Countersink Question

[tinnerjohn]

Im the back of mind I seem to recall reading or being told that a for best results you should lightly countersink before tapping a hole. I'm making a list of small tooling I need to order and found at least three angles of countersinks. Is there a preferred or recommended angle? I wish I could remember everything I've read, seen and been taught over the years, but fortunately there are forums like this. John

 

[JimDawson]

82° is the most common, and is the standard for countersinks for Imperial screws, 90° is the standard for metric screws. Technically, I suppose a 60° would be the correct one to use for a tapped hole because threads are 60°, but I don't own any.

Either would work fine for countersinking a hole before tapping, and yes is does help and makes for a more professional looking job.

 

[Andre]

I notice it helps a little to help the tap grab, but not enough help to justify the extra setup time. Most of the time your countersink angle isn't on the threaded portion anyway.

 

[tinnerjohn]

Thanks Jim. I was thinking 82, but wasn't sure. Its been awhile since I tapped a hole, I've chased a lot of them over the years when rebuilding or repairing stuff. I have some projects in mind that are going to need threads, so I'm trying to tool back up. John

 

[tinnerjohn]

One thing I remember (I think), is that it makes starting the screw or bolt a lot easier. John

 

[TOOLMASTER]

tapped thousands of holes. if you counter first it leave a little cleaner start thread...but no biggy to do it after either

 

[kenscabs]

82 is the countersink for a flat head screw. For threading use a 90 and only drill just a bit wider than the major diameter of the thread.

 

[Bluedog]

I think a countersink also going to keep the tap from raising some material around the hole which would be good for parts fitting flush together.

 

[neshkoro]

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

 

[JimDawson]

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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