Knife handle failure...

[EdCaffreyMS]

With the thin blade, and the lack of mechanical attachment, you're going to keep seeing that knife over and over again. G-Flex isn't going to solve your issue(s). If the guy is reefing on the knife enough to cause flexing along it's length (which is pretty much assured in a wood carving scenario with that thin of a blade) the handles are going to keep pulling away from the tang. After looking closely at the pictures, I doubt even Acraglass would keep those scales down. My advice is to use either loveless or corbys, along with good "epoxy".

Another facet of a situation like this is that the client is only going to tolerate it for so long....then he's going to get frustrated, and tell anyone who will listen that you make cruddy knives that the handles keep coming off of (or something like that). Sometimes as a knifemaker, you have to insist to clients that certainl things are just necessary. If a client just won't go for it, I just won't build them a knife....its not worth your reputation.

 

[wmhammond]

I would like to ask a question about peening. Say you have a wood handle, maple maybe, and three 1/4' pins in the handle and you are ready for glue up and assembly. So you glue it all up and put it together. Do you then peen the pins before you clamp it up? Next question, how tight do you peen it down to the wood? I ask that because you are probably going to grind off the "Mushroom" end of the pin when you begin to finish the handle. Last question, when you peen the pin does it cause the pin to bulge out in it's middle where it goes through the handle wood and the tang making it fit tight and create a mechanical bond. If it doesn't, when you grind off the "mushroom" top of the pin you loose the mechanical bond, don't you? On a related topic, when you glue, pin and peen a bolster how do you then finish grinding the bolster and not cause it to overheat and breakdown your epoxy. Dumb questions, sorry.

Wallace

 

[Wayne Bensinger]

Certainly not dumb questions, very good questions. The way it was explained to me and the way I've been doing for a while now is, and it worked for me on a few handles, if your pinning wood, you'd would want to use a tapered reamer to oversize your pin hole a few thousandths on the outside of the scale or block. But you must be very careful with wood especially when doing that so as not to put to much pressure on the wood, you just want to expand the pin, obviously, and not split wood. I used very light tiny taps with the peeling hammer, it takes time, don't rush it with big smacks. Also, make sure the opposite side of the pin is on a very solid vise or anvil so each and every blow of the hammer is only contacting metal and not wood on either side. Do both side the same amount of taps to expand the pin equally. Then you do you grinding/ shaping of the handle. On your second question, I think patience there as well, as your using these different materials you'll soon find how to and how not to use them properly. After your glued, pinned, peened and you start to grind, just take it slow till you get the head of the pin down to the meat of the handle where the heat will be dispersed by the bigger mass of the handle. You may need to cool it a few times during the procedure, especially it seems on some of the softer S.S. They really seem to heat up quickly, zero to smokin hot in a few stokes of the hacksaw,lol!
That's how I've done those type projects and have some good results, hope it helps, maybe there will be some others ideas out there.


Wayne

 

[Faron Moore]

Very well put Tracy,most guys don't understand , that stabilized wood is still wood and should be treated as such,I insist that all My Clients put some sort of finish on there handles,Me personally I love TRU-oil if it's good enough for a 10K gun stock it's good enough for a $300 knife.

 

[dkemppai]

With the thin blade, and the lack of mechanical attachment, you're going to keep seeing that knife over and over again. G-Flex isn't going to solve your issue(s). If the guy is reefing on the knife enough to cause flexing along it's length (which is pretty much assured in a wood carving scenario with that thin of a blade) the handles are going to keep pulling away from the tang. After looking closely at the pictures, I doubt even Acraglass would keep those scales down. My advice is to use either loveless or corbys, along with good "epoxy".

Another facet of a situation like this is that the client is only going to tolerate it for so long....then he's going to get frustrated, and tell anyone who will listen that you make cruddy knives that the handles keep coming off of (or something like that). Sometimes as a knifemaker, you have to insist to clients that certainl things are just necessary. If a client just won't go for it, I just won't build them a knife....its not worth your reputation.

Hi,

I had another chat with the guy tonight. He hasn't used this knife since it was repaired the first time! He had elbow surgery and hasn't touched the knife! So that blows the hard use theory out of the water.

He also verified they burn wood and the house is very very dry. His said his brand new wood flooring is coming apart right now!

Given this new information I very strongly believe it's drying out and shrinking. The fact that the still attached scale bent the tang (until it was removed) supports the theory. Also, the handle failed at the end, not the in the middle of the knife. If it were hard use, one would guess the front of the handle would let go first. (If you've seen them fail at the back end, please do share!) Also, I've seen red oak move 3/8" per foot seasonally, so I know it moves a bunch.

At this point, the consensus seems to be that mechanical fastening of some sort is needed. Epoxy alone won't do it. Even the gflex probably isn't up to the task. I doubt any of structural adhesives or urethane is going to alone either.

My guess is that mechanically fastening with simple pins/corby's won't do. I'm guessing the wood will still move and will just split. I've got some ideas on how to accomplish the fastening, but want to ponder it some more...

As for your concern regarding the client, it is a valid concern. Fortunately he's a local guy and he's sort of a friend of the family. So, Luckily, he is understanding about this whole thing. In the end, he will get a good knife. Either this knife or another one, and he knows it.


Thanks,
Dan

 

[EdCaffreyMS]

Given this new information I very strongly believe it's drying out and shrinking.

There's something going on here that we're missing. I didn't go back and double check, but I thought you had said this was stabilized oak? If so, it would have had to be less then 11% moisture to be stabilized....otherwise it would have come out of the stabilzing process horseshoe shaped. If it wasn't stabilized, was it allowed to cure well before being used as handle scales? Here in Montana, its VERY dry, and I generally allow woods and other natural materials to "climatize" at least 6 moths before being used for anything dealing with knife handles. The only time I can remember anything like this happening with one of my knives was when I decided to try boiling/pressing sheephorn.....it was allowed to dry for 3 months, then put on a large camp knife that went to coastal Florida. A couple of months later the handle scales had pulled through loveless bolts, and were trying to go back to their natural shape.....later I discovered it was the difference the huge difference in humidity. Those scales were taken off, and replaced with micarta in order to solve the issue.

Were it me, after the second time the scales came loose, they would get torn off, thrown away, and replaced with something else. As I said, theres something going on here that we're missing.

 

[C Craft]

I may be very wrong but I think there is your answer or at least a big part of it! The handle is thick enough at the Ricasso it can't flex, much (the normal place one would think it would flex. However the knife is flexing at the heal of the handle! The flex is breaking the bond and if I am right there ain't any kind of material that is going to stay adheared with out corby bolts or pien-ed pins! This bond is going to have to go thru the knife from side to side.

As I stated in an earlier post Oak is very dense and doesn't flex well at all. That is what is ripping the bond from the steel of the knife and Oak slabs. You said it never breaks any where else!

I would think of using another material that will flex with the blade and I would still go for pein-ed pins or bolts. When you said the knife flexed but popped back into shape after removing the Oak slabs, there was something that told me there was your answer. When I saw that pic I was sure that was the culprit!

Think about it a second if you are still doubting what I said. You have a knife that holds a good edge but flexes. Just what the customer wanted, he just can't have it without something to help hold the scale to the blade. Tell him that if he likes the way the blade performs and the way it holds and edge he is going to have to compromise on the handle material and the bolt idea because, the knife is flexing while it is doing it's job and to hold a handle material to that knife he is going to have to give something!

EDIT:
I had to satisfy my own curiosity, so I just went and clamped a piece of Red Oak in my vice. I cut some scales sometime back they are very seasoned. The scales are about
1 1/8"W X 1/2" Th X 12" L. I left about 6" of it sticking out of my vice. I then taped a strait edge against the Oak slab at the top.

I am 6' and about 260lbs, putting all my weight on the slab sticking out of the vice I could only flex an 1/8" or less. I will bet if you clamp that blade in a vice and lean on it the tail is going to flex more than an 1/8". The strain your customer is putting on that blade is causing the heal of the handle to flex time and time again till it breaks the bond.

It don't matter if it is stabilized or not Oak don't flex very much at all, not unless it is punky and that is when it needs to be stabalized. Most of the time the taper to the heal would not create a problem but, then again not everyone is using a knife for carving. He doesn't have to to twist the motion of carving makes the blade flex. I don't think it is a flaw in the stabilization process or for that matter your design. It is just one material won't flex and the other will!!!! IMHO

OK going to add one more thing and then I am done, this was from your very first post!
Quote:
Also, This guy's carving style is pretty forceful. He doesn't break blades, but puts a lot of pressure on the knife and wood. I spent some time watching him carve before we designed the blade. He knows how to handle a knife, but he does work them hard. No doubt this knife gets used harder than any of my other knives. The blade has taken the work just fine, and he loves how sharp it stays. However the scales just aren't sticking.

 

[dkemppai]

There's something going on here that we're missing. I didn't go back and double check, but I thought you had said this was stabilized oak? If so, it would have had to be less then 11% moisture to be stabilized....otherwise it would have come out of the stabilzing process horseshoe shaped. If it wasn't stabilized, was it allowed to cure well before being used as handle scales? Here in Montana, its VERY dry, and I generally allow woods and other natural materials to "climatize" at least 6 moths before being used for anything dealing with knife handles. The only time I can remember anything like this happening with one of my knives was when I decided to try boiling/pressing sheephorn.....it was allowed to dry for 3 months, then put on a large camp knife that went to coastal Florida. A couple of months later the handle scales had pulled through loveless bolts, and were trying to go back to their natural shape.....later I discovered it was the difference the huge difference in humidity. Those scales were taken off, and replaced with micarta in order to solve the issue.

Were it me, after the second time the scales came loose, they would get torn off, thrown away, and replaced with something else. As I said, theres something going on here that we're missing.

Hi,

Yeah, I sure missed something!

This oak was stabilized by WSSI. When I cut this oak it seasons as an oversize block for over a year, then gets cut down to scale sized pieces and seasoned for many (6+) months more. Before it went to WSSI I dried it down as far as I could. When Mike got it he checked it, and it was at 7% moisture. After the process, it sat in my 'go to' cabinet for about another year. The scales moved a little during the stabilization process, but not after they arrived back here.

I've been using this cut of wood for about a decade. The only thing that's new is the WSSI process. I normally use a very slow process with penetrating oils. I tried to hurry up the process by stabilizing the wood... ...I'm really starting to regret that now. I'm not saying anything bad about the WSSI process, just that this wood may be a poor choice for stabilizing.

At this point, I'm more interested in learning about potential weaknesses in my process than making money on this knife. Sometimes you just have to pay the piper...

Thanks,
Dan

 

[dkemppai]

I may be very wrong but I think there is your answer or at least a big part of it! The handle is thick enough at the Ricasso it can't flex, much (the normal place one would think it would flex. However the knife is flexing at the heal of the handle! The flex is breaking the bond and if I am right there ain't any kind of material that is going to stay adheared with out corby bolts or pien-ed pins! This bond is going to have to go thru the knife from side to side.

Yeah, but the kicker is this knife wasn't used since it was repaired, and it failed again! Unless I'm missing something, a knife sitting in the sheath shouldn't flex!

...However, you now have me thinking. The knife failed at the rear of the handle, while sitting in the sheath. That's the only part exposed to the dry air in the house, the rear of the handle!!! And the scale that stayed on is tucked against the belt loop. The one that pulled off first, is the one exposed to the air!

Why didn't I notice that until now...


Dan

 

[C Craft]

OK I missed that it hadn't been used! :12: Dang it I thought I had this one nailed!!! Now I am baffled. If he never used it I can't imagine enough temp, humidity, climate period change to pop the scales.

I give up, someone else is going to have to figure out this one!

 

[dkemppai]

OK I missed that it hadn't been used! :12: Dang it I thought I had this one nailed!!! Now I am baffled. If he never used it I can't imagine enough temp, humidity, climate period change to pop the scales.

I give up, someone else is going to have to figure out this one!

Yeah, that makes two of us who are baffled! I would have put $100 down that it was fixed for sure last time... ...I would have lost that bet!

I'm milling out some parts now (as long as the CNC doesn't crash again). When I get some pictures, I'll show y'all what's in mind right now...
You can either praise my brilliance, or shoot me down in flames!

Dan

 

[dkemppai]

EDIT:[/SIZE]
I had to satisfy my own curiosity, so I just went and clamped a piece of Red Oak in my vice. I cut some scales sometime back they are very seasoned. The scales are about
1 1/8"W X 1/2" Th X 12" L. I left about 6" of it sticking out of my vice. I then taped a strait edge against the Oak slab at the top.

I am 6' and about 260lbs, putting all my weight on the slab sticking out of the vice I could only flex an 1/8" or less. I will bet if you clamp that blade in a vice and lean on it the tail is going to flex more than an 1/8". The strain your customer is putting on that blade is causing the heal of the handle to flex time and time again till it breaks the bond.

It don't matter if it is stabilized or not Oak don't flex very much at all, not unless it is punky and that is when it needs to be stabalized. Most of the time the taper to the heal would not create a problem but, then again not everyone is using a knife for carving. He doesn't have to to twist the motion of carving makes the blade flex. I don't think it is a flaw in the stabilization process or for that matter your design. It is just one material won't flex and the other will!!!! IMHO

Hi,

First, let me start off by saying, it sounds like I'm disagreeing with all of your points. I am listening to the points everyone has brought up, and am very seriously taking them ALL into consideration. I do appreciate all of you taking your time to post comments. So, as I may disagree with some point, keep in mind I am listening to what you are saying.


I've attached two images...

The poor quality image should address your point about scale flexibility. You can see a 1/4" wide screwdriver prying between the scale and tang, and the scale is clearly flexing. (If you need to, hold a piece of paper up to your monitor, and you can clearly see the scale is bending a lot!) This photo was taken while I was trying to remove the scale. It would not pop! (Only heat would get it to pop.)

You will want to note the grain is perpendicular to the handle, not parallel to it. It's very similar to what you would see on the end of the block of wood. From what I've been told the lignocellulose grows very differently in this portion of the tree. The strongest grains are not in the direction to prevent flexing of the handle. It's also why the rays (which typically run cross grain in red oak) are running the length of the handle. Anyway, you can see it's not cracking, even though it's truly a cross grain cut. It's a very tough piece of wood, and surprisingly flexible.

That said, I also think this the exact source of my problem! Red oak shrinks very little longitudinally, but it shrinks significantly cross grain. Since the cross grain direction is in line with the handle, this piece will pull in a direction parallel to the handle when it shrinks. It sort of explains how the scale was able to pull enough to bend the tang. I'm still not sure what all of the implications are just yet...

Anyway, I'm thinking about mechanical fastening under the scale. Attached is an image of one proposed solution. After the screws are shortened, three sets of these will fit under the scales. This will provide attachment down the whole length of the scale, and should also put the epoxy into compression and tension as opposed to shear. Material is Bohler 440C with lots of surface area, and lots of angular contact points, with half a dozen US grade 8 screws. After having some time to think about the failure mode, I think that something like this may work.

Thoughts and opinions are most certainly welcome!


Also, Ed, I am very seriously taking into consideration your comment about just throwing the scales away and putting something else on there... ...have not forgot your wisdom in that regard.

Thanks all!

Dan

 

[Doug Lester]

You've got a good idea of following Ed's advice and starting over on the scales. I would say that the scale that is shown is definitely warped and is toast. I had scales that had be "stabilized" with Nelsonite do exactly the same thing in just a matter of three or four days of being glued on with pins. There was nothing to do but put a new handle on the knife.

Doug

 

[C Craft]

Well I will say this, I am glad its you and not me!! :what!: Not being mean but this one has really got me baffled. :les:

It is hard to have more humidity than we do here in Fl. but I have never had a set of scales crawl off one, yet, :nothing:(knock wood)!!! I have had them to swell proud of the steel of the handle, or shrink slightly flush of the steel of the knife. If you are going back with Oak I would try a different tree, cause this one is doing some extremely weird things!! I suppose it could be the direction of the cut, or it could be the stabilization treatment or a combination of both but, I have been working with wood all my life as a carpenter and I know I have seen some strange things! However a set of scales crawling off of knife setting in a sheath that is already acclimated to the climate that it is in, and never used. That is a new one. You are getting a bond from looking at the pics, and if it is not from use, process of elimination says it is the scales!!

Seriously satisfying the wants of your client is always utmost of importance! However years of construction experience allowed me into insight of some areas I draw the line. With construction it was, "is it against the codes or dangerous, or do I know from my own experience that won't work"! Usually that is an assessment made at the beginning!

If a clients want to use a specific material on a project and I know from experience it will never work. Then you have to put your foot down and say NO, it will never stay I have done it before and I won't use that material because, it is not going to stand up to the conditions it will be exposed to and therefore, I can not guarantee my work.
That philosophy has cost me some jobs in the past. However when the client came back after getting someone else to do what I refused to do, and confessed it did come apart, just like I said it would. Well it is reeeeeeeeeeeal hard not to say, "I told you so", but that don't make for good business!!!! :biggrin:

In this case getting him what he wants is going to require he give a little or some thought on your part!

If I am understanding you correctly you are going to embed these fasteners in the backside of the scales. I may not be getting what you are saying!!!

Is that correct, they are to be embedded in the scale??

If that is correct, how are you going to tighten the screw without the screw either being exposed or at the least drilling a hole and then plugging it???

I am getting in the court with ED, on trying some other material W/fasteners ( I mentioned that earlier) but, you will have to get the client to agree with that one. I would lay it out to him because like others have mentioned you are going to loose this client and he going to talk bad about your product.

Tell him I will replace this once again but this time w/fasteners and/or a different material. He obviously likes the knife. So tell him flat out the strain that carving is putting on the knife is causing the knife to flex, (which is what is supposed to do) but, that strain is going to rip apart any material I put on this knife handle without some kind of fastener. Remind him that you have always done him right in the past and there is no reason to lead him astray this time!!

Good luck!

 

[dkemppai]

Well I will say this, I am glad its you and not me!! :what!: Not being mean but this one has really got me baffled. :les:
------------------
Seriously satisfying the wants of your client is always utmost of importance...
------------------
...In this case getting him what he wants is going to require he give a little or some thought on your part!
------------------
Is that correct, they are to be embedded in the scale?? If that is correct, how are you going to tighten the screw without the screw either being exposed or at the least drilling a hole and then plugging it???

Tell him I will replace this once again but this time w/fasteners and/or a different material. He obviously likes the knife. So tell him flat out the strain that carving is putting on the knife is causing the knife to flex, (which is what is supposed to do) but, that strain is going to rip apart any material I put on this knife handle without some kind of fastener. Remind him that you have always done him right in the past and there is no reason to lead him astray this time!!

Good luck!

I wouldn't wish this bit of painful learning on anyone. I fully understand the relief knowing it isn't your knife...
I agree it has to be the scales, all the evidence is there. Unfortunately, I didn't see it before attempting the first repair. Simply thought it was an epoxy failure. That'll learn me!

The idea with these brackets is to give something for the epoxy to really bit into. Like a hidden pin, but with some serious teeth built in. These would get bolted to the tang, and a matching recess would be cut into the scales. Then epoxy the scales down as normal, but filled with epoxy and with the extra bite from the new hardware to really tie it all together.

It should help help on a couple of fronts. First the way the wood is moving, it puts epoxy in compression/tension and not shear. Second is the recesses in the scales will reduce the cross sectional area of wood, which will reduce the forces the wood can exert. Also, unlike simple hidden pins, epoxy will have a toothy surface to bite into over the whole length of the tang. In theory it should be stronger than a couple of corbys. My gut tells me this extra hardware will solve the issue...



The guy really fell in love with these scales. They really are nice. Long term I need to figure out how to make this work. However this is enough pain for knife.

This weekend I'm going to sit down and have a cup of coffee with the guy. I'll explain the situation and the cause of the failure. I'm going to propose replacing the scales as an option and recommend that route. If he really wants these scales, I'll give it one last try with the understanding that any other failures means I choose the material on the handle....


Again, thanks to all for the input!

Dan

 

[dkemppai]

You've got a good idea of following Ed's advice and starting over on the scales. I would say that the scale that is shown is definitely warped and is toast.

Hi Doug,

The only reason the scale is bent in the photo is the screwdriver was crammed in there and turned. Otherwise they are perfectly straight and flat. They are shrinking length wise, which is the root of the problem.

But, yeah, different scales may be the key here...

Thanks,
Dan

 

[C Craft]

Man I really meant that statement in the best of light, I know what you are in the middle of and it ain't fun!:001_unsure:

I have been in the spot you are in right now, not as a knife maker but as a contractor! After eating the job two times in a row, because of his choice for materials, I had a gut feeling it was going to fail and it did, costing me big bucks! I basically told the client that I was going to give him a choice of materials and none of those choices, were the one that failed two times in a row before!

If that was not acceptable he would get a refund and he could get someone else to do the job. That is when I basically implemented my policy that if you want a material that I feel is going to fail, then I will tell you that it is going to fail and we need to use another product. If you don't want to do that then I respectfully decline to the job but, I am going to tell you that up front!


Quote:
"The idea with these brackets is to give something for the epoxy to really bit into. Like a hidden pin, but with some serious teeth built in. These would get bolted to the tang, and a matching recess would be cut into the scales. Then epoxy the scales down as normal, but filled with epoxy and with the extra bite from the new hardware to really tie it all together."

That will be messy at glue-up because, that much epoxy is going to try its best to run out but, I see now where you are going with it!

 

[dkemppai]

Man I really meant that statement in the best of light, I know what you are in the middle of and it ain't fun!:001_unsure:

That will be messy at glue-up because, that much epoxy is going to try its best to run out but, I see now where you are going with it!

I know how you meant it. No worries my friend! All is good!
Agreed, messy glue-up. However, at this point it's the least of my concerns! (I usually end up wearing epoxy anyway! )

My day job is in a very high tech business. We put stuff in harsh environments where it can and will fail. Sometimes we break very very expensive things. But, every failure is an opportunity to learn how to improve. Every failure makes us that much better.

In the end if I learn something and the guys is happy with the knife, that's all that matters. If others can learn a bit from reading here, all the better!


Thanks,
Dan

P.S. I see you're in FL. Feel free to send some of that sunshine and warm up this way. We're 24 below zero Fahrenheit right now!

 

[wall e]

"He also verified they burn wood and the house is very very dry. His said his brand new wood flooring is coming apart right now!"
Am I the only one seeing this point? If the wood flooring us coming apart is a huge red flag that anything wood is going to twist and warp and act up in that enviroment. If its that dry and hot the how do you make a handle behave other than pinned and wire wrapped? Im no knife expert or a carpenter just a country bumkin who sees things differently.

 

[KDX]

I have hardwood floors and need to keep my humidity around 40% or I will notice a change in the flooring. Going from around 7% (stabilized) to close to 0% (where his house probably is from burning wood) is enough to make the wood respond in some way. Micarta or G10 would solve the issue.