Does anyone epoxy without clamping?

R

Ryan J

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Jul 14, 2014
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Hello everyone, I searched this question but couldn't find it posted.

I was watching a video about gluing wood on Mathias Wendell's YouTube channel the other day. He performed very thorough tests on joint strength at different clamping forces. His surprising results were that loosely clamped, loose fitting joints were far stronger than tight fitting, tightly clamped joints. So I did a little more digging and found this article about epoxy http://www.woodweb.com/knowledge_base/Epoxy_Adhesives_Tips_and_Techniques.html

It states the same about epoxy. Many manufacturers recommend a minimum thickness of epoxy thickness to maximize strength. We all know clamping too hard squeezes out to much epoxy and compromises the joint. So hence the question, does anyone epoxy without clamping? I'm wondering if anyone has tested scale to tang bond at different clamping forces or if they can point me in the right direction to someone who has. I've seen videos testing surface prep but not clamping force. I wonder if greater joint strength can be achieved by not clamping at all.

Just thought I would check before I spent the time and money to test it myself. Thanks
 
I set my blade on a granite slab with wax paper and position the scale on the epoxied blade with a can of soup sitting on the tang. I only do one side at a time so it takes 2 days to glue up a knife. I drill for pins after the first side sets up and then the second side. I epoxy the pins in after the scales are fully set up. I use G-flex epoxy and I usually drill an extra hole or two in the tang and also cut shallow grooves in the tang with a Dremel tool and a fiberglass reinforced wheel in a cross-hatch pattern for better adhesion. I have never had a knife come back to me with a separation of scales and blade. I do not peen my pins. If a knife is specified for heavy use I offer Corby bolts or Loveless bolts but I do not think it is necessary and my own personal knives are not peened or bolted. I cannot say this is the best way to put a knife together but in my opinion it is (unless you use Corby or Loveless bolts) . Larry

VgYxILLm.jpg
 
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Actually i am not surprised at all; Clamping is the way we ensure a "parallel" and invisible joint, for this reason the load doesn't need to be high, just evenly spread.
The clamping pressure only have to defeat the surface tension of the glue which tends to push the scales from the tang, showing the gap.
The chain links of the glue composition have some give before failure, if the joint lenght (tang---scale) is short, any pull load will reach the failure of the few molecular chain's links, on the contrary a bigger length counts more links, and the load stay under the sum of their failure points as they all give for their "allowed lenght".
 
Us the lightest weight clamps possible to assure a straight joint. Over-clamping will leave a "glue starved" joint ... which will fail easily. The "bond line" thickness has ben studied a lot by the epoxy makers, and should be between .003 and .010".
 
Thanks everyone for the replies. Stacy how is the bond strength effected if the epoxy joint is greater than .010? And am I understanding you correctly that the primary purpose of clamping is to create a straight glue joint?
 
Actually, as an engineer, I don't trust any chemical adhesion as eventually it ages and breaks. I prefer mechanical attachment first (i.e. pins) backed up by epoxy for both ultimate strength and fill. Both is the answer to me. If only one available, I'll take pins and or bolts first. If its a hollow handle attachment like stag, I'll fill it with epoxy, prefer devcon, and pin/nut and bolt it afterwards.

My total knowledge exhausted, back to sleep.

Larry
Tinkerer
 
tinkerer said:
Actually, as an engineer, I don't trust any chemical adhesion as eventually it ages and breaks. I prefer mechanical attachment first (i.e. pins) backed up by epoxy for both ultimate strength and fill. Both is the answer to me. If only one available, I'll take pins and or bolts first. If its a hollow handle attachment like stag, I'll fill it with epoxy, prefer devcon, and pin/nut and bolt it afterwards.

My total knowledge exhausted, back to sleep.

Larry
Tinkerer
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I'm not a Scrooled Engineer :)
but I prefer the mechanical, Loveless or Corby attachment also.
I mainly use the epoxy as a sealant to keep moisture/blood etc out from under the scales. I do also agree that as little possible pressure on the epoxy is a good thing and only use G/Flex.
 
Agreed!
Corby bolts and a high grade long life bond epoxy will make a solid and lifetime handle construction. The reason I like structural resins, like T-88 and Acraglas is they are as strong or stronger than the wood they bond. Flexible and highly adhesive resins like G-flex are also superb. They are all designed to last a long time.
 
I aim for an absolutely flat attachment, but we all know that this is almost UN-obtainium when working with natural materials. The Corby or Loveless fastener is more than robust enough to retain the handle scale, even without epoxy. I use epoxy to fill any minuscule gaps and then tighten the fasteners sternly enough to flatten any existing couple of thousandths of and inch gap between surfaces together, yet not over stress the scales, etc.. If I squeeze all of the epoxy out of the interface and end up with no epoxy between the surfaces, then it means I've well fitted the components.

In all reality, by apply the epoxy to all mating surfaces I suspect that I ultimately end up with to a thin layer (~.005") of cured epoxy between most all surfaces, in any case.
 
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Mike, I agree that the Corbys and the Loveless bolts make the strongest hold and some of my customers like the looks of Loveless bolts with contrasting metals like stainless and brass. I use G-flex and drill holes and make grooves in my tangs so that I can feel confident with mosaic pins and other pins that have limited mechanical hold. Your knives look great and will probably last for generations the way they are built. Larry
 
hsc3_90293 said:
Ian Hall introduced me to these clamps and I've found them to be the most suitable for the right pressure.

http://www.irwin.com/tools/clamps/handi-clamps
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I use these types of clamps for all sorts of stuff. They are great for applying a wide variety range of pressure from very light to quite heavy. Can painfully squish your finger and leave you with a black fingernail as my son discovered while goofing around with his friends.
 
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