I use a ton of epoxy as part of my work plus fixing all kinds of stuff at home, on cars, guns, knives and more. I’d like to take a few minutes share some lessons learned with you to bear in mind on your next project that involves epoxy:
Buy quality epoxy – not cheap junk. Epoxy is a generic term and a lot of the no-name blister pack retail stuff is crap. Go for brand names. If they list real specs about the formulation then it is probably legit.
I recommend industrial epoxies and not the consumer stuff. My hands down favorite epoxy is Brownell’s Acra Glas liquid. It is strong and resists breaking down from repeated impacts very well. It’s one down side is that it takes a long time to set up so it may not be your best bet if you need something to be fixed and back in service quickly.
Know your application and match the formula to your need – there is no magical formula that does everything. You may need a putty, a fast cure, a short pot life, higher heat resistance, improved impact resistance, shear strength, etc. Figure out what you need and then look for the epoxy that will work best for you. At any given time I probably have 3-4 different formulations on hand.
The longer it takes an epoxy to cure the stronger it is. All things being equal, an epoxy that cures in 24 hours will be stronger than one that claims to do so in 5, 10 or 30 minutes.
Read the package – setting up vs. curing and reaching full strength are two very different things.
If you want to get epoxy to flow into wood or difficult areas, heat it up. The liquid thins as it warms up but note this will also speed up how fast it sets up and cures.
As epoxy gets colder, it takes longer and longer to cure. If you are working outside, use a space heater, flood light or other heat source to keep the epoxy and the work piece area being repaired at least 70F. I shoot for 80-90F.
Epoxy can get really thick as it gets cold and not want to come out of the containers. Either keep it inside where it is warm or at least warm it up before you use it,
Epoxy resin can sugar with age just like honey. What I mean is that will develop a solid mass in the resin bottle – it’s not really sugar! If you heat up a container of water, take the resin container’s lid off and then set it the container in the water, the resin will warm up and the solid will dissolve back into liquid. I buy 28oz or larger bottles of Acra-Glas that I don’t always use right away so when it sugars, I do this.
As mentioned above, I buy my epoxy in bulk. Acra-Glas can be measured by volume and it has a ratio of 1 hardener to 4 resin. The way I deal with this is very simple – I use 10cc syringes without needles. I have on syringe in a cup that I use for hardener and one syringe stored in a cup that I use for hardener. The reason I do this is that the two parts do not react to the air very fast. I may be able to use one syringe for a several weeks/months before it stops working so I set the syringe in its dedicated cup when done to be used again. I do not use fresh syringes every time. A 100 count syringe pack will last me at least a year.
You can definitely color epoxy. You can buy purpose-made dyes such as So-Strong or add in powdered tempra paint.
You can add fillers for strength or looks. When filling gaps, I mix 1/32″ milled glass fibers with the epoxy. The ratio depends on the epoxy you are using, how thick/pasty you want the result to be or how much you want it to still flow into place.
To get rid of bubbles you either need to draw a vacuum, apply pressure or at least use a heat gun to thin the epoxy once it is applied and this allows the trapped air to escape.
When I am gluing big objects together, such as wood panels, forms, or other construction I will use a cartridge based epoxy. My favorite is Hysol E-20HP. To use a cartridge, you need the dispensing gun and also the correct mixing tip. This allows you to squeeze the trigger and properly mixed epoxy comes out of the tip. When you are done, you just let the tip harden in place sealing the epoxy. When you are ready to use the gun again, you simply remove the plugged tip with a new one. This allows for you to deploy a bead of epoxy very quickly but the con is that you throw away a tip every time you stop. You also can’t color the epoxy first but it is fast and convenient on larger projects.
The surface must be clean for epoxy to work best. Remove dust, dirt, oil, etc.
A rough surface is always better than a smooth surface. I always recommend sanding, brushing or blasting a surface to improve adhesion. Not only do you increase the surface area but you also are creating a texture where the epoxy can get under the base material in thousands of tiny places to really grab hold.
Wear disposable gloves to avoid making a mess. I buy boxes of the Harbor Freight 5 mil nitrile gloves when they go on sale for $5.99/box of 100. They really are a good value for a medium-light duty disposable glove.
If you need to clamp parts together, wrap the assemble with wax paper to avoid gluing your clamps to the work piece – yeah, I’ve done that.
Whenever possible, I prefer to clamp work together to get this best bond.
Check, double-check and come back in again later and check your work again to make sure nothing has shifted.
I hope these tips help you with your next project.
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I am a huge fan of Nepalese khkuris including ones from Himalayan Imports and GK&Co (Deepak Sunar). I do like customizing them also and have made handles many ways for both the full-tang and rat tail tang blades. What I am going to show below is a rat tail tang and you’ll notice the curve the tang has. This is the traditional tang and is very strong. Westerners have a mistaken belief that full-tang is better.
The Nepalese bladesmiths, known as “kamis”, have evolved their design over centuries based on real world experience. Their rat tail tang is very strong, allows for the traditional handle to be changed relatively easily and since the handle can flex somewhat on the tang, some of the shock is absorbed there vs. by the wielder’s hand. When the British arrived they mandated a full tang on their Army models based on their experience and beliefs. In short, when you are looking at khukuris, do not discount rat tails as weak because they are not.
The first step I do is to blast my slabs of Micarta to prepare them for maximum adhesion. I am a zealot on cleaning too before gluing. Do not attempt to glue the shiny micarta to the blade or it will knock right off with the first shock. Basically we are going to make a handle by sandwiching a piece in the middle that has the tang outline cut out between two outer slabs. These are black canvas micarta slabs that have already been blasted – that is why they are dull.
The thickness of the middle slab needs to be the same thickness as the thickest part of the tang to keep things simple.
Next, I lay the middle slab under the tang and trace its outline.
I was doing two blades at once. See the one above sitting in the cut out notch and the one below I have just traced the outline with a Sharpie marker. Please note I have not taped the edge of the khukuri’s blade yet. I would recommend you do that at some point to protect yourself.
This is slightly out of sequence but see the two round drill holes at the end of the tang? I did them before sawing to make turning around at the end easier. The numbers marked on the micarta correspond with which of the two blades I was working with.
I would then use a jig saw or band saw to cut the section out where the handle went. Note, I more often use a band saw these days and you can do whatever works for you.
[Update 7/19/18: Don’t buy the above Skilsaw. It’s not strong enough and I wound up giving it to a friend. Either get a Dewalt scroll saw or use a band saw]
See how the tang fits in? It does not need to be perfect as this will all be filled with structural epoxy.
I do not have a photo, but I would abrasive blast the tang until it was clean shiny steel. I would wear nitrile rubber gloves and hose everything (tang and slabs) down with brake cleaner to make sure no oils from my skin contaminated the work pieces. Note, I often drive a 1/8″ brass cross-pin in through the thick part of the tang to lock everything in place just in case and also use a piece of thick wall 3/8″ brass tube at the rear to make a lanyard hole. I did not do these things on this particular model and they are features to consider. For people new to this, I would recommend the brass cross pin. I always do this now even though I have never had a handle fail but I evolved this method and learned over the course of a number of years.
Next, take the outer slabs and round the outside edges over. What you want to do is to create the taper you want before you glue the handle on. It is hard to sand up front on the handle once it is glued together. I would take the three pieces, clamp them together and then work on the belt sander until I got the shape I wanted on the front leading edge. This is all we want to shape at this point. I always preferred to do the majority of my shaping once the handle was epoxied onto the blade.
For gluing the handle, I will only recommend Brownell’s AcraGlas liquid. It is a very strong, durable, and shock resistant epoxy. Absolutely do not use a cheap epoxy as it will likely break down and crumble (“sugar”) over time with repeated heavy blows. Always bear in mind that the big khukuris are choppers and heavy. What you do needs to hold up under extreme use compared to many knife handles that see very light relative use. To be safe, I would recommend you always abrasive blast the steel and the micarta before applying the epoxy – don’t try and just get by with sanding or otherwise scuffing the surface. By blasting you are almost doubling the surface area for the epoxy to adhere to and the irregular surface creates countless shapes where the epoxy can get under “ridges” in the micarta and the steel to really securely hold the parts together.
Follow the AcraGlas mixing instructions to the letter. I add in a bit of milled 1/32″ glass fiber to increase the strength in the filled areas. The ratio for AcraGlas liquid is 1 part hardener to four parts resin and I’d add about 1 part of the glass fiber. It is a bit of a balancing act because you do not want to make the resulting epoxy too thick. You need it to run in, fill voids and seep into the micarta as much as possible. [To get the most out of your epoxy, please click here to read a post I did a while back detailing my lessons learned over the years.]
Next, cut a piece of wax paper to wrap the handle. You want to apply a ton of epoxy, clamp the heck out of it and let it sit and cure for 24 hours. When you remove the wax paper, if there are any imperfections you need to fix by adding more glue, first blast the surface, clean it and then glue it. Do not just put epoxy on top of epoxy without preparing the surface first.
Next, if you haven’t done so yet, tape your blade’s cutting edge to make sure you don’t get sliced when sanding the handle. When working with a belt sander it can grab hold of the work and surprise you – you don’t want a sharp edge to be flying around!!
I do a lot of my handle work on a Rigid oscillating belt edge sander from Home Depot with 40-80 grit sand paper. Hook your shop vac up to suck up the dust and be sure to wear both a good dust mask (such as a N99 rated mask/respirator) and eye protection. The dust goes everywhere so be sure to have the vacuum hooked up and stop periodically to clean up and also to inspect your work.
In terms of shaping the handle, I will relay a piece of funny sounding advice – remove all the material that isn’t part of the handle. Really useful, right? When the fellow told me this years ago his point was that making a handle is applied art. You are sculpting a handle by removing material and working towards a shape you have thought out. I would remove a bit and test the feel, remove a bit and test the feel over and over.
I have experimented with many shapes over the years and it is really up to you. I would stick with coarse sanding to keep the handle from being slippery and did both one handed and hand-and-a-half models. In all cases, I wanted to user to have control while chopping / hacking with the blade. One real strong recommendation: ALWAYS build a finger stop or hand stop into your design. You do not want a hand to slide forward onto the blade. I always built the stop into the handle but you could certainly make your own metal cross guard or do something else — just be sure to protect the user’s hands.
The below blade is acid etched with a combination of apple cider vinegar and phosphoric acid and then everything, including the handle, had boiled linseed oil (BLO) applied to it. [Click here for my post about acid etching blades.]
This is a handle from a big HI WWII model blade. Note the lanyard hole at the end. I would drill the hole both for a friction fit and I would cut the tube longer than needed, blast it, clean it and then apply epoxy liberally before inserting it into the blade. I would then sand it down to size as part of the final shaping of the handle.
This is black paper micarta that comes out a beautiful obsidian black. It is on a long, elegant 24″-ish Sirupati. Notice the oversized pommel to serve as a hand stop and the finger groove up front for indexing and grip. This is a hand-and-half design meaning a person could grab hold with their second hand if they really wanted to.
The cool thing with the handles is that you have a ton of materials and options to consider to make a very unique functional piece. I hope this blog post gives you some ideas.
If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at in**@ro*********.com. Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.
Folks, I work a lot with epoxy and reply on it as a structural adhesive to both fill gaps and bond parts together. I’ve done everything from fixing car parts, wood furniture, tools, rifle bedding, scope mount bedding, custom knife handles and much more with epoxy. It is incredibly versatile but you need to do some planning to really get what you want out of it predictably.
In case you didn’t know it, “epoxy” is a general term for a wide range of cured polyepoxide resins glues with different physical characteristics such as how long they cure, strength, temperature resistance and so forth (click here if you want to learn more about the chemistry). There are a ton of options out there as quality manufacturers experiment with different resin and hardener formulations. In short, not all epoxies are the same and for people concerned with the quality of what they are building, they need to think things through. For quite some time I’ve wanted to write down a series of tips for folks to get strong reliable results so here they are:
Buy a quality brand epoxy to begin with
What I have found over the years is that not all epoxies are created equal so spend the money and buy quality epoxy. There can be a huge difference in how well the epoxy will last over time and/or how strong it really is. Do not buy the bargain basement junk. In general, if the maker lists all the physical properties then it is a well thought out and executed formula. I have three epoxies that I use the most in order are Brownell’s AcraGlas liquid (not the gel), Locite E-120HP, JB KwikWeld and ITW Devcon Plastic Steel. Once in a while if I need a fast cure epoxy, I will get a retail blister pack of some five minute epoxy and I’ll explain more in a moment.
Strongly consider what your application is
Epoxy comes in many formulations. They can vary the chemistry of the resin, the hardener and the filler to behave differently. Consider the following example characteristics:
Liquid, Gel/Paste or Putty/Bar — The liquid can seep into pores and fibers plus it can be spread but it can run into places you do not want. Gels and pastes tend to stay put better but do not seep in as well. The really thick puttys and bars are great for filling space or creating an impromptu clamp or to seal a hole but they definite don’t sink in much.
Temperature – you need to think both about the temperature when you are mixing and applying the epoxy as some will not set up at all if too cold. You also need to think about the heat when in operation because many epoxies soften and lose their bond the hotter they get. For example, you may apply epoxy to an exhaust manifold but it will blow off when it gets hot.
Pot life – this is how long you can still apply it before it starts to thicken. Some folks will refer to this as working time. You need to mix the two parts together, apply the epoxy, position and clamp the work before you run out of time. Keep this in mind.
Cure time – this is how long until the epoxy reaches full strength
Color – you can get epoxies in different colors
Ratio / mixing – some are by volume or by weight. The easy consumer stuff is usually 1:1 by volume but when you get into the more sophisticated epoxies the volumes vary or a digital scale is needed
Heat resistance – some epoxies resist heat better than others before they soften and “let go”
Shock resistance – some formulations hold up better than others before they start the break apart and “sugar”. Sugaring refers to the powdery look epoxy gets as it breaks apart. Brownell’s AcraGlas, Loctite E-120HP, JB KwikWeld and ITW Devcon Plastic Steel have all held up very well for me under shocks. My go-to epoxy for most work is Acra-Glas liquid because it holds up so very well.
Others – there are other factors that may matter to you but the important thing is to think through your application
Go with as long of a curing time as you can for maximum strength
What many people do not know is that the faster an epoxy cures, the weaker it is. Conversely, the longer the formulation takes to cure, the stronger it is. All things being equal, a 24 hour curing epoxy will be stronger than 90-second, 5-minute, 30-minute and so forth epoxies. Now there is a time and a place where speed is needed and also situations where strength is paramount. When I make khukuri hands and other things where strength is critical, I always use a 24 hour epoxy.
Use the Proper Ratios
Be sure to carefully follow the mixing ratios. For volume ratio work, I use 10cc or larger syringes without the needles on them to meter liquid resin and hardener. For example, I like AcraGlas and it is 4 parts resin to 1 part hardener. I keep two syringes separated that I re-use over and over. With the syringe in the holding cup labeled “resin”, I use it to draw 4 cubic centimeters (CCs) of resin out and squirt it into a mixing cup. With the hardener syringe, I meter out 1 CC of hardener into the cup. Now you can vary that. If you need a smaller about, meter out 2 CC of resin and 1/2CC of hardener. The syringes really help. If you are doing larger volumes then either use bigger syringes or disposable cups that have measurements printed on the side. Also note how I pour from the bulk container into the smaller intermediary containers that are easy to work with plus I avoid contamination, dropping a big bottle, etc.
The Loctite E-120HP comes in a specialized dispenser tube that uses a gun and tip to do all the mixing. It’s cool as can be for volume work where additional coloring or fillers are not needed.
For the Devcon Plastic Steel, I use my digital scale.
Here’s one thing not to do: Some guys have heard that if they add more hardener it will cure faster. This may be true but the resulting cured epoxy will be weaker. Do not deviate from the manufacturer’s recommendations if you want the physical properties they report.
Mix thoroughly
Folks, I can’t stress this enough. Mix the heck out of the two parts and combine them thoroughly. If you are doing larger volumes, consider doing what is known as a double pour. Pour the two parts into a first container, mix them thoroughly and then pour the combination into the middle of a second container and mix. What a double pour does is avoid having unmixed materials that have stuck to the walls of the container come out when you are applying the epoxy. Keep your pot life / working time in mind.
Most of the time I am using a generic 5oz plastic cup and plastic knife to do the mixing. I buy them by the hundreds for Ronin’s Grips and they are cheap regardless. Do not use styrofoam.
Prepare the surface
Whatever you want to bond epoxy to had better be clean and free of oils, greases, waxes, release agents and so forth. Second, the more abraded the surface the better. If you abrasive blast a surface not only can you double the surface area being bonded together but the irregular surface creates many opportunities for the epoxy to get “under” material to create a better grip. If you can’t blast then at least sand the surface with 80-100 grit sand paper.
So here are two rules to bear in mind when it comes to the surface:
Clean, clean, clean and wear gloves to not contaminate the surface with oil from your skin
Shiny is bad. A polished smooth surface will not give you anywhere near the bonding strength that a blasted or abraded surface will. I blast everything that I can – metals, micarta, plastic and even wood. It makes a world of difference – seriously.
The following is a bakelite handle from an electric griddle of my parents’. The unit works great and has sentimental value so I cleaned it, blasted it, cut a quick cross hatch pattern to give even more grip and then cleaned it again. It set up like a rock and we used it all Memorial Day morning to cook hundreds and hundreds of pancakes with no problem.\
Heating Epoxy
Heat can help you two ways. First, by warming epoxy it tends to flow better. If you need to to soak into wood or other surfaces, consider using a heat gun to blow/chase the epoxy into the wood. Do not burn the epoxy – just warm it up. Second, in general, warming epoxy up tends to make it cure faster. Now there are limits and you need to either experiment or talk to the vendor before doing anything too radical. I will often use a halogen light or other heat source to warm the surface up to 80-100F. In chemistry, there is a formula known as the Arrhenius Equation that notes that for each additional 10 degrees Celsius added, a reaction rate doubles (click here for more info on the equation). My experience is that you want the heat to penetrate and warm all of the epoxy and not just the surface and you also do not want to burn the epoxy. In general, I do not exceed 100F but that is just me. I found something that works good enough and have just stayed there.
Also pay attention to the minimum temperature requirements for curing. Some epoxies will not do anything at all at freezing. Some take forever to cure at 50F. It just depends. When in doubt, use a lamp or something to gently heat the part.
Coloring Epoxy
What many folks do not know is that you can actually color epoxy. I have found two approaches that work. First, use powdered tempera paint. You can stir in a bit of black powder to get black epoxy. Now I did this starting out and have since moved to using epoxy dyes so I am added less powder to the mix because I want to save the volume for glass fillers which we will talk about next.
Fillers
You can modify the physical strength of epoxy by adding a substrate or fillers. For example, fiberglass is matted glass fiber that bonded together with epoxy made for that purpose. Folks working with carbon fibers are using epoxy for bonding that together. I add 1/32″ milled glass fibers to my epoxies to get more strength. If I want more of a paste, I add more glass fiber and if I want it to be more of a liquid, I use less. The exact volume of glass fiber depends on what you are trying to do. Some vendors will give you recommendations and others will not.
Clamping / Work holding
In general, you want to apply the epoxy and then clamp everything together really well and then let it sit. You may choose to use traditional clamps, vacuum, etc. Bear in mind two things:
1. Be careful that you secure the material and that it can’t shift while curing. I can’t tell you how many times I have checked stuff and found out it moved and had to change my approach. Figure this out before you apply the glue in case you need to make something, change your approach, etc. Check it regularly to make sure it hasn’t shifted regardless. Every time I think something can’t move – it does.
2. The epoxy will run out of what you are working on. Decide how you are going to deal with it. Wax paper can protect your tools and table. You can scrape the epoxy off after it has partially cured. You can wipe things down with acetone when partially cured. Just think it through otherwise you are going to glue stuff together really well that you do not want bonded – trust me. It is a real headache so plan for seepage/dripping and how you will deal with it.
Patience
This is something I have gotten better at over the years – wait the recommended amount of time. If they say 24 hours then wait 24 hours. If you have questions about using the part sooner then ask the manufacturer. For example, you might be able to assemble something after 10 hours but not actually put it under strain for 24 hours. Factor in the temperature. The colder it is then the longer it will take. Remember what I said about the heat from lamps above.
Safety
Yeah, I had to add this. Follow all guidance from the vendors. The resins aren’t too bad but some of the hardeners are nasty. Wear rubber gloves, use eye protection, work in a well ventilated area and wear a real good dust mask when sanding. I use N99 masks now for everything.
I hope you found this general epoxy guidance helpful!
If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at in**@ro*********.com. Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.
