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NW MN | I thought I’d share a little Saturday morning shop project and scratch my teaching itch after being out of the classroom for several years now. Hopefully someone can learn something or at very least get a little entertainment from this.
I bought an attachment for a tool that is made to metric specifications and is supplied with metric M4 flathead screws. The tool is made with 6-32 threaded holes to mount the attachment. Hole patterns match perfectly but the fasteners were the issue. Metric flat head screws come with a 90 degree countersink angle and inch flat head screws come with an 82 degree angle and also in 100 degree.
My quality standards for this project were well above just sticking an 82 degree head down a 90 degree countersunk hole and calling it good enough, so I made what I needed. I spent far more time looking to see if a 90 degree head 6-32 screw was commercially available than it took to make 4.
1. Make a fixture. Faced off a scrap piece of aluminum round stock and drilled and tapped to 6-32. I did not care about the sticker causing the hole to not be concentric to the stock as this would not be used again or removed and reinserted into the chuck during production. It would stay concentric to the lathe headstock axis as long as it wasn’t disturbed. I was using a 3-jaw chuck anyways, which usually only keeps .001-.003” radial runout to the stock.
2. Use a 6-32 nut to jam the screw into place in the fixture.
3. Set the compound rest in the lathe to 45 degrees to cut a 90 degree chamfer into the screw.
4. Cut the screw head angle to 90 from 82 degrees.
5. Turn the head diameter down to fit in the available space.
6. Touch up the burrs with a file.
Edited by ShopTeacher 11/23/2024 10:49
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 IMG_1901 (full).jpeg (178KB - 6 downloads)
IMG_1902 (full).jpeg (114KB - 5 downloads)
IMG_1903 (full).jpeg (168KB - 4 downloads)
IMG_1904 (full).jpeg (68KB - 3 downloads)
IMG_1905 (full).jpeg (88KB - 2 downloads)
IMG_1906 (full).jpeg (124KB - 1 downloads)
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How to make inch flathead screws fit metric countersinks.
