A gap showed up between the scale and tang

[Hengelo_77]

Got this knife very close to being finished. After about two weeks I noticed this gap.
I think I know why, but do you guys have any input?

I left the roling skin on the blade for the looks. After HT I cleaned the tang with some coarse sandpaper.
But that only must have sanded the tops of the uneven surface, leaving the deeper parts dirty with the "HT skin".
So the epoxy only adhered to the high parts of the steel and to the dirt in the low parts, thus creating a poor epoxy job.

Is that happened?
So should I have roughed up the tang way more, removing the whole roling skin?

I think I will pop off the scales and put on new ones to be safe. Just in theory is there an other way to fix this?
Thin CA? Transparent epoxy?

 

[Teppojutsu]

Could the scale have just warped a little bit?

 

[Stacy E. Apelt - Bladesmith]

There doesn't appear to be any significant rivet or bold holding down the scales. They warped in clamping and from sanding and humidity.

With no rivet to prevent the warp, the end lifted off the tang.

Also, you probably over-clamped the scales and squeezed out all the resin, leaving a glue starved joint. Use only light clamping pressure ... just enough to hold the sales in place while the resin cures.

A good practice is to "Swiss Cheese" the tang by puting a bunch of holes through the tang to make "glue rivets" that bond the two scales together through the holes. This makes a very strong handle and greatly prevents warp. Another good practice is to relieve the tang or scales a bit ( grind the surface down in the middle), leaving only the perimeter touching. This makes a shallow reservoir of resin in the center that gives a stronger bond.

 

[Hengelo_77]

Thnx for the input.
Here is a pic of the tang before glue up.
I used four hidden pinns (in the middle row of holes), two massive pins and tho with thread to give the epoxy more to hold on to.
What do you think of my idea of "hardening skinn" in the deeper parts of the roling skinn being a barrier between the epoxy and steel?

Should I have had holes closer to the end of the scales as well?

 

[Teppojutsu]

Will the gap go away if you clamp it?
I used to work in a wood shop and I picked up some cool tricks for getting glue into tight spots if you think it can help .

I'm unsure as to which glue your using if I'd will "readhear" to itself .

A nifty trick to get glue into spots like that are with thin plastic like a Hershey bar wrapper dipped in the glue wiggle it in dipped in the glue .

You can also use a vacuum to suck glue through the crack (this one is worth money )

 

[john april]

i had that happen. the scale was not dry and it warped. i bought a moisture meter to avoid it. 5-8% moisture means its dry enough. you could use ca glue to fill the gap, but if it happened because the scale was not dry, it may warp more and pull off again.

 

[Nathan the Machinist]

I had that happen one time just like that, and it was also cocobolo on a liner acting like a bimetallic strip.

If you're going to sell it, it probably ought to come back off. If you're not it might be worth trying to salvage.

I'll touch on the obvious stuff:
Did you clean both surfaces well with solvents first?
Are you using a good quality epoxy such as Acraglas?
Is your epoxy fresh, was it measured out and mixed very thoroughly?
Did you over clamp it and squeeze the epoxy to thin?

I grind the tang lengthwise on my platen to get a good rough surface to bond to. It's tricky not to get the grind out into a visible area though so you have to stop short, so this problem may have still happened.

I scallop out areas on the back of the scale to hold additional epoxy, and when I apply the epoxy I "rub it in" with a screwdriver on both surfaces to insure it fully wets.

 

[Roamad]

What kind of wood are the scales? It also looks like you used two liners. What are they made of and how did you prep them?

I had this happen once on a knife I made with vulcanized fiber liners. Separated in the same spot as yours. I suspect that area of the joint was glue starved, as Mr. Apelt describes. Since then I've been more careful about excessive clamping force.

As for your question about the rolling skin: I suspect that wouldn't cause your problem as long as the glued surfaces were cleaned thoroughly with acetone or something similar first. How did you clean your surfaces before gluing?

 

[Hengelo_77]

The spacers are Koa veneer (left overs from a non knife project)
I epoxied the cocobolo scales and all the spacers together before I epoxied them to the tang.
I used UHU endfest, a high quality slow bond epoxy.

It is not a knife I will be selling it is a "lets make a knife again and get yourself back in to knife making again"-knife to be used by my self on a camping trip.
The epoxy I used was measured out by weight but the epoxy might be over a year old.
Do we have the problem there?

I did clean everything well with acetone. I aplie quite a bit of acetone, then whipe it off with clean textile (cotton) to remove the solved grease, fat and dirt.

I think that I should have roughed up the tang with a cut off wheel in my Foredom to completely remove the roling skin.

But as Nathan sayed I have to be very carefull to not damage the visibale part

 

[Nathan the Machinist]

The epoxy I used was measured out by weight but the epoxy might be over a year old.
Do we have the problem there?

Old epoxy can still set up hard, but lack good adhesion.

Some of the better quality epoxy have very long shelf lives, 5 years or more.

If in doubt I mix some up and bond a liner to a piece of wood, let it sit a few days and try to peal it off. That will tell you if you're getting good adhesion.

Given the failure you've had, I think it would be prudent to test your epoxy in this way ^ to confirm it's still good.

 

[daizee]

I've had that happen a couple times. Once due to clamping too hard without enough epoxy (pre-wet each mating surface), and once due to using wood immediately after cutting scales from its wax-covered block.

I like to put divots on the inside of the scales that match my thru-tang epoxy pins. If making a multi-layer handle, I make sure a couple of those hidden divots go all the way through all the liner materials to contact the outer layer too. Maybe the more experienced can say if this is a good idea or not.

 

[Matt Rochester]

Hidden pins keep the scales from shifting but don't apply any clamping force. It likely separated due to a few things already mentioned but even with that a mechanical fastener like corby bolts will usually keep it from happening. I think your best bet is to remove them and fix it right. I feel eventually it will continue to separate.

 

[Bill DeShivs]

Divots, holes, hidden pins, and roughing up surfaces will not help things like this.
You need mechanical fasteners that hold the scale down- peened pins, bolts, screws.
If you use mechanical fasteners, you really don't need any glue, but many use it to seal the tang.
Modern epoxies are very good, and they PROBABLY will hold for a long time.
Mechanical fasteners WILL hold.

 

[Fish30114]

A little different opinion of what may be happening--with that big pin sitting back from the front edge quite a bit, if it is actually pulling down on the scale a bit, it may be leveraging up the scale towards the front. I can tell you that Stacy's input of only using minimal clamping pressure to avoid glue starved joints is quite important, but in your setup, you need to make sure the front of the scale is actually squeezed enough to counter the pressure from that closest giant pin. I recently was building a knife for a customer with camel bone scales, and when I dry fitted everything up I used Kant Twist clamps and squeezed the middle of the scales, and I noticed when I added pressure the front portion of the scale rose up from the blade the smallest bit--just another thing to think about, I think your blade has plenty of places for epoxy to take root.

Good luck!

 

[Stacy E. Apelt - Bladesmith]

I tried all sort of pins, rivets, hidden, etc. Eventually I switched to using Corby bolts on all knives with scales. I have never had a problem since that day.

What I would do with your knife is put a few drops of thin CA in the gap. Allow them to wick under the scales, and apply a few more. Repeat until the gap is filled. You may have to let it sit overnight and repeat several times before it gets completely filled. Once filed, clean off the front edge with acetone and lightly re-sand the side edges and polish.

 

[MBurks]

A little different opinion of what may be happening--with that big pin sitting back from the front edge quite a bit, if it is actually pulling down on the scale a bit, it may be leveraging up the scale towards the front. I can tell you that Stacy's input of only using minimal clamping pressure to avoid glue starved joints is quite important, but in your setup, you need to make sure the front of the scale is actually squeezed enough to counter the pressure from that closest giant pin. I recently was building a knife for a customer with camel bone scales, and when I dry fitted everything up I used Kant Twist clamps and squeezed the middle of the scales, and I noticed when I added pressure the front portion of the scale rose up from the blade the smallest bit--just another thing to think about, I think your blade has plenty of places for epoxy to take root.

Good luck!

If I'm understanding you you are saying the epoxy is shrinking as it cures, is that correct?

I assume the large holes in his tang are just epoxy pins so it would have to bethe epoxy that is pulling the center together.

I had never considered that but it is good to know if that is the case.

 

[Teppojutsu]

Old epoxy can still set up hard, but lack good adhesion.

Some of the better quality epoxy have very long shelf lives, 5 years or more.

If in doubt I mix some up and bond a liner to a piece of wood, let it sit a few days and try to peal it off. That will tell you if you're getting good adhesion.

Given the failure you've had, I think it would be prudent to test your epoxy in this way ^ to confirm it's still good.

This... it's probably best to know where the problem started .
If you test the glue and it's good you can cross that variable out.

Then Mabey lay a straight edge on the handle to see if it's the handle material or the blade.

In woodworking good squeeze out of the glue from the joint is a good thing imo unless the glue will mess with the Finish (which normally you can just sand it off)

 

[Teppojutsu]

Divots, holes, hidden pins, and roughing up surfaces will not help things like this.
You need mechanical fasteners that hold the scale down- peened pins, bolts, screws.
If you use mechanical fasteners, you really don't need any glue, but many use it to seal the tang.
Modern epoxies are very good, and they PROBABLY will hold for a long time.
Mechanical fasteners WILL hold.

Very well put... I agree about the fasteners even though there are plenty that use just glue. It's nice to have a fastener.. I like the way many here use a single domed pin very nice imo

 

[Teppojutsu]

If I'm understanding you you are saying the epoxy is shrinking as it cures, is that correct?

I assume the large holes in his tang are just epoxy pins so it would have to bethe epoxy that is pulling the center together.

I had never considered that but it is good to know if that is the case.

On the epoxy packages don't they tell you about shrinkage?
I know while thumbing through my Brownell catalog they have tons of epoxy like acraglass and I believe they list the shrinkage factor not sure on this though .

 

[Roamad]

Seems to me even simple pins, epoxied on with the scales. help hold things together. Maybe not as well as bolts or rivets. But still, by coating the pins and pin holes with epoxy, you are creating a gripping force that runs perpendicular to the handle as the glue sets up, and not just parallel to it like the scales themselves. Hope I am making sense here. Would like to know what some of our experts think about this.