Hole clearances?

I am doing a small plastic enclosure that has a rectangular power jack and a round audio jack hole.
My question is, how much clearance/tolerance should be given to these holes meaning what should be the margin between the case plastics and the jack component? The ME has it at 0.16mm - 0.2mm gap is that too little and tight?

So if a audio jack’s cylinder is 4mm in diameter, what should the hole diameter be?

Thanks for any standard/typical gap sizing recommendations.

Also, if there is draft angle, should the defined hole size be the smaller hole and then the larger hole be the natural result of a degree of so of draft? So do I always give the hard dimension to the smaller of the two holes that travel the wall thickness?

Interesting question about the audio jacks. I wonder if there is a TRS connector spec similar to the NEMA spec for wall outlets and electrical plugs. Maybe you UL has something on this?

  • .16mm-.2mm does not sounds too bad. However, it is going to be dependent on what the tolerance of your molding process is and how consistently you can maintain that gap. Obviously if the parts can only be made to within +/- .5mm, that gap is not going to work.
  • In order to better understand this one, perhaps you should locate several products that have similar features and measure them to establish some sort of baseline. As far as fasteners go, you will typically use a 4.3-4.5mm hole for a 4 mm machine screw. Sure they are different, as you are not wanting the housing to be bearing on your audio jack. Consider what the largest hole you can make is and shrink it from there as needed.
  • Applying draft can be done in a variety of ways. When it comes to drafting surfaces of holes through a wall thickness, the difference in dimensions is going to be minimal. This is also going to be dependent on where the parting line of your mold is and how the part is being drawn. When it comes to controlling a dimension, always control the one that is more important. In this case, as you are trying to maintain a clearance between an audio jack and the hole, you are probably going to want to control the smaller dimension.

Anymore, I use between .1 and .2 mm for hole clearances (per side). With cnc machining and a good molding vendor, you’re going to be fine with that. As already mentioned, check with your molding vendor and go within tolerance of their capabilities.

If you went with a 4.25 mm diameter hole, you should be fine.

Oh, I forgot to answer the draft question.

Hold the dimension that you need to maintain. So, you would hold the 4.25 dimension if you follow my guidance. Also, you have to look at it from the perspective of the tool/toolmaker.

You should typically (but remember rules are meant to be broken) think in terms of making sure the draft works for optimal mold release. What I mean by that is think in terms of having the draft open towards the core of the part (the core being the side that you want the plastic to stick to when the mold opens). So the smaller dimension (4.25mm) on the outside of the part, and the larger dimension on the inside of the part.

Aside from simply understanding the tooling process, what is your reasoning for asking this question? Are you trying to get it tighter than you’re ME’s tolerance?

A ME said 0.25mm minimum and up to 0.5mm gap to be safe of tolerances.

So a 4mm dia audio jack would have a hole of at least 4.5mm and up to 5mm dia.

5 mm is overkill. .25 - .5 tolerance overall is what is needed (not per side). .5 mm per side would look like a gaping hole around your connector, especially on a small part (e.g. a cell phone).


Agreed. The hole tolerance should be considered diametrically, not radially.

OK. Yes it is a realatively small product.
The jack is mounted at the edge of a PCB on standoffs.
I’ll try 4.5mm hole then to be a bit safe which means 0.25mm per side.

This would have been a great topic for the Materials & Processes Forum…

if it’s machined, aim on the small side of your range - you can always drill a hole bigger.

If it’s molded, aim on the large side of your range, you can always machine away material on the core to make the hole smaller.

A standard CNC house will guarantee .005" on a hole diameter, but most will come in at about .002 or 003 (plus or minus).

I would be half tempted to make a quality control jig just in case the molding shrinks or drifts, so you can get a control on the location of the hole using a 4mm shaft or something to check for clearance for each piece (or sample if you are doing volume) Make sure you have a flat datum to measure from and itll help with any quality headaches you have with the molding.