What is the Alure of D bits?

[Martin W]

I am a little slow out of the gate. Had to google it, I had never heard of a D bit before.

 

[projectnut]

It can be made fairly quickly, when you don't have the correct size drill. It's for "when you absolutely, positively need that bit NOW!"

I'll keep them in mind should the need arise. However as far as drills are concerned, I think I have enough to cover the bases. I have numbers from 1 to 90, letters from A to Z and fractions from1/64 to 1" by 64ths, and larger drills to 1 3/4" by eighths. To be sure I have a sufficient number in stock I by sizes under 1" by the by the pack, (usually 10 to 12 per pack) and those over 1" individually as needed. I also have the bases covered for countersinks, counterbores, and reamers. Over the years I have modified or created grooving tools or other form tools from standard end mills or HSS lathe tool blanks.

I watched the Blondilocks video about sharpening D bits linked from another thread. When she mentioned McMaster sold blanks for D bits, I took a look at the prices. Most were in the $30.00+ range. I was a bit surprised that anyone would be spending that kind of money on a blank unless the form they were trying to create was so obscure that was the only way it could be created.

 

[jwmay]

I was a bit surprised that anyone would be spending that kind of money on a blank

Nobody is. But faceless companies will all day long. Or anyone who can roll the cost into a quote/business expense . Lol

Aren’t some of us using the term “D bit” a little less accurately than the definition would allow. A “D bit” is so called literally because of its shape, right? And its existence is specifically for engraving.

So if you made some special profile cutter using a d bit grinder, or a hand grinder, or a set of files, or whatever, that cutter is not a “D bit”.

Honest question gentlemen.

 

[jwmay]

Nvm. Wikipedia set me straight.

But according to them, some of you aren’t right either. Lol!

 

[dbb-the-bruce]

Pretty much already covered but....

For hobbyist / weekend machinist, quite convenient as you can make pretty much whatever you need on demand. All it takes is a little time, but not much.

I have a D-bit grinder, primarily for sharping other stuff, but made for D-bit. I needed perfect press fit flat bottom holes in brass for 1/16 dia. x 1/32 magnets. It was very easy to make a D-bit for this and I could grind it to just the right diameter by trial and error.

The magnets have a plating/coating and are brittle enough that the fit was odd sized and had to be just right or they would just fracture when pressed.

I keep all of my used up carbide end mills and engraving bits (already split) as handy stock for making random D-bits. I've only bought a few pre-split blanks for a few sizes I didn't already have.

 

[pontiac428]

I was a bit surprised that anyone would be spending that kind of money on a blank

Broken drill bits and toasted end mills are tossed or lying around like cigarette butts to many of us, but there are bit blanks hidden inside of them. I make "blanks" more than I want to, so I have plenty without spending cash on them. Any of the cold working tool steels work great and don't cost much at McMaster by the stick. A few feet of 1/2 and 3/8 makes a ton of cutting tools. Drill rod and HSS blanks are eBay lot fodder and can be had for a song if you're patient and avoid the gougers.

 

[7milesup]

I am a little slow out of the gate. Had to google it, I had never heard of a D bit before.

Yeah, me too. Now I am trying to figure out what, where and when.

 

[homebrewed]

I used a variation on a D bit to make a long-shank countersink for a project I was working on.

Call it a "V" bit since the included angle was 82 degrees. It worked just fine, at least on the aluminum "U" extrusion. I needed to countersink a hole on the inside of the extrusion so the countersink had to be long enough to go all the way to the other side. I turned the V on my lathe, then milled the flat face. After that I hardened it and touched up the cutting edge with a diamond hone.

 

[pontiac428]

This book is helpful

38 - Tool and Cutter Sharpening.pdf

PDF File

1drv.ms

This book shows D-bit drills and similar types with a writeup

12 - Drills, taps and dies.pdf

PDF File

1drv.ms

And this is the manual for the Deckel SO grinder, which includes toolmaking info.

DECKEL OPERATING INSTRUCTIONS.pdf

PDF File

1drv.ms

 

[Jake M]

I used a variation on a D bit to make a long-shank countersink for a project I was working on.

Call it a "V" bit since the included angle was 82 degrees. It worked just fine, at least on the aluminum "U" extrusion. I needed to countersink a hole on the inside of the extrusion so the countersink had to be long enough to go all the way to the other side. I turned the V on my lathe, then milled the flat face. After that I hardened it and touched up the cutting edge with a diamond hone.

You just reminded me of one of those applications I mentioned earlier where they "might be preferred". I hesitate to call it a D bit, since I ground it on a grinder, but it pretty much is exactly the tool you describe, except at a different angle. Some of my dumpster dives are prone to finding things with center features already in them. And probably beaten and smashed apart the quick way, since they were garbage anyhow. Or they have cast in center features that work fine on specialized centers, but not mine. I made a "D bit" looking tool for a tailstock drill chuck to recover mangled center features with the donor clocked in a chuck. Single flute drill, boring form tool, I don't know what you'd call that, but a D bit grinder would have made short work of it.