Jan 26, 20182260 views

Ferrum Forge Knife Works - improved pocket clips

Hey everyone,
Some of you may have seen the discussion about pocket clips in drops for Falcon and Crux knives. We've been reading all you comments and working closely with Ferrum Forge, WE Knife, our engineering team, and a testing lab on this for the past few months, and we're pleased to introduce a new-and-improved version.
This version is making its debut on the new Falcon Wing Edition that launches today (1/26/18), and will be available to members as an accessory soon (hopefully, sometime in March). Here to tell you more about the process, and the results of our testing, is our lead engineer John Yu.
Take it away, John! [Continued below...]
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Howlhatler, Spike_SPGL, and 14 others
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Stickied
Hi everyone! For those of you who don’t know me, I’m a mechanical engineer here at Massdrop, and I help manage development and production of many of the products we manufacture.
TL;DR We are preparing to implement a new pocket clip design into production. The re-designed clip is easier to use and has a higher yield strength, so it should be an improvement on all fronts. Following the first shipment of the Massdrop x Ferrum Forge Falcon knives, a few customers voiced concerns about the pocket clip permanently bending and deforming, often due to the clip getting caught on an object when the user is navigating the environment of daily life. We wanted to take a deeper look into this and see what the root cause of these issues were, and understand if there is the opportunity to make this part perform better.
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Since a pocket clip is essentially a cantilever beam with force applied to the free end of the beam, root cause of the failures are plastic [permanent] deformation clip along the length of the beam. The first version of the clip features a design of varying thickness and a relatively short thin section. The thinnest portion of the beam is the first deflect when force is applied, thus the design only allows a relatively short portion of the clip to flex under load; this situation forms a stress concentration at the thin section of the part. Once the force applied exceeds the yield strength of the material, the clip will deform permanently.
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After a few rounds of design iteration, review, and prototyping (a joint effort with the teams at Ferrum Forge and WE Knife) we arrived at a final design.
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The new design extends the thin region of the pocket clip to allow for more deflection before the material yields and permanently deforms. To ensure the new design is a quantifiable improvement, we sent some samples of each design (keeping the material of the clips the same, so the only variable is geometry) to a test lab to perform cantilevered force testing. The test data is plotted below:
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This plot shows the load (x-axis) vs. strain (y-axis). Strain is measure of the amount the part is deforming under load. The following areas of the graphs are significant:
  • The linear portion of the lines show the parts deforming elastically, meaning if the applied force is removed, the part will return to its unloaded state. For the best reliability performance of this part, we want to ensure the maximum expected loads fall within this region of the force response curve.
  • The point where the lines transition from linear response to non-linear/chaotic response is the condition where the material is yielding and transitioning to plastic deformation. The further this point is along the X-axis, the higher load the part can withstand before it deforms permanently. With this in mind, the following conclusions can be drawn:
  • The new clip design yields at a higher load than the old design.
  • New clip 70N = 15.73 lbf = 7.13 kgf.
  • Old clip 60 N = 13.48 lbf = 6.12 kgf
  • The slopes of the linear regions of the lines indicate the incremental amount of force required to open the clip. In this case, the steeper the slope, the more the clip will deflect when the same amount of force is applied. For our part, this means:
  • The new clip has a steeper slope than the old clip, which means it is easier to open.
  • Another way to interpret the differences in strain rates is: given a set thickness that the clip must be opened (e.g. the thickness of a pocket), the new clip design requires less force to open, and therefore has a bigger margin of safety from its yield strength.

We hope you enjoyed this glimpse into some of the work we do to ensure our products are the best they can be. It’s incredibly rewarding for me as an engineer with a focus in user-centered product design to be able to take in such direct feedback and translate them into meaningful product improvements.
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Since you have intimate knowledge of ferrum forge knives can you tell me what the coating is on the standard grey titanium handles. The crux I just received sparkles in just the right light. I like it, just curious
Gunnersmate2
I believe it is a stonewash. It is beautiful but can be sensitive.
That's a good fix for the pocket clips. I would buy many of these knives, but I like to carry my knives clip down in my pocket. If there was a way to communicate to manufacturers to make knives have an option to change the clip's side, I would definitely consider buying the knife.
What is your take on the Kabar #1001 USA two blade bone handle pocket knife?
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Should just offer every confirmed buyer a free replacement and not charge extra. Based on the replacement policy, it seems like all one has to do is break the current clip they have to get a new one for free; how to prove they broke it on accident or on purpose? For me, so far so good on the original clip, but good to know that if and when it breaks I'll be taken care of.
Too bad they are not offering to replace the first design clips for free. Knives were shipped with the first design long after the issue was recognized with the clip.
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I would like to submit a ticket for a replacement clip. Had it bend a week after I got the knife. Johnny Mullins, jmullins@outlook.com. Thank you
Zman_11
You will have to do that here - https://www.massdrop.com/transactions
Can you send me a reminder when the clips are ready to go?
Glamdring
We'll send an email to everyone who bought Falcons. If yours bent or broke, please submit a help ticket so we can prioritize your order and process it appropriately: https://www.massdrop.com/transactions
Will we be able to order these when they are ready? Mine broke off and I'd love to replace it.
Davit
Yes, just submit a help ticket here anytime: https://www.massdrop.com/transactions
How about a deep pocket clip, if you are going to all of this trouble to fix a bad design on the old clip then why not give us the option of a new deep pocket clip. Personally if I have a choice between a regular clip and a deep pocket clip I will choose the deep pocket clip every time, they also seem to be a stronger clip as far as not bending to the point or past the point of no return, so to speak. Even if you don't replace the old one with a deep pocket clip it would be nice if we could purchase the deep pocket clip as an upgrade, just my two cents. I have purchased both knives that were sold on here, the Falcon and the Crux and absolutely love both of them. I did add little color to my Falcon and like the way it turned out, let me know what you guys think.
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waders69
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scumdrop
Wow, those are beautiful, very nice.
Thank you Massdrop/FF/WE for addressing the clip concerns. But 17% improvement on this part does not sound too promising...
Do you have pictures of where the new design clips bent? I'll bet they bent at the radius by where the clip is fastened to the knife. If the radius of that area was increased to a similar radius as the old design in the same area, i can see this would greatly improve the loading the clip can withstand.
It is nice to see that the clip would be easier to lift. Will make it nicer to put in the pocket. But I'll likely get my replacement clip and leave it off the knife in fear of bending it like the original clip.
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You'll just have to boof it
Phucanese
Not trying to be a jerk here, but asking for easier lifting and more resistance to bending or at least deformation, sets up a dichotomy of sorts. At least from my perspective.
The design should not be around the max force but rather max deflection. the clips should be designed to go over belts for example so I would suggest making sure that the clips can bend enough.
xrlonly
You may get a "Steve Jobs" response in that you are using the device wrong. These clips are designed to clip over a pocket, as evidence by the name "pocket clip". Making them large enough and flexible enough to fit over a belt, especially thicker ones like my 5.11 gun belt would doubtfully work on a knife this small.
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