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Learning how to build Lotus Seven replicas...together!
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 Post subject: Re: Drill bits
PostPosted: November 13, 2013, 8:55 am 
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Joined: February 28, 2009, 11:09 pm
Posts: 1310
Location: Connersville, Indiana
Lonnie-S wrote:
So, what I think I'm getting here is that after you sharpen a drill bit, you don't necessarily have to re-harden the freshly exposed surfaces?

If I'm wrong, or if a person just wanted to do so, what would be the procedure to re-harden a typical, low cost drill bit once ground?

Cheers,

Lonnie, you just don't want to be playing that game.

If a drill is so bad that it needs to be rehardened, throw it away and buy a good one. You are talking incredibly cheap drills or drills intended for woodworking. A HSS drill will last many, many times as long and will NEVER need to be rehardened. That is good, because the heat treating requirements for HSS are so rigerous you would never be able to do it at home. If your drill is capable of being rehardened, it is not worth the time or effort.

Resharpen the drill, try filing the point. If you can, throw the drill away, it is not worth messing with. If you can't it is fine.

Bill


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 Post subject: Re: Drill bits
PostPosted: November 13, 2013, 10:38 am 
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Joined: October 24, 2008, 2:13 pm
Posts: 4048
Location: Carlsbad, California, USA
@BBlue

Thanks Bill, that's just what I needed to know.

Cheers,

Lonnie

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 Post subject: Re: Drill bits
PostPosted: November 13, 2013, 12:51 pm 
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Joined: July 6, 2008, 11:15 am
Posts: 1049
Location: Cave Creek, AZ
Okay, there is one theme in this thread that is a little mis-leading and that is the use of multiple bits to creep up on the large size hole you need. That is not correct. The pilot hole should be a shade larger than the web of the final bit. The web is the place where both flutes come together at the tip. The flutes of the final bit should be cutting their full width at the middle of the cut.

If you use a 7/16th bit right before the 1/2", the outside edges of the 1/2" bit will be the only part touching the material, and this causes the tips to break off. To drill a 1/2" hole in mild steel, I would center punch, then use a 1/8"-3/16th" pilot bit and then the 1/2". Cutting oil is a must on both or you will heat up the bit enough to dull it on the cut.

If the bit squeals when your cutting, the bit is dull or sharpened wrong AND you need oil.

Tom

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 Post subject: Re: Drill bits
PostPosted: November 13, 2013, 12:57 pm 
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Joined: August 12, 2012, 6:38 pm
Posts: 1935
Location: worcester county, Massachsetts
I'll add my voice to the noise. after reading through this entire thread, I find that I apply possibly the most locostish bodgy techniques, but, I can't (or won't?) argue with the results. YMMV, YRMV, AMFYOYO, etc.

over the 3+ years of the b-3 proj, I have ceme to these understandings:

1. if you're drilling steel, slow speed and lube. there's this stuff called "Anchor Lube" works really well. I also use light thread cutting oil. or 3-in-1. or 5W-20. don't mind the mess.

2. sheet metal = step drill, unless you're match-drilling. then use a drill bit. and pilot drill the holes first.

3. for big holes in thick materials, step up the drill size as others have mentioned. doesn't necessarily have to be in .063 increments. for example, for half inch holes, I started with a .25, then did the half inch. (this was in the drill press) worked out fine

4. become familiar with common numbered wire drill sizes for specific clearance holes. for example, a 3/16 pop rivet takes a #10 bit, and a 1/8th pop rivet takes a #30. buy multiples of those.

5. don't be afraid to resharpen bits on the bench grinder by eye. takes a bit of practice, but once you get the hang of it its cake. I don't bother with files, takes too long, and wipes out the file. I resharpen on the bench grinder regularly, the hard part is keeping the bit point centered.

6. using a hand drill, keep your bit speed down. in fact, regardless of bit size and, bit life is helped by drilling at the lowest speed possible. high speeds will easily overheat the bit and dull the flutes.

7. centerpunch 2-3 times. get a nice deep dimple, that'll help keep the drill from walking. if circumstances permit - drilling steel but not sheet metal, enlage the snap-punch dimple with a good solid whack using a hammer and hammered centerpunch. in aluminum, snap the snap punch multiple times, and then start the hole with a really slow drill speed so it stays in the dimple.

8. McMaster-Carr. go there.

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