How to measure countersink angles of countersunk holes in sheet metal panels

CarolX

Super Moderator
Super Moderator
#11
RCW said:
I am trying to measure the countersink angle of countersunk holes in sheet metal panels. I was told this could be done by using ball gages, placing several balls in the countersink, measuring their height off the panel, then by "using trigonometry, just calculate the angle."

Has anyone done this before? If so can you provide better instructions than what is listed above and/or the proper trig formula to use? Is there a better/easier way to measure the countersink angle? (I was looking into handheld gages to do this but they approximately $1000 each and have to be made for a specific diameter hole.)
Sorry RCW that I did not see your post until now - I work for a sheet metal fab shop - and we countersink all the time. Starrett and Barcor make countersink gages...Starrett can be found here

http://catalog.starrett.com/catalog/catalog/PLH2.asp?NodeNum=24649&Mode=PLIST

The cost is very reasonable and you don't need to have it made for a specific diameter.
 
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RCW

Quite Involved in Discussions
#12
(With all due respect and unless I am really missing something here.......)

The coutersink and chamfer gages listed in the Starrett link above measure the large diameter of the countersink hole, not the angle of the chamfer. This also holds true for the Barcor instrument. (I am the process of purchasing my chamfer gage (a.k.a. diameter checker) from Brunswick Instruments.)

J&L Industrial Supply sells a flat, laser-cut metal gage with all the common countersink angles on it. I think this is the way I'm headed.
 

CarolX

Super Moderator
Super Moderator
#13
RCW -

You are measuring a countersink in sheet metal, correct.

What is the method used to create the countersink - punch or drill?

Can you confirm the angle by verification of the tool used.

We punch most of our countersinks. We use 90, 100 and 120 degree tools. If the wrong tool has been used, the set-up person usually can't achieve either the top diameter or the thru hole.
 

RCW

Quite Involved in Discussions
#14
CarolX said:
RCW -

You are measuring a countersink in sheet metal, correct.
Correct.

CarolX said:
What is the method used to create the countersink - punch or drill?

Can you confirm the angle by verification of the tool used.
Either unknown or not always known. 99.9% of our sheet metal work is done outside of the company.


CarolX said:
We punch most of our countersinks. We use 90, 100 and 120 degree tools. If the wrong tool has been used, the set-up person usually can't achieve either the top diameter or the thru hole.
Can an incorrect angle be determined by visual inspection and/or placing the correct screw or other fastner in the countersunk hole? Yes, quite easily.

However, I need actual data to put into First Article Inspection forms (i.e. countersink 100 degrees plus or minus 2 degrees) and without proper gaging or methods, it is quite a headache.
 

CarolX

Super Moderator
Super Moderator
#15
RCW said:
However, I need actual data to put into First Article Inspection forms (i.e. countersink 100 degrees plus or minus 2 degrees) and without proper gaging or methods, it is quite a headache.
RCW -

I work for a sheet metal fabricator. We punch most of our countersinks. The standard process it to punch a pre-hole (this will be the finished thru hole size), then punch the countersink with a countersink tool. This tool is designed to produce a specific countersink size at a specific angle. A 100 degree countersink tool can not produce a 98 degree to a 102 degree countersink, in other words, the angle is fixed and can not be adjusted. The variables are the thru hole and the countersink size.
 

RCW

Quite Involved in Discussions
#16
CarolX said:
A 100 degree countersink tool can not produce a 98 degree to a 102 degree countersink, in other words, the angle is fixed and can not be adjusted. The variables are the thru hole and the countersink size.
I acknowledge that countersink punches are not adjustable. However, without trying to open a can of worms, is your 100 degree punch truly 100 + 0.000 degrees? There has to be a small amount of offset from nominal. (Maybe not, I'm not in the business.)

The tolerance referenced is directly from a customer's drawing. On some of their drawings it seems like they are requiring tolerances without even fully understanding the fabrication process.

Finally, most of the nonconforming countersunk holes I have seen here have been made using a drilling countersink process, as opposed to stamping. The operator pushed the countersink through too far. The angle is correct but the outer diameter of the countersink is too large.
 

CarolX

Super Moderator
Super Moderator
#17
RCW said:
I acknowledge that countersink punches are not adjustable. However, without trying to open a can of worms, is your 100 degree punch truly 100 + 0.000 degrees? There has to be a small amount of offset from nominal. (Maybe not, I'm not in the business.)
Yes, I am sure there is, but I have never taken this to that level.

RCW said:
Finally, most of the nonconforming countersunk holes I have seen here have been made using a drilling countersink process, as opposed to stamping. The operator pushed the countersink through too far. The angle is correct but the outer diameter of the countersink is too large.
Exactly why we went to puched countersinks years ago.
 
S

sergiov

#18
We have Laser Scanned Sheet Metal triangules with the desired angles.
With the laser scan, we can certify the correct angle is being used.
It will just be inserted on the hole and that is it. It has been good enough for FAR's
 
J

JonathanG

#19
RCW:

I'm not sure if you or anyone else has looked at this thread for years, but I may be able to give additional help or advice. I currently work in aerospace, and we do both countersinking (machined) and 'dimpling' (or 'punched' as it has been called here).

Checking either can be straight forward. We often use 100 deg countersink gages to check the outer diameter, but usually our countersinks are 100 deg (although usually the customers may allow +/- .5-1.0 deg tolerance), depending upon the customer drawing and/or fastener callout. Since we typically don't worry about the angle, we don't use tools for checking taper angles that often, but there are gauging tools if you don't want to resort to using ball gages.

If you just want to verify the angle is not another standard angle, there are blade templates/gages for checking them. If you want to know the actual angle, there are some two-plunger gages (similar to single-plunger countersink and chamfer gages) that'll measure the angle, but often you'll need to customer order these. Ball gaging and mold with an optical comparator are often good (we used molds with optical comparators for checking large proprietary buttress threads in the oil & gas industry), but you could also use a plug gage (go-/no-go gage). If you know the fastener to be used, and you're worried about depth, I'd check the fastener to spec and place it in the taper as previously suggested... if concerned about depth precision, there are rivet head/flushness gages (essentially plunger dial indicators mounted on a three-point base) for checking smoothness.

Any of these should work, depending on what you're actual concern is with your supplier and your customer requirements.
 
B

bronco-vinny

#20
RCW Had posted

Originally Posted by RCW


Finally, most of the nonconforming countersunk holes I have seen here have been made using a drilling countersink process, as opposed to stamping. The operator pushed the countersink through too far. The angle is correct but the outer diameter of the countersink is too large.

OUr process is both punch and drill.
This is my curent problem our counter sink and diameter are to print but the thru hole is over. If we control the thru hole our counter sink is under size. Specialy when dealing with thin material.
Is there a standard or a BAC spec that allows this for over size thru hole.

The shops i have worked at for some reason have and under standing that it is allowed because of the material thikness. But i need it documented to justify it.

:thanx:
 
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