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countersink angle measurement

G

garageguy

Super User
Premium Member
a while back I was doing a restoration of a vehicle that had a lot of countersunk bolt and screw holes. This was a WWII vehicle with BSF fasteners and getting the right countersink angles was frustrating. Since then I have had the same experience with all kinds of csk screws. What methods do you guys use to get the right countersink for various fasteners? I know there aren't that many but trying to measure with a compass or protractor or whatever is tough with small screws especially. Any tips? Drill test holes? what do you do?
 
garageguy said:
a while back I was doing a restoration of a vehicle that had a lot of countersunk bolt and screw holes. This was a WWII vehicle with BSF fasteners and getting the right countersink angles was frustrating. Since then I have had the same experience with all kinds of csk screws. What methods do you guys use to get the right countersink for various fasteners? I know there aren't that many but trying to measure with a compass or protractor or whatever is tough with small screws especially. Any tips? Drill test holes? what do you do?
Click to expand...

Ive been known to use modelling clay for jobs like that. It can even be baked to get a really hard template if needed.

The real problem is making a tool to cut the bottom angle. I usually grind the end on a drill bit.

There is probably a much better way, but that's my goto approach. Looking forward to hearing what others do.
 
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I don't think I've had to do this, but three ideas occur....1) use a optical comparator, easiest but not everyone has one...2) take a photo or scan,enlarge it 20x and measure in a program or print and measure with a protractor. camera and screw axis have to be as close to parallel as you can get. Lastly....its a taper, so measure the diameters and distance between them and do the trig. In such a small size that will have lots of error but hopeful suggest a number close to some standard.

Edit, thats for the screw, for the hole, do what Susquatch suggests, some clay and then measure the clay.
 
Mcgyver said:
I don't think I've had to do this, but three ideas occur....1) use a optical comparator, easiest but not everyone has one...2) take a photo or scan,enlarge it 20x and measure in a program or print and measure with a protractor. camera and screw axis have to be as close to parallel as you can get. Lastly....its a taper, so measure the diameters and distance between them and do the trig. In such a small size that will have lots of error but hopeful suggest a number close to some standard.
Click to expand...

Sorry, I assumed he meant the hole!

Measuring a screw is a "hole" lot easier..... If you have one!
 
My question is mostly about measuring the screw csk angle so I can drill the right hole angle. a 3/8 csk bolt is easy but a #8 screw is the pits. Modelling clay might help. Never thought of that.
 
garageguy said:
a while back I was doing a restoration of a vehicle that had a lot of countersunk bolt and screw holes. This was a WWII vehicle with BSF fasteners and getting the right countersink angles was frustrating. Since then I have had the same experience with all kinds of csk screws. What methods do you guys use to get the right countersink for various fasteners? I know there aren't that many but trying to measure with a compass or protractor or whatever is tough with small screws especially. Any tips? Drill test holes? what do you do?
Click to expand...
Imperial flathead screws are 41 degree or 82 degree inclusive angle so just use a 41 degree countersink. An easy way of testing is to countersink a test hole and then put black marker on it. Put the screw in the hole and rotate it and then check how the marker has rubbed off.
 
Chip Maker said:
Imperial flathead screws are 41 degree or 82 degree inclusive angle so just use a 41 degree countersink. An easy way of testing is to countersink a test hole and then put black marker on it. Put the screw in the hole and rotate it and then check how the marker has rubbed off.
Click to expand...
Also, metric is 90°, British and aero fasteners are 100°, so have a couple of those countersink for testing.
 
It just occurred to me that in a person's spare time it might be nice to make a gauge that would accommodate a bunch of different sizes of screws and bolts to check csk angles. Sort of like a cross section of a funnel. hmmm.....brain is working...dangerous, I know.
 
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