Question on drilling/countersinking alloy sheet metal
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  1. #1
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    Default Question on drilling/countersinking alloy sheet metal

    I need to put some countersunk holes in a sheet of laser-cut carbon steel (14 or 12 gauge). Ideally this would be an alloy, likely 4130 but it may also be non-alloy cold rolled. I will likely have the holes pre-cut for #10 flat-head wood screws, there will be around 30 total. Question:

    1. Is it "easy enough" to countersink holes in 4130 alloy?
    2. Is there an effect of "hardening" from the later cutting? Since drilling is easier than countersinking, I'm thinking I could:
    *entirely pre-cut the main diameter (about 0.19" dia)
    *cut it smaller, say about 0.10" and then drill out to remove the heat-effected area and then make it easier to countersink?
    *not pre-cut any holes at all (the positioning of the holes isn't really an issue), just drill out then countersink.

    I've had a bit of experience in the past and, overall, my "memory" is that countersinking holes in alloy steel is tough with a cordless drill (it's a large sheet) but the holes were first laser-cut so maybe that had a further effect on it?

    Thanks,
    The Dude

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    I did some 5/16 hole countersinking in plasma holes (plasma over water table so as hard as theory allows) and it was not fun at first. ended up with expensive (but cheap?) carbide counter sinks from lowes and switched to cordless because I was frustrated with extension chord unplugging... went like butter. that was on 1/4 hot roll a36. I did chip a few of the cute little things countersinks, but they worked - on a Friday order - Monday deliver job.

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    Carbide countersinks in a cordless should get the job done. I've reamed laser cut 1050 and 1095 and carbide generally does the job.

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    anything over .03 carbon will harden from heat.
    Otherwise you are just trying to chew threw oxide.

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    It also depends on laser assist gas. If using Nitrogen carbide is a must. Nitrogen makes the edges very hard. I got one csink done in 14g 304 with HSS and gave up. Even with most of my weight is was tough with carbide.

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    Can you avoid flat head screws and use something like flanged round head screws, like McMaster 90399A247 or use countersink washers with oval head screws? It's common practice for mounting sheet metal panels such as instrument enclosures on welded frames for example. I find it's hard to make flat head installation look good so try to use them only where I really need the clearance. If you need to use 4130 I suspect the application is a bit more exotic though!


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