View Full Version : Making a tapered D bit.

brian Rupnow
12-10-2014, 02:33 PM
This morning I decided to try my hand at making a tapered D bit.--This is a direct follow up to my post about making a tapered reamer. As in all things, I started out by modeling what I wanted to build, and creating a detail drawing of it.
http://i307.photobucket.com/albums/nn294/BrianRupnow/BrianRupnow021/TAPEREDDBIT_zps7d1753f4.jpg (http://s307.photobucket.com/user/BrianRupnow/media/BrianRupnow021/TAPEREDDBIT_zps7d1753f4.jpg.html)

brian Rupnow
12-10-2014, 02:38 PM
One of the things I have learned.--Every time I cut a piece of drill rod with my band-saw, it costs me $50 for a new band-saw blade. so--Out to my big ugly old reciprocating hacksaw that I built 40 years ago to cut off a 4" length of 1/2" diameter drill rod.
http://i307.photobucket.com/albums/nn294/BrianRupnow/BrianRupnow021/TAPEREDDBIT001_zpsa493e754.jpg (http://s307.photobucket.com/user/BrianRupnow/media/BrianRupnow021/TAPEREDDBIT001_zpsa493e754.jpg.html)

brian Rupnow
12-10-2014, 02:39 PM
Then into the lathe, face both ends, swing the compound rest around to 8 degrees and cut the taper.
http://i307.photobucket.com/albums/nn294/BrianRupnow/BrianRupnow021/TAPEREDDBIT003_zps1bdbae88.jpg (http://s307.photobucket.com/user/BrianRupnow/media/BrianRupnow021/TAPEREDDBIT003_zps1bdbae88.jpg.html)

12-10-2014, 02:44 PM
Hi Brian, you also want a glass finish on the taper, and use lots of lube when reaming.

brian Rupnow
12-10-2014, 02:46 PM
Now it doesn't show up very good in this picture, but after cutting the taper, I turned a 3/8" length of shaft down to 7/16" diameter right adjacent to the taper. Why did I do that?--Because I don't absolutely trust the vernier on the mill quill downfeed, and I wanted to be able to have a surface I could set the micrometer against to measure how close my cut was getting to the centerline when I got set up in the milling machine. I couldn't think of a good way to do that without having this small turned down area.
http://i307.photobucket.com/albums/nn294/BrianRupnow/BrianRupnow021/TAPEREDDBIT008_zpsd964c4a3.jpg (http://s307.photobucket.com/user/BrianRupnow/media/BrianRupnow021/TAPEREDDBIT008_zpsd964c4a3.jpg.html)

brian Rupnow
12-10-2014, 02:51 PM
So, here we are in the milling machine, milled down to .002" shy of the centerline. I used a 7/16" diameter endmill and cut with the end of the mill down to the depth I needed to go. Then I used a 3/8" ball nosed end mill to put the radius in the heel of the cut. I dressed the newly milled flat area with a medium grit flat diamond file. (one of a set of 4 cheapies that I bought from BusyBee Tools .
http://i307.photobucket.com/albums/nn294/BrianRupnow/BrianRupnow021/TAPEREDDBIT011_zpsc707136e.jpg (http://s307.photobucket.com/user/BrianRupnow/media/BrianRupnow021/TAPEREDDBIT011_zpsc707136e.jpg.html)

brian Rupnow
12-10-2014, 02:54 PM
After heating the new tool to an orange/red with my acetylene torch and dunking it into a can of water, I dressed the flat side with a few more stroked of the diamond file (I'm not really sure it was necessary, but I did it anyways). Then I set up a scrap piece of aluminum in the lathe and drilled a 0.195" hole in the end of it. That is the bore through the carburetors I want to build.
http://i307.photobucket.com/albums/nn294/BrianRupnow/BrianRupnow021/TAPEREDDBIT012_zpsf9bf258c.jpg (http://s307.photobucket.com/user/BrianRupnow/media/BrianRupnow021/TAPEREDDBIT012_zpsf9bf258c.jpg.html)

brian Rupnow
12-10-2014, 02:57 PM
The new D-bit works very well!!! It cuts smoothly and leaves a nice finish on the tapered hole it cuts in the aluminum. I did not relieve the non cutting side of the new D bit--I left it full size, reasoning that it would prevent the D bit from wanting to be pushed away from the side that was doing the cutting and possibly break the bit.
http://i307.photobucket.com/albums/nn294/BrianRupnow/BrianRupnow021/TAPEREDDBIT013_zps3fe68c8a.jpg (http://s307.photobucket.com/user/BrianRupnow/media/BrianRupnow021/TAPEREDDBIT013_zps3fe68c8a.jpg.html)

brian Rupnow
12-10-2014, 03:17 PM
So---The making of the D bit was successful, and worked great. I am not certain, but I THINK I have to grind an angle on the very nose of the taper. Now we get to the sad part of the story. Although the operation was a success, the patient died!!! The protractor on my compound rest is one of those "By Guess or by God" kind of things. It is not engraved very well, and difficult to see. I estimated where 8 degrees would be, and used my cad program to determine that if the taper extended back .999" from the end of the material, it would leave me with a .188" diameter at the very tip, which would fit nicely into a pre-bored 0.195" hole. Damn Damn Damn--I didn't check that before I hardened everything. The small end of the taper turned out to be .215" diameter, and it leaves a shoulder at the end of the tapered hole--Exactly what I wanted to avoid!!! I have one trick left. I have made up an aluminum bracket which clamps in my toolpost to hold my heavy duty pneumatic die grinder. I may put an abrasive cut-off wheel in it and try to turn the taper down a bit more until the small end reaches the diameter I want. Fortunately I haven't changed the angle setting on my compound rest. At any rate, it has been a great learning experience.---Brian
http://i307.photobucket.com/albums/nn294/BrianRupnow/BrianRupnow021/toobig002_zpsa90183d0.jpg (http://s307.photobucket.com/user/BrianRupnow/media/BrianRupnow021/toobig002_zpsa90183d0.jpg.html)

12-10-2014, 03:38 PM
Nice presentation there Brian. I am wondering how accurate and close to true the reamed bore is compared to one done with a multi flute reamer? Have you indicated the bore with a DTI?


brian Rupnow
12-10-2014, 04:31 PM
WELL!!! That went amazingly well!! I have a whole flock of small, unidentified grinding wheels mounted on 1/4" shanks that I have had, well, forever. I mounted my pneumatic grinder in a home made aluminum clamp and mounted it in my lathe toolpost, and with the lathe turning at 970 RPM I took multiple cuts .001" deep until the small end of the taper measured 0.188" diameter just as I wanted. The angle of the taper is not terribly important. It probably isn't exactly 16 degrees included angle, but it is certainly close enough for a carburetor air horn. Not wanting to start crowing about it too early (in case my "external grinding" had somehow rendered the tool inoperable), I again dressed the flat side a bit with a fine flat diamond file, then flipped my "test piece" with the .195" hole through it over and proceeded to put in a new taper. The nose of the tool fits INTO the hole now, cuts a lovely taper, and doesn't leave any "register" at the bottom of the taper.---Hooray for my side!!!
http://i307.photobucket.com/albums/nn294/BrianRupnow/BrianRupnow021/goodtaper002_zps56ab1bb2.jpg (http://s307.photobucket.com/user/BrianRupnow/media/BrianRupnow021/goodtaper002_zps56ab1bb2.jpg.html)
http://i307.photobucket.com/albums/nn294/BrianRupnow/BrianRupnow021/goodtaper008_zps44e92ca5.jpg (http://s307.photobucket.com/user/BrianRupnow/media/BrianRupnow021/goodtaper008_zps44e92ca5.jpg.html)

brian Rupnow
12-10-2014, 04:33 PM
Nice presentation there Brian. I am wondering how accurate and close to true the reamed bore is compared to one done with a multi flute reamer? Have you indicated the bore with a DTI?


Ironwoodsmith--The key thing is ---It's "close enough" for my purposes. I have not indicated it.---Brian

12-10-2014, 05:47 PM

Good show, but an OT question. In the picture of the recip hacksaw it looks like the yellow rear fender wheel and tire of an old car in the background. If so, for those of us into old cars, what is it? Picture please :).

12-10-2014, 06:18 PM
Great post Brian!! (and another question,,, Lol,, On the power hacksaw, is that a flywheel ring gear i see?)

12-10-2014, 06:24 PM
Yeah, I saw that too. I am going to guess it is a '32 Plymouth or maybe a '33. Anyway, I am also lusting to see it.


brian Rupnow
12-10-2014, 06:51 PM
Guys--I have been into hot-rod building and drag racing most of the past 50 years. That vehicle is the last hotrod I built 10 years ago before arthritis made it just too difficult for me to continue building them. It is a 1930/31 Ford model A roadster pickup with a small block Chev V8 in it. That car is my daily driver during the summer months. It sleeps under a couple of bedsheets in the garage during the cold winter months. Sasquatch--Yes, that is a flywheel ring gear. When I built that big old saw, I was a young engineer with no money but lots of good ideas. I made about a thousand miles of "wrought iron" railings as an evening and weekend part time business during the 1970's, and couldn't afford a real power hacksaw, so I designed and built that one for about $3.11:p:p. The motor is a 1 HP unit out of a walk in freezer, with a belt drive to the jackshaft. the jackshaft has a starter pinion on the other end and drives the flywheel ring gear. The gears are out of an old Chev V8 and they were free. An absolutely perfect 18:1 reduction and hardened to boot!!! that saw will cut up to a 5" diameter piece of steel.---Brian

12-10-2014, 09:33 PM
Thanks for the interesting info. Always interested in shop built things.

12-10-2014, 10:08 PM

The hole produced by the D-bit will reflect the bit itself exactly. If the bit is the correct angle, that's what the hole will be and if the bit has a rough or wavy contour the hole will as well.

Nice presentation there Brian. I am wondering how accurate and close to true the reamed bore is compared to one done with a multi flute reamer? Have you indicated the bore with a DTI?


12-10-2014, 10:19 PM
Thanks Brian,

Very nice ride.

12-10-2014, 11:45 PM
Good to see a 'working' thread here once in a while ;) Two things to mention--really minor comments, actually:
1) I would guess you're not usually using your larger bandsaw for workpieces in the 1/2" diameter range. You might check the tooth pitch; it could be the offending cause. I like breaking out the hand saw and filling up on my Popeye spinach every once in a while :D I find it odd you used a power tool at all.
2)There was no need to use two milling tools for that cut. Think: peripheral cut. It results in a great finish, seems to require less power input* and leaves the radius you wanted all in one go. In other words, the 'flute' could be made with only a 3/8" end mill. Rotate the workpiece 90-degrees from how you show it in post #6 (http://bbs.homeshopmachinist.net/threads/65285-Making-a-tapered-D-bit?p=952855#post952855) above, and you'll see what I mean.

* just my humble opinion informed by hand feeding cutters.