# Making a tapered D bit



## Brian Rupnow (Dec 10, 2014)

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.


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## Brian Rupnow (Dec 10, 2014)

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.


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## Brian Rupnow (Dec 10, 2014)

Then into the lathe, face both ends, swing the compound rest around to 8 degrees and cut the taper.


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## Brian Rupnow (Dec 10, 2014)

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.


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## Brian Rupnow (Dec 10, 2014)

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 .


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## Brian Rupnow (Dec 10, 2014)

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.


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## Brian Rupnow (Dec 10, 2014)

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.


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## Brian Rupnow (Dec 10, 2014)

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


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## Steve J (Dec 10, 2014)

So what is the rule of thumb on the mill cut? Slightly more than half the diameter or slightly less than half the diameter?


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## bazmak (Dec 10, 2014)

They are cheap and quick to make,why not make another.You will probably make many more.Set up the lathe and cut a piece of mild steel until you get it right.Barry


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## Brian Rupnow (Dec 10, 2014)

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!!!


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## Brian Rupnow (Dec 10, 2014)

Steve J said:


> So what is the rule of thumb on the mill cut? Slightly more than half the diameter or slightly less than half the diameter?


Slightly (.002") less than half the material diameter.


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## ShopShoe (Dec 11, 2014)

What Bazmak said.

When I tried this over a year ago I made about four variations of the tool I wanted to end up with from the beginning of the process, then selected the "best" for making the part. In a "Real World" situation, I would probably be fired for inefficiency for doing that, but I made an early decision that I would rather be orderly making several tries from the beginning instead of doing the whole thing over again and again and spending more time overall doing so.

Making one of these doesn't take a whole lot of time so extra work doesn't leave one so frustrated as spending a whole day on a part that gets filed under "small scrap pieces of stock."

--ShopShoe


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## ShopShoe (Dec 11, 2014)

Brian,

I see you made another post while I was typing.

Congratulations. I'm glad this worked out.

Can't live in my shop without my air die grinder and the little stones and also the diamond files.

--ShopShoe


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## werowance (Dec 11, 2014)

Brian,  when I made my taper bit,  I used angle blocks to set my compound to the face of the chuck,  seems to have hit right on for me.  don't know if that trick would work for you though.


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## deverett (Dec 11, 2014)

Brian Rupnow said:


> Slightly (.002") less than half the material diameter.



Brian.  I'd be interested to know how it cuts because I have been told to keep the material to* + .002"* admittedly for parallel D bits !

Dave
The Emerald Isle


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## Charles Lamont (Dec 11, 2014)

I am probably teaching grandma to suck eggs, but just in case: hardening and not tempering leaves the tool very brittle and prone to chipping or breaking. You have managed to get away with it this time probably because you are working in ally. I try to temper tools like this until I can detect the slightest colour change on the honed cutting surface. It makes them a lit tougher without sacrificing hardness.


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## goldstar31 (Dec 11, 2014)

I hope that I have not going to wander off course or steal Brian's interesting  post but  ?????

Silver steel or whatever it is called is nothing more than annealed very ordinary tool steel and as such is capable of being machined with ordinary tools and then hardened to ANY hardness. Somewhat rudely, that is what it was and- ever more shall be so. It will harden with water, oil or as I remarked - stuck into an old potato. Looking back a few years, it was what EVERY model engineer used as his ONLY method of removing metal.
It was how EVERY model engine was made. It was how EVERY fullsize locomotive was made and earlier still how every cathedral was made. A hammer,  a chisel.

Is there something that has changed?

As far as Brian is concerned, he has gone down a traditional road- and succeded. My only criticism is that he used Oxy/Acetylene as the heat source. To me, it is a bit 'iffy' as he was probably adding carbon. Nevertheless, I would mention that other model engineers, clock and watchmakers have case hardened silver steel rather than over temper it.

Would somebody explain or comment, please? 

Norman


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## Brian Rupnow (Dec 11, 2014)

deverett said:


> Brian.  I'd be interested to know how it cuts because I have been told to keep the material to* + .002"* admittedly for parallel D bits !
> 
> Dave
> The Emerald Isle


He was asking about the mill cut depth. My answer was that you stop cutting .002" from the centerline. we are both saying the same thing. You do NOT cut material away below the center.---Brian


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## goldstar31 (Dec 11, 2014)

Brian Rupnow said:


> He was asking about the mill cut depth. My answer was that you stop cutting .002" from the centerline. we are both saying the same thing. You do NOT cut material away below the center.---Brian


 
I don't think anyone would be happy with 'negative' rake:wall:


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## tornitore45 (Dec 12, 2014)

There is no need to case harden Drill Rod or Silver Steel since it has already ~1% carbon.  Heat with what you have and quench in Oil or Water or Brine depending on the grade. (If you are inclined to be that sophisticated, otherwise water works or it may crack a large part.)
If you plan to cut steel, temper to a pale yellow and quench or set in the toaster/oven set to ~ 400 F for about 20 minutes, look out for SWMBO.  If you cut only Aluminum tempering is optional.

Case hardening is not really an home shop option, at least in my shop.


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## tornitore45 (Dec 12, 2014)

A job well done Brian!   I hope you protected the lathe way from the grit, rag not shown in the photo.


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## Niceonetidy (Dec 12, 2014)

I use this method for making plug cock taps and valves. Cut the taper on the D bit, and then the plug while the cross slide is at the same setting. Always works.

Cheers

Colin


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## Brian Rupnow (Dec 12, 2014)

tornitore45--My lathe thanks you. I haven't used it much since I ground the tapered D bit, and it was pig dirty. I just spent an hour doing clean up duty and re-oiling the ways and all the rotating and sliding surfaces. I don't clean my lathe that often, as nobody sees or uses it except for me, but it was in really nasty condition. I generally just use the shop vac to pick up all the chips and crud, but it needed a lot more attention than that.--Thank you for the reminder.---Brian


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## Cogsy (Dec 12, 2014)

I don't clean my lathe overly much either, although I'm trying to get better work habits in general. I think what tornitore45 was hinting at was the grinding grit that would have come from your grinding operation. Likely hardened metal dust and abrasive from the grinder. It would make a fantastic grinding paste for your lathe ways, etc. Most people cover everything possible up with rag before grinding on the lathe.


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## goldstar31 (Dec 13, 2014)

My two pennorth? Lathes and all machine tools suffer from grit and turnings becoming trapped under sliding parts and arguably, the bit that suffers most is under the saddle. Well, ALL the ones that I have come across. If there is a gap- no matter how small- the pressures will physically force the saddle down onto the ways. Clearly, you have a new cutting tool that is under the cutting tool.

Today, it is worse! If there is one of these Turcites or Moglices or Devcons - to name a couple or four- the assorted abrasives and turnings will embed themselves into the soft medium. Can things be worse? Let me assure you that cast iron is yet another and possibly more serious problem.

My take- of course

Norman


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## tornitore45 (Dec 13, 2014)

Yes, is good practice to cover, before, and clean up after either grinding or machining cast iron, that is if you want your machines to last.

I am a little compulsive (some say a lot), I clean the shop and the machine often because I can not think and operate in the mess and the chips all over.


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## MCRIPPPer (Dec 14, 2014)

would this method be accurate enough to cut tapered holes to match with a tapered part and transmit torque without a key? i want to make a flywheel for an engine with a tapered crankshaft (12mm diameter, and 5:1 taper) and also a clutch output with the same taper. the flywheel has a key to set timing, but the clutch side relies on the friction of the hardened steel crank and the aluminum tapered bore.


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## bazmak (Dec 14, 2014)

Its easier and normal practice to make the male fit the female.Would work
but how accurate would the d bit be compared to the the existind shaft


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## goldstar31 (Dec 14, 2014)

MCRIPPPer said:


> would this method be accurate enough to cut tapered holes to match with a tapered part and transmit torque without a key? i want to make a flywheel for an engine with a tapered crankshaft (12mm diameter, and 5:1 taper) and also a clutch output with the same taper. the flywheel has a key to set timing, but the clutch side relies on the friction of the hardened steel crank and the aluminum tapered bore.


 
I'd have a think- and then another. I recall removing a clutch on a 997 Mini Cooper which had been put on at 140lbs/feet----------------and had fretted.It took a 1" BSW puller and a 14lb sledge hammer to move it- with 2 of us. One a blacksmith and the other the son. 

My take is that one laps the two to a blued fit - and then inserts the peg-before putting in the bolt. 

I have been following the discourse with interest and one thought is that it is not normal to trust the so called protractor on a top slide.I would have used Pythagorus and his trusted sine bar. The hypotenuse is ideally 10" but I settle for my 5" one. One of my old mates put one(10") on the back of his Myford and off set by a quarter of an inch-- and arguably got better Morse tapers than Mr Morse's own mob.

Frankly, One uses in model practice a setting bar( homemade of course) which is 10" exactly  and with two disks to make the hypotenous - and THEN set the top slide to follow the imaginary triangle. You can do it with a small boring head- with round ended centres in the chuck end and the boring head. Yes, you can use female ends with ball bearings but it is fiddly. I've reached an age when my balls are difficult to find:hDe:


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## MCRIPPPer (Dec 14, 2014)

these parts need to fit an existing shaft with the taper already made. its a mass produced small 2 stroke engine, costing only about $150 for the cheapest ones. so i doubt there was any lapping going on. if i set up my taper attachment using a dial indicator on one of the crankshaft tapers, would that produce a reasonable accuracy? i have machined MT2 tapered shanks for my drill chucks and other attachments that work great, but have never made a tapered hole.


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## goldstar31 (Dec 14, 2014)

It's school boy maths. We were reminded of the :-
Squaw on the hippotamus hide is equal to then sum of the  squaws on the opposite two hides. 

or if you want the highbrow version, it is the 6th Proposition of Euclid.- the solution of right angled triangles.

And the exciting bit is the proof

QED

Norman


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## MCRIPPPer (Dec 14, 2014)

i prefer using trig functions.


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## Charles Lamont (Dec 14, 2014)

If you set the existing crankshaft between centres and a use DTI to set the slide round to match the taper (small end towards the headstock), you wont need any trigonometry. And you can bore the hole without needing to make a reamer. Check it with blue before you take the job out.


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## MCRIPPPer (Dec 15, 2014)

well i made a d bit, but have not hardened it yet (made it out of O1). put crankshaft in lathe, indicated and adjusted taper attachment, but taper, made small tweak to get it cutting a PERFECT fitting taper. (i was amazed when i put some prussian blue and it transferred nearly 100% after a quick polishing with some worn out 600 grit!!!) milled it almost half way leaving .002"+ on thickness. did a test cut on some aluminum 6061 and it cuts a beautiful tapered bore that fits perfectly on the crank. i did notice it didnt fit at first before the bit made its way through the part out the other side. maybe it needs a bigger pilot hole. but this worked great!


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## bazmak (Dec 15, 2014)

Love it when a plan comes together


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