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Thread: 82 and 90 degree countersinks
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19th November 2012, 01:22 PM #1
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82 and 90 degree countersinks
I found out something I didn't know today- the heads of countersunk imperial screws have an 82 degree included angle, whereas metric screws use 90 degrees. You probably all knew that.
Ideally a bloke would own one of each countersink, but I'm over cheap countersinks and the price of a GOOD quality countersink (e.g. Bordo) seems to be in the order of $40-50. Is it really necessary to use the correct countersink for the screw? If I can get away with having only one included angle, should I buy 82 or 90?
Chris
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19th November 2012, 01:27 PM #2
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Unless the job particularly called for or needed an angle different to 90 just get the 90.
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19th November 2012, 01:35 PM #3
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thanks pipeclay.
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19th November 2012, 01:35 PM #4
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Not forgetting that if you put an 82 screw into a 90 C/S then all the stress is on the rim of the screw and there'll be a gap underneath, taking no stress.
Going the other way around leads to a gap at the top (a ring around the screw head), and all the stress is at the bottom of the screw head.
Lee Valley have a reasonable range.
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19th November 2012, 09:08 PM #5
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They do, but they only advertise them as being suitable for wood. They might be suitable for steel, but i wouldn't want to find out the hard way. Plus they only have 82 degree countersinks.
Originally Posted by FenceFurniture
Melbourne Bolt Co has a Bordo 20mm 90 degree single-flute Cobalt HSS bit for $50. There are some Dormers on EBay, but postage kills them.
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