I have been hunting around the Internet looking for good tutorials on how to assemble hidden tang handle and it's been hit or miss. Through trial and error I have found some methods and wanted to share them here.
In it's simplest form a hidden tang the handle need only have a block of wood and some careful fitting. The next logical step in handle construction is to add a pin to mechanically secure the handle to the tang. For this example, I've made it a multiple piece handle with the main components being a bolster, block and pin.
The bolster or guard has to be slotted very carefully. Normally, I drill a series of small holes in a straight line and then join these into a slot with a needle file. Typically the holes are 3/32" and the slot is widened to around 1/8".
Start the holes in a nice straight line with a punch. Leave about 1/32" between the drilled holes. Otherwise the bit may want to slip into the adjacent hole. If it starts to slide, very carefully drill from the opposite side. You'll want to mark and punch that too before drilling.
Only one face of the bolster will be seen. The backside will be hidden, so we only need to perfect the one side. You can taper the slot at the backside and focus on less material at the opening on the visible face.
I like to get the fit about 90% of the way then tape up the blade and clamp it in the vise between two pieces of wood. Slip the bolster on the tang. Then using a piece of pipe over the tang, tap gently until the bolster is "pressed" on to the tang right up to the shoulders.
The photo shows the slotting of the block to accept the tang. Slotting the block is not as super-critical as slotting the bolster was as this end will be unseen. A drill press is handy for this. I usually make three holes in a line. The middle hole goes deeper than the two outside holes. The hole size is slightly larger then the tang is thick; around 1/8"to 3/16" for most knives I make.
The slot is never perfect off the drill press. Sometimes you need to wiggle the drill and enlarge the inside of the slot. This doesn't have fit perfectly, but it should be snug when the tang is pressed all the way in. One trick is to use a broach to gouge out the slot.
Most of the blocks I use are a minimum of 1" x 1" x 4-1/2" long. Woods like cocobolo (shown) make excellent kitchen knife handles because they are hard, oily and quite resistant to moisture common in the kitchen environment.
Hidden Tang with Pin
One trick to ensure the fit is tight is to mark the hole with a spacer missing. Then adding the spacer after the hole is drilled will force a tight fit. Of course the spacer must be thin and chamfering the pin will allow it to get started in the hole and "pull" the components together.
Here I have left one spacer out. I'll push the tang and components right tight and mark the hole with the fine sharpie.
This is the finished product.