A mechanism for sharpening pencil leads

[Nigel Graham 2Participant @nigelgraham2]

It’s certainly an intriguing project!

Given that the torque to be transmitted is very low, I wonder if friction-drives rather than toothed gearing would be suitable. This approach seems once to have been very common.

The shuttle-winder on my old sewing-machine uses that principle. A rubber-tyred wheel on the winder is driven by the smooth rim of the flywheel. The latch holding the two in contact is spring-loaded to give adequate pressure.

While on the Very Big scale, a fairground Big Wheel used on Weymouth seafront this summer was driven via rubber-tyed wheels acting on a track on the main wheel frame, rather than the sprockets and chain more common on these rides.

 

Amnd with the newly sharpened pencils you can design the world-beating, “Patent Improved Device for Attracting and Neutralising Small Rodents”.

[cedric 1]

On cedric 1 Said:

I wonder in this day and age, could a small laser be used to cut the point on the lead? That would really impress one’s mates. Only Buck Rogers carries a laser pencil sharpener.

I tried a form of electrical erosion but of course it didn’t worked for graphite. I just set the lead on fire. I’m open to any exotic suggestions to replace the grinding style sharpening. But a laser that could melt the binding agent used on pencil leads is dangerous at least for eyes. To much precautions would be required.

[howardb]

On howardb Said:

Back in the sixties I did a year of my apprenticeship in a design/production drawing office.

The draughtsmen there used conventional lead pencils, as did I.

6H 4H 2H and H – HB was used rarely except for rough sketching.

The sharpening method was to pare the wood part back with a sharp penknife and sharpen the lead to a chisel point on a sandpaper block.

This gives the draughtsman the ability to increase or decrease the thickness of the lines he wants, by slightly turning the pencil as he draws with it.

You can use the same technique with 2mm dia clutch pencil leads, which for tech drawing purposes are never sharpened to a point.

I beg to differ. I (and my colleagues) always had a conical point on the opposite end of the lead from the chisel point, for text and the fiddly details which weren’t straight lines.  In the late seventies we had to use plastic draughting film and plastic pencil leads (N grades for erasable and P grades for permanent) and they were horrible.

George

[Alan JacksonParticipant @alanjackson47790]

“I beg to differ. I (and my colleagues) always had a conical point on the opposite end of the lead from the chisel point, for text and the fiddly details which weren’t straight lines.  In the late seventies we had to use plastic draughting film and plastic pencil leads (N grades for erasable and P grades for permanent) and they were horrible”.

When plastic leads and plastic film were introduced it needed a new style of drawing. The plastic leads were quite brittle and snapped easily if the pencil was progressed in the  normal manner i.e. sloped slightly backwards then moved to draw the line with the lead subject to a bending moment. Used in this manner the lead easily snapped, resulting in the pencil steel lead sheath scraping over the film surface and removing the etched surface of the film leaving a polished surface which would not retain any plastic lead.

What you had to learn was to push the sloped pencil so that the lead was in compression. Doing this enabled that much more force could be applied resulting in solid black lines. I use to prefer a rather thick 0.7mm lead for most ocassions, and to draw a fine line one used to rotate the pencil while drawing the line.

Complex drawings were much easier to keep clean because there was very little lead dust created. You could easily spot an inexperienced user, by hearing the ‘click’ that broke the lead, then curse the fact he had scraped the film surface.

[GeorgineerParticipant @georgineer]

What a pity that Management didn’t see fit to teach us that in the seventies!

George

[Paul LousickParticipant @paullousick59116]

I still have my old Faber Castell clutch pencil sharpener, Rotring pens, compass set and set squares. The pencils are hiding somewhere. Sharpeners are still available.

[JasonBModerator @jasonb]

Copy the sharpener in the push button and mount it on a shaft so it can slide but not rotate.

Fit other end of shaft to a small electric motor

Spring around shaft so sharpener is pushed away from motor.

Electrical contact each end

When you put the blunt lead in the sharpener, pushing it will compress the spring, complete the electric circuit and the sharpener will be rotated by the motor.

Probably wants a gear head motor as you don’t want things going too fast.

[JasonB]

On JasonB Said:

Copy the sharpener in the push button and mount it on a shaft so it can slide but not rotate.

Fit other end of shaft to a small electric motor

Spring around shaft so sharpener is pushed away from motor.

Electrical contact each end

When you put the blunt lead in the sharpener, pushing it will compress the spring, complete the electric circuit and the sharpener will be rotated by the motor.

Probably wants a gear head motor as you don’t want things going too fast.

The pencil sharpener looks like this. I have no idea how to make one. I think there are 2 parts press fitted into the top button. But how to make such a deep V shape cut?

[Colin Bishop 2Participant @colinbishop2]

In my wildest dreams I had never guessed that simply sharpening a pencil could be such a complex engineering task! Is there something a bit anal going on here? A standard pencil sharpener for standard pencils plus a proplling pencil in various diameters has always been enough for me. Both are sufficient to leave the desired marking.

Life is short.

Colin

[V8EngParticipant @v8eng]

Our Chippies used to sharpen their pencils (ordinary and flat lead) using the nearest chisel!

[Speedy Builder5Participant @speedybuilder5]

Anyone remember those “propelling” pencils, where a short sharpened lead was attached to a plastic stub and the “pencil’ was like a Biro but filled with about 15 of these sharpened stubs. As a stub wore down, a push button mechanism ejected the blunt stub and presented a new one. – It never caught on and disappeared shortly after it was introduced.

Bob

[V8Eng]

On V8Eng Said:

Our Chippies used to sharpen their pencils (ordinary and flat lead) using the nearest chisel!

Someone bought me a sharpener for flat pencils that goes in your cordless drill, chisel is also what I tend to use.

[bernard towersParticipant @bernardtowers37738]

Still got 5 or 6 of those Speedy Builder!!!

[Colin Bishop 2]

On Colin Bishop 2 Said:

In my wildest dreams I had never guessed that simply sharpening a pencil could be such a complex engineering task! Is there something a bit anal going on here? A standard pencil sharpener for standard pencils plus a proplling pencil in various diameters has always been enough for me. Both are sufficient to leave the desired marking.

Life is short.

Colin

Plus 1 for that

[Speedy Builder5]

On Speedy Builder5 Said:

Anyone remember those “propelling” pencils, where a short sharpened lead was attached to a plastic stub and the “pencil’ was like a Biro but filled with about 15 of these sharpened stubs. As a stub wore down, a push button mechanism ejected the blunt stub and presented a new one. – It never caught on and disappeared shortly after it was introduced.

Bob

I recall something very similar, except when the stub at the business end wore out, you pulled it out and pushed into the other end to force a new one into position. Problem was, any sort of pressure would push the one in use back inside the pencil….

Rob

[Alan Jackson]

On Alan Jackson Said:

On Colin Bishop 2 Said:

In my wildest dreams I had never guessed that simply sharpening a pencil could be such a complex engineering task! Is there something a bit anal going on here? A standard pencil sharpener for standard pencils plus a proplling pencil in various diameters has always been enough for me. Both are sufficient to leave the desired marking.

Life is short.

Colin

Plus 1 for that

I suppose you could say an off the shelf lathe or mill is all that is needed to shape metal. But plenty here seem to like modifying them and trying new things like fitting an ELS or CNC conversion when changewheels and handwheels will do the job. Same for model boats, the sail boat I had as a kid got from one side of the boating pond to the other but I see people making far more sophisticated ones with electric or steam power.

[jaCK HobsonParticipant @jackhobson50760]

Consider making a pencil that sharpens as it writes? I have no ideas 🙁

I have a Uni Kuru Toga .5mm but it doesn’t seem to work well for my useage style. Maybe good for kanji, no so good for sketching.

[Colin Bishop 2Participant @colinbishop2]

For most male engineers, the most important attribute for a pencil is to have lead in it…. Quite where this leaves model engineers I wouldn’t care to speculate.

[Sonic EscapeParticipant @sonicescape38234]

Today I tried to make a grinding wheel to better understand what power is required. So I made this thing from stainless steel. I used a giant file to make the taper because the Sieg C0 doesn’t have a compound slide. The lathe is also misaligned and the tailstock is not adjustable. I was making a circle with the drilling bit! I start to dislike more and more this lathe.

The file was so rough that it magically created a helical pattern. Not bad. Could be sharper but since it came for free… I tested it in this way

I discover that a motor of this size is struggling. It could be also because of the non ideal grinding pattern. I’ll try to make some axial groves with Dremel. Dividing head seems overkill for this job.

[JohnFParticipant @johnf59703]

Not really in line with the OP’s mission but here’s an interesting post on another forum

https://www.ukworkshop.co.uk/threads/pencil-sharpener.122888/

John

[Clive FarrarParticipant @clivefarrar90441]

As someone who made pencils for a living for 25 years I would not recomend a rotary sharpener.

Yes they do exist and Derwent ( Cumberland Pencils ) did indead sell several types over the years.

but they are not the best in terms of potential pencil life. The leads are not that strong in  regards to sideways rotational force.

Do it the good old fashioned way with a very sharp pen knife or a scalpel cutting londitudinally along the pencil ( away from you ) .

If you must go mechanical then the machines in the factory were a 600mm diameter drum approx 200mm wide with 80 grit sand paper.  the pencils were fed in over a specially shaped rubber covered sole plate that would ROLL the pencils across the width of the drum to gradually create the point.  The special shape started with a hump the lifted the pencil up above the grit and then tapered down to datum as the pencil rolled across the drum face.

 

Good luck

[John HaineParticipant @johnhaine32865]

https://altrish.co.uk/2025/03/24/rotring-300-2mm-clutch-pencil-modification/

[lalan45Participant @lalan45]

Fun project idea, One thought is to keep it simple: fix the lead in place and rotate the cutter instead, like a tiny lathe with a conical grinding bit. A small DC motor with a bevel gear or flexible shaft could handle the angle without complex gearing, and you’d avoid having to spin the pencil at all.

[Paul LousickParticipant @paullousick59116]

I just came across this video of an original machine for sharpening pencils.

https://www.facebook.com/reel/868754285910298

[Paul LousickParticipant @paullousick59116]

And another design

https://www.facebook.com/reel/900504008984593

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