# D-Bits



## Blogwitch (Jun 21, 2012)

D-bits, in my view, are one of the most underated tools you can make, but when push comes to shove, they can get you out of deep doo-doo when required.

This describes one that I made when I required a 22 degree angle inside a nozzle I was making. The angle couldn't really have been bored out as the depth was too long for such a tiny boring bar to survive the ordeal. People have other ways to do it, this is the way I found satisfactory for my use.

Mounted up a piece of silver steel (drill rod), and faced off the end.








Kicked the topslide (compound) over by half the angle required, in this case 11 degrees.







Then using the topslide, the taper was being cut.







The taper was finished when the small end was at about 2mm. I will be drilling a 3mm hole thru the nozzle material, so this D-bit will not require a cutting edge putting onto the very end, if it did, I would just give it a 5 degree cutting angle straight across the front face, after it is hardened.







The machining marks were gently removed with fine emery.







The bar was accurately measured up (this was 3/8" or 0.375"). Then it was divided by 2 and the figure rounded up. It was at this stage I changed my normal making practice. I would harden at this stage and grind the end down on my surface grinder. But because most people don't own such a machine, I am going to do it the normal way.







Mounted up perfectly level in the milling vice, the bar is reduced down by not quite half it's diameter. One or two thou larger is ideal.







Mine measured up when finished at 0.1885", one thou over half size. Take good notice on this shot, the 'halving' was done for a longer length than the taper, this is so that you can use the shank size to get to your half figure, rather than attempting to measure on the taper.







This is what it looked like close up. The machining marks are only tenths of a thou deep, so no worries over those. I would forget about deburring, as you can easily take too much off the edges and prevent it being sharpened.







It was now time to get things warmed up and hardened.
Just the part that was machined was heated up to cherry red, and held there for a minute or two, then it was quickly quenched in water.
This should make the tool as hard as glass. I don't bother tempering the tool, and that is just a personal thing.







The machined face is then gently smoothed down on a smooth oiled stone until the machine marks are gone. You should end up with edges as sharp as a razor.







So that is the D-bit made.


These aren't all the ones I have made over the years, just a few good ones that I hung on to. These are the straight sided ones. To give some idea of scale, the bolt in the middle is 6mm by I think 30mm long.







These being the taper ones I have made. I never realised I had made so many over the years.







Now if you need to discuss D-bits, you have a post to do it in.



John


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## Sshire (Jun 21, 2012)

Thank you John 
I've been wanting to try a D bit, but every description was something like, "grind off 1/2 of the diameter you need. You're done."
Your pix and description are crystal clear as usual.
Thanks. I'm going to make one this evening.
Best
Stan


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## Don1966 (Jun 21, 2012)

Thanks John for the documentary on the D bit. I have made a few but I need to use them more often.

Don


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## monty621 (Jun 21, 2012)

Interesting that you only harden the cutting end. My one attempt a D-bit was a long, thin one (about 0.1" x 6") where I just hardened (and tempered) the tip. Just a little bit too much pressure while drilling and it bent up near the chuck. Based on that, next time I need to make one I figured that I better harden (and temper?) the whole thing. What do you think?

Greg


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## marcel (Jun 21, 2012)

Thanks for the info of D bit
I have made a few with a Deckel so
http://www.dialog5.com/OtherDownloads/AnleitungDeckelSOE.pdf
in here you will find more examples in 
unfortunately in German
groet Marcel


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## Blogwitch (Jun 21, 2012)

Greg,

You have seen my little collection, and there are some thin ones amongst them.

Every one of those shown were given the same treatment that I described, just the cutting end, and have never had any trouble with them twisting.

All I could suggest is that yours may have dug in too deeply, or hit a hard spot, and so the tip stayed solid in the job and twisted the shank. 

BTW, twist drill shanks are left soft.

All the other gents, thank you for the comments.

Here is the D-bit in action boring out a nozzle.

I had marked it up so that it would penetrate to about 35mm. The lathe was set to it's slowest speed of 65 RPM.






It is then a matter of pecking into the hole and clearing very often. As you can see, it is doing a lovely job of scraping the shape out of the inside. That 1 or 2 thou thicker than centre and razor sharp edges are critical.








John


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## steamer (Jun 21, 2012)

Nice write up John!

Dave


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## idahoan (Jun 21, 2012)

Thanks John,

I have only made one or two of these over the years and my current project will most likely need one.
It it good to see the procedure done by someone as skilled as you.

I didn't know about the .001 over size on the radius; I always thought the cutting edge was on the centerline. Or is it on center line after honing?

Dave


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## bezalel2000 (Jun 21, 2012)

Hi Bogs

That's an impressive range of cutters thanks for sharing the technique.

There is one that appears to be unique, can you tell us about the the centre bored bit. ???
did you need a nipple at the bottom of the hole for some reason?

Curious minds!  scratch.gif






Bez


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## Blogwitch (Jun 22, 2012)

Bez,

That one was from a few years ago, and from what I can remember, it was to do with some kind of replaceable spraying nozzle that needed to be made in a one piece screw in unit. The liquid was fed down the centre drilling with air feed holes around it, in the recess.

Not my design, someone elses, I just had to make about 100 of them. I think it was something to do with spraying liquids in a green house environment. You tend not to ask too much when making for someone else.

That was the easiest and cheapest design to get the job done without multiple tool changes.

Sketch at bottom to show roughly what it ended up like.


John


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## Blogwitch (Jun 22, 2012)

Dave,

I was always led to believe that the 1 or 2 thou over size was not only to help locate the d-bit more accurately, but also allow a few more wipes over the sharpening stone before it became undersized and of no more use.


John


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## Siddly (Jun 25, 2012)

Very under-rated tool the D-bit...

This is one I made with a pilot and a depth stop. It's what is called in the gunsmithing trade a 'chamber reamer' - for making the recess in the breech end of the barrel where the cartridge goes. It's for the little .22 rimfire long rifle.


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## abby (Jun 25, 2012)

Make cheap radius cutters too !


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## Siddly (Jun 25, 2012)

abby  said:
			
		

> Make cheap radius cutters too !



Hadn't seen those before, thanks. Any notes on making them ?


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