What is CA glue and how does it work?

[Keithbrad80]

I was bored this morning and read another post of someone having trouble with CA glue stain and what they should do now. I figured it may be helpful to some to create a post with all the information (hopefully) that you may need on CA glue, followed by several tests of different species of wood and their reaction to CA glue and if there is anything that can be done to hide it. Thanks in advance for reading sorry about the length!

 

Many experienced modelers will advise against the use of CA glue, also known as super glue. They often give the reason that an undesirable residue is left behind that is impossible to hide or remove, and this lesson they share with others is usually derived from personal experience. Imagine for a moment (or think back) that you recently bought your first wooden ship model, you spent weeks fairing the hull and preparing for planking, you then spend weeks or months planking the hull only to discover a pearly luster covers the sanded planks of your hull. A number of questions usually pop into the modelers head; why did this happen? Can I fix it? How do I prevent this from happening again? It seems that I see this on an almost daily basis, someone who has built a model with CA glue and ended with less than satisfying results, and hopefully this collection of information on the subject can answers any questions you may have about the adhesive substance. 

 

A quick note: I am not a chemist; I am just a modeler with some free time who decided to look closer at CA glue and its applications. All of this information is available to you online, I just complied it here and added my input. Enjoy!

 

We should start by defining what a glue is, according to Merriam-Webster, a glue is any solution that binds something together. Within a standard glue is a cocktail of chemicals that react together with water to harden, or cure to create a strong bond. This bond is what holds your material together, I like to think of a PB&J sandwich, if you make the sandwich and pick up just the top slice of bread, the entire sandwich comes off the plate because the peanut butter and jelly hold the top slice of bread to the bottom. This is known as mechanical bonding, and while there are several types of bonding, we will only discuss mechanical and chemical bonding. 

 

Mechanical bonding is a bond made by an adhesive that does not go through a chemical change. Mechanical bonding is typically the type of bonding we are all familiar with, a good example is PVA wood glue. But mechanical bonding also refers to any method of physically bonding two things together, this means that anything from staples and nails, to glues and epoxy can be considered forms of mechanical bonding. Water is the binding agent and base within PVA wood glue, and once applied to a piece of wood allows for the glue to seep into the pores of that wood and solidify, when two pieces of wood are clamped together, the glue forms “columns” of glue within the pores of the wood. I like to think of this as a million microscopic screws holding the wood together. Because PVA wood glue is water based, it can generally be removed before curing by wiping it away with a damp paper towel, and if you waited until after it cures, it can be cut off the model or sanded away. Notice that PVA wood glue changes chemical states, not chemical composition, which is what makes mechanical bonding different than chemical bonding. 

 

Chemical bonding and mechanical bonding have some similarities, but the major difference is the change in chemical composition when applied to a surface. CA glue is the industrial name for a family of adhesives called Cyanoacrylate, these glues are not water based like PVA wood, glue but instead have an acrylic base similar to the paint. The glue we use for scale modeling is called ethyl 2-cyanoacrylate. This essentially means that when CA cures its, creates a sort of plastic bond between the two pieces, changing its chemical formula and chemical state at the same time. Earlier I mentioned both types of glues require water to cure, but we have already established that CA is not water based, so where does the water come from? 

 

When a drop of CA glue is released from the bottle it instantly starts reacting with the air around it, creating a rind of sorts on the outside of that droplet of CA glue. The water in the atmosphere reacts with the CA glue starting a reaction that creates long, super strong chemical chains that are difficult to break once cured. The chemist who developed this glue realized the cure time and the surface area of the exposed glue are directly proportional, meaning a thinner layer of glue equals a shorter dry time, duh! As a base, CA is incredibly thin stuff, at 20 degrees C, CA glue has a viscosity of 2 CPS (centipoise) compared to water at 1 CPS at the same temp and cooking oil at 84 CPS. When you apply CA to wood, it instantly penetrates those pores and at the same time reacts with the moisture of the atmosphere and the wood, instantly curing. This is the cause for the notorious CA glue “stain”. 

 

This next idea is a simple one but one that not many may realize, wood is a porous material, which means it is not a homogenous solid, and you only have so much space. Sometimes it helps me to think of this idea as a hotel, you only have so much vacancy before the building is filled to capacity and if someone is staying in a room, you can’t have someone else stay in that room at the same time. It’s a similar idea with wood, if you fill the pores with CA you can’t refill those pores with a stain or some other kind of finish. Once you put CA on a wooden surface, it becomes very difficult to remove because as you sand the surface, you just unveil more and more CA stain. CA glue is basically plastic, so when you apply it to wood you have to keep in mind that certain finishes will no longer be very effective on that surface. As a rule of thumb, if you know something won’t stick on a plastic model, I don’t use it on CA, for instance wood stains. I have seen time and time again, people post pictures of their seasick green deck asking where they went wrong after staining, and the answer is generally CA glue. This is because wood stains are usually oil based, and oil-based stains want to fill the pores that the CA has already filled, so it just sits on the surface, waiting to be wiped off. So now you see the problem with CA glue, it fills the pores and prevents stains and other finishes from attaching to the surface or filling the pores of the material. 

 

Before I talk about the positives in my mind of CA glue, we should talk about the physical hazards of CA glue. The obvious is the getting glue on your fingers, while annoying it’s not going to kill you if you get some on your fingers. When CA glue reacts with water, it produces two biproducts: heat, and a vaporized form of CA glue. Heat is released during the anionic polymerization process, and the heat is enough to vaporize small amounts of the glue, so when you use CA and see a small plume of smoke come off, that is CA that has reached such a high temp that it turns to gas. It should go without saying that you probably shouldn’t breathe these vapors in. 

 

Personally, I don’t think CA glue is that bad of a product, I used it to plank the entire hull of my 1:96 Flying Fish and had no problems because I painted the outside. I use generally use it when the piece won’t be seen or will be painted, because it is very fast drying and very thin, so I can hold my two pieces of wood together and apply to the glue to the joint, knowing that it will fill that joint. In reality the best modelers will incorporate all kinds of glue that will best fit the project, but next time you go to use CA, make sure you think of the entire project and ask if that is the best glue to use for that application. 

 

As a modeler yourself you may be asking, who cares? Why did I spend 10 minutes to read this, and what should I do now? Well, the next part of this post is a test that I am going to develop to test CA glue. Over the next few days, I am going to test several common types of wood and their reaction to CA glue and if there is a product that will do a good job of concealing CA glue stain. Thanks again everyone. 

 

Bradley 

[ccoyle]

Another CA characteristic that some are unfamiliar with is that the bonds it forms have a low shear strength, which means that they don't resist impact well. When CA is used to bond materials that aren't particularly porous, such as styrene or metal, a jolt to the joined pieces will often knock them loose.

[Bob Cleek]

CA adhesive is the Devil's spittle! It's hot and sticky, and there's always a high price to pay for using it in the end! 

 

 

Edited February 7, 2021 by Bob Cleek

[Keithbrad80]

57 minutes ago, ccoyle said:

Another CA characteristic that some are unfamiliar with is that the bonds it forms have a low shear strength, which means that they don't resist impact well. When CA is used to bond materials that aren't particularly porous, such as styrene or metal, a jolt to the joined pieces will often knock them loose.

This was something I intended to mention but forgot, thanks for adding that! 
 

for any wondering what exactly shear strength is, imagine you place your hand on top of a deck of cards and push forward. The bottom card sitting on the table won’t move but the cards on top slide forward, this diagonally distortion of the deck of cards is called shear strength. It becomes very important when talking about vertical structures and their ability to support objects that are not directly on top them, so to the side. Like Chris said, one little bump and it’s coming loose. This is an excellent illustration that shows shear force a little better. 
 

Bradley

[James H]

I use CA gel to do second planking and never had any issue whatsoever. Just use it sparingly and don't get clumsy with it.

 

For some, it's almost like they don't like using a 'new fangled glue' and want to stick to the old stuff. Fair play, but there can be elements of snobbishness from those quarters too. Many other glues also create a chemical bond, so what's the problem? Should I boil down animal bones to make my own glue and use that instead?

 

In the end, use whatever works for you. 

 

By the way, nice first post on CA. An excellent read.

[Keithbrad80]

21 minutes ago, James H said:

By the way, nice first post on CA. An excellent read.

Thank you! Like you mentioned, use the glue that works best for you!

Regardless of everyone’s individual thoughts on CA, I hope this thread provides some clarification on the substance. 
 

Bradley

[Jaager]

From a practical perspective, should not the force arrows on normal stress (sigma) be at 180 degrees?  What I would call prise resistance (because I have not seen the technical data before now.)

To stack the deck against CA a bit more, most of the stress that wood to wood bonds encounter on a ship model tend to be sheer.

 

1 hour ago, James H said:

but there can be elements of snobbishness from those quarters too.

When the bias and any criticism is arbitrary or from a traditionalist position,  snobbery and elitism is a valid accusation.

For wooden ship models, that would apply if the elitist preference was hot pot hide glue.

When the suggestion to avoid CA is based on demonstrated, and unnecessary failures inherent with the material, ( often experienced first hand) ,  it is more of a flashing warning light that is apparently unsuccessful in resisting the power of modern product advertising, and illusory convenience factors.

[Roger Pellett]

I recently posted an experience that I had with CA that resulted in a trip to the local emergency room.  It’s in the Shore Leave “What did you do today thread.”  I agree with Bob.  It’s the Devil’s Spittle.”

Edited February 8, 2021 by Roger Pellett

[turangi]

Great post! Another thing to remember is that CA is available in different formulations and not all are super thin. The thicker formulations include an additive (rubber?) to create a different characteristic and possible help with sheer strength if that is a consideration. I have recently used a gel formula to do deck planking and it is easy to apply a small amount that will spread out as pressure is applied to the plank without excessive squeeze out and is easy to control. When planking the hull If I encountered a small gap between planks I applied medium viscosity in the gap, wiped away the excess, and immediately sanded the area and it filled the gap wonderfully. This is to be a painted hull so I had no concern with stain issues. I had occasion to remove an already installed deck plank and was impressed with the holding power, wood was left behind, perhaps not an desirable thing in some situations but easy to remedy in mine. 

 

I prefer to use wood glue if possible if possible but often CA obviates the need for clamping and the quick set time is a blessing.  

Edited February 8, 2021 by turangi

[Keithbrad80]

19 minutes ago, turangi said:

Great post! Another thing to remember is that CA is available in different formulations and not all are super thin. The thicker formulations include an additive (rubber?) to create a different characteristic and possible help with sheer strength it that is a consideration. I have recently used a gel formula to do deck planking and it is easy to apply a small amount that will spread out as pressure is applied to the plank without excessive squeeze out and is easy to control. When planking the hull If I encountered a small gap between planks I applied medium viscosity in the gap, wiped away the excess, and immediately sanded the area and it filled the gap wonderfully. This is to be a painted hull so I had no concern with stain issues. I had occasion to remove an already installed deck plank and was impressed with the holding power, wood was left behind, perhaps not an desirable thing in some situations but east to remedy in mine. 

 

I prefer to use wood glue if possible if possible but often CA obviates the need for clamping and the quick set time is a blessing.  

Another excellent addition to the list of CA characteristics!
 

I actually planned on posting again tomorrow about the different variations of CA and how to properly apply them without making a mess. I’ll cover more of the chemistry and why we have thicker variations in that post. Thanks again everyone for reading this topic! 
 

Bradley

[Clark Griswold]

Based on my usage of CA the bond strength isn't the big concern when working with wood; it is the strength of the substrates.  The most common failure I've had using CA to bond wood is the wood itself parting at the limits of the adhesive spread due to tensile and cleavage stresses being greater than that of the wood fibers.  Depending on the size of the pieces being bonded its non-plastic bond can be problematic (smaller, more dense pieces tend to work best) due to shrinking and swelling, particularly dissimilar woods.

 

When working on natural or stained wood models I use CA only when absolutely necessary as a tack weld while the wood glue is curing.  It just isn't worth the heartache or physical pain that comes with errors and clumsy technique.  When the model is to be painted or fiberglassed I have done as Turangi spoke of and even done some very unnatural things with wood in a pinch.

 

I wouldn't go so far as calling it Devil's spittle, but it is remarkable at propagating unforeseen (and sometimes impossible to mitigate) problems.  CA is like any other tool in the shed.  It has things its meant for and does them very well; outside of that you are rolling the dice and will often get away with it.  When it doesn't work it really doesn't work and we only have ourselves to blame.

[Gregory]

13 hours ago, Jaager said:

To stack the deck against CA a bit more, most of the stress that wood to wood bonds encounter on a ship model tend to be sheer.

Could you elaborate?  

The sheer strength seems to be more of a problem with non porous materials, which doesn't include most woods.

 

In what way, would the planking on a ship model, be subject to stress after the CA has cured?

[Keithbrad80]

Wow, I have learned a lot about CA glue. If you are following along to this point then you hopefully have a pretty good understanding of what CA glue is and how it works. In this next post I want to take the opportunity to discuss just a bit more the chemistry and then talk about the differences between CA glue types and finally bonding. Personally I have always thought the best way to fully understand a topic is to understand the theory supporting it, and so the best way to understand CA glue is to understand the individual components that make up the glue and what happens when it comes out the bottle.  

 

One thing I meant to cover in my last post that was covered earlier was shear strength, in ship model building a lot of joints experience shear stress, for instance when you glue planks to a bulkhead or frame, the glue that holds them together is experiencing shear stress. This topic of shear stress and CA glue gets complicated very quickly, but to hopefully summarize, shear stress is the force experienced when both compressional stress and friction are acting on an object. Imagine a deck of cards on a table, if you apply shear stress to the top card, it will slide forward while the card touching the table stays still. I made an attempt at learning about shear stress in glues and adhesives and I came across three methods that have been discovered to increase shear strength of CA glue. The first is the metallization of the surface the glue is being applied to by integrating chromium nanorods in a 50nm thick layer, basically microscopic rods of chromium are “painted” onto the surface of the object being glued then CA glue is applied on top. I have no idea why this works, but its sounds far to difficult and expensive to work for this hobby so that is out. Another method I stumbled across is the introduction of amines, AKA ammonium hydroxide, another very harmful substance, literally a few breaths of the stuff will kill you, so I suppose that method is out for now as well. The final method I came across is the addition of rubber. I should say now that rubber is not the additive in CA that makes it thicker, I will talk about that in a bit. The addition of rubber changes the glue all together, bringing the color from clear to black, but there is an issue with this stuff, it only works on non porous surfaces like glass, but it seems to work well for that application if you need it. Once again we are at square one, and it seems for the time being that the shear strength of CA glue cannot be improved on surfaces like wood. Maybe one day. Last note about shear strength, thick CA glue exhibits a really interesting chemical property that explains why CA glue does terrible in the presence of shear stress. Thick CA glue imparts thixotropic properties, which basically means, its is usually in a solid state, unless it experiences shear stress, where for some crazy reason that I could figure out, it turns to a liquid! Well sort of, under normal conditions as shear stress decreases the viscosity of CA glue increases (cures) but when put under shear stress the viscosity of CA glue actually decreases, which drastically decreases the bonding strength of the adhesive. So the more stress CA glue is under, the more viscous it becomes, which is a bad thing.

 

Let’s finally talk more about ship modeling. If you were to jump on Amazon or a site like ModelExpo and search “CA glue” you will get a ton of results for all sorts of applications, how do you figure out which one works for you? Ultimately it will always come down to your personal preference and what you find works, but generally there are a few options to chose from. While any CA glue or super glue will work fine for wood adhesion, there are generally a few different thicknesses that you can chose from, all of which have different application in the modeling world. The thickener in CA glue is silicon dioxide, AKA quartz, and as you can imagine, the more SO2 that is added, the thicker the glue. There are certain brands of CA that replace the SO2 with calcium oxide, which creates a thick clear glue that when dries, closely resembles mortar, which is super strong. From what I have researched, it does not appear that the thickness of CA glue correlates with an increased shear strength. 

 

CA glue with no SO2 is called super thin or thin CA glue, this stuff is basically water, once it leaves the bottle it will spread out into a very thin layer, deeply soak into the wood and instantly cure, creating a super tight chemical bond. This type of CA is guaranteed to leave a stain behind, I have never not had a stain after using the stuff, keep this in mind when modeling. If the piece you are gluing is going to be seen I would not use super thin CA as it is nearly impossible to remove. Medium thickness CA like James mentioned does a great job for certain applications like second planking. Medium thickness CA does well because the viscosity of the glue is enough to prevent the glue from spreading to thin, as well as keeping the glue from soaking to deep in the pores of the wood. I havnt used enough medium thickness and thick CA glue to know whether or not there will be a significant glue stain, I have actually never used thick CA glue so I dont have much to say about that topic. 

 

One of my final subjects on this topic is the idea of bonding, which is what occurs during the curing process. When CA glue is applied and the chemical reaction is over, the bond that formed between your two pieces of wood closely resembles plastic. Often this plastic like bond between two pieces of wood is stronger than the wood itself, meaning in thinner or smaller pieces or weaker woods like basswood, you will probably break the wood before breaking the bond. I would guess the number one question asked about CA glue is how you remove the stain left behind after curing, and the answer is you cant get rid of it. You can debond the glue and chemically separate the two pieces, but you cannot remove the glue. Imagine a piece of wood, you fill the pores with CA glue which discolors the surface, and you want to remove it, in order to remove it you would have to clean out the pores of the wood which I’m not sure is possible. CA glue does have a life span btw, about a year from the manufacturer date, or a month or two after opening, how ever before opening if refrigerated you can extend the life span by about 6 months. If you drop the temperature below 0 F you can almost stop the chemical reaction from happening all together, increasing the life span indefinitely. CA glue can bond with other stuff as well, to create a different substance all together, mixing it with the saw dust of the species you are working with creates a very strong and light filler. Alternatively you can mix CA with baking soda to create a very light and very strong filler.

 

After reading about CA as much as I have today I would have to disagree that CA is the Devils spittle. CA glue is every where, it holds your shoes together, a lot of furniture incorporates the glue, turns out if you add some stuff it becomes antimicrobial and can be used to seal lacerations. It’s used as a temporary bond while welding, and is the primary adhesive in most implantable medical devices. It bonds metal, wood, leather, paper, and pretty much any other porous material, its cheap, easy to acquire and dries instantly. It may not be the best adhesive for ship modeling but I think it has its place, just like every tool. My very last point, CA glue is a chemical just like any other chemical and should be handled appropriately. It should be stored in a cool dry place avoiding direct sunlight to extend the life span. 

 

My next post is a collection of tests that I am going to preform on different common wood species. I want to test different methods of removing CA wood stain, I also want to test different stains and paints on wood and how CA glue effects those paints. I’m mostly interested in ways to cover CA glue stain, and ill share my findings with all of you. 

 

Thank you for spending the time to read through my research on this glue, I hope that this collection of information proves useful for those that may be just entering this hobby or for any who may be unsure about the product.  

Bradley 

Edited February 8, 2021 by Keithbrad80

[Gregory]

You have inspired me to do some testing..

[Jaager]

7 hours ago, Gregory said:

Could you elaborate? 

Up thru the hull planking stage, we are building in different worlds,  POF vs POB. 

A frame that is overlapping  timbers is mainly subject to sheer forces while being shaped.

The same while being planked.

For deck components being knocked in a lateral direction seems more likely than their being levered up.

For planking itself,  I see at least two possible stress sources.  If a plank is not pre-bent  to sit on the hull, if it has to be held down until the bond cures to keep it from going back horizontal, it will pull up on the bond forever (noemal stress).  If it has been bent thru the thick dimension instead of being spilled,  It will exert a lateral force (sheer) and a twist  (normal) even if it has been pre-bent and is a push fit at assembly.  Nature never sleeps.

 

I think it was Underhill, that imprinted this at my beginning of this, but the belt and suspenders philosophy ( chemical and mechanical bonds for as much as possible ) but it has stuck like an obsession.

[Bob Cleek]

28 minutes ago, Jaager said:

I think it was Underhill, that imprinted this at my beginning of this, but the belt and suspenders philosophy ( chemical and mechanical bonds for as much as possible ) but it has stuck like an obsession.

Excellent point! It may seem redundant when building and glue bonds are young, but it really pays off over the long haul when parts and pieces don't start falling off five or ten years later!

[Gregory]

What kind of shear forces are we talking about in psi when it comes to model ship planking or even deck fixtures?

 

I am reading numbers in the hundreds for various types of glues including CA, on various types of materials.

[Jaager]

23 minutes ago, Gregory said:

am reading numbers in the hundreds for various types of glues including CA, on various types of materials.

I am not going to look at the units involved, but I guess that it is force per square inch or something similar.  For most of a ship model joinery the surface area involved is pretty small.  So that reduces the bond exceeding force when the equation is applied to the individual situation.

[kurtvd19]

C/A glue doesn't have a lot of shear strength - but I don't anticipate planking being subjected to much in the way of shear force.  Or decking, or deck furniture. 

As to hiding the glue on bare wood that I commented on earlier...  The Journal currently at the printer features on of Steve Wheeler's models.  There is a photo of the hull showing the glue marks in a photo before finish was applied.  The photo that shows the marks best is the exterior of the hull but the interior had similar markings and the photos of the finished interior show none of the marks after the finish was applied.  Invisible on the finished model. 

[Keithbrad80]

3 hours ago, Gregory said:

What kind of shear forces are we talking about in psi when it comes to model ship planking or even deck fixtures?

So the adhesive that holds the deck furniture to the deck experiences compressional stress, not shear stress. I found a patent by a Japanese company filed in 1989 that discuses their shear strength testing of the adhesive. The units are kilogram-force per square centimeter, a form of stress, those units are derived from all sorts of math that would take me awhile to describe, they report shear strength of around 300 Kgf/cm^2 of most glues they tested. 

 

2 hours ago, kurtvd19 said:

Invisible on the finished model. 

I didnt have much work to get done today so I had some time and conducted over 40 tests of CA glue in various environments with various wood species. One test I will talk more about later, was a single drop of CA on basswood, followed by a single coat of satin finish poly, the CA glue immediately become invisible. 

Edited February 9, 2021 by Keithbrad80

[Gregory]

11 minutes ago, Keithbrad80 said:

300 Kgf/cm^2

 

That appears to equal 4267  pound-force per square inch 

https://www.convertunits.com/from/kgf/cm2/to/psi

 

 

 

[Roger Pellett]

The definition of stress, is force divided by area.  In my world it is pounds per square inch.  This definition applies to stress acting in any direction; compressive, tensile, bending, shear, torsion, etc.

 

The actual failure mechanism is much harder to define, especially as there is often more than one type of stress  acting simultaneously in any given situation.  For example the double planking in a POB model is subject to bending stresses due to the curvature of the hull.  Simultaneously there is also a shear stress acting parallel to the length of the planking between the two layers.  Shear stresses along the longitudinal axis are what cause beams (planking) to resist bending.

 

Roger

 

 

[Gregory]

Any guess about how many pounds per square inch is going on there? 

Or should we be talking about ounces?

[Keithbrad80]

52 minutes ago, Gregory said:

Any guess about how many pounds per square inch is going on there? 

The exact measure of stress being applied to an object is probably different at every point in the hull based on a bunch of factors, so to give an exact number is very difficult. There are a lot of different stresses being applied to a plank on a hull and in some cases its not hard to exceed the breaking point of CA glue. Some models that have a steep curve at the bow or stern probably generate a lot of constant stress in longer planks, shorter planks don't have to bend as far. I don’t want to go to deep into the physics of the wood here but for this exact reason a lot of people choose to use a different glue. 

 

Also ounces, are used to describe things like mass, weight or volume. Some of these units can be very confusing to fully visualize what they mean, so for this instance square feet works perfectly fine as long as you do the proper conversions, which you did so nice work! 

 

[Gregory]

10 hours ago, Keithbrad80 said:

Also ounces, are used to describe things like mass, weight or volume.

I used it as a fraction of a pound, in terms of pound-force.  Perhaps I used it improperly.

 

What is the proper expression when pound/square inch <1 ?

 

It would be possible to measure the spring-back force on a twisted/bent model plank.

 

Do you think it would approach a pound or more?

 

CA two strips of bass wood together and measure the force it takes to slide them apart, or how much force it takes to pull them apart.

( In my experience, the wood splinters and comes apart before the glue joint separates )

 

There may be any number of reasons to choose not to use CA on a wood model ship.

The bond strength with wood, is not one of them.

 

As with any adhesive, there can be inferior formulations, and improper use.

 

The bond strength of CA  can be thousands of pounds per square inch when properly used.

I fail to see how the bond strength of CA  is a consideration when it comes to wood ship modeling, unless it is a question of the necessity to un-bond at some point.

 

 

Edited February 9, 2021 by Gregory

[Keithbrad80]

16 minutes ago, Gregory said:

I fail to see how the bond strength of CA  is a consideration when it comes to wood ship modeling, unless it is a question of the necessity to un-bond at some point.

After as much research as I have done on this, I’m starting to feel the same way. Modern formulations of CA glue are so much stronger than it use to be. 

[Gregory]

A little test I did this afternoon..

 

 

 

 Some 1 x 13 mm boxwood with a 90° twist.

 

Are there shear forces at work?

[Keithbrad80]

There is probably some shear stress, but for a shear stress test the best method is a pull method. glue two planks together just as you have and instead of twisting them, hold onto the clamps you have and try to pull them apart horizontally, if that makes sense.  I did a few of my own as well that I plan to post tomorrow hopefully. 
 

Bradley

[Gregory]

16 minutes ago, Keithbrad80 said:

for a shear stress test the best method is a pull method. glue two planks together just as you have and instead of twisting them, hold onto the clamps you have and try to pull them apart horizontally,

 

Actually I did that..  About two minutes after I glued them up.  I pulled with my fingers because the clamps slipped off too easily.

 

I was thinking about hanging it up with some weight, but don't have a quick way to do that without some further thought, but I will work on it later.

 

I need a good fish scale to get a meaningful number..

 

Edited February 9, 2021 by Gregory

[Keithbrad80]

23 minutes ago, Gregory said:

 

Actually I did that..  About two minutes after I glued them up.  I pulled with my fingers because the clamps slipped off too easily.

 

I was thinking about hanging it up with some weight, but don't have a quick way to do that without some further thought, but I will work on it later.

 

I need a good fish scale to get a meaningful number..

 

No one is going to believe me until I post pictures but this stuff is amazing! I did exactly what you did, glued two pieces together clamped one side and put weight on the other. I ran out of things I can weight this piece of wood down with. I drilled a small hole on one piece and put a metal sleev in the strengthen that point then I fed metal wiring through that and tied it off to different stuff. I did a couple different tests but I first tried a gallon of vinegar, 10 pounds no problem. Next up 5 bricks, mine are 5 pounds each, that’s 25 pounds, again no problems. Then I though ok what would really break this joint? I tied that off to my 100 pound lathe and it picked it up no problem. It only held for a second before that metal sleeve ripped through the wood. How’s the joint you ask? As strong as ever! I have a completely different kind of test I want to conduct as well in regards to strength of the glue. I haven’t taken to many pictures yet because I was amazed that it withheld any of that to begin with. The psi isn’t all that impressive, according to my math here lifting that lathe of 100 pounds with an area of .75 inches resulted in 133.3 psi. If I had a better method for testing this I’m sure I could pick up lots more. For this test I actually don’t care about the psi though, because I feel like lifting that much weight has proved that modern formulations of this glue are really good and much stronger than most think. 
 

This is the only picture I have taken so far, it’s just after the sleeve in the wood broke. 
 

 

Hopefully you believe me that I’m not making this up lol, I’ll take better pictures later. 
 

Bradley