The Perfect Pen Knife Handle

the perfect exacto handle

If you’ve ever tried to use a pen knife for anything other than cutting open a box or slicing material in one direction, you’ll know they really aren’t that ergonomic. When [Seamusriley] started Architecture school a few years ago he started on a journey — an epic journey to make the perfect pen knife handle.

He started by analyzing existing handles — the biggest problem with them is the skinny pen shape causes hyper-extension of the first joint in your index finger, so once he identified that as the root cause he started crafting a more ergonomic version. He started out with foam, then up to wood carved by hand, then 3D printing, and back to wood — but this time, with a CNC machine. Literally dozens of prototypes later, he’s come up with a very nice pen knife handle, so much so, he was asked to present it around Boston at design events!

This is a great example of the hacker mindset — identifying a problem, trying out a solution, trying out another solution, trying out a solution… and then finally getting to a finished product. It’s the tenacity that keeps us going which rewards us in the long run.

[via r/somethingimade]

44 thoughts on “The Perfect Pen Knife Handle

          1. Boohoo? Seriously, the internet is 80% porn of all tastes, preferences, colours, species, 5% Facebook, 5% pictures of cats, 9% youtube and 1% miscellany. If you want to be this protective of the kid, the only way is scissors applied to his ethernet cable.

          2. You can’t really hide all the explicit content on the Internet, I’d say you can’t even block all of the porn sites reliably.
            I have to say I pity those that think they can ‘protect’ their children from the explicit content on the Internet. Not only that’s impossible to do properly, it’s also very, very stupid if done improperly. BUt then, I can understand – not all the people are as gifted as to actually be able to explain things to their children.

          3. You should also recommend to your friends kids that they don’t leave the house. There’s people in the world that speak the same and worse than what is typed on this little site.. and that’s just at the schools they attend.

          4. Of course those that replied don’t get it.
            I said that I can not recommend this site to kids because of comments like that. Frankly the comment in question has zero value to start with. When I tell a friends kid that they should look at a site I am saying that it is site filled with good content and is not offensive to how they are raising their kids. I have to be more restrictive in what I recommend to others children than I would my own.

            Some idiot making a joke about a sex toy means that I can not recommend it to a 12 year old.

          5. Your comment is just as useless and here is why: You cannot in good conscience recommend something to someone’s child in which you have witnessed possibly offensive material. Including but not limited to harsh language, suggestive language, and discussion of illegal or possibly illegal activities. And to such I will say again. That is life. That happens everywhere. The only thing you can really recommend to them is to read a book and sometimes that’s not always safe. So really there are quite few things that you can recommend to someone else’s children. Mostly it’s because you should recommend it or run it past their parents first. Even with teachers, things must be filtered through them or else they can only suggest material that was developed for the appropriate age.

          6. I can understand – these are your friends and you’re not to debate their values in parenting, however inappropriate they might be. However, there isn’t a rule anywhere on HaD not to post any explicit material (that isn’t against the law) or swear. If you don’t like it or can’t recommend this place due to this, there’s Instructables. Or maybe – I don’t think anybody really discusses dildos there. But then, it’s not full of hackers of all kinds – mostly serious business(c). Enforcing your personal code of conduct on somebody and calling them names if they don’t conform is the last thing you should ever do.
            Besides, you’re not the person to ultimately decide if a comments has any value. I, for one, think the comment like this has a value – maybe one day I’ll participate in Dilduino development and this idea will help. However, your comment certainly has no value to me – you’re expecting people to do what they’re not obliged to do, and you’re angry because they do not.

          7. @CRImier
            I never said it was a rule or that it should be forbidden. I simply stated that posts like this have consequences and what they are. The value of that comment vs the value of fewer people getting value out of the site is one for the owners of the site to decide. I for instance see no value in the comment. I was simply defending someone’s right to be offended by a comment that add no value and that a large number of people would find offensive.
            I have been coming here for years and will probably continue too because I find value in it.

          8. Can you be sure your friend’s kids have not already found this site? You must wrap them in tin-foil just to be sure. I am sure your friend will agree to allow this. It’s the only way to be sure.

      1. It is a readily available, cheap rubber tube that anyone can buy (outside perhaps some catholic countries) that I imagine works will for the modelling hand tool grips as the other poster suggested. I wouldn’t get too hung up about it.

        Some of the air drying clays can be very foam like and work quite well for this sort of thing as well.

          1. @reboots, I am from Sweden, NOBODY here has any problem with the things you mention.
            Dirty jokes and sexuality is not the same things though, but I do not expect you to understand the difference.

            Would you go into a class of sixgraders and tell dirty jokes?

            Why in Hertz name do you want to scare away the female hackers/makers from HaD?
            That is just beyond stupid.

          2. Why in Freuds name do you think females would be more likely to be scared away by a juvenile dildo-joke than males? Are you a really a swede or just happen to live here? Your comment reflect sweden in 1955.

          3. @Dietr, pure experience and I was not born in 1955 so I wouldn’t know.
            I’m from northern Sweden, I do not know any men that are deterred by juvinile jokes, but they have manors.

    1. ಠ_ಠ * ∞

      @jgo – I realize the color scheme of HaD MIGHT resemble PH? Are you actually 9 years old or just displaying the attitudes 50 year old creep looking to start a flame war about personal kinks, politics, sexuality on a site relating to math, reason and logic.

      Congratulations, you sparked a flame war by being yourself.

      Unless you contribute an idea to a project or task shortcut, suggest an alternative, criticize with a solution or ask for understanding as to why & how task or project is accomplished.


  1. Small quibble – “penknife” usually refers to a folding pocket-knife (eg a Swiss Army knife), whereas Mr Riley seems to have re-engineered what I would refer to as a hobby knife, X-Acto knife, or craft knife. Cool handle for that.

    If you’re using a pocket-knife for hours, you’re using the wrong knife. Or you’re marooned on a desert island.

    1. What I came here to say- these days it’s a bit odd that “pen knife” doesn’t refer to knives shaped like pens, but that’s the way language is. We managed to rebrand night light candles as tea lights, maybe “pen knife” is next up?

      Anyway, from reading the bit about spending eight hours a day crafting wood handles, it seems like this guy could really have done with some shapelock/instamorph. Make a prototype, see where the shape needs to change, remould it, repeat. If I used these blades a lot I’d probably make a shapelock grip for the regular blade holder anyway.

      1. “night light candles” were always “tea lights”. At least so far as the small candles in a shallow metal container are concerned. They were and are used to keep some styles of teapot warm. They are used in a similar capacity to warm incense and some fondue pots. But warming tea was their original use.

  2. I remember a search for a good shape for a handle for a vegetable peeler knife some time back — one that could be used by older people. Turned out the best solution was to just put a bicycle handle over the existing handle (with some filler).

  3. When I saw the subject I was also imagining my little pocket Buck knife having a pleasant to hold body. The image of his really nice hobby knife looks very much like one of my X-Acto Curve knives (™-Knife.aspx) which is indeed, very comfortable to use.

    I agree with the HAD author’s assessment that the development of this handle was a “great example of the hacker mindset”, and one that the designer at X-Acto must have had as well.

  4. The article leaves off his most recent step: selling the handles for $65-90 on Etsy, and preparing a Kickstarter!

    Nice process and result. I wonder if he considered other blades besides the X-Acto system. Over time I’ve come to realize classic X-Acto products are terrible from every angle: overpriced, unergonomic and underengineered, they have no advantage beyond the ubiquitous brand. The aluminum handle corrodes, the blade isn’t fixed at a consistent angle, and the collet doesn’t grip unless you tighten it to the point of flaring and cracking the nut, at which point the handle is best discarded–which I’m sure is the idea.

    I worked for several years in a production hand bookbindery, and we used standard #6 medical scalpels with #25 blades (Havel’s brand). Good ergonomics, sharper and more effective than X-Acto knives, and very cheap. I recommend this system for anybody wanting to do a lot of very fine detail 2D work. (The blades are thinner and more flexible than crafting knives, so may not be suitable for some applications like wood carving.)

    Interestingly, scalpel handle ergonomics are still a matter of some debate. Here’s an informative paper which parallels [Seamusriley]’s investigation, bringing a lot of ergonomic science to bear, and producing a somewhat different “ideal” result:

    Improving the Ergonomic Design of Scalpel Handles

    A second link is going to drop me into the mod queue, but I wanted to mention that Fiskars offers this intriguing take on craft knife ergonomics:

    And they also have a swivel version!

      1. Also: Proper syringes of all reasonable sizes are cheap and on the shelf at the local farm store. And antibiotics are cash-and-carry there, too. I can imagine quite a lot of other medical-ish stuff being sold there, too (including quite possibly proper scalpels), but haven’t had a reason to look.

  5. One of the best moves I made regarding hobby knives was switching to scalpels- a little bit more expensive, but significantly sharper, and the blade bends a bit, resulting in nice, smooth cuts.

  6. A great deal of work was done on knife-handle ergonomics by Ernest “Mooney” Warther many decades ago. Some study of the Warthers website ( or a visit to their museum if you’re in northeast Ohio is quite instructive.

    Heck, his 10 cut pliers are worthy of their own HAD entry (google “warther pliers” for a variety of links, including:

  7. These designs including the Fiskars are for flat work, fine if cutting stencils. In detail work on restoration that we do, angle of attack is in your two hands not on a desk. You shift your grip on the same tool for different ways of getting to the details. Round means uniform hand-ability.
    I constantly rail against using folding blade hunting knives in the shop. If the handle is big enough to hold and do good work then the blade is big enough to gut and quarter a deer. The stiffer X-acto blade in the bigger handle should be a first use tool in much of the work we do.
    Rule one; If you have to touch the blade while doing work, it’s too big. This includes the other thumb on the back of the blade, it’s so much easier on the thumb using the collet area of the handle.
    I have only cut my hands twice, with (pocket,pen,hunting,etc) type knives both times.
    Here in the US I thought a penknife was like an X-acto with a safety cap.

  8. Not trying to be “that guy” but how’s this different than the knives used in wood working? Particularly those used in chip and fine carving. Diy is great but reinventing the wheel wastes time.

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