Lisa Vanderpump's Husband -- I Was Attacked with a Concrete Chipper ... And Then Extorted

Lisa Vanderpump's rich husband Ken Todd says he has a concrete reason to file a fat lawsuit ... claiming a construction worker attacked him with a cement chipper, then tried to extort him for $50,000.

Todd filed the lawsuit against Kevin and David Cazaref, claiming the two brothers had been hired to do construction work on Ken's P.U.M.P. Lounge in West Hollywood.

Ken says he observed Kevin (a man twice his size) using a concrete chipper unsafely last week, so Ken confronted him and attempted to show Kevin how to use it properly.

Kevin must have taken offense ... because Ken says the worker then "became enraged, grabbed and violently hurled the heavy concrete chipper" at him ... hurting his hip, leg, and knee.

According to Ken's lawsuit, Kevin's brother David approached threateningly in Kevin's defense -- at which point nearby police officers became involved.

No arrests were made, but Ken says the brothers later contacted him in an attempt to shake him down for $50,000 in exchange for keeping quiet about the altercation.