Wikepedia gives a very good definition of trhe word chamaras follows,
"Chamar ("tanner"; from the Sanskrit Charmakara) is a prominent occupational caste in India and Nepal. Chamar is a Dalit sub-caste mainly found in the northern states, such as Punjab, Haryana, Himachal Pradesh, Uttar Pradesh, Bihar, Baluch and in Nepal at least north to the Himalayas. The traditional occupation of this caste was processing, manufacturing and trading in leather and leather goods. Most of the Chamars have now given up the leather related work. Agriculture is also their most important occupation in which they engaged either in their full ownership or on share cropping basis in which they get 1/4rth, 1/3rd or one half of the farm produce depending upon their agreement with the land owner."
Chamar, Tanner Charamkara