probably have some very small radii where it transitions from clearance on the screw to the countersink. In reality we should probably be using a different screw type because with positional tolerances, some of the heads are probably getting too much of a side load.

nick_papageorge073

S1mon said:

In the case where I wanted to do this, it's in an aluminum die casting. The cavity pins are likely ground steel and probably have some very small radii where it transitions from clearance on the screw to the countersink. In reality we should probably be using a different screw type because with positional tolerances, some of the heads are probably getting too much of a side load.

Ah. Yes if its in the tool its a different story. I've only done a couple of small zinc parts over the years, but a bunch of plastic injection molded parts. We never used c-sunk screws due to the stress concentrations caused by the knit lines, which would allow the c-sunk screw head to overcome the hoop strength. IDK if cast parts have the same issue? 

S1mon

Yep, plastic + countersunk screws = disaster.

I already changed some screw types on another assembly from countersunk to socket head caps because they're holding a plastic part which was cracking (definitely not my original design). Cast aluminum parts probably have some risk at the extremes for the reasons you stated, but we've never seen failures in this application. There is a possibility that they are post machining the holes to improve the flow, but I haven't seen the tool design.

david_mcmahon

PeteYodis said:

Yes, this is a known need for sure.  But to explain further... you need to be able to pick which particular fastener type you want to add a relief for.  There could be several different valid options that would all require differing amounts of relief based on head geometry.   It's possible an improvement like this will really start to pair holes with content.  

Think this is pretty simple - maybe I am missing something. We just need two more options added to the countersunk hole - countersink/counterbore diameter and counterbore depth. See example below (from Solid Edge).

PeteYodis

@david_mcmahon Sure on the hole feature side, but you will be looking up dimensions of various different fasteners in order to bury them sufficiently.  My point, is that it would be nice to point at a specific fastener and have the hole built properly for it.  Would save time. There is no universal countersunk fastener type.  There are numerous different types with all sorts of different head geometries.  There are other potential advantages to pairing things too.

S1mon

@PeteYodis
The enemy of the good is the perfect.

It would be great to have some defaults which make some sense and are related to real hardware, but it's likely that "head clearance" height dimension is going to be highly dependent on the context and design goals, not the hardware itself. Right now, I can't use the hole feature to make this shape, and unlike a regular counterbore, there's no quick hack with move face to get this geometry from a countersunk hole. About all I could do is use a counterbore and add draft, or I just have to revolve a cut and pattern it.

PeteYodis

@S1mon Oh we know very much.  We are building a platform that is not perfect for sure.  And of course, flexibility rather than rigidness to things would be what we offer.  A recess parameter does not need to wait for content pairing, but could be made much better with it.  And again, I think the effort to design holes is almost always in mind with something to fill that hole -  so the closer we could eventually mimic that workflow, the more we could improve the activity in numerous different ways.   

Dean_Gardner

@PeteYodis, you just need a depth input text box on top of the standard c'sink hole OD, if you want to keep it simple, that is.  Default of 0.5mm seems to be standard.  You get the chance to change the C'sink OD in the custom drop-down, so it all works well.  Can't see any problems with it working seamlessly

ondřej_michálek

I have similar question. I'd like for the countersink OD to go through the whole part. when I offset the mate connector and it passes some point the hole is burried in the part instead of goind to the surface. I model for 3d printing.

I believe this might also help @Dean_Gardner as he might then just offset the hole into the part