- Joined
- Feb 16, 2010
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- 3,668
Several people advised that I post a thread about this, even though the final knife isn't done yet. This is a proof of concept prototype and not a finished knife. However, the knife snaps open and closed, just like I think a slipjoint should.
The OAL is 3 3/4", edge length is 1 3/8". Liners, pin, and spring are 6-4 Titanium, blade is S30V. Washers are .003" teflon coated fabric.
First, for the sake of the argument, we'll call it a pivot axle, bearing, whatever, just not a pivot pin. There are no other pins holding it together at this point. The back spring was spot welded in place to one liner then heated with a torch and adjusted. Then, the second liner was spot welded to the spring/liner. The blade was installed and the pivot peened into place.
The problem with spot welding three layers is that the spot weld is very small in the middle layer. A 1/4" tip gives about a 1/16" spot in the middle layer. Luckily, that's all we need for a spring that's only 1/16" to begin with. I tried about 5 welds before getting it right. The biggest problem being that my 220v Miller is a little hot for this task. I have to just bump the switch a couple times. The first bump barely turns the metal red, give it a couple seconds to normalize and the second bumps gets it orange. When it turns orange it's done. Total time on each weld is well under 1/4 second. The pressure had to be adjusted to very light contact. You can see some weld marks at the tip end where the pressure was too high and it squeezed the molten titanium together. You can barely see the final weld through all three layers, expecially after a little grinding. However, I can't pry them apart and that's what we need in a good weld. Destruction testing of one of the test pieces showed that a hammer and chisel could separate the pieces, but it was still stronger than a pin.
Yes, I know there are lots of construction problems, namely the spring isn't flush when closed, the ricasso is lopsided, and the back stop on the blade is incorrect. That's why it's a prototype, to learn from. The next build will have lots more finish to it.
The OAL is 3 3/4", edge length is 1 3/8". Liners, pin, and spring are 6-4 Titanium, blade is S30V. Washers are .003" teflon coated fabric.
First, for the sake of the argument, we'll call it a pivot axle, bearing, whatever, just not a pivot pin. There are no other pins holding it together at this point. The back spring was spot welded in place to one liner then heated with a torch and adjusted. Then, the second liner was spot welded to the spring/liner. The blade was installed and the pivot peened into place.
The problem with spot welding three layers is that the spot weld is very small in the middle layer. A 1/4" tip gives about a 1/16" spot in the middle layer. Luckily, that's all we need for a spring that's only 1/16" to begin with. I tried about 5 welds before getting it right. The biggest problem being that my 220v Miller is a little hot for this task. I have to just bump the switch a couple times. The first bump barely turns the metal red, give it a couple seconds to normalize and the second bumps gets it orange. When it turns orange it's done. Total time on each weld is well under 1/4 second. The pressure had to be adjusted to very light contact. You can see some weld marks at the tip end where the pressure was too high and it squeezed the molten titanium together. You can barely see the final weld through all three layers, expecially after a little grinding. However, I can't pry them apart and that's what we need in a good weld. Destruction testing of one of the test pieces showed that a hammer and chisel could separate the pieces, but it was still stronger than a pin.
Yes, I know there are lots of construction problems, namely the spring isn't flush when closed, the ricasso is lopsided, and the back stop on the blade is incorrect. That's why it's a prototype, to learn from. The next build will have lots more finish to it.
