Kum Automatic Longpoint Sharpener

Kum Automatic Longpoint Sharpener
The Kum Automatic Longpoint Sharpener (Automatic Langkonus Spitzer in German) is definitely known on the net. It’s often touted as being one of the best sharpeners made today.

After trying it myself, I felt that what I had previously read and heard didn’t really communicate how the Longpoint works. I doubt I’m alone, so with the help of a picture or two, I hope to clarify matters.

The sharpener is an oval prism container, with two externally accessible holes. It comes with two spare blades tucked into a corner of the container. This is a very nice touch. I’ve never seen a spare sharpener blade for sale at an art supply store or stationer, and it’s nice to see a sharpener given a longer life with this addition.

Let’s get to the sharpening method. The left hole has a exit diameter of about 2mm, which is the diameter of the pencil lead or core. Thus the blade catches and sharpens the wood of a standard pencil, but misses the core. (See photo.) The pencil is then placed in the second hole, where the lead gets sharpened to a very fine point.
Kum Automatic Longpoint Sharpener
So when I saw this, all I thought was that this looks like the way pencils were sharpened a few years ago. Essentially, the angle of the point produced by sharpeners has been increasing over the years. If you like this very sharp point, and don’t mind the extra work of the dual sharpening, this may be the product for you.
Kum Automatic Longpoint Sharpener
One other thing to consider is that this sharpener is quite wasteful, and discards more of your pencil’s core than a standard modern sharpener. Recalling high school geometry, the formula for the volume of a cylinder is

V = ?r2h

and the formula for the volume of a cone is

V = 1/3?r2h

so turning a cylinder of lead into a cone of lead discards 2/3 of that lead.

For a 2mm lead, the radius is 1mm. The Longpoint produces a point of 3mm, so we have

V = ?*1mm2*3mm = 9.4mm2 will result in 6.3mm2 discarded to create a 3.1mm2 point.

A point which will be much harder to keep unbroken, by the way.

A more modest 2mm long point would produce only 4.2mm2 of waste.

The 2/3 of the lead discarded in making a point actually could be an argument in favour of mechanical pencils.

I’m sticking with regular sharpeners, but it’s nice to know about this alternative.

37 Replies to “Kum Automatic Longpoint Sharpener”

  1. I have the same sharpener and although it worked well in the beginning, the blades needed replacement within three months. Also, the sharpener body is made of a light magnesium alloy or something that acts like plastic so if you misalign the screw, it’ll mess up the threads without much resistance and you’ll have a ruined sharpener like I have. I’ve replaced it with a Panasonic KP-4A. It runs on batteries and has a helical wheel which will dull a lot slower than straight edges. It’s worth a look.

  2. I like sharp points, and the KUM often, though not always, delivers. There have been times when it has splintered the wood casing around the lead. Still, it is the best manual sharpener that I know. And portable. For home and office, I use the amazing Wescott I-Point with auto stop as well as a very efficient Panasonic KP-310. These sharpeners give perfect long points every time in seconds.

  3. On the other hand, don’t you get more inch per lead from a long point, requiring less sharpening? I sharpen when the line becomes too broad. With a long point this eventuality does not occur until much more has been written, thus the relative waste of the core between a short and long point is a wash in my unscientific opinion.

  4. Did a few calculations, based on the assumption that you’ll use the pencil point until the radius is .5mm. This radius will occur at half the sharpened (lead) length with 1mm radius lead. Also, I’ll assume you’re using 10cm of your pencil.

    So, with a 2mm sharpener, you’re using lead cones 1mm long and .5mm radius at the base. With a 3mm, cones 1.5mm long and .5mm radius.

    Assuming infinite sharpness, over 100mm of lead, you’ll get 100 sharpens using half of a 2mm point each time (using .785 sq mm each). And, 75 sharpens using half of a 3mm point (using 1.18 sq mm each). Used lead volume is about 79 sq mm in either case.

    However, if you assume that the point, which would be 2 or 3mm if it were infinitely sharp, is only sharpened until the radius at the end is .25mm, then the long point gets a slight volumetric advantage. You get 200 sharpens, using .5mm length each, of the 2mm points. Volume each is .72 sq mm. You get 150 sharpens, using .75mm each, of the 3mm points. Volume each is 1.082 sq mm. The 2mm point uses 144 and the 3mm uses 162 sq mm over the same 10cm length of total used lead. Total lead volume is 314 sq mm.

    For those numbers you compute the difference of two cones. Take the volume of the infinitely sharp cone, and subtract the tip of them. In this case, take away the volume of a .5mm long, .25mm radius at the base, section for the 2mm sharpener. For the 3mm, take away a .75 by .25mm cone.

    The lesson? If you want to use more of your lead, don’t sharpen the point past a useful tip diameter. If nothing breaks off, you’ll always get the same total line-length per pencil, though.

    Narrower angles may use a bit more of your lead, but the angle is much less important. Also, the assumptions aren’t completely accurate, as I’m assuming a 90 degree writing angle.

    And, of course, if you use, say, a .3 to .7mm section of your points, versus a .5 to .9mm section, you’ll use less of your lead and “sharpen away” more. But, to fret over that would be to complain that a tube of .5mm mechanical pencil leads should cost less than a tube of .7mm leads, as the former contains a smaller volume of lead.

  5. This is an awfully late comment, and I feel a bit silly saying anything after Renard’s excellent analysis, but here goes:

    I’ve recently used this sharpener on the following pencils:

    California Republic Prospector, Golden Bear, Forest Choice and Palomino
    Musgrave HB and Test Scoring 100
    Helix Oxford
    2 different types of really junky, no-name pencils with awful, scratchy lead

    The only problem I’ve encountered was a tendency to break off the tip near the end of 2nd stage sharpening. Very frustrating. It only occurred with the Forest Choice and Musgrave HB pencils.

    I’m pretty sure it was user error, though. Today I sharpened a new Musgrave and it broke twice as described. Then I changed part of my method, and voila! No more breakage.

    The change? Rather than hold the pencil and sharpener vertically during the second stage, trying to apply significant downward force to speed the step along and get a good point quickly, I held both horizontally and took my time.

    This is a very small-sample test, obviously, but I’m well enough convinced that I’ll be sharpening this way from now on.

  6. OK, this is no good. I’ve just changed the blades in my KUM Longpoint sharpener, and it’s snapped off the tip of my Palomino 3 times in a row!

    I will be very grateful if anyone reads this comment any time soon with some advice. Even just commiseration at this point would be nice. I never had any such problems before, but now, in the last 2 weeks (mind you, I’ve only had this sharpener a month) it’s been driving me absolutely batty!

    It was one thing when I thought I wasn’t being careful enough and it was only eating inexpensive pencils, but these are my Palominos, we’re talking about here. Messin’ with my Palominos is like messin’ with my emotions, man!

    *Sigh* If anyone has any kind words or advice, I’ll be watching this space. I know this review is close to a year old, but it’s the most involved discussion on this product I’ve found anywhere.

    Meanwhile, I’ll be writing KUM.

  7. I have been having the exact same problem with mine. I LOVE this sharpener, but after a couple of weeks it eats up all my pencils, no matter how careful I am!

  8. I had the same experience as Breck and Mill with this sharpener eating my (Palomino!) pencils. It didn’t happen immediately after I got it, but the problem became intolerable within a couple of months. Maybe the screws holding the blade loosened and caused a pinch. I didn’t have that much curiosity. I just switched to a different sharpener, the excellent DUX 3-way adjustable (SKU: DX4322), and have never looked back.

  9. I have had nothing but problems with KUM sharpeners, either the blades dull after a few months or the plastic housing (Color Combi model) developed cracks. Now DUX sharpeners esp., the 3-way Brass is good and also their nostalgic cylindrical sharpeners are sturdy and well made. The blades keep their sharpness for a long time.

  10. Hi PaddlePressure and Samy, these are very interesting comments! Especially as KUM does have a reputation for quality. After reading your recommendations, I will have to try some more DUX products.

    (If someone wanted to write a sharpener comparison article, I would be happy to post it.)

  11. Breck and Mill:

    I’ve had the exact same problem, and it has caused me to give up completely on the Kum automatic long-point sharpener. So far now, I’ve bought three of the things, and after about the same period of time as you mention, all they would do is snap off the lead in the second-phase sharpener. Yes, I tried it through three sharpeners. Yes, I’m not very bright. I really liked the results when it worked, though. However, I also tried replacing the blades, and the same thing occurred. As to why is anyone’s guess. I would recommend sticking with the standard stenographer’s long-point sharpener. I’ve used these for a couple of years now, and they work impeccably. In my opinion. …

  12. I’ve had an identical experience of initial joy at perfect points followed too quickly by frustration as even the most delicate of turns fails to prevent that maddening ‘snap’ sound.

    Although it’s only been three days and the long-term results remain to be seen, I am every bit as pleased with the sharpener from classroomfriendlysupplies.com as I initially was with the kum 2-stage. We’ll see how it plays out.

    It’s a little expensive (15 + 10 shipping), and a little too large to travel with IMO. But it gets the long-point job done in one stage, and stops automatically.

  13. primitiveworker… Whoa! I think the pencil demimonde has found its first auteur. I’m going to buy one of those and take it clubbing tonight. Rave on dude!

    Seriously, it looks like a good sharpener. I’d like to be able to mount it on a wall though. Hundreds of satisfied teachers can’t be wrong can they?

    Long points make it (pencils) better!

  14. primitiveworker, thanks for the heads up on the “classroomfriendlysupplies.com” sharpener. I just bought 2 of those and what a joy it is! The gearing is all metal drive, the case is made of heavy gauge steel and it makes a superb long point. In other words it is built like a tank. Note, it does not sharpen large diameter color pencils.

    If you buy it on ebay, from the same person you can get a better deal (32 USD for 2 including shipping). It is a good bargain

  15. I know this pencil sharpener. I know how to mount it on the wall at least in a classroom most classrooms have a 1/2″- 3/4″ board on the wall where the ones with four screws goes and the board is 6″ high X 8″ wide.
    What I did was bought a 3/16″ piece of steel from the local hardware store along with some data staples these happened to be by Gardner Bender blue in color has a 1/2″ of the nail that goes into the wood.
    I cut a piece of steel about 6″ long and ran it threw the two bottom holes
    (remove the handle on the sharpener first) and simpley tacked the data staples over the steel rod. I used two on each side and rotated sides.
    There use to be a two nail data staple but I could not find them anywhere.
    The kids will have to use their weight to pull it off just like the four screw ones.

  16. My KUM automatic long-point behaved just the same way. It worked well for a couple of weeks and then the second stage started breaking off the point everytime. Pencils of all kinds: Palomino, Tombo, Staedler,Faber-Castell, Ticonderoga, Mirado, Golden Bear, Chung Hwa suffer the same fate. Only one of my stenographer’s long point works well, the other snaps the point all the time just like its expensive automatic sibling. Now at work, I use either the good stenographer’s long point sharpener or use the first stage with the auto followed by a lead pointer (Gedess) to finish shaping the core. Another great sharpener is the Caran d’Ache table top unit which I bought back from Switzerland but it works so well that I am afraid it may “walk away” at the office, so I keep it now at home.

  17. Hi Jeremiah, thank you for your comment.

    A number of people have mentioned problems with this and other KUM sharpeners.

    Sharpeners are pretty clearly a weak point for those who use pencils, and many of the ones that seem to offer a new solution don’t hold up under use.

    I am glad to hear a good report about the Caran d’Ache desktop model – it is not cheap.

  18. My Classroom Friendly sharpeners (I have 4) do not have all metal gears and that is, IMHO, their design weakness. The rotating gear is metal but the stationary gear is plastic. I had 3 of these all year (2008-2009 school year) in my high school classroom (130 9th grade math students) and they worked great for the first half of the year. But one-by-one each sharpener had a plastic tooth on the stationary gears break off. The sharpeners still function, but they have lost their delightful “smoothness” (they have a hitch in their giddy-up) and they don’t produce as clean of a point. They break a lot of leads now whereas before they almost never broke any. A replacement gear is not available. I looked for and found a similar design with all metal gears by Kikkerland (Amazon.com) but the two I bought as test units have a moderate in one case, and severe in the other case, tendency to sharpen unevenly (where one side of the point still has wood on it). They are wall mountable and not really made to be portable (the opposite of the Clasroom Friendly’s). I installed one and stored the second :-(. The Classroom Friendly’s were the perfect sharpener but I can’t recommend them because of the plastic gear issue. An adult could probably use one a lot longer but teens are very tough on everything…teachers, sharpeners, you name it :-). Anyway, I am still looking for the perfect sharpener, until then the manual black Bostitch wall mounted (MSR1) is still my workhorse.

  19. for all who look for the perfect sharpener, for me Ive found the solution DUX Variabel in solid heavy brass

  20. John, thanks for that detailed summary. I hope it can benefit other teachers – it sounds like there is a serious need for a good heavy-duty wall-mount sharpener.

    Alex, I looked up the Variabel on Google, and found that very sharpener listed in the 1971 Alvin catalogue, with the same name, at leadholder.com! It is a classic. I should get one.

  21. The KUM Automatic Longpoint Sharpener is still my all time favorite sharpener with that one concern of the blades dulling after about 200 or so sharpenings. But dear friends do not lament so sadly as this is one of those sharpeners with the easiest of all fixes. You can remove the blade and hone it and it will work even better than when you first bought it. Yes those little 15/16″ blades are slightly convex, and really tiny, but it’s still easy peasey to hone them. If you’ve ever sharpened or honed a pocket knife or kitchen knife then you already know how to do it. If not it’s easy and cheap to do it and it’ll only take a couple minutes. The cheapest way to hone your blades is to get yourself a scrap piece of leather and impregnate the flesh side with a little bit of that jewelers rouge you can find at any Home Despot or Waly’s Mart type store in the Dremel tool section, it’ll set you back around two bucks. Swipe the angled edge a few times and then swipe the back flat a few times and look at that your sharpener blade is sharper than when you first got your sharpener.

    I have three KUM Automatic Longpoint Sharpeners and as soon as I received each one I removed the blades and honed them and now even many of the most difficult pencils and leads sharpen up easy. Oh and if you do strip out the threads on your sharpener you can put a very small dab of crazy glue or 5 minute epoxy in the hole, insert your screw and your good to go. If you ever need to remove the screw again just take it slow and easy and screw gently in and out until the glue releases its hold. The trick is using an almost microscopic dab of glue as it will give the screw enough strength but it won’t be so much to glue it in place permanently.

  22. Thanks for the tip Seamus. I took the second blade out of my KUM sharpener and gave it the treatment you described, except I used my trusty old Arkansas stone and some oil. It worked very well and took very little time considering the benefit. The sharpener now easily puts a very sharp point on softer pencils such as H or HB. Harder leads like 8H are a horse of an entirely different wheelbase though. For those I’ll stick with my old standbys, the X-acto electric, and emery cloth. It’s a lot messier, and more work, but when you’re done you have a needle sharp point ready for some serious work.

  23. What kind of grid do you need for that, a stone in the hundreds like for a knife or something in the thousands like for a razor? My guess would be something in the high hundreds. Do you hold the tiny blade with your hands? I imagine it would be difficult to get the angle right.

  24. I’m not sure what hardness is of the Arkansas stone I have. I bought it many years ago at a hardware store that is no longer around. Yes, you can hold that blade in your hand and get the angle right. You just have to get the “feel” of full contact when it’s on the stone (just tip the blade back and forth a few times to get that feel). I have also made a contraption for holding the blade at the proper angle, but frankly, the job is done so quickly that it’s not worth the fuss of using gadgets. Just a few passes on the angled and flat sides and you’re in business!

  25. I am writing in response to John C’s comments about the Classroom Friendly Pencil Sharpener. It is true that some of the pencil sharpeners that were sold had plastic gears. As soon as I realized this flaw, I contacted my supplier to correct this weakness. Since then, my Classroom Friendly Sharpeners all have the durable steel gears. This has corrected the problem and extended the life of the sharpener indefinitely. I apologize to you John C, and any other customer that may have received a faulty gear. Please email me your address so that I can send you the replacement gears for your sharpeners. I stand by this sharpener as one of the best on the market.
    Kindest regards.

  26. Nice blog!

    Typo fella.
    “The Kum Automatic Longpoint Sharpener (Automatic Langkonus Spitzer in German) is definitely *known* on the net.”

  27. I experienced the very same problem with mine, too. I think the name “Automatic” means that it automatically breaks the lead. A fall from grace.

  28. I know I’m super late to the party on this one, but I have not had any of these issues. The KUM has worked perfectly for me every time. I primarily use Ticonderoga #2 Soft Pencils for my son or Field Notes Pencils for myself. The point has turned out exactly as advertised each time. I usually sharpen the lead several times in the #2 hole before I have to use the #1 again.

  29. I have the same problem also , i used it for less than a month and the day before the problem occurs , it is still working well on the same pencil but then the other day , it keeps snapping pencils. Wasted my nice Mitsubishi 9000. Even pencil with harder leads such as faber castell grip 2001 HB is broken.

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