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Old 04-21-2009, 03:23 PM   #1
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Default choosing the correct countersink?

I need to countersink some holes in the bottom of my chassis for M3 screws...how do I know what angle countersink to get? According to Wiki there are 60*, 82*, 90*, 100*, 110*, and 120* angles on screwheads, so is there a standard angle on all M3 screws or does it vary by manufacturer/material, and is there a way to accurately measure the angle on such a small screw? Thanks!

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Old 04-21-2009, 03:34 PM   #2
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I'm a 15 yr tool maker, 82 degrees is the standard our shop uses for flat heads screws. That's english or metric. It works for 100k rubber molds, so it should work on any rc car.

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Old 04-21-2009, 03:43 PM   #3
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Thanks for the quick response, but I've found some conflicting information. Some sites say 82* is standard for machine screws, and some say 90* is standard. Lining up the cross-section of the screws I have with the corner of a piece of paper looks like 90* to my eyeballing so I think that's what I will go with...an 82* screwhead fits better in a 90* countersink than a 90* screwhead in an 82* countersink, correct?

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Old 04-21-2009, 04:10 PM   #4
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82 deg. is typical for standard US threaded flat heads like 4-40s and such. 90 degrees is more common for metrics like M3. Either one would be good enough for r/c applications, but for metric i'd be more inclined to use a 90deg over an 82 deg.

-James
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Old 04-21-2009, 04:32 PM   #5
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Now the issue is finding a 90* locally...the ACE up the street had about a half-dozen sizes/brands of 82* but zero 90's!

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Old 04-21-2009, 04:43 PM   #6
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Most likely a normal hardware store won't carry it. Check the phone book for tool supply houses. You can also pick them up online from www.mcmaster.com or www.mscdirect.com
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Old 04-21-2009, 05:01 PM   #7
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Quote:
Originally Posted by JamesArluck View Post
82 deg. is typical for standard US threaded flat heads like 4-40s and such. 90 degrees is more common for metrics like M3. Either one would be good enough for r/c applications, but for metric i'd be more inclined to use a 90deg over an 82 deg.

-James
You are correct sir. You can really get away with either though... Not saying its correct, but i've used 82 on metric screws before and had no issues.. Having the correct angle will keep the screws from backing out as easily though.
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Old 04-21-2009, 05:40 PM   #8
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Another reason to go to a tool shop. Most hardware store countersinks are designed for wood. You won't get much use out of it working on a graphite or aluminum chassis.
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Old 04-21-2009, 06:10 PM   #9
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Default countersink

I think sears has the 82 degree carbide in a 1/8th shank.
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Old 04-21-2009, 07:08 PM   #10
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Thanks for the help guys...there is a Grainger nearby so I'll check them out tomorrow.

-rocky b
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Old 04-21-2009, 07:15 PM   #11
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if you find one online, could you please post where on here? I was doing this exact same research yesterday and most of what I found was for wood and plastic.

BTW - FWIW, I found that 90 degree (or 45 depending on how they measure it) was the norm for metric countersunk fasteners.
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Old 04-22-2009, 01:59 AM   #12
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http://www.mcmaster.com/#3210a65/=1jvyni
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Old 04-22-2009, 09:48 AM   #13
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mcmastercarr is the easy way to get your hands on countersinks. if you have the ability to go to a tool and die shop. palm abrasives for Pacific northwest. you take one of your machine screws you desire to copy the angle of. and put the countersink shank down, and screw tool end up and you can match the angle easily. or get a 2 dollar protractor from the grocery store (kids school supplies) and measure it.
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