explanation: it is a metaphor to show off one's skills in front of experts. Mostly used for self-modesty.
quarrying a pile of soil by the river, Li Bai's name is eternal;
a poem comes and goes, and a big axe is made in front of Lu Ban's door.
This is a poem entitled Li Bais Tomb written by Mei Zhihuan in the Ming Dynasty. Li Bai, whose words are too white and he likes drinking, is called Li Chenxian, a great poet in the Tang Dynasty. There are all kinds of mythical legends about his death. For example, some people say that Li Bai visited Dongting, Yueyang and Jinling (now Nanjing) in his later years. One day, Boating boats quarried the riverside (quarrying, now in dangtu county, Anhui Province, bordering the Yangtze River in the north). At night, the moon was bright as day, and Li Bai was drunk in the boat. When he saw the shadow of the moon in the water, he leaned over to catch it and fell into the river. Some legends are even more magical. It is said that at this moment, the river suddenly became stormy, and there were giant whales, two fairies, holding a jingle, and asked Li Bai to sit on the whale's back, with music leading, and fly away. Of course, these legends can't be believed, but in quarrying, many places of interest appeared later. There are not only Li Bais Tomb, but also the Xianlou and the Moon Catching Pavilion, which have aroused the interest of countless tourists. It's ridiculous that some tourists who want to pretend to be elegant even make up random questions in Li Bais Tomb. This poem by Mei Zhihuan is a mockery of such tourists. He thinks that scribbling crooked poems on the grave of a great poet is simply "making a big axe in front of Lu Ban"-it's too careless.
Lu Ban, who is said to be Gongbo, was a native of Lu in the Warring States period, also known as Lu. He is an expert at making delicate instruments, and people call him "homo habilis". Folks have always regarded him as the ancestor of carpenters. Who dares to show off the skill of using an axe in front of Lu Ban? In other words, trying to show one's skills in front of experts is a ridiculous act of being too modest, which is called "playing axe in front of Lu Ban's door" or "playing axe in front of the door". It is similar to the saying that "playing with a big knife in front of Guan Gong".
Liu Zongyuan, a writer in the Tang Dynasty, said in his preface to "Singing a Peace Poem for Wang's Matches": "To hold an axe at the door of the class is to be strong." (Ying refers to another ancient axe master. See "Axe Correction". "Strong face" means having the cheek. ) It seems that the idiom "teach others to teach an axe" was not only born out of the above-mentioned poem of Mei Zhihuan in the Ming Dynasty, but had its embryonic form as far back as the Tang Dynasty.
This idiom is sometimes used as a word of self-modesty, indicating that you dare not display your skills in front of experts.