Here is a still-life of what was in front of me earlier while fitting a peghead to the end of a dulcimer:
I make most of the parts and do most of the assembly of my dulcimers on a solera. On the left of the solera is a dulcimer waiting for a peghead. On the right of the solera is a peghead waiting for a dulcimer. This could be a match made in heaven, but only if they fit together perfectly.
On the back corner of the bench is my glue pot with hide glue hot and ready for action. Hide glue works extremely well but requires tight joinery so mating surfaces must fit up against each other as precisely as possible.
I prepare both mating surfaces for gluing by making them flat and true. I use the file and scraper shown in the photograph to take down any high spots and check my progress using the blade of the machinist’s square as a short straight-edge. I also have some sanding blocks I’ve made that serve as fine files of specific shapes and sizes that sometimes come into play.
Since hide glue contains a lot of hot water the wood will swell a bit when the glue is applied. The peghead assembly also has a lot of end grain that will go into the joint and end grain can suck up enough glue to starve the joint.
I solve both problems by applying hide glue to both surfaces to be joined and let the glue dry overnight. This sizes the end grain by letting it soak up a lot of glue before the joint is assembled. Hide glue can be glued to itself so when adding fresh, hot, hide glue to the joint for assembly it will melt into the glue that sized the end grain.
Before I glue the joint I check both surfaces to see if moisture from applying hide glue the day before has caused any warping or swelling of the surfaces. If so, I level down those spots, add hide glue, put the joint together, and move on to the next adventure.