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Knife Making Adhesives Information

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We sold Acraglas for several years and have never had a problem. It is an excellent epoxy that has worked well for decades.

We now recommend West System G/flex epoxy to knifemakers.

West System has been in business for decades. They are famous for their marine grade epoxies. In June 2007 they introduced G/flex. It is a tough two part epoxy that is specifically designed to bond metals, plastics, fiberglass and difficult to bond woods. It can even bond materials underwater. This epoxy withstands expansion, contraction, shock, vibration and can repeatedly handle temperatures up to 200°F. At this temperature it will be more flexible and less resistant to heavy loads, but it returns to full strength as it cools to room temperature.

If G/flex is so good why does West System still sell their other epoxies? The following is a quote from West System:

With all the attributes and improved properties of G/flex, you might be asking whether you still need West System 105 Resin-based epoxy? The answer is that G/flex can't do some things as well as 105 epoxy. Examples include barrier coating and fiber glassing with heavier fabrics. Although G/flex flows nicely when spread out on a surface, it is less than ideal as a coating because of its higher viscosity. West System 105 epoxy is better for wetting out fiberglass cloth, especially for clear finish projects like wood strip canoes and kayaks. West System 105 epoxy is also a better base for creating fairing putties because its lower viscosity allows you to add more low-density filler to it. This translates into a fairing putty that sands and carves more easily because of the higher filler loading.

Barrier coating, wetting fiberglass cloth and easily sanded fairing putties have nothing to do with knifemaking. G/flex is ideally suited to knifemakers.

The pot life of G/flex is 45 minutes. Pot life is the amount of time before the epoxy gets too thick to pour into a tang hole. The working time is 75 minutes. Working time is how long you have before the epoxy in the mixing container is unusable. Both times are longer than Acraglas. The initial cure time is 3-4 hours. The workable cure time is 7-10 hours and a full cure in 24 hours. We recommend waiting 24 hours. All times are based on a temperature of 70°F.

West system makes thicker formulation of G/flex called 655. The thicker G/flex is too thick to use for hidden tangs. It comes in toothpaste style tubes. Some of the bond values for 655 are higher than 650. We will sell 655 if we get enough requests.

The most accurate way to dispense resin and hardener is by weight. G/flex resin and hardener do not weigh the same by volume. If you are going to dispense the resin and hardener by weight, make sure you use the correct weight ratio.

Mix Ratio By Weight:
1.2 parts resin
1.0 part hardener

Mix Ratio By Volume:
1 part hardener
1 part resin

The table below shows examples of testing done by West System. We limited the data to show G/flex 650 and the 105/205 resin/hardener results.

 Test Material   Resin   Hardener   Surface Preparation & Conditions   Tensile
 Aluminum 2024 T3   G/flex 650   G/flex 650   Sanded With 80-Grit, 860 Etch / Dry Surface   2,731 
 Aluminum 2024 T3   G/flex 650   G/flex 650   Grit Blast, 860 Etch / Dry Surface   1,856 
 Bronze    G/flex 650   G/flex 650   Sanded With Scotch Brite™ Pad   2,962 
 Bronze    G/flex 650   G/flex 650   Sanded With 80-Grit   2,782 
 Bronze    105   205   Acid Wash   2,196 
 Bronze    105   205   Sanded With Scotch Brite™ Pad   1,478 
 Bronze    105   205   Sanded With 80-Grit   1,305 
 Copper    G/flex 650   G/flex 650   Sanded With 80-Grit   2,334 
 G10    G/flex 650   G/flex 650   Sanded With 80-Grit / Dry Surface   3,459 
 G10    105   205   Sanded With Scotch Brite™ Pad & Water   1,718 
 G10    105   205   Sanded With 80-Grit   1,560 
 G10    105   205   Sanded With Scotch Brite™ Pad & Until Dull & Washed   1,535 
 G10    105   205   Sanded With Scotch Brite™ Pad & Water   1,382 
 Steel - Galvanized   G/flex 650   G/flex 650   Wet Sanded With 100-Grit   2,562 
 Steel - 1018   G/flex 650   G/flex 650   Sanded With 80-Grit / Dry Surface   1,772 
 Wood - Ipe   G/flex 650   G/flex 650   Sanded With 60-Grit    2,134 
 Wood - White Oak   G/flex 650   G/flex 650   Sanded With 80-Grit   1,935 
 Wood - Purpleheart   G/flex 650   G/flex 650   Sanded With 60-Grit Parallel To Grain   1,731 
 Wood - Teak   G/flex 650   G/flex 650   Sanded With 80-Grit Parallel To Grain   1,413 

Tips, Do's & Don'ts

Mixing Containers:
We recommend mixing epoxy in plastic cups, not wax paper cups. After epoxy is mixed it will generate heat. If you have enough epoxy the wax will melt off the inside of the cup and contaminate the epoxy.

During an Acraglas test we used the mixing cup that came in the kit. After about ten minutes the wax melted off the outside of the cup.

The best way to mix epoxy is to dispense measured or weighed amounts of resin and hardener into a small cup. Thoroughly mix the epoxy for a minute. Dump the epoxy into another cup. Scrape the sides and bottom until the first mixing cup is empty. Thoroughly mix the epoxy again in the second cup. Using two cups minimizes the chances of have unmixed pockets of resin or hardener in the bottom of the cut. Don't try and save a few pennies by using one cup. The cost and time of removing/destroying materials is not worth it.


The cure rate of epoxy is affected by temperature. The times listed by almost all epoxy are based on 70°F. The rule of thumb is 20°F will cut in half or double the cure time. If it is a hot day and your epoxy is curing too fast, cool it down. If you want to reduce the cure time, heat it up.


Resin & Hardener Storage:
Heat and ultraviolet rays will shorten the shelf life of resin and hardener. We recommend storing in a refrigerator. All of the adhesives we sell are stored in a refrigerator. If you don't have a separate shop refrigerator, buy one. Don't store knifemaking chemicals with your food.


Resin to Hardener Ratio:
Don't try to outsmart the chemical engineers who designed the epoxy. Don't think, "a little extra hardener will make the epoxy harder", or "a little less hardener will make the epoxy more flexible". Altering the specified resin to hardener ratio will result in bad epoxy.

The most accurate way to dispense resin and hardener is by weight. Most resin and hardener do not weigh the same by volume. If you are going to dispense the by weight, make sure you use the correct weight ratio.

If you are too lazy to correctly dispense the proper ratio by weight or volume please let me know so I don't buy a knife from you.


Thinning Epoxy with Solvents:
Adding solvent is a quick, simple and bad method of thinning epoxy. The strength and moisture resistance of the cured epoxy are drastically affected. Adding additional 5% lacquer thinner makes about a 60% reduction in viscosity but reduces the epoxy's compressive strength by 35%. Adding more than 5% solvent results in an excessively flexible cured material.

Adding a solvent may cause shrinkage of the cured epoxy. Applying thinned epoxy is likely to trap some of the solvent. In thick applications the epoxy cures very quickly and not all of the solvent has time to evaporate before the epoxy hardens. Over time, the solvent works its way out and the cured epoxy shrinks and in many instances cracks. Shrinkage can continue to be a problem until all the trapped solvent works its way out of the cured epoxy.

Bottom line, if you don't mind your epoxy being weakened, the bond being compromised and shrinkage, use a solvent to thin your epoxy.


Minimum Epoxy Thickness:
If you squeeze out all the epoxy will the bond hold? Of course not!

When using G/flex, the minimum thickness for a maximum strength bond is .008". All high quality epoxies have similar minimum requirements. If you hollow the back of your scales, then squeeze out the epoxy on the edges, don't be surprised if the edges separate or curl back. Epoxy cannot do its job of sticking things together if it is too thin or nonexistent.

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