Screwgun Recommendation

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If you're using a grinder, water is just fine. The idea is to keep it cool.

Uh, no, take a look at the shank lengths. It's 1/4" hex stock, _not_ the outer diameter. #71433 would have probably done you, #71435 definately would.
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Chris Lewis,

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You are no machinist. The water does more than keep it cool. It needs a lubricant and the water does not do a very good job of lubrication. Oil or coolant keeps the part from becoming brittle.

I am not talking about the hex part, but the cylindrical part that the bit sits in. The diameter is too large. The OUTER diameter is why I can't use the DeWalt bit holder. The OUTER diameter needs to be turned down ABOVE the hex.
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Maybe I'm missing something, but if the hex is long enough to clear the housing entirely, why do you care how big the outer diameter is?
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Mike Dobony wrote:

I can picture how cooling would prevent brittleness. I can't imagine how lubrication could prevent brittleness.
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Mike's gotten confused. You don't use lubricants with grinding wheels. Grinding wheels should be used on dry metal, they rely on both the abrasion and instantaneous melting (the sparks) to cut. With hardened steel or carbide, the melting does more of the cutting than the abrasion does.
If you're sharpening a chisel on a grinder, you'll often need to keep a cup of water around. The idea being that you need to keep the edge of the blade from getting too hot ("burning") by periodically dipping the chisel in the water. If it gets too hot, the hardened steel of the blade detempers and gets soft - you end up softening the chisel so it won't keep an edge. You either have to regrind the chisel to remove the softened spot, retemper it, toss it out, or retire it to opening paint cans and chopping thru nails.
Note with high speed grinders (eg: dremels, bench grinders) you _don't_ put the coolant on the wheel. You periodically cool the work by dipping it.
My idea was to use a grinder to turn down part of the body of a hex bit holder because he didn't have access to a metal lathe. Yes, it's quite tricky, but it can be done - eg: by placing the hex bit holder into a drill, starting the drill, and holding it against a bench grinder wheel. The grinder will heat up the bit holder. Periodic dipping in water will prevent it getting too hot. Softening it isn't likely a big problem, but causing it to get too hot might loosen it on the hex shank.
If you use a lubricant on a grinding wheel, at best you'll slow its cutting down. More likely, you'll foul the wheel, spray gooey gunk all over the place, and perhaps start a fire (depending on what the lubricant is).
When you're cutting metal with edged tools (eg: lathe or milling machine), the metal is being cut, not melted. The cutting tool is going _much_ slower. Depending on the material, depth of cut, etc, sometimes you need a lubricant to prevent the metal or tool bit from overheating and detempering/burning.
Lubricants do dual function - by lubricating the cutting action, they reduce heat production. They also provide a direct cooling function by transferring what heat is produced away from the work.
You may not be able to turn down the body of a hex bit holder on a lathe using regular tool bits. The body is hardened at least somewhat (otherwise it'd simply break in use), and many will simply be too hard to cut with regular lathe bits (perhaps only with carbide bits). If a hacksaw or file won't cut it, you'll have a real problem with a lathe.
Generally speaking, once metal is hard enough that a hacksaw or file won't cut it, only a grinding wheel will touch it.
And BTW: different materials use different lubricant/coolants. IIRC, cast iron works well with straight water. Steel is most often done with Dromus, which is bought as a concentrate and diluted 10:1 with water before use. [I'd have to pull my machinist references out to find out what's in Dromus]. Lard (yes, lard) is good with some materials. "Sulfurous oil" with others. Etc.
There are a few lubricants that work with almost everything - these are usually commercially-made mixtures.
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The picky may notice that there are _some_ grinding setups designed to be cooled with a continuous stream of water. These are low speed grinders (up to 200RPM or so) _mostly_ used for sharpening woodworking tools - allows you to fine grind for long periods of time without overheating and detempering the metal - in contrast with a standard bench grinder that's usually running at 3600RPM with silicon dioxide (hard!) wheels that will burn a chisel quite fast if you're not careful. Wet grinders are not suitable for general metal shaping.
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Chris Lcan picture how cooling would prevent brittleness. I can't imagine how

nope
While you don't see it in the average shop, there are plenty of wet high speed grinding processes. Full flood coolant on a surface grinder or cylindrical grinder. Taking a part out to dip it in water is not a production oriented process
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I think it's save to omit high speed production grinding systems from what a guy who can't afford to have a metal lathe - the context of the original thread.
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Depth adjust. I didn't have time to mess with this and needed it right away so I went ahead and bought the Ridgid.
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