Scales - glue joint failures
- Thread starter Xunil
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see full tangs are strong yes, but so are stick tangs when made correctly. full tangs are heavy, the handle material is tempermental, shifting, cracking and warping, full tangs have a habit of getting water in-between the tang and the scales, causing rust and corrosion. full tangs do look nice, they do feel very strong, but in my mind the stick tang is the superiour design for bushcraft as they are just as strong, can hold up better to the elements, are less tempermental and lighter in use.
On balance, and in all fairness, serious issues with scales are very rare on full tang knives otherwise nobody would be using them, ever. If failure was commonplace folks would take the more reliable solution every time.
I have had one knife returned because of this problem in over 20 years of making them, which was a week or so ago, and it is pictured above. In this case there was no ill will as a result of the material lifting since the knife is a prototype of a design in progress and no money has changed hands. If this was a client project where a final sale had been completed the story could well be very different - I would potentially have a dissatisfied customer on my hands.
My own preference is hidden tang and I make no secret of it, but it is dead easy to introduce problems to hidden tang construction (particularly when peening the tang at the end) which, instead of securing the handle material can do the exact opposite or even overstress the material to the point where it fails.
Bottom line - I advise clients based on their requirements but if they choose a full tang then they won't ever be happy unless they have one, so that's what they get.
In theory both construction methods can produce a good, strong knife. Both can also be thoroughly loused up and both can fail miserably due to any one of a number of factors, most of which are caused by the maker and some of which are caused by the materials themselves or environmental extremes.
The strength factor is academic under normal use and would only ever make itself felt when subjecting the knife to extremes beyond the normal scope of daily work.
I still say that full tang knives have the market share mainly due to economics. Steel is inexpensive to buy but costly to work, so why machine excess away and work on a more critical fit on a hidden tang knife when you can simply flatten the tang and inside edge of two slabs and get the whole lot assembled.
Same argument applies to Scandi grinds - what's the quickest and easiest grind to do ?
Economics governs a lot more than most give it credit for. A fringe benefit is the Scandi grind is good for carving, but the main underlying rationale behind it is very probably down to it being the quickest, least labour intensive method of construction there is.
It is far too easy (and usually inaccurate) to categorically state that X is better than Y.
Seriously - how much can a 3mm or thicker knife flex under normal use to compromise the tang-to-scale joint ?
All else being equal you can good or bad results using either format and full tang knives do not encourage scale/handle failure by default.
I could cite a bunch of very old (over a century) full tang knives I have as examples, and I have a couple that I made about 25 years ago now that are still going strong with no failure and no sign of any.
I keep coming back to the handle material or perhaps the chemical residue in the stabilising process in relation to the wood as a common denominator.
I have had one knife returned because of this problem in over 20 years of making them, which was a week or so ago, and it is pictured above. In this case there was no ill will as a result of the material lifting since the knife is a prototype of a design in progress and no money has changed hands. If this was a client project where a final sale had been completed the story could well be very different - I would potentially have a dissatisfied customer on my hands.
My own preference is hidden tang and I make no secret of it, but it is dead easy to introduce problems to hidden tang construction (particularly when peening the tang at the end) which, instead of securing the handle material can do the exact opposite or even overstress the material to the point where it fails.
Bottom line - I advise clients based on their requirements but if they choose a full tang then they won't ever be happy unless they have one, so that's what they get.
In theory both construction methods can produce a good, strong knife. Both can also be thoroughly loused up and both can fail miserably due to any one of a number of factors, most of which are caused by the maker and some of which are caused by the materials themselves or environmental extremes.
The strength factor is academic under normal use and would only ever make itself felt when subjecting the knife to extremes beyond the normal scope of daily work.
I still say that full tang knives have the market share mainly due to economics. Steel is inexpensive to buy but costly to work, so why machine excess away and work on a more critical fit on a hidden tang knife when you can simply flatten the tang and inside edge of two slabs and get the whole lot assembled.
Same argument applies to Scandi grinds - what's the quickest and easiest grind to do ?
Economics governs a lot more than most give it credit for. A fringe benefit is the Scandi grind is good for carving, but the main underlying rationale behind it is very probably down to it being the quickest, least labour intensive method of construction there is.
It is far too easy (and usually inaccurate) to categorically state that X is better than Y.
Seriously - how much can a 3mm or thicker knife flex under normal use to compromise the tang-to-scale joint ?
All else being equal you can good or bad results using either format and full tang knives do not encourage scale/handle failure by default.
I could cite a bunch of very old (over a century) full tang knives I have as examples, and I have a couple that I made about 25 years ago now that are still going strong with no failure and no sign of any.
I keep coming back to the handle material or perhaps the chemical residue in the stabilising process in relation to the wood as a common denominator.
Yup. maybe the chemical used in the stabilissation has changed/been substituted for more economical component that has a detremental effect on bonding.
The company I work for spends a lot of effort to ensure that even the packaging used to ship components is not made using any contaminants.
but if you only see faluires using box burl and other woods from the same batch of stabilisation do not fail then the wood is most likely.
As for quick setting adhesive.....I used some 90 second setting types for other jobs and a 10 minute setting for handles.
yes the chemical reactions become exothermic and give off heat energy, but the volume of adhesive in the joint is so small the change will not be noticeable and any that is generated will sink straight into the tang.
The steel will take many Watts to increase the tang temperature enough to change it dimensionally.....I cant remember the calc off hand......so If quick setting is to be avoided then i would suggest is is based on the difference in chemical make-up of the adhesive and not the tiny amount of heat generated....I think holding the tang in your hand whilst assembling would heat the tang up more than the adhesive setting
Correct me if you like
Mojo
My main gripes about rapid setting epoxy are the relatively short window of opportunity to work with it combined with the fact that some brands can be brittle once the glue has cured (by comparison to slow setting epoxy).
This is very much a brand thing and I doubt it applies to all glues.
On the flip side you can be in business and working on finishing out a knife grip in pretty short order using the rapid set stuff.
I don't use it after a bad experience, but several folks I know do use it with excellent results.
No correction required (you'll be relieved to note), despite my somewhat cautious and slightly paranoid concerns
This is very much a brand thing and I doubt it applies to all glues.
On the flip side you can be in business and working on finishing out a knife grip in pretty short order using the rapid set stuff.
I don't use it after a bad experience, but several folks I know do use it with excellent results.
No correction required (you'll be relieved to note), despite my somewhat cautious and slightly paranoid concerns
Yup, if you're setting a joint to last a life time you should be patient enough to let it cure for a few hours.
Also the way it is dispensed can effect the joint......some epoxies come in a syringe which helps keep the mix ratio within working limits. where as other epoxy adhesive is just in tubes and you have to guess at the correct volumes......this will effect adhesive brittleness and strenght in my opinion.
Which do you use Xunil.....i'm just investigating
Mojo
Also the way it is dispensed can effect the joint......some epoxies come in a syringe which helps keep the mix ratio within working limits. where as other epoxy adhesive is just in tubes and you have to guess at the correct volumes......this will effect adhesive brittleness and strenght in my opinion.
Which do you use Xunil.....i'm just investigating
Mojo
I've always had great results with Devcon 2 ton, but I used to get two part slow set epoxy from the late, great Bob Engnath years ago which was great. I've no idea what the brand was but he decanted into smaller containers and sold it on. Either Sheffield Knifemaker Supply, Texas knifemaker supply or Knife & Gun (I forget which) used to do the same and theirs was great too.
The Araldite industrial epoxies are good as well - I'm not impressed with the standard Araldite products by comparison. Good is not the same as great...
The Araldite industrial epoxies are good as well - I'm not impressed with the standard Araldite products by comparison. Good is not the same as great...
Ok I was more getting at the final measuring out of the epoxy adhesive and hardeners to ensure they are within the limits as set out on the material data sheet.
Most of the ones I have used are +/- 10% which if you are measuring out by eye is tough to achieve......
Also mixing thoroughly is not to be underestimated as any pockets of adhesive/hardener that are not fully mixed will give weak sections of the joint.......you know this already but just for any one new to adhesive....
I ve used 3M Dow and other adhesive.....personally they have all done the jobs asked of them but really need to be researched as to how the data sheet expect them to be prepared.
Mojo
Most of the ones I have used are +/- 10% which if you are measuring out by eye is tough to achieve......
Also mixing thoroughly is not to be underestimated as any pockets of adhesive/hardener that are not fully mixed will give weak sections of the joint.......you know this already but just for any one new to adhesive....
I ve used 3M Dow and other adhesive.....personally they have all done the jobs asked of them but really need to be researched as to how the data sheet expect them to be prepared.
Mojo
Ah, my bad...
I usually measure out into small medicine pots so if I'm looking for a 50/50 mix I can guarantee that's what I'm using (by volume). Some of the more challenging ones are by weight, and the hardener and adhesive have different specific gravity weights, which is where a good set of digital scales comes in handy. I used to use my reloading scales before I got rid of all my firearms stuff.
Anyway, pots or pots and scales, depending on 'by volume' or 'by weight'.
I find ambient temperature can really influence things even more than humidity, especially when the temperature is low. That said humidity tends not to vary massively here in the UK - it's usually too busy raining for that to happen
I usually measure out into small medicine pots so if I'm looking for a 50/50 mix I can guarantee that's what I'm using (by volume). Some of the more challenging ones are by weight, and the hardener and adhesive have different specific gravity weights, which is where a good set of digital scales comes in handy. I used to use my reloading scales before I got rid of all my firearms stuff.
Anyway, pots or pots and scales, depending on 'by volume' or 'by weight'.
I find ambient temperature can really influence things even more than humidity, especially when the temperature is low. That said humidity tends not to vary massively here in the UK - it's usually too busy raining for that to happen
I hear you....the whole density of part 'A' to part 'B' and working out volumes is fun.....but at home I just stick with the simple stuff as I do not have any scales for personal use.
Yes temperature is a big factor:.....not sure if it is the same with all chemical reactions but a rule of thumb that every 10 degree rise the curing time halves for the two part epoxies...as you can now see if an adhesive starts to exotherm it can effect the curing time....again not going into detail but I do not remember seeing any performance drop off when curing at elevated temps unless diss-similar materials are being joined
Nice chatting to ya
Mojo
Yes temperature is a big factor:.....not sure if it is the same with all chemical reactions but a rule of thumb that every 10 degree rise the curing time halves for the two part epoxies...as you can now see if an adhesive starts to exotherm it can effect the curing time....again not going into detail but I do not remember seeing any performance drop off when curing at elevated temps unless diss-similar materials are being joined
Nice chatting to ya
Mojo
I've used this on a couple of knives very cheap but works very well indeed, i've no links with the seller just a happy customer
http://cgi.ebay.co.uk/EPOXY-GLUE-AD...Scrapbooking_Glue_Tape_EH&hash=item518d143886
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