Small Transport; Low Wing; 2 Recip Eng
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 40; Flight Crew Total 11000; Flight Crew Type 3000
Confusion; Distraction; Situational Awareness; Time Pressure; Workload
ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action
Procedure; Weather; Human Factors
I was flying on a direct route to AGC through the Columbus Approach; I asked for a deviation due to weather.  The controller did not want to issue a deviation.  I again requested and he provided a short time deviation.  He stated that I would need to return to the heading of 090 for the remaining flight.  I responded that I could not due to weather.  He demanded that I return to the heading of 090. I was looking at a very large thunderhead and headed directly into it. He stated that his radar was showing nothing and I must maintain the given heading.I have both WX weather on board; ADS-B in weather and on board RCR 150 weather radar.  All indicated that I would encounter a rain storm and possible a thunderstorm.  He again demanded I return to the heading of 090.  At this time I was VMC and canceled the flight plan for IFR.  He responded to display the VFR code.  That was the last transmission from the controller. I then proceeded VFR through the area of weather and maintained VFR all the way through although at lower.I have never in all my flying for almost XX years had a controller demand that I maintain a given heading when I'm looking at a very large thunderhead.  I think that the flight safety was compromised due to the proposed heading I was given.  I was given no other alternate than that heading.  I was very glad to have VFR weather to continue.  Had I been solid IMC; there would have been no other alternate to a safe flight.  I consider the controllers' actions a compromise of safety.
Pilot reports of requesting a deviation for weather. Controller did not want to give the deviation but did. Controller let aircraft deviate for a while then told pilot they had to return to the previously assigned heading. Pilot stated this would put aircraft back into the storm and did not want to. Controller demanded the aircraft return to the heading. Pilot was in VFR conditions and cancelled IFR.