Countersink Question

Why was my reply copied by Jim?


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Actually it was ''quoted'' by me. I'm agreeing with you:), note the :+1: below.
 
Got it. Thanks. Now I understand how that works!


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neshkoro said:
If you don't want to buy too many tools an 82 degree countersink works well and then it also can be used for countersinking flat head screws.
I've been in the business for 50 years and it was common practice to countersink all threaded holes before tapping. The countersink diameter should be just slightly larger than the diameter of the tap. The countersink should be done before tapping as most of the time the tap will throw up a burr. If you tap first and then countersink you take the chance of pushing that burr into the threads. If the part gets heat treated you might have issues starting the screw as the burr might be in the way. Just my opinion.

Bill
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Bill is quite right about tapping after counter sinking. The tap will not only push a burr up but can also raise some material right around the hole. Counter sinking slightly larger than the outside diameter of the tap first will lessen the raise spot or eliminate it all together depending on the material being tapped. It is always a good idea to run a file or stone over the hole to make sure there is no raised area.
 
Bill explained it exactly the way I see it! When a guy at work brings me a piece he made with threaded holes that have not been countersunk ( slightly) first I can tell cause it doesnt have that "finished" looks to it
 
I used to work for a Tool and Die shop that did a lot of work for a high end electronics company building does for them. They demanded that all the die components that. had screw or dowel pin holes be counter sunk. The screw holes also had to have the threaded holes counter drilled 1/64" larger than the major diameter Han the major diameter of the thread. The counter bore would be about 1/8" deep. A lot of work but they wanted quality.


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neshkoro,

Many places did that so the first thread would not break out if a bolt was over tightened. Or at least that was the excuse I kept getting for years of machining.
 
That's the reason.


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i use my old aircraft countersink a lot...the old offset design spinner...

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