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?
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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?
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.
Choose a #6 or #8 flathead screw and simply countersink only deep enough to flush the head. No need for "dimpling".
Or use a "aircraft countersink cage". Be careful about the angle as screws and rivets are different angles.
Bil lD.
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.Quote:
Originally Posted by Tom M King
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
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.
For sheetmetal:
https://www.mcmaster.com/screws/flat...file~undercut/
I've countersunk #6 FH screws in .040 aluminum.
Attachment 436174
T
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
Quote:
Originally Posted by Ryan Yeaglin
+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.
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.
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.