Introduction: Making Cast Resin Aluminium Honeycomb Knife Scales

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About: Amateur Bladesmith, hobbiest woodworker, and a bloody good cook

Howdy yall, been a while but im back again to spit some knowledge and show yall how to barely do something technically correct! This week, were going to dive into a way to make a pretty cool looking material from some pretty basic supplies with minimal work, truly the holy grail of knifemaking.

Enough prose, im going to show you how to make a set of cast urethane resin knife scales. Now, added bonus, the same process will work without the honeycomb or with different resins, so really youre learning 3 things for one read-through! Word of warning, ill be using some tools that while not super-advanced or hard to obtain, are a bit rare in the common shop. Ill try to present alternatives, but dont have pictures for the alternative methods and really do recommend investing in the fancy gear if you intend to do this more than once.

Enough faffing about, lets get to it!

Step 1: Tools and Materials

Time to talk tools. All said and done, all you really need for this is a resin to cast, a mold box to cast it in and something to mix the resin in, but im still going to bore you with the details.

Software:

  1. A casting resin - For this tutorial, ill be using Smooth-Cast 326, a 2 part urethane casting resin that im partial to. Its low viscosity, easy to mix, relatively fast curing while still having a good working time, and cures to a transparent amber making it easy to color. Alternatives to this are pretty limitless, Aumilite is one that i know of, you could use a castable epoxy, whatever, just make sure that you research whatever you use because the mixing ratios areng going to be the same as shown
  2. Aluminium Honeycomb - You dont have to buy from McMaster, thats just an example. Im using 1/4" thick for this to match the final thickness i want for knife scales. I got mine from eBay as a 10"x12" sheet, which i cut down into a bunch of 1.5"x5" blanks to fit my mold. Easy to cut, just needs scissors. You can skip this if you would rather just have a solid resin block, without the honeycomb effect
  3. Resin Colorants - Unless you want some really boring scales, or clear depending on the resin, you need a way to color it. Make sure that these are compatible with your resin! Incompatible colorants can cause your resin to fail to cure, not a pretty sight. Since im using a Smooth-On resin, ill be using their So-Strong colorants. These things are insanely concentrated, a very tiny amount will color a large amount of resin, so they go a long way (for reference, i use a single drop in this tutorial)
  4. Resin Fillers, Powders and Effects (optional) - In addition to colors, you can add a variety of things to your resin to give different effects, like glitters, metal powders, or just fillers designed for added strength. Here again, youll need to make sure that your filler is compatible with your resin. I want a kinda sparkly effect for these scales, so ill be using another Smooth-On product, Cast Magic, specifically the Silver Bullet variety
  5. Acetone - For cleaning

Hardware:

  1. Mixing Cups - I like standard paper Dixie cups from the supermarket, theyre cheap and disposable, plus a handy size. They also dont react with the resin i use, or the solvents i keep around (acetone melts solo cups, ask me how i know)
  2. Mixing Sticks - You may be tempted to grab a popsicle stick, i recommend against it. Urethane resins react poorly with moisture, and wood holds moisture. Might be a placebo thing, but for me, using wood tools for mixing has always led to very bubble-filled castings. Stick to metal or plastic. Disposable plastic knives are a favorite for me, as theyre cheap and readily available, but its a bit wasteful. If resin casting is something you plan on doing more than once, invest in a set of these silicone stir sticks. Nothing to interfere with the resin as silicone is inert, easy to clean, reusable
  3. A Mold - Should be first on this list, now that i think of it... Im using a silicone mold i made that has 2 cavities in it that measure 1.5"x5"x.3125". Ideally you should use a silicone mold, but if you dont have one and cant make one, you can substitute, you just need something that the resin wont stick to. My recommended alternative is to get a white plastic cutting board, something made from HDPE like this, cut that into strips and use hot glue to make a box. The hot glue will hold it together long enough to use as a mold, and at the end you just knock the pieces apart
  4. A Scale (optional depending on resin) - You need some way to precisely meter out your resin components. The resin im using can be mixed 1:1 by volume OR 115:100 by weight. I like going by weight for larger amounts. Be sure to double check how your resin needs to be metered
  5. Vacuum Chamber (optional) - Extremely useful for getting air bubbles out of resin so they dont end up in your casting. Im using a basic pressure pot with lid that i made to hook up to a basic vacuum pump. You can skip this without too much detriment, theres just more of a risk of bubbles
  6. Pressure Pot (optional) - Much like the vacuum chamber, this will help make sure that your final casting doesnt have bubbles or voids. Its pretty much a lidded container that you pump compressed air into. Again, you can skip this, but having one will make your castings so much better its worth owning one if you plan on casting things more than once or twice.

Pretty sure thats everything, but its entirely possible i forgot something. If i did, itll pop up later in the 'ble, so read the entire thing before you start

Step 2: Material Prep

Alright, now its time to start getting started! First up is the most important part: Preparation. Specifically, preparing your mold and stuff going into the resin. In this case, the mold itself needs no prep work for me, the resin im using doesnt stick to silicone so i dont need to add any sort of release agent, just make sure that the mold is clean and its good to go. Your mileage may vary based on what sort of mold youre using and the accompanying resin. If you arent using a silicone mold but are following my recommendation of using HDPE plastic sheets to build a mold, you also shouldnt need to apply anything to the mold as HDPE is naturally non-stick, but again, read the instructions for whatever resin youre using to determine your needs for release agents.

The aluminium honeycomb does require prep. First, you need to cut it to fit your mold. In my case, i already did that, but did a test fit just to be sure. Second, you need to make sure that the aluminium is clean, otherwise the resin wont stick to it and youll have a really crappy material at the end. Any oils or grease on the surface will compromise the bond, but luckily cleaning is easy: take the acetone from the materials list, pour it in an appropriate container and submerge the honeycomb. Let it sit there while you go through the next steps.

A word on the solvent; Acetone is a pretty powerful solvent. Itll eat through most paints, isnt the nicest stuff to have on your skin and should be used in a well-ventilated area. That said, this is not an area that you want to skimp on. Cleanliness directly affects the end result of this project, and soap and water wont cut it. You need something that cuts through anything on the metal and dries without a residue, and nasty though it may seem acetone is the nicest way to do that. It might also seem like just another thing to spend money on, but after spending $40 on the resin and $20 on the honeycomb, plus your time, you dont want your project to fail because you didnt want to spend $12 for a gallon of acetone thatll last you forever

Step 3: Measuring and Mixing

Now that youve got your mold prepped, time for rubber to hit the road and to start playing around with the resin. Slap on those gloves i forgot to mention you needed and lets get to it!

As mentioned, ill be using Smooth-Cast 326, a 2 part urethane resin, so lets dig a bit into the terminology. A 2 part resin has 2 components that you mix together to start a chemical reaction that ends with a block of plastic, with "urethane" being the type of plastic. Other kinds of plastic you can get from this process (and use in your casting) include epoxy and polyester.

That bit of terminology out of the way, time to talk numbers. With casting resins, theres 3 that are super-important to know. First is the ratio, that is to say how much of part A you need to mix with part B in order for everything to work properly. I mentioned it before but the resin im using can be mixed either 1:1 by volume, i.e 1 cup of A to 1 cup of B, or 115:100 by weight, 115 grams of A to 100 grams of B. Ill be measuring mine by weight, check your specific resin for the proper measuring method. Get this wrong and your resin wont cure properly.

The next 2 important numbers are both time. The first of this duo is pot life, also known as working time. This is the amount of time you have to introduce part A and B to each other, then get them mixed and poured into your mold. This amount of time can range from 90 seconds to 1 hour, and its important to know how long you have. The 326 im using has a pot life of 9 minutes, check your specific resin. The final important number is cure time, how long it takes for your resing to completely turn into a plastic after you mix it. This will let you know how long itll be until you have a finished product, and ive seen it range between 20 minutes and 3 days. Stuff im using is 1 hour, check yours to get the proper number.

Now that ive got all the terminology out of the way, time to tell you what to do, but be warned, the majority of the information will be in the pictures, this is just a summary. Here are the steps:

  1. Calculate out how much resin you need to fill your mold, and from there the amount of A and B you need to decant. I know my mold takes 80 grams of resin to fill, but i want to mix 90 grams, just to be sure i have enough. Applying my mix ratio, i need to decant 48 grams of A and 42 grams of B. Do the proper math for your mold size and resin ratio
  2. Add color, generally to part B but again, check your resins instructions. Mix color into B, do not add part A yet. Fillers go in at this time too. A word on fillers, theres a ton of things you can use, but test new fillers in small batches to make sure that they dont inhibit the resin curing. Also, heavier fillers will sink in thinner resins, plan accordingly. An additional note on dyes, dont add more than about 3% by weight of your resin, otherwise you might have some problems curing. Different colors of dyes can be combined to make more colors, but again be warned that the So-Strong dyes are extremely concentrated. Add more than a drop, total, and you can end up with a resin thats nearly black. Plan accordingly, plan to fail a batch or two while youre learning
  3. Vacuum degass (optional). Place the cups with the resin components into a vacuum chamber, apply vacuum until the bubbling from the resin stops
  4. Remove cups from vacuum, add A to B, mix thoroughly, scraping the sides and bottom. If you dont mix everthing well, your resin wont cure properly, if you mix too long itll solidify in the cup. Know your pot life, make sure you have enough time!

Again, check the pics for details, then move on to the next step!

Step 4: Pour One Out

Alrighty, time to get to pouring. This step is dead simple youre thinking, right? Just dump and go, after all!

Well, not quite. Theres a tiny bit of a method to is, least if you wanna minimize air trapped in your casting (you do). First, remember that honeycomb you stuck in the acetone a while back? Go take it out of the acetone and let it dry, but dont touch it! Wear gloves or use tweezers or something, the metal is clean and it needs to stay that way. Once the solvent has flashed off, gently place it in your mold. If you arent using the honeycomb, skip the last paragraph. Probably shouldve said that sooner...

Anyway, once your mold is ready, and assuming your resin is properly mixed, time to start pouring. The proper technique is to pour the resin in a stream at the lowest part of your mold, with an open face mold. Since we're casting a flat rectangle, the lowest point is anywhere. In this case, i like to pour in the dead center of the mold, at the same spot the entire time, and let the resin kinda flow itself out. This will let the resin seek out the little nooks and crannies on its own, forcing air out as it goes. If you just dump it everywhere all at once, air can get trapped. Best to let it flow out on its own, in my opinion.

Once your mold is filled, you have 2 options. You can either let it sit and cure, or you can transfer it into a pressure chamber to cure under, well, pressure. Curing under pressure is an additional step that requires some specialized tools, but results in massively better finished products. It does this by either compressing any air bubbles in the resin down to the point where theyre invisible to the naked eye, or by forcing the air to dissolve into the resin (think of CO2 in soda), depending on who you ask. How isnt really important as far as im concerned, just the results, so into the pressure pot it goes!

Stick it in the pot, bolt the lid down, and crank it up. Ive got my pot set to 60psi, ive found that to give me the best results. Generally, more pressure means fewer bubbles speak through, but be careful and pay attention to your pressure pots pressure rating! The only difference between a pressure pot and a bomb is how the pressure is released. Could be by you turning a valve and venting the air safely, could be exploding. On that happy note, pressurize your blanks, then walk away until the cure time for your resin passes. For my resin, thats 1-4 hours, depending on the thickness of the casting and ambient temperature.

Step 5: Wait

Your resin is curing, so hurry up and wait. Come back in a few hours, or hang around for a bit of learning

I mentioned in the last step that resin curing depends on the casting thickness and ambient temperature, this seems like a good time to elaborate on that. Resins in general cure via an exothermic reaction, that is to say that they take in a couple chemicals that react to each other, and that reaction produces a finished product and waste heat. Now, the speed that the reaction of the chemicals happens at increases based on the temperature of the chemicals, as they get hotter they react faster (light a building on fire and people run a lot faster). So, if the resin is already warmer, like if youre doing your casting work in a hot room, then the cure time will be on the lower end of the estimate. Thats lesson #1.

So, lesson #2. Remember how i said that curing is an exothermic reaction and that it puts off heat? Well, resin will heat itself as it cures, and hotter resin cures faster, so the resin will actually speed its cure time as it cures. The more resin you have curing in one spot, the more heat it puts off, the faster it all ends up curing. If you were to mix up a gallon of a really fast curing resin and just leave it in one big pot, it can actually boil itself! The higher the volume of the resin, the faster its going to cure, so a 1/16" sheet of resin will cure a lot slower than a 1/4" thick sheet. The thicker your casting, the closer to the low end of the time estimate for curing youll have to wait.

A final warning, remember how i said that resin can put out enough heat to boil itself? Yeah, thats why most resins have a maximum recommended casting thickness. Again, read the spec sheet for your resin to make sure its appropriate for what youre trying to do, cause if you to take a resin with a maximum casting thickness of 1/4" and cast a 2" thick layer, bad things can happen. Information is important, part of why i like Smooth-On; all their products have extremely detailed data sheets, and if i have any questions about applications for their products i can talk to their support staff to get them answered. I know i sound like a shill, but im honestly just an extremely satisfied customer. If youre interested in casting anything, or moldmaking, go check them out and look through the catalogue

Shouldve spent enough time reading this, the resins probably cured by now. If youre curing outside a pressure pot, poke your casting if you can. If you can leave a fingerprint, its not cured enough to demold. Wait some more. If youre curing under pressure, vent the pressure and poke it. If you leave a fingerprint, reapply the pressure and leave it longer. If you take the pressure off a half-cured casting, any air bubbles in the cast will re-expand and *%$ up your cast, not good

Step 6: Profit!

So, youve put in the effort, mixed and poured your scales, and now youve waited for ages. Are you done? Well, give your casting a flick, does it feel solid and not mushy? Then yeah, youre probably just about done, time to demold. If youre using a silicone mold, flex the sides to break the urethane free of them, then just pop your scales out, easy as pie. If youre using my recommended alternative of a mold box made from pieces of HDPE stuck together with hot glue, you should be able to break the box free of the mold by knocking the sides apart. If youre doing something else, may the gods help you because i sure cant

And thats it, youre done, you should now have a completed set of scales, ready to start attaching to a knife or whatever. The aluminium honeycomb is dead soft, it wont hurt standard woodworking tools, ditto for the resin. The resin itself you can sand, cut, drill, machine, whatever, even grind without too much trouble. You dont want to get it too hot while working it, its still plastic, but overall most castable resins are incredibly easy to work with. As far as longevity on a knife handle goes, well, unfortunately a urethane or epoxy resin handle probably wont hold up quite as well as something like G10, but its still a remarkably durable material, and well worth it for the looks.

Want a set of scales like this, but lack the materials or time to make your own? Want a silicone mold like the one im using? Check out my Etsy shop Project Epic Fail. I sell knives, resin casting and supplies, and a bunch of other random crap. Any questions on the project? Leave em in the comments and ill get them answered if i can! Thanks for following along!