I agree pics would help. But I have done some knives with gaurds and I tried solder once a very long time ago and never did it again. If its a hidden tang simply first make the hole in the brass small so the tang wont fit through it then file it bigger going slow so it fits somewhat tightly. This has always been a problem for me I am impatient
But if its some what tight I do the handle next and when you make the hole for the pin in the handle. Make sure that pin holds the handle material forward very tightly then when you epoxy everything together the handle material (and some epoxy that gets in there will hold it tight up agents the shoulders of the blade and all of mine none have ever come loose. One technique Ray taught me to keep everything tight is to cut a piece of thin spacer material for in between the guard and handle material. But when you drill the hole in the handle material and the tang....do NOT put the spacer on just the handle material straight up agents the guard drill the hole through the tang. Then when you assemble everything to glue up then put the spacer between the handle material and the guard. The spacer is just thick enough to slightly off set the hole in the handle material and the tang so when you glue everything the pin should now be tight enough that you will have to tap the pin through with a hammer but now everything is held very tightly forward up to the shoulders of the knife....this is how I do it and its worked evrytime