Summary

Have a pocket knife that you really wish had a clip? I did, so I made this 3D printable mold. I used vacuum resin infusion which I had access to in my research lab to lay carbon onto the mold and infuse it. After it cured and after some shaping with a dremel, I had a nice new knife clip.

Instructions

Step 1, Print the mold. This can be done with any material, at whatever settings you're used to. A high level of infill is not essential, although less than 10% may result in the mold caving in under pressure.

Step 2, Treat the mold. I used an acetone vapor bath (having printed the mold out of ABS) to smoothen the surface. I then added several coats of Freekote release agent, although many people use car wax as well. Lastly, I laid down a layer of peel-ply, which is a special type of thin permeable fabric. Not all of these may be completely necessary; the purpose of all of this is to ensure that the epoxy does not stick to the mold, as a part glued to the mold is useless. Do what you think is necessary, and experiment first.

Step 3, Lay fibers into the mold. I used 3 layers of woven carbon fiber, at 0/90, ±45, 0/90 orientations, with fiber weight at 300g/m^2. I cut the fiber so it would overlap the edges of the mold, ensuring I would have the mold completely covered, and enough area to cut my clip out of.

Step 4, Infuse with resin. I did this using the vacuum resin infusion method. This is done as follows: set the mold (mold, peel-ply, fiber) on top of a glass plate. on top of the fibers, add an additional layer of peel-ply, and a larger layer of vacuum bagging. Insert a disposable host on either end, and use tacky tape to seal all around the hoses and vacuum bagging to the plate. run one hose to a vacuum pump, turn it on, and clamp off to seal the other hose. Check for leaks. When satisfied, dip the end of the sealed off hose in a cup of epoxy, and unclamp the hose. Resin will be sucked through the fibers to the other hose. If you notice bubbles appearing, it is likely because you have a small leak that you did not know about, so stand by ready to attack leaks with tacky tape, as these bubbles will result in a part with cavities between fibers, which will make it much weaker. When the resin reaches the other end, clamp off the resin supply end hose again. Allow resin to cure before removing the vacuum. (I have a resin trap between my vacuum pump and my part, with a pressure guage and a valve between the trap and the pump. This allows me to turn on the vacuum to vacate the trap, close the valve, and turn off the pump. This allows me to keep the vacuum even with the pump off, as well as to check for leaks easier, as I both don't need the pump running so leaks are easier to hear, and because I can watch the pressure gauge and observe any increases in pressure, indicative of small leaks that I may not be able to hear).

Alternate Steps 3 and 4: Alternatively, either pre-preg could be used (pre-impregnated fibers), or resin could be brushed on. The challenge will be getting the fibers to conform to the curves of the mold. One method of doing this is rather than using atmospheric pressure and a vacuum, use a balloon pressing the fibers into the mold. This would be similar to the bladder molding process.

Step 5, Remove part from mold. If you think you may want to make more, be careful with the mold, so as to not destroy it.

Step 6, Trim edges to the desired shape. I used a dremel tool for this, and I was able to get 2 knife clips out of one mold/infusion. Also drill the required holes.

Step 7, Attach clip to knife. I'll let you figure that part out, although watch out for rotation. My knife only has one hole in the tail of it, which means with one small bolt through that hole and attached to my clip, the clip can rotate about the axis of the bolt. A drop of super glue under the clip solves this, although this means I would be unable to remove the clip without damaging it if i wanted to in the future (you can dissolve the super glue with acetone, but that will also affect the resin in the fibers). If you have 2 holes, make use of both of them.

And you're done! Cheers!

Let me know if you have any questions on the process. My background is in composites processing and I had all the resources of a composites laboratory to work with, so the infusion step only took me about 15 minutes to set up, although most people do not have such resources. Let me know and I will be happy to help if you want to either learn more about the processes I mentioned, or try to figure out another way to do it given the resources you have.

Knife Clip Mold

Knife Clip Mold

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