Help designing a Machine Shop Turntable- Flexure Rigidity questions

[nezednemo]

TL;DR Summary

How to calculate deflection on a center supported plate with localized downward force applied.

Good morning, I’m designing a turntable for a machine shop. The machine that rides on this platform weighs 6000 pounds and sits on (2) wood blocks (For ease of pickup with a fork lift). I’m trying to understand flexure rigidity and choose the right thickness of A36 steel plate.

I work closely with a metal supplier, so it is possible for me to get the chemistry on the plate, but I don’t know exactly what units to ask for.

The current plan is to use A36 ¼” Mild Steel diamond plate. I can increase the thickness of the plate to 5/16 or ⅜ if it significantly increases flexure rigidity.

I intend to reinforce the plate by welding flat bar around the edges (to reduce deflection) and adding ball transfer bearings around the perimeter of the rotational axis (to disperse weight transfer). A baseline of deflection of the plate without such supports will help me choose the right reinforcement strategy. My goal is to keep the plate as low as possible to the ground.

Thank you for looking over my project and let me know if there’s any way I can increase the clarity of my request.

 

[Lnewqban]

What makes you believe that the location of the center of mass of that machine will be exactly aligned vertically with that central bearing.

If not, would that bearing be anchored down to a concrete slab?
If so, how much moment is rated to support?

Being a machine shop, would the machine be subjected to horizontal forces or moments in a production process?

 

[nezednemo]

What makes you believe that the location of the center of mass of that machine will be exactly aligned vertically with that central bearing.

If not, would that bearing be anchored down to a concrete slab?
If so, how much moment is rated to support?

Being a machine shop, would the machine be subjected to horizontal forces or moments in a production process?

1. It will not be as the machine will have parts added during the rebuild process. I over estimated the weight on each wood block to compensate for this. The machine weight is closer to 5400lbs totally assembled.

Beneath the bearing would be another steel platform that could be picked up with a forklift.

Between the two platforms I am budgeting for (8) ball transfer bearding which are rated for 340lbs each

The reason I’m looking for deflection information is so I can calculate a good clearance between the ball transfer bearings and the top rotating plate.

There are no expected horizontal moments expected in the application of this device.

 

[nezednemo]

 

[Lnewqban]

Between the two platforms I am budgeting for (8) ball transfer bearding which are rated for 340lbs each

The reason I’m looking for deflection information is so I can calculate a good clearance between the ball transfer bearings and the top rotating plate.

Why the diamonds?
You could get more resistance from a flat plate of equivalent total thickness.

Why the clearance for the ball bearings?
Any deformation will rotate around from one ball bearing to the next.
If too much deflection, it will transfer a moment onto the central bearing.

Could you bend the edges of the plate down?

 

[nezednemo]

For some reason I thought diamond plate would offer more resistance- because the extra ridges are generally above the profile of the plate. But a flat plate is totally doable.

I can’t bend the edges down (no suitable brake) but I can weld 1.5” flat bar to the outside edge.

The reason I planned to add tolerance for the ball transfer bearings was because I thought too much force on them could damage them, but I see now how the force would just transfer to the next support- so I’ll just Bring them up to touching when the plate is not under load.

Thanks for this advice.