Boring/drilling a conical hole

In article , snipped-for-privacy@gmail.com writes

If you can mount the item in a lathe and the hole is large enough*, you can bore it taper by setting the topslide to the desired angle (or, better, use a taper turning attachment if you have one - if you don't know what that is, you almost certainly don't have one!).

*You can get extremely small boring tools, though you have to look hard for them, and they are rather fragile; also tend to be quite short, for obvious reasons. Take small cuts!

If the hole is small, or for some reason you can't mount it in a lathe (too big, awkward shape, don't have lathe) you can step drill the hole so it comes out slightly smaller than the desired taper (some geometric calculations required here) and then finish it to shape with a taper pin reamer, if one is available with the right taper. Otherwise, you will have to make a reamer with the right taper. For brass, aluminium or mild steel, a simple V-shaped form tool will probably work, go slow to reduce chatter.

David

is it the same size as a pencil sharpener ..

if so i would sharpen a slighly smaller drill bit to the shape of the hole ... drill it ...

then bore it out with a tiny boring bar made of hss.

all the best.mark

Drill or bore a series of stepped holes then ream out using a custom tapered D bit as a reamer.

Sort of depends how big, how deep, how accurate etc. The most obvious way is to set the top/compount slide at the appropriate angle and bore in the usual fashion with a boring bar, just using the topslide for (mostly) axial movement of the tool. Taper drills and reamers are also available for specific tasks. If the angle is very important you can set the top slide angle with a DTI or some other measuring instrument.

If you literally want a pencil sharpener complete with slot opening in the side of the 'cone' you'd probably want to cut the slot after boring. Perhaps with a slitting saw, or maybe a slot drill or if you have one possibly even a slotting head in the mill.

If you have the gear to do it, tapers can be bored with some boring/facing heads used in a mill. Can't say I've ever done it and the gear ain't cheap, but as an acedemic study it is possible.

All depends on what you've got, what you need to achieve and how much time/money/effort you care to invest in the job.

Richard

Material? Size?

Nick

Hi Guys , many thanks and sage advice as usual. I need to make some actual pencil sharpeners (sort of school project). Like this

I have some phosphor bronze but probably need to buy some brass stock. The hole is at an angle to the radial axis ( is that the correct way to describe it ?. The conical hole terminates in a drilled parallel hole from the opposite side. Cheers Nick

Nice little project. What (machine) tools have you access to? The item shown has a milled slot in the top where the blade is mounted. If you have access to a mill, the slot in the side for shavings and the seat for the blade will most easily be done on the milling machine.

The main body is a job for the lathe. The tricky (interesting ) bit is the tapered hole not because it is tapered, but because the axis of the cone is not parallel to the face of the body (or not perpendicular to the axis of the body, if you'd rather describe it that way). The outer surface of the cone is parallel where the slot is cut through.

Given the nature of the job ie not terribly accurate, I would probably make a tapered 'D' bit to cut the taper after a pilot has been drilled as suggested earlier in the thread. That way you can do the job in a drill press with the sharpener body held at an appropriate angle. To bore the hole in a lathe, you are going to need some jig of some sort, possibly to fit in a 4-jaw chuck or perhaps bolt to a faceplate in order to hold the body at the necessary angle.

Going back to the slot, if you do not have a milling machine, it will have to be done in the lathe and again you will probably need to make a jig of some sort to hold the body nicely (without damaging it) whilst you hold the milling cutter in the lathe chuck. Given that it's a school project and the technicians will not be the most skilled, make sure that the jigs are 'very' adjustable to accommodate generous tolerances of component manufacture. You will probably want some 'jig' even if you have a mill - say a pair of half clams to fit in the table vice, counter bored to act as a stop and made of something soft (alloy? hard wood even?) so as not to damage the knurling which will have to have been done already.

To summarise:

1)Turn & knurl OD (possibly also drill & tap centre hole(s) for blade screws) 2)Part off 3)Mount at angle and drill, ream/bore the tapered hole 4)Mount and mill slot(s)

N>>> > Like in a pencil sharpener. Does anyone know ?.

Nice project! Pilot drill, (step drill and) finish with a self made conical D-bit. Clamping in the right angle can get interesting. Easy on a mill with a tiltable head or table.

Nick

I am a total newbie , but am lucky enough to have a decent job. Thought the pencil sharpener would be a good way to get me going as well as for my daughters school. I have a small Cowells mill. Although I have a vice for it is not a tiltable one , doubt I would get one that small . Have a larger Sobo one. I have an ancient super 7 which is just fantastic -

Think I will have to make a jig of some sort.?? I like Richards estimate of =A375 , probably conservative. Cheers Nick PS I am off back to Guy Lautards book to learn bout D-bit .

In article , snipped-for-privacy@gmail.com writes

Well, it's newer than mine, and has pxf, and I'm jealous of that. Mine has a gearbox though. It's easier to fit a gearbox than pxf (I retro-fitted mine).

Incidentally, I see some of the photos suggested you were setting up the lathe by levelling it. The best readily accessible description I have found for setting up a lathe is in Tubal Cain's "Workholding in the Lathe" in the Workshop Practice series.

David

What's a pxf?

Steven Shand

Power cross-feed.

Mark Rand RTFM

Cheers but I hope your RTFM isn't directed at me.

Nah, it's been what passes for my .sig for the last 15 years

Mark Rand RTFM

TMBR#1..3? Great books! Big joy reading them all in one go.

Nick

Well, Down to blackgates yesterday. Very helpful. I am overjoyed to have made a D - bit router.

The photos show some of its construction. I can see you guys covering your eyes at the milling (1/4 " end mill , 3/8 silver steel in toolholder. - I haven't yet got any workholding on the crosslide. ebay myford vice coming.) However it worked a treat. I was worried about the thickness of the router . Seems Ok for light cuts in mild steel. What really let me down was the tufnol jig. Just was way too not rigid. Back to the drawing board. Thanks for everyones help. Nick

Why didn't you use it in the tailstock?

Success is good to have. :-)

The D-bit? A tad less (1%?) than half the diameter.

Nick

Nick, Couldn't see from the pic's if you had drilled a pilot hole just less than the small end first ?

Also you need to grind the front edge of the cutter with front clearance and a bit of back rake. I know you may not know these terms so looking at the cutter from the top going away from you the front face wants to slant left to right so the left hand tip is cutting first. same looking at it side ways with the front tip to the left. The end also needs to slant from tip down to the right, again so the tip cuts first. Only a few degrees 3 to 5 will do, any more and it will grab.

.

MORE!!!

Mark Rand RTFM