OT...Countersink In Sheet Metal?

[Derek Arita]

I have a steel shelf made of about 16ga. sheet....guessing. I want to attach it to brackets, with screws in the top surface of the shelf. I want the screw heads to be flush, so how can I countersink the heads?

[Tom M King]

I have a tapered "punch", and do the dimpling in the hydraulic press. I'm sure you could do it by hammering, on a soft piece of wood, but they wouldn't be shaped perfectly. I'll see if I can find a link to the dies.

edited to add: I looked, but all the dimple die sets are really expensive. I have a small steel rod that I turned the angle on the end to push the dimple. It's backed up by whatever I have handy that has a hole the right size to go under it.

[andy bessette]

Choose a #6 or #8 flathead screw and simply countersink only deep enough to flush the head. No need for "dimpling".

[Bill Dufour]

Or use a "aircraft countersink cage". Be careful about the angle as screws and rivets are different angles.
Bil lD.

[Derek Arita]

I have a tapered "punch", and do the dimpling in the hydraulic press. I'm sure you could do it by hammering, on a soft piece of wood, but they wouldn't be shaped perfectly. I'll see if I can find a link to the dies.

edited to add: I looked, but all the dimple die sets are really expensive. I have a small steel rod that I turned the angle on the end to push the dimple. It's backed up by whatever I have handy that has a hole the right size to go under it.

I like that idea. Cheap. Maybe I can use the actual flat head screw as the punch? I'll experiment on some scrap. I thought there might be some kind of simple screw die tool.

[Bill Dufour]

I read that after it was built Lindbergh's plane had all the skin taken off and every rivet was redone to be flush using some new technology to reduce drag.
Bill D

[Ryan Yeaglin]

drill a clearance hole for whatever size bolt you choose, then countersink into both the shelf and bracket. Add a few drops of oil and go slow as to not burn up your countersink. Also a dimple punch will not work for the fact that when you draw the shelf to bracket tight, it will press out the dimple and leave a raised screw/bolt head.

[Wes Grass]

For sheetmetal:

https://www.mcmaster.com/screws/flat-head-screws/phillips-flat-head-screws/system-of-measurement~inch/flat-head-profile~undercut/

[Tony Latham]

I've countersunk #6 FH screws in .040 aluminum.

436174

T

[Bill Dufour]

Image of a countersink cage FYI. Each click of the adjuster is about 1/1000". So plenty accurate for this job. Ebay is loaded with the bits and threaded drills. 1/4-28 is the most common size.
A Boeing shank works fine in any standard drill chuck
Bil lD

[Thomas McCurnin]

drill a clearance hole for whatever size bolt you choose, then countersink into both the shelf and bracket. Add a few drops of oil and go slow as to not burn up your countersink. Also a dimple punch will not work for the fact that when you draw the shelf to bracket tight, it will press out the dimple and leave a raised screw/bolt head.


+1. With a punch, it will leave a nice dimple for a drill bit to get started, but ..... will also leave a reverse dimple on the other side. Drill a starter hole, like a 1/16th with oil, then your actual clearance hole, then a countersink with oil.

Real machine shops, not home shops, use an aircraft countersink cage, which form very precise countersinks. That's the way the pros do it. I am not a pro. I am a hack.

[Rob Luter]

The undercut screws Wes suggest above should work with a shallow countersink. I use them for door strike plate attachment. You don't say what the brackets are made of, but if they can be countersunk a bit at the point of attachment the screw will draw the sheet metal shelf material down into the bracket when it tightens up and assist in getting things flush.

[Derek Arita]

OK...just tried something and it seems to work...at least on the scrap sheet I have. I took a countersink to a scrap of 1/4" MDF. I then drilled a hole in the center of the countersink that fits a screw tightly. I then drilled the same sized hole in the sheet metal. I used the countersunk MDF as a die and used the screw to pull the sheet down in the countersink. It worked great and didn't cost me anything. I think this will work just fine for my purposes. Thanks all for the help.