Building the Pivot

This weekend was filled with fatherly duties, so the time I was able to spend out in my little shop was quite limited.  In spite of that, I was able to make a little progress on the two knives that I'm working on.  Since I haven't shown how I build my pivots, I took some progress photos of how I achieve this, the most important part of a folding knife.  After all, if the pivot doesn't work right, you don't have a folder.

This is where we begin, with enough parts to complete two pivot systems.  My pivots are composed of a 3/16" bushing, two 1/2" washers and a 1/8" pivot pin and screws.

Here is what the system looks like.  The blade has a 3/16" hole drilled through the tang.  The bushing fits perfectly in the tang hole and will be lapped until it is the exact width of the tang plus the washers.  The pivot pin then passes through the bushing and will be trimmed to length and tightened down with the screws to hold the assembly together.

First, we need to determine the thickness of the blade tang and the washers in order to know the needed length of the bushing.  I use a pair of digital calipers to take this measurement.

Here is the little gizmo that makes lapping the bushing to length easy.  I bought this pivot lap from USA Knifemakers.  The bushing fits into the bottom of the puck and the plunger is pushed down as the whole thing is rubbed on some abrasive.  It works pretty slick.

To hog off long sections of bushings, I used the pivot lap on my shop-built horizontal disk grinder.  I check the length of the bushing often, and when it gets close to the desired length, I switch off the grinder and hand sand the bushing to final size.

Perfect!

Next, the blade tang needs to be fitted to the back spacer so it is in the correct open position.  I leave the spacer long so that it can be adjusted to the correct length.  To do this, I black out the tip with a black marker and use an Exacto knife to mark where the spacer needs to be trimmed to.

After a little grinding, the blade stops in the correct open position.  Check another step off the list.

The screws of the pivot come from the supplier much too long.  I developed this little jig to shorten screws in a short time.  It's just a square piece of titanium that has a tapped hole in it.  I screw the pivot screw through the jig to just the right length that I need.

On the back side, I use a pair of wire cutters to nip off the end.

The screw gets lapped on the disk grinder, giving me a screw of the perfect length.

Next, it's time to get the pivot pin trimmed to correct length.  To do this, I assemble the knife with the pivot system in place as shown above.

A quick spin on the disk grinder takes the excess off of the pivot pin.

The last step to complete the pivot assembly is to deal with the pivot screw heads.  For the bolstered knife, pockets get drilled in the back sides of the bolsters which will allow the screw heads to be concealed below.  The titanium scales get a through hole that the screw heads will fit into.  The above shows the end of this step.

Well, not a lot of progress made this weekend, but that's alright.  Next week should bring about a lot more progress.  I look forward to seeing how these two knives turn out.

Thanks for stopping by the Robinson Edge.

-  Brandant Robinson