If there is no taper, then nothing is happening when you drive the peg. Even if the taper is for a short part of the length, that is where the work is getting done....
Sorry Dave...not only does that not make sense to me from an engineering or mechanical perspective it is not true historically in timber frames or furniture that I have read about, seen, restored, or studied...???
"Most"...(virtually all?) pegs/trunnel, be it in a chair, table, door, window...or...timber frame...are typically solid full cylinders (or squares) from end to end (once driven home.)
The..."happening"...is created by the "offset" between the hole (square mortise) in the tenon and that of the hole/mortise in the received member. It is the "offset" that creates the draw, and not the "taper."
...If you tried to drive a pure cylinder through a draw bored joint, you would destroy the tenon relish, not draw the joint tighter.
Sorry again, but if that was the case, I would have destroyed thousands of joints at this point...and I haven't thus far...
Most "turned pegs" and riven...come as full cylinders and only have a slight "coving," "rondel" or "point" on one end that facilitates them properly engaging the "offset" and begins drawing the joint together...That is if the joint hasn't be "podgered" as I suggest is a much better practice...
There is no doubt that..."draw pins" (aka "timber framing "podgers")...be they for furniture or timber frames (we love them!!! and think they are a must have to draw these joints consistently and well...) are tapered for a portion of their length...Again...this is only to facilitate the ease of entry before driven home...it also is to facilitate their extraction once the proper..."draw"...is completed..
The following photos are PE approved pegs...Note that the pegs/trunnel are all full cylinders except for the very end...
Below is typical from a vintage frame that has not been moved and is original in materials and modality of construction...Note that few (if any) of the trunnel are tapered or "wedge shaped." These are full cylinder pegs and commonly found as such in most timber framing cultures whether "round peg/trunnel" or "square pin"...there is no inclined plane...
Classic Draw Pins and/or Podgers and a "offset Pricker"...
Anatomy of a well "drawn" furniture joint, a die plate or "peg shear"...Again the pegs produced are in a full cylindrical geometry...
