Hi NormK,
I would like to correct my previous calculation on how much force you need to push the car screw jack in kg. This formula has a very long calculation and derivation and to simplify, here is the formula below.
Fh = (Wm+(Wp/2)) x cos A / (2 x cos (90 - A))
Where:
Fh - Horizontal Force of the screw jack
Wm - Weight of the mower
Wp - Total Weight of the platform/arms excluding base
A - Angle of the arm with respect to horizontal base
Assuming: Wm = 30kg, Wp = 15kg, A = 5 degrees
Fh = (30+(15/2)) x cos 5 / (2 x cos (90 - 5))
Fh = 214.3kg or 2102N of force
The actual force is much higher and needs a cross member that can withstand 214kg or force.
Go ahead on building this one. This is for you to make your life easy to work with mowers. You only buying your time to build it. Use a welded rectangular angle bar for your base and platform and place a rail on the platform for the mower wheels to seat so the middle of the platform is clear to access the blades or engine mounting bolts if you want to work on the platform. Attach a flap on the front of the platform that will fold down when fully up or open up when it's full down for the mower to ramp up. Wish for your full hip replacement recovery.
Cheers,
TheCarbyMaster