Why does Johnny Tremain have to hide his work from Mr. Lapham in Chapter 1 of Johnny Tremain?

Although Johnny does not show his work to Mr. Lapham in Chapter 1, I am not certain that he is actually hiding his handiwork from his master.  It is true that he hopes to finish mending a buckle before the old man comes down for breakfast.  Although it is not clear whether the buckle is his own or part of a job he is doing for Mr. Lapham, if it is indeed his own, he may be hiding the work he is doing because he is not supposed to be working on his own projects on his master's time.  As an apprentice, Johnny is technically

"little more than a slave until he (has) served his master seven years...he (has) no wages...the very clothes upon his back belong(s) to his master".

Later in the Chapter, when Johnny is working on the sugar basin ordered by the illustrious Mr. Hancock, he never gets around to showing what he has done to Mr. Lapham because he is not satisfied with the quality of his work.  Johnny knows that something is not quite right with the handles and the winged woman decoration he has replicated, but he does not consult with his master because the old man's abilities have declined to the point to where Johnny doesn't believe he will be able to help.

The one thing that Johnny does purposely hide from Mr. Lapham, and everyone else except Cilla, is a silver cup left to him by his mother.  This cup is not Johnny's work, but it has on it a distinctive mark that identifies it as having been made by the wealthy Lyte family.  Before she died, Johnny's mother had told him that only in the event that "there is not one thing left for (him) and he (has) no trade and no health, and God Himself has turned away His face from (him)", is he to take the cup and present it to Merchant Lyte.  The cup will prove that Johnny is kin to him, and in pity, the rich man may help his desperate relation (Chapter 1).