The first was in Hebden Bridge on Friday 24 June, the second in Halifax town centre on Tuesday and the third in Brighouse yesterday afternoon.
Two men were arrested on Wednesday night but six more have now been arrested in planned police operations.
All eight have been arrested on conspiracy to commit robbery.
Detective Chief Inspector Chris Gibson, of Calderdale Police, said; “Whilst there have been no physical injuries sustained during the incidents, clearly this has been very distressing for victims, and has caused understandable concern across the communities of Calderdale.
“We have a large number of officers dedicated to these enquiries. Criminals targeting our communities are not welcome on our streets and we will do everything within our power to detect offences, apprehend those responsible and bring them to justice.
“I would also like to thank the members of the public and local businesses owners around the targeted premises for their continued support and cooperation and for coming forward with information to assist with our enquiries. If anyone who has any information who has not yet come forward, I would ask for them to do so.
“I would also like to thank those in Brighouse yesterday who made efforts to apprehend the suspects even though they were believed to be in possession of weapons, showing great bravery and selflessness, and true community spirit in their actions.”
The seven men – aged 38, 36, 29, 27, 27, 22 and 20 – and a 16-year-old girl, all from Calderdale, are in police custody.
Anyone who has any information is asked to contact Calderdale CID via 101, or crime charity Crimestoppers in confidence on 0800 555 111.