Drillbit choices

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Old 01-08-21, 10:41 AM
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Drillbit choices

I need to drill about a dozen 3/8 holes in metal. I own a 3/8 drillbit rated for wood. How unadvisable is it to use it?
 
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Old 01-08-21, 10:53 AM
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Depending on the type of metal you may not even be able to drill one hole.

When I use metal drill bits to go that large I'll drill several holes starting from a small one, to a midsized one and then the final size. It's easier on the bits and makes for a cleaner hole.
 
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Old 01-08-21, 12:59 PM
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As PJ mentioned. Pilot drill your holes first with something about 1/8". Then step up to an intermediate drill size then do your final 3/8". You should be OK with brass, aluminum, copper and mild un-hardened steels with a regular twist drill bit. For hardened steel & stainless you can still use a cheap HSS drill bit if it's sharp.

You can run your small drill bits at a higher rpm. As you move up to larger bits turn at slower rpm and push harder. Keeping the drill bit & hole wet with oil will help with the cutting and will prolong the life of your drill bits.
 
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Old 01-08-21, 02:09 PM
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The drill bit needs to be made of material harder than the material being drilled or the drill bit cutting edges will just dull and not remove material. Wood bit cutting edges are perpendicular to the bit axis and cut the full diameter as it moves thru the material. Wood bits are made from steel with low toughness. Metal cutting drill bits have the cutting edges at an angle (60 degrees) to the bit axis and removes material from the center out to the full diameter as it moves thru the material. Metal cutting bits are made from steel with high toughness and hardened thru a heat treating process. Drilling holes in thin metal is difficult as the metal cutting bit will tear the material as the bit exits the material unless clamped between supporting surfaces. A special metal cutting drill bit, called a step drill bit is made for making holes in thin metal. Each step in the bit makes the hole diameter larger.
 
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Old 01-08-21, 03:11 PM
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I was really hoping not to buy yet another set of drill bits but I succumbed.
 
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Old 01-08-21, 04:04 PM
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You can never have too many tools.
 
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Old 01-08-21, 04:55 PM
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I agree. I have many sets of drills.

As an electrician and especially as a past mobile electronics installer.. I've bought and used many unibits. Based on the material to be drilled they are fairly indispensable. I have several from Klein, Milwaukee and even Harbor Freight. The HF bits were fairly reliable.

Three piece Unibit set

 
 

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