All Day Dan

My Feedback: (5)

How do you dimension a 90 degree flat head screw in a .2 inch thick plate? What is the correct clearance drill, in inches, for a 6mm screw? Thanks, Dan.

Propworn

My Feedback: (3)

Ok 6 MM is .24 inches or very close to 1/4 inch so clearance for a 1/4 screw would work. 9/32 would work.

You would use a 90 degree countersink and let it follow the hole going deep enough for the head to sit flush or a little below the surface.

If the material is thin enough that the countersink actually opens up the hole and extends out the other side you may have to countersink the threaded hole to give clearance for the head of the screw because its thicker than the material your attaching.

For thin materials they make screws and countersinks up to 120 degrees. The 90 degree is most common.

All Day Dan

My Feedback: (5)

Thanks Propworn. I'll stick with the 90 degree screws and countersink. Do I control the depth of the countersink by dimensioning the diameter of the hole at the surface a little larger than the screw head?

Propworn

My Feedback: (3)

It will be larger than the head so you must make sure you have enough material so the countersink does not break out. Trial and error work well here a test piece clearance drill for the screw and countersink until the head is where you want it, flush or below then you will have an idea how big the countersink will end up. Set the stop on the drill press if you are using one and the repeatability should be the same. If your doing it by hand you will have to keep checking it with a screw. Remember if the head extends below a thin piece you may have to countersink the threaded hole so the head does not bottom out on the threads.

Dennis

All Day Dan

My Feedback: (5)

Dennis, thank you for all the information. I found this hole chart on the net. Dan.

All Day Dan

My Feedback: (5)

This may work. Dan.

Propworn

My Feedback: (3)

Good general rule of thumb however screw manufacturers don't always make the screws the same. Some might have a sharp edge at the head some will have a bit of a land which will need to sit deeper in the countersink to get the head level. You will need to check the screw to make sure.

Here are a couple of handy apps for your cell phone if your doing anything mechanical.

Nice Calculator
https://play.google.com/store/apps/d...RealCalc&hl=en

Machinist Calculator has drill point and countersink, drill charts etc.
https://play.google.com/store/apps/d...adesmath&hl=en

Machinist Buddy more in depth with conversions, charts, geometry etc.
https://play.google.com/store/apps/d...nistcalc&hl=en

All Day Dan

My Feedback: (5)

All good information. Dan.