82 and 90 degree countersinks

[jack620]

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. :wink:

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

[pipeclay]

Unless the job particularly called for or needed an angle different to 90 just get the 90.

[jack620]

thanks pipeclay.

[FenceFurniture]

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.

[jack620]

Lee Valley have a reasonable range.

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.

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.