Countrsink lead-in for internal threads--is there a std?
Countrsink lead-in for internal threads--is there a std?
(OP)
I'm looking for a standard or information regarding the countersink on an internal thread.
I have an engineer who insists on specifying a countersink on all internal threads. I have contended that it is standard machine shop practice to put a 90° csk as a lead-in (he always specifies 120°) a little larger than the major dia.
"Prove it!" he said.
I thought I had seen it in Machinery's Handbook, but I couldn't find it, and a search of several hours and many keywords turned up nothing--except this site, which I had never heard of before.
Anyone have any info/ideas?
Thanks,
WGC here.
I have an engineer who insists on specifying a countersink on all internal threads. I have contended that it is standard machine shop practice to put a 90° csk as a lead-in (he always specifies 120°) a little larger than the major dia.
"Prove it!" he said.
I thought I had seen it in Machinery's Handbook, but I couldn't find it, and a search of several hours and many keywords turned up nothing--except this site, which I had never heard of before.
Anyone have any info/ideas?
Thanks,
WGC here.





RE: Countrsink lead-in for internal threads--is there a std?
for drilling for heli-coil inserts, but
our shop normally chamfers 90 as you
suggest for standard internal threads.
I have not seen a standard for countersinking
tapped holes for threads but have read
that the c'sink diameter should be greater
than the major diameter of the thread.
Will look forward to other opinions.
RE: Countrsink lead-in for internal threads--is there a std?
That said, I think the 120 deg csk used to be customary, but CNC shops have adopted the practice of using the same 90 deg cutter for spot drilling, countersinking and chamfering, to save tool change time. That's the 'new' custom.
Mike Halloran
Pembroke Pines, FL, USA
RE: Countrsink lead-in for internal threads--is there a std?
RE: Countrsink lead-in for internal threads--is there a std?
RE: Countrsink lead-in for internal threads--is there a std?
Helpful SW websites every user should be aware of FAQ559-520
How to get answers to your SW questions FAQ559-1091
RE: Countrsink lead-in for internal threads--is there a std?
Your Engineer is right, buy him a coffee then tell him to get back to work.
RE: Countrsink lead-in for internal threads--is there a std?
RE: Countrsink lead-in for internal threads--is there a std?
or aligned.
RE: Countrsink lead-in for internal threads--is there a std?
RE: Countrsink lead-in for internal threads--is there a std?
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Countrsink lead-in for internal threads--is there a std?
Isn't the chamfered washer supposed to take care of
the bolt fillet radius problem?
RE: Countrsink lead-in for internal threads--is there a std?
On tapped holes the issue is that without a chamfered hole there is a possibility of a burr that will extend above the bearing surface. When the mating part is placed on this it can be forced down, effectively 'closing' the thread and creating an increased potential for cross threading.
I have not seen any standard practice to chamfering tapped holes and I looked for it just like you have. IMHO the best way to do it (unless there is a definite reason to specify a specific configuration for perfomance resons) is to simply indicate "chamfer all tapped holes" and leave it open for the vendor to make them the easiest and lowest cost way he can.
We have not found a significant difference between 90 and 120 degree holes for cross threading and we have tested for just that condition. The experimental noise was much greater than the impact of the chamfer angle.
RE: Countrsink lead-in for internal threads--is there a std?
RE: Countrsink lead-in for internal threads--is there a std?
ALL TAPPED HOLES SHALL HAVE A CHAMFER OF DIMENSION MAJOR DIA+.010/+.020 X 90°-120°.
(And I was so sure I was right... darn! I probably ought to hire him back...)
RE: Countrsink lead-in for internal threads--is there a std?
shouldn't it be 45 to 60 degrees.
RE: Countrsink lead-in for internal threads--is there a std?
ALL TAPPED HOLES SHALL HAVE A 90°-120° CSK WITH A DIAMETER EQUAL TO THE MAJOR DIA +.010/+.020.
RE: Countrsink lead-in for internal threads--is there a std?
Sorry to be picky.
RE: Countrsink lead-in for internal threads--is there a std?
RE: Countrsink lead-in for internal threads--is there a std?
RE: Countrsink lead-in for internal threads--is there a std?
RE: Countrsink lead-in for internal threads--is there a std?
RE: Countrsink lead-in for internal threads--is there a std?